This article describes the design of small-sized speaker systems intended for use in recreational areas away from home, which have a higher quality of reproduction of musical soundtracks than serial portable tape recorders and high-class radio tape recorders.

How to make a speaker system with your own hands

The article briefly explains the ways and reasons for choosing such a technical solution. These acoustic speakers can be built by novice radio amateurs, as they require a small amount of materials, therefore, a small amount of labor for manufacturing and are easy to set up. The technology for making acoustic systems with your own hands is described in detail for beginner radio amateurs.

The construction of small-sized acoustic systems with one's own hands was caused by the need to listen to music recordings with higher quality while on vacation away from home than is possible with portable tape recorders and high-end radio tape recorders. We are not talking about high-quality Hi-Fi sound, so it was necessary to find a compromise between sound quality and the volume of the device.

Two-way acoustics Melodiya-101-stereo

The basis was taken as a two-way acoustic system of class I radiola “Melody-101-stereo” with dynamic heads of types 10GDN-1 (6GD-6), 6GDV-1 (ZGD-2) and with overall dimensions of 300x171x168 mm, but with a different configuration and a slightly smaller volume of the speaker system box (photo at the beginning of the site).

The boxes were made of 12 mm thick laminated plywood. The side walls and the front panel, with cut-out holes for dynamic heads, are connected to each other using wooden slats with a cross-section of 15x15 mm, PVA glue and short nails.

Nails should go into the plywood to a depth of no more than 8 mm. The rear part of the side walls was also initially covered with slats with a cross-section of 15x15 mm along the entire perimeter at a distance of 12 mm from the edge for fastening the rear wall with screws.

Initially, the speaker system box was a closed type, it contained two electrodynamic heads of types 25GDN-3 (15GD-14) and 6GDV-1 (ZGD-2) with a simple filter, similar to the “Melody-101-stereo”, from one isolation capacitor between the heads with a capacity of 2 µF.

These speakers were chosen for the following reasons:

• reproduced frequency range of the speaker 25GDN-3 65-5000 Hz;
• main resonance frequency 55 Hz;
• nominal electrical resistance 4 ohms;
• reproduced frequency range of the 6GDV-1 speaker 5000…18000 Hz;
• nominal electrical resistance 8 ohms.

The result is a complete matching of reproduced frequency ranges from 65 to 18,000 Hz without a mid-range speaker. Practical tests of the sound of this acoustic system by ear gave a result that was lower than expected in terms of reproduction of lower sound frequencies. Obviously, the reduction in the volume of the box had an effect.

Having analyzed all possible ways to improve sound quality, with the same dimensions of the speaker system, it was decided to supplement the box with a slotted bass reflex on the rear side and install dual heads of the 25GDN-3 type, in which the resulting equivalent volume is half that of one of the same heads .

The volume of the existing box, as it were, almost doubles for the outer head, given that the inner head occupies part of the useful volume. As a result, the reduction in the volume of the box compared to the Melodia-101-stereo speaker system was compensated by the use of dual heads.

Speaker drawings

The design of an acoustic system with dual speakers and a bass reflex is shown in Fig. 1, where the following are indicated:

1. Bass reflex baffle.
2. Guide rail.
3. Rails for fastening the side walls, front panel and rear wall.

Dual heads of the “diffuser to diffuser” type reproduce the lower frequencies of the audio range more efficiently (Fig. 2), but they overwhelm the mid frequencies. If you want to build a higher-quality small-sized acoustic system, it is enough to supplement it with a mid-frequency head, for example, type 3GDSH-8 and a crossover filter similar to that used in the acoustic system. In this case, the height of the acoustic box (Fig. 1) must be increased by the size of the diameter of the midrange head plus 20 mm.

Dual speakers of the “diffuser-by-diffuser” type normally reproduce mid-range frequencies, since the diffuser of the outer head faces the listener, and improve the reproduction of lower frequencies and frequency response compared to a single head. This speaker is a two-way speaker, which needs to be taken into account; therefore, in this case, the option of doubling the heads according to the “diffuser by diffuser” type is more acceptable. A drawing of the dual head mounting unit is shown in Fig. 3.

To attach dual heads to the front panel, cut out of plywood 5...6mm thick
ring 10 with an inner diameter of 110 mm and an outer diameter of 160 mm, onto which the head is placed coaxially and the mounting holes are marked with a pencil. The holes are drilled with a drill with a diameter of 3.3 mm. A ring with holes is placed at the place where the double heads are attached to the inside of the front panel 11 and the centers of the recesses for the heads of the mounting screws 7 are marked. 7 M4 screws with round heads and a length of 25 mm are screwed into the holes of the plywood ring 10.

If the plywood is very dense, you can pre-cut threads in it with an M4 tap. After this, recesses are made on the front panel for the heads of mounting screws with a diameter of 7 mm and a depth of 4 mm. This operation must be performed very carefully so as not to drill through the panel. First, to accurately place the mounting screws, the recesses are made with a drill with a diameter of 2 mm, clamped in a hand vice, and then the recesses are expanded in the same way with a drill with a diameter of 7 mm.

After this, the ring on the side of the front panel and the place where it is installed on the inside of this panel are generously lubricated with PVA glue or epoxy resin, including the recesses for the screw heads. The ring is put in place and pressed or nailed with short nails. Excess glue from the front side of the front panel is immediately removed with a damp swab, and epoxy resin with acetone. The ring remains in this state until the glue has completely polymerized (for reliability, it is better to wait 24 hours, since the strength of this fastening is very important).

To double dynamic heads, a separating cylinder 4 is required, which seals the air volume between the diffusers and on which the inner head rests. In the author’s version, the cylinder is glued together from two layers of linoleum on a felt base 5 mm thick. The internal diameter of the cylinder is 114 mm, height 60 mm.

The height of the cylinder may be different, depending on the modification of the heads, but it must be such that the gap between the diffuser of the inner head and the magnetic system of the outer head is at least 10... 15 mm. To make the first layer of the cylinder, a strip of linoleum 358×60 mm is glued at the ends with “Moment” glue, with a felt base inside and fixed with tape along the outer surface.

The second strip, 60 mm wide and a length determined locally, is glued to the first layer of the cylinder and secured with tape. The ends of the second layer of the cylinder should be joined on the opposite side. In the side walls of the finished cylinder, opposite the terminals of the external head, holes are drilled along the diameter of the mounting conductors with which this head is connected to the speaker system circuit.

To fasten (Fig. 3) both heads, it is also necessary to have four bushings 6 25...30 mm long with an outer diameter of 8...10 mm with M4 through thread, four studs 5 60 mm long with M4 thread at both ends of 20 mm, 8 nuts M4, 12 cardboard or textolite washers 2.8. First, the external dynamic head 9 is installed on the screws 7 of the glued ring and secured with bushings 6 through washers 8. Stripped and tinned mounting conductors of sufficient length are inserted into the holes of the separating cylinder 4. The cylinder is installed on the dynamic head 9, and the conductors are soldered to its terminals.

Studs 5 are screwed into the bushings 6, onto which support nuts with washers are screwed, and the internal head 3 is installed until it is tightly aligned with the separating cylinder 4. Cardboard or textolite washers 2 are put on the ends of the studs 5 and nuts 1 are screwed on. RF head 6GDV-1 with pre-soldered conductors are attached to the front panel in the usual way with screws. Capacitors C1 and C2 are glued to the bottom of the speaker system with Moment glue. A “Tulip” type socket is attached to the rear wall for connecting the connecting cable between the speaker system and the power amplifier.

After fastening the parts, they are connected to each other according to the circuit diagram shown in Fig. 4. Capacitor C1 80 μF consists of several standard ones connected in parallel. The diagram shows that the internal head is bypassed by capacitor C1. Due to the fact that the length of sound waves in the mid-frequency range is commensurate with the distance between the diffusers, sound signals emitted by the internal head arrive at the diffuser of the external head with significant phase shifts, distorting the frequency response.

For example, an audio signal with a frequency of 3000 Hz, the wavelength of which is 11.5 cm, having passed a distance between the diffusers of 6 cm, will change the phase to almost the opposite and slow down the radiation of this frequency by the external head, i.e. will create a frequency response failure at this frequency. In this variant of dual heads, the midrange frequencies must be reproduced only by the outer head. and lower frequencies, the wavelengths of which are significantly greater than the distance between the diffusers, are reproduced by both heads and the phase inverter passage.

The resistance of the shunt capacitor at the upper frequency of the midrange should be several times less than the resistance of the internal head. The total electrical resistance of the 25GDN-3 speaker at a frequency of 1 kHz is 4 Ohms, and at a frequency of 5 kHz it is approximately 5 times greater. In this case, at a frequency of 5 kHz, the resistance is 0.4 ohms. In similar acoustic systems, the dimensions of which are not critical, the internal head can be bypassed with a series LC circuit, covering a frequency band of approximately 400 Hz...6 kHz.

In three-way speaker systems, dual drivers of any type operate only at the lower audio frequencies, and the mid and high frequencies are suppressed by the low-pass crossover filter, so additional bypassing of the internal speaker is not required. There is not enough space for the bass reflex to pass through on the front panel, so it was decided to place it on the rear side. The location of the bass reflex passage does not play a special role in the operation of dynamic heads in the region of their main mechanical resonance. The only drawback of this option is that such a speaker cannot be leaned against the walls of rooms or furniture.

For ease of manufacture and setup, the bass reflex is made in the form of a narrow slot formed by the upper wall of the box and a flat partition 1 along its entire width (Fig. 1). The partition 1 is made of plywood 6 mm thick and is fixed in the grooves formed by the upper slats 3 for fastening the side walls of the box and the guide rails 2, fixed at a distance of 6 mm from the upper side slats. The upper rail 3 for fastening the rear wall is moved lower to a distance of 21 mm from the upper wall. The back wall is cut off at the top by 21 mm and secured with screws.

Initially, partition 1 has an area approximately equal to the upper wall and the ability to move in the grooves to adjust the bass reflex. Tuning the bass reflex consists of achieving a minimum voltage on the dual heads at the main resonance frequency of 55 Hz by changing the passage length by moving the partition. Setting up the bass reflex is described in more detail in (4) and (5). After adjusting the bass reflex, mark the line where the partition meets the back wall with a pencil. The partition is removed, the excess part of the partition is cut off, and its end is treated with emery cloth.

After these operations, the back wall is removed, and the grooves, crossbar and edges of the partition are lubricated with PVA glue. The partition is inserted into the grooves in its place, and the squeezed out parts of the glue are evenly distributed with a narrow brush along the joints of the partition with the slats. After complete polymerization of the glue, the strength of the partition is checked to ensure that there is no vertical movement in the grooves to prevent rattling. If gaps are found between the partition and the guide rails, fill the gaps with PVA glue.

After this, the back wall is attached - and the speaker system is ready for use. Before installing the rear wall, a layer of plasticine about 1 mm thick is applied to the mounting rails to seal the speaker system housing. In conclusion, it should be noted that the above modernization of the acoustic system has yielded positive results and has been successfully used for several years.

October 24th, 2017

I dedicate this material to all do-it-yourselfers and wish them good luck in their work.

Start

Dear friends, allow me to introduce myself. My name is Yuri. He received his name in honor of Yuri Alekseevich Gagarin, like many boys during that period. It was so popular when I was born. Apparently, the energy of that time and the name of the first cosmonaut was, to some extent, passed on to me and became part of the soul, requiring activity. During school years, activity was multidirectional, but did not include studies. This did not become a hindrance in life. Graduated from Technical University with honors. I did not change my profession, chosen on the basis of the maximum complexity of the specialties offered by the university I entered, and I still earn money from it. They trained me to become a designer of hydraulic machines and their automation equipment.

In his free time from work, all sorts of hobbies continued. In another emotional outburst, which happened quite recently, I discovered a wonderful Audiomania store, in particular, its “Do it yourself” section. What I saw there on my first visit was a youthful dream. True, in those days it was impossible to imagine such a thing. The assortment of this store opened the door for me to the world of realizing ideas. I think, like for many other people obsessed with ideas.

In addition to my passion for audio technology, which accompanies me throughout life, I love photography, read science fiction (definitely about space travel - that same energy works out). And one more hobby - I have been making wooden furniture for almost a dozen years. Nowadays we already have serious experience as a cabinetmaker, which allows us to make furniture professionally.

Creating acoustics, which will be discussed, is one of my long-time hobbies. But the accumulated experience, today's opportunities and new desires have allowed us to set ourselves a difficult task - to create acoustics for the home that convey the dynamics, scale and emotionality of concert music performance.

To all readers - my immense affection and best wishes.

Yuri Kobzar

I'm an amateur. I will try to write only about specifics. I will share my practical experience in creating high-level acoustic systems. I address this information to fellow fans who like high-quality sound, who get pleasure not from the background, but from listening to music. People who are in the world of sounds have preferences and favorite records.

In the spring of 2017, something happened to me. In the evening, on the veranda, the chirping of birds reached my ears, a real warmth wafted through, somewhere turned green, the first vegetative aroma arrived, I wanted to sip wine and listen to music. Without analyzing (everything can be attributed to fluctuations of the soul), I felt the need, and I had the idea to acquire good sound for the home. Moreover, there is “music” in the house. But at that moment the term good sound suddenly took on a different meaning. Memories of randomly listening to music in a store (in the high-end room), a great opportunity to experience the highest quality sound from several friends, came into my head. All this happened years ago, but the need for good sound took shape in the spring of '17. Despite the fact that a reverent attitude towards “good” music has accompanied me all my life, and I almost always had the opportunity to listen to sound of decent quality, it suddenly became clear: the music sounding from acoustics should not just be clean, detailed, powerful, deep, natural, bewitching or even amazing (body at high volume is a joke). The sound reproduced by acoustics must convey the emotions of the soloists and musicians, and all those who prepare the recording for us, the listeners.

According to preliminary estimates, possibly overestimated, it turned out to be unaffordable to buy such equipment. I didn’t want to waste money on something good that was available. Thus, the task arose to build the highest class acoustics available at home. Without laboratories, high-precision measurements, but so that the breed, solidity and eliteness of the sound is undeniable. To create just such an impression from listening.

As a small digression, it should be said that the idea had a basis. I had certain skills at my disposal: in my youth I built acoustics in a “closed box”. I was happy with the sound of it. Various transistor amplifiers were soldered together, one model is extremely high quality. Now, in addition to the previous half-forgotten knowledge, skills and experience, I have added a love for making furniture from wood and a certain set of carpentry tools. Additionally, I wanted to acquire a high-quality tube amplifier. In order to shorten the implementation of the plan, I offered participation to my enthusiastic friend and do-it-yourselfer, who has the base of the radio department of UPI (Ural State Technical University). It was agreed that acoustics (selections, calculations and implementation) would be my task, and the lampmaker would be part of it.

From this position they began to “shake the old days.”

Choice

The issue of building an AS began with the study of theory and related materials. I, like many builders of their own acoustic systems, faced the question of choosing an acoustic design. Knowledge, information, opinions began to accumulate and be systematized, but the answer to the question about the type of acoustic design of the speakers remained open. At this time, three 75GDSh3-1 broadband heads became available to my partner. The local cultural center decided to throw away two stage subwoofers that had worked for more than 30 years. Each had two speakers. In one of them, the speaker failed, hence the decision to throw it away. Listening to the speakers "on the floor" confirmed the expectation of "no sound". Listening in the original subwoofer box did not change the ratings. Almost without enthusiasm, I began to dig through the Internet on the topic of using speakers of the existing type in speakers. Materials from comrades who had already built speakers based on these speakers were quickly found. I liked the option with “tekuvete” (tqwt) Voight pipe - I am attaching the material, the authorship has not been established, see link). I liked this option, among other things, because of the “open body”, for which some people already liked it. Why: No or minimal speaker damping as needed. In other words, there are no obstacles created for the dynamic head during operation, and this, as I understand it, means a minimum of conditions for creating external resistance and, as a result, distortion. Also, the resonant frequency of the speaker in the housing with the pipe does not change. This, in turn, should ensure the reproduction of a richer bass component, which is the basis of the rhythm, providing volumetric sound and enhancing the psycho-emotional perception of the musical program. With internal resistance (after listening to the speakers), with the fear of getting a weak result and, nevertheless, with hope, I bought three sheets of 12mm construction plywood to replicate the proposed design in the material. The modification consisted of using radial transitions in each corner (for the first time I bent plywood), installing a stiffening rib inside (taking into account the dimensions and thickness of the material) and installing a rigid removable rear wall for the convenience of subsequent possible damping.

I don’t give the manufacturing technology. Open it too. Considering my experience in working with wood, I believe that each craftsman who undertakes the manufacture of such a structure will have his own specific design and manufacturing work. The specifics are related to the conditions, skills and set of tools. I got used to working with glue, refusing metal fasteners (except for the removable back wall). This ensures the absence of technological racks that take away volume, giving additional geometry in the sound channel, which from my point of view - a certified hydraulics specialist - is not good for the movement of a sound wave along the channel. And the task, by the way, is to create conditions for its smooth, laminar (there is a term meaning the absence of turbulence) movement along the channel. This reduces the likelihood of overtones that are unnecessary for high-quality sound.

The sound of the built speaker surprised me right away. Powerful, bright, beautiful and different from my signature three-way bass reflex (FI) speakers of the English brand. Significantly excellent. With emphasis on the word “excellent”. The surprise was intensified by the fact that there was England, the intelligence of engineers and large-scale production, and here was a 35-year-old miracle in a plywood box. After the first surge of emotions subsided, it became clear that one speaker was not enough for this speaker. There are not enough tops and... bottoms. The bass is low, beautiful, with many shades (which is not heard on the FI) and, at the same time, weak. You can talk yourself into such a sound, but the drawback is noticeable.

Having doubts about the ability of this speaker to play bass in a wideband speaker system, I built a tapering labyrinth - a transmission wave line (TVL). According to reviews online, this is exactly what is needed. I describe without details or arguments in favor of such a decision. I do not provide recommendations and dependencies for constructing TVL. Everything is on the Internet. I made this design more technologically advanced: with legs, without roundings. It should be noted that the speaker turned out to be more compact in size. Here's her cut.

Many authors on the network mention the importance of correctly made calculations of the transmission-wave channel, the absence of fundamental errors, the complexity of the design and the need to accurately repeat it during manufacturing. At the same time, apart from geometry and rules for choosing speakers, there is actually nothing in their approach. When drawing the design of speakers with TVL, I was accompanied by a feeling of deep understanding of mechanics, but not acoustics. I did everything on faith. After all, many people have already shared practical experience, achieved results and photographs. Many were satisfied with the resulting sound. This is a weighty argument.

I took construction plywood again. This time, two sheets, taking into account the remains from the previous version. Made it quickly and accurately. It should be emphasized that the bodies of such structures are excessively rigid, even when using 12mm plywood.

So, the listening experience is very good. The disadvantages are the same. If the lack of highs is a speaker design, then the lack of bass is a matter of the cabinet. It should be said that the bass has become more expressive and emphasized. This was noted independently by all audition participants. The surprise was as follows. At first, we listened to each speaker separately. I wanted to hear its capabilities and compare it with another option. Moreover, the first experiment of repeating the design yielded only one column. Then they were connected together. The effect was amazing. Not only a panorama of sound, a stage emerged. First of all, the sound itself has changed. Its power, openness, and lightness stunned me! Yes, later, while listening to an unequal pair of speakers, I had to raise the HF and LF on the amplifier. But the sound was not just beautiful. He held, pulled to himself. My favorite tracks sounded as if I was listening to them for the first time. On many, shades of bass and mid frequencies began to be heard, the existence of which I had not even suspected before with English floorstanding speakers. The wife's friend, who was present with her in the house in the next room while testing a pair of speakers at various volumes and styles: chamber music, jazz, electronics, left and said that she had been to the Philharmonic or a concert. This phrase was not delicacy towards the owners, but similar to the truth. The propagation of sound across adjacent rooms was a pleasant surprise. This will be an important point when receiving guests to create light, unobtrusive musical accompaniment in several areas at once. He started turning on the equipment every time he passed by. And, in the end, after three days, he finally gave up and asked the future owner to take this test version of the acoustics home to listen to until the time came for the production of ceremonial-looking speakers.

The conclusion was this: if I had chosen the speakers in the store, the sound of the resulting speakers (not the plywood look, of course) would have suited me completely. The resulting sound is said modestly. The sound is great. When a pair of speakers are playing, the high frequencies are almost enough. This is not sand, the speaker cannot reproduce it. But what it reproduces already satisfied our requirements. The resulting sound was shocking, turning something inside me, causing lumps in my throat. No exaggeration. There was only one “thorn” left - the bass on the amplifier was turned up to maximum. However, the owner of the speaker also liked the sound. Later, it was even decided to make the final version based on TVL: the dimensions and sound of the bass prevailed.

ordeals

Meanwhile, the issue of creating speakers for “own use” has become urgent. There is a high probability that after the speakers on the 75GDSh3-1 speakers, the search for good sound would have come to an end. It happened quite quickly, and it almost hit the mark. Fortunately or unfortunately, there was no second pair of 75GDSh3-1 or 3-3 heads. While crawling on the World Wide Web, collecting and analyzing information, continuing my studies, I began to closely examine the acoustics of the English company Tannoy. An ideal speaker is a device capable of linearly reproducing the entire spectrum of sound from one point. And life consists of compromises. Creating acoustics is a search for the optimum among many compromises. Each version of the speaker solves its own problems and becomes a tool in the hands of marketing: a successful combination of speakers in the speaker system, beautiful (correct) frequency separation, protruding bass, a clicking tweeter, a unique design, the use of valuable wood in the case, or simply a well-known brand. All together or separately is designed to convince the buyer of the correct choice. The older Tannoy acoustics (Westminster and Canterbury) interested me in appearance, and they are built on just one speaker. Sound from one point! The ancient, well-known company, which maintains its leading position to this day, has its admirers. I soon learned that the Tannoy acoustics are still two-way, but the LF/MF and HF speakers are coaxial. From an engineering perspective, this solution turned out to be very attractive. Great solution. On the same network I read the praise of some and the disappointment of others of the owners of this acoustics after moving it from the salon to their home. I remembered that I myself appreciated the sound of Tannoy several years ago in the listening room of a store. Then I liked the Cornwall version of the American Klipsch more. And another understanding came - good acoustics do not always sound good (on different musical material and in different rooms), and this fact had to be somehow taken into account when designing your own speakers. For example, Tannoy is equipped with two controls for adjusting the midrange and treble.

Given the need to accept compromises, the intention was to create something similar to Tannoy Westminster or Canterbury. It turned out that you can order complete copies of Canterbury speakers at “affordable” prices in China. They even offer their own speakers. There were no reviews about the quality of the system and sound. I decided not to risk it. After analyzing the accumulated information, I began to search for the design of Tannoy acoustics. I found something for Westminster speakers, and in one Polish chat - 150 photos of the process of making a copy of this acoustics. The decision to repeat almost happened. Stopped planning the installation site. Still, Westminster is designed for a large space. Of course, it is possible to install them in a room in an ordinary apartment, but the discrepancy between the dimensions of the living space and the two huge speakers is striking. I have a private house and some free space is available for accommodation. However, this option (with difficulty) was rejected from implementation. Because of the size and the unavailability of native Tannoev speakers (as well as their high cost). In addition, the design will be largely guesswork (precise drawings are not available). In this case, you cannot expect high sound quality. I wanted to have a controlled process. The study of the issue continued, but the coaxial Tannoy speaker did not give rest. Frankly, I continued to look for reasonable opportunities to purchase Tannoy heads until I came across the Spanish Beyma. This manufacturer offers a coaxial two-way speaker design that interested me. Here is a photo of a coaxially installed tweeter in the center of the woofer.

The characteristics of the reproduced frequency band were not as “chic” as those of the Tannoy. But, I remember, when in my youth my friends and I connected different heads to an audio frequency generator, we were surprised at the limited range of audible frequencies. The effect at low frequencies was especially interesting: significant movements of the speaker cone are visually observed, and at the same time there is practically no sound. Therefore, having had some doubts, I chose the 15XA38Nd speaker from the Spanish Beyma with a neodymium magnet. Of course, I was confused by the lack of traces on the Internet of using this speaker for home acoustics: both on Russian and Western resources. The power rating of the speaker was confusing: 350 W for low frequencies and plus 90 W for high frequencies. The head size was 15 inches. The lines I read from someone online remained in my head: “...transmission of the grandiose character of concert-scale sound is achieved with heads 12 inches and higher.” I agreed with this statement in my heart. And the parameters of Westminster and Canterbury confirmed the correctness of this phrase. It was also clear that the dimensions of the acoustics with these heads would be significant. But the characteristics of the speakers, their declared sensitivity of -99 dB, pushed aside the last doubts. The decision to take the risk was made. For those interested, you can find the characteristics of the head online or on the Audiomania website.

I ordered the speakers and had to wait almost three months for delivery. At this time, the issue of acoustic design returned again. Without digression, I will say that the material “Rogozhin’s Labyrinth” seriously helped me confirm my choice. It can be easily found on the Internet. I do not provide a link, since the author asks for prior approval (although the material is available for free). But there, thanks to Rogozhin, both justifications and practical recommendations are given. I would venture to make a statement: this is the only material without water, to the point, with a full set of recommendations for practical results. Hence its popularity.

After this stage, the ordeal of making a decision was left behind. Ahead were the pleasant hardships of night acoustic calculations and speaker cabinet design.

A little "around the bush"

Everything stated above briefly represents the path traveled. I described it for those who are interested in creating a high-quality speaker system with their own hands and who are faced with similar questions. The process of developing the speaker from scratch is described here, and the path was completed completely until the creation of a prototype. Anyone who wishes can also walk the entire path, more consciously. It will be possible for someone to cut corners on it.

A few words about Rogozhin's labyrinth. The attractiveness of this design lies not only in the opportunity to obtain excellent acoustic sound results (I say this with understanding), but it also opens up the possibility of designing the appearance and internal architecture in the widest range. Ultimately, this technology allows you to create speakers “for yourself.” Some kind of custom tailoring. It is extremely convenient and attractive. Probably everyone understands the difference between a purchased ready-made cabinet and a built-in one or one formed according to specific requirements. The functionality and adaptability of the second option are higher. If you take into account the possibility of creating an appearance according to your requirements, connecting the appearance of the speakers, color with the interior in the placement area, the value of the option further increases.

I will not hide that the understanding of the goal during acoustic calculations according to Rogozhin’s recommendations should be clear. At the first stage, this is achieved by following the instructions given in the material and, already at the second stage, ... gained experience. In order to achieve the desired result, I had to perform many acoustic calculations to obtain the optimum and build six experimental options in order to reach the seventh - the final one. By comparing the results obtained in material and sound, you can clarify the calculations performed and make the right choice of option, adjusting it to your preferences, ensuring excellent speaker sound.

For those who are not tired

Quite a practical side. So, the choice of dynamic heads is behind us, and the choice of design (labyrinth channel) is also behind us. On Rogozhin’s recommendation, I installed the Hornresp program from an Australian developer. After following the step-by-step instructions, I got the first result. I will say this, almost blindly I had to perform at least a hundred calculations to meet all the requirements. What you need to strive for - the instructions were given by Rogozhin. Next I share my own experience.

First of all, a photo of the attempts made to find the desired sound:

Here are five housing options for one type of speaker. All options, except the last one (this is the sixth option, obtained by altering the fifth), are made in the size of 1520 mm in height (the height of the plywood sheet). The width and depth of the housings are different and depend on the design cross-section of the channel. The internal architecture is also different. The first option (the right body in the first photo) is made of 15 mm plywood. Body weight - about 70 kg (without finishing). All subsequent ones are 12 mm plywood and weigh from 35 to 55 kg. Light vibrations of minor surface areas on 12 mm thick speaker cabinets are present at a power supply of 100 W. To be honest, the developed sound pressure at such power in a limited space cannot be sustained for long. It's good that there are no neighbors behind the wall.

Thus, at a comfortable volume level, cabinet vibrations and overtones are not noted. By the way, no overtones were noted at any volume level.

It was noticed that the volume of the third mode quenching chamber (CMQC is my term), which is located in the S1-S2 channel area, directly affects the quality of quenching of this mode. We reduce the volume of the CGTM while maintaining the length of the channel section, the range of the mode increases (in the figure above, its surge corresponds to a frequency slightly above 100 Hz) and, on the contrary, with increasing volume of the CGTM, the surge of the mode decreases. The change in the volume of the CGTM was carried out by changing the cross-sectional area S1.

Crossover debugging

The approaches and features of creating acoustic design for speakers were described above. It should be noted that the dimensions and weight of the speakers are impressive, the power of the speaker used is high. When acoustic systems were conceived, there was a belief that they should be listened to with an input power of 0.5 Watt. This circumstance was one of the limitations when choosing a speaker. There was doubt that a powerful speaker would provide effective operation with low power input. Despite the available power reserve, the built speaker prototypes perform this function, providing excellent sound with minimal power input. Moreover, without detracting from the grandeur of the sound.

Currently, the resulting speakers are connected to a Sony amplifier, whose volume level is calibrated in decibels. Late in the evening, when there are no extraneous sounds, the acoustics sound great and bright at a volume of minus 66 dB. I would also like to note that the speaker power reserve guarantees operation of the speakers with minimal linear distortion at any volume at a comfortable level.

So, debugging the sound in the crossover.

I was initially disappointed with the set of speakers I received and the FD-2XA crossovers I ordered from the manufacturer (Beyma, Spain) for these specific speakers. The first turn on at low volume led to complete bewilderment. The sound was simply terrible. At low volumes there was almost no bass. As the volume increased, they turned into something completely absurd, emitting incredible muttering. There was no music as such.

After a 3-4 hour run at high volume (70-90 W), the speakers started working (warmed up). However, dissatisfaction with the sound did not disappear. No soulfulness, no grandeur of bass, no desired emotions. Only commendable sound detail.

As I mentioned earlier, sound development was carried out in two directions: searching for optimal labyrinth parameters and working with crossover. The labyrinth work is given above. The crossover also taught its lessons. His diagram was found on the Internet. It consisted of first-order filters with a matching circuit for the input complex impedance of a low-frequency loudspeaker. The crossover frequency, according to the Beyma website, is 1800 Hz.

Of course, I could describe in detail all the searches and adjustments of the resulting filters, but something tells me that such a presentation would be boring and uninformative. I will state it in the abstract.

1. It turned out that after turning off the 15 microfarad capacitor, bass reproduction became more pleasant.
2. Tests have shown that the acoustics produce audible distortion on some musical compositions. It was possible to establish that the distortion is caused by the high-frequency part of the speaker. Distortion disappears when the cutoff frequency of the high-pass filter is shifted to 2500 Hz and higher.
3. To reduce the brightness, one might even say, the “loudness” of the speakers in the midrange, instead of a 2.2 µF capacitance, it is better to use a 0.68 µF capacitance.

After such changes, the sound became very good, but still not entirely satisfactory. An attempt to leave the woofer without inductance L1 did not further improve the sound of the speakers. However, the uneven frequency response of the speaker needs to be compensated. The manufacturer's inductance was kept in its place. Its influence is well felt.

And so, after a long period of listening to various genres, after trying to vary the values ​​of the remaining filter elements right while listening, “on the fly,” so to speak, I turned off the RC matching circuit (8.2 Ohm and 8.25 uF - indicated in the diagram). The effect was amazing. The feeling of a loudspeaker sighing, having found freedom, previously held by some kind of noose. The previously held sound broke out, flew, became light and noble. It is impossible to convey in words the newfound lightness and virtuosity of the updated sound. Exactly that sound has appeared, from which an internal response arises, chills go through the body, and pouring music fills all the cells of the brain.

It should also be noted that the Beyma crossover inductors are not serious. They are wound with 1mm copper wire. For the woofer, the inductance parameters are 1 Ohm and 1.44 mH. At high powers, loss of bass energy is guaranteed. Taking into account the inductance parameters of the low-pass filter obtained by measurement, I ordered inductances for the low-pass and capacitances for the high-frequency sections of a higher class.

Total:

The work performed made it possible to adapt the parameters of the resonant channel to the selected speaker and ensured that the speakers sounded no lower than the expectations drawn by consciousness. I'll write about the sound below. All work took about five months (weekends and evenings, taking into account the presence of a fuse, time for listening and analysis, for the following calculations, etc.) and required certain costs. I can confidently say that the sound level corresponds to acoustics in the price range of two million rubles. Actual costs, especially taking into account existing equipment, are disproportionately lower. The path traveled was not easy. The created speaker sounded not only thanks to the accurate or successful calculation of the resonant channel, intuitively, to some extent, the chosen speaker, and its approach to modeling and manufacturing the body. Let me remind you that the built acoustic system is a two-way system, the presence of a crossover is mandatory. Working with the crossover also allowed me to contribute to the final sound and gain useful experience. Damping was not used in the speaker design. Perhaps I will make an attempt to evaluate the effect of damping in a specific case. I can say that the accumulated experience made it possible to evaluate the two options mentioned at the beginning of the manufactured speakers for the 75GDSh3-1 speakers, to see the shortcomings of the bass settings and to make adjustments.

Currently there is no ready-made front speaker option for the 15XA38Nd speaker. There is a project. A new calculation has been made for speakers with a 75GDSh3-1 speaker with increased bass output. The new variant will be equipped with a BC25SC06-04 tweeter. Taking into account the existing workload and delivery of additionally ordered components, these projects will be implemented no earlier than October-November of this year. The results will be presented. Part of the speaker cabinet design for the 15XA38Nd head is shown below:

Sound

It is possible that I have developed sentimentality. The achieved sound of two-way speakers on one track or another led to mental and heart trembling, to holding one's breath, and provoked repeated listening to the compositions one liked. The correct or incorrect sound is not discussed. If the sounding speaker evokes in the listener the conviction of reality from the heard music, vocals, sounds and overtones, the goal has already been achieved. If individual turns of a musical program can dry out the throat and make the eyes wet, the task has been completed to the maximum. I am inclined to believe that the built prototypes of future speakers are close to the coveted maximum.

Frankly, if I had not received such a result, I would not have allowed myself to openly share my work. Perhaps someone will say, beginners are lucky. I was doubly lucky. Two pairs of magnificent speakers based on 75GDSh3-1 speakers, released in Soviet times, which endured 35 years of stage life, and a pair of new ones, based on 15XA38Nd speakers from the Spanish Beyma. Let him be lucky, but for those who consider it possible to make such speakers, taking into account the additional recommendations provided in the material, the result is guaranteed. It is for such people that I write.

Recently, acoustic systems with open acoustic design - shields or shallow open boxes - have gained recognition among some radio amateurs. Even industrial acoustics have been produced using this design, which have been highly praised by experts. The photo shows a famous Jamo R909 system.
Some of the problems with this solution are outlined in the article, my translation of which is given below.

Preface

At the beginning of their evolution, acoustic systems (AS) were only of the open type. Then, gradually, but almost completely, there was a transition to closed design. We will consider bass reflexes, bandpasses and other options as closed speakers, i.e. designs in which the front side of the diffuser directly radiates the speaker into the room, and the back into the closed volume of the box or into the room, but through resonators or other structures that impede the movement of air.

Closed designs made it possible to sharply reduce the volume of speakers and radically expand the frequency range downwards. The industry has almost completely switched to producing speakers specifically for closed designs. Entire generations have grown up who have heard nothing but ZY. However, many people think that “they threw out the baby with the bathwater” because they believe that the sound of the middle frequencies, the main ones for the perception of frequencies, has deteriorated.

Therefore, among radio amateurs and some acoustics manufacturers, interest in open acoustic designs has again appeared (hereinafter, for simplicity, we will call them OY). The problem is that today they practically do not produce special speakers for OY because they are in low demand, small companies can produce them for amateurs, but due to the small circulation they will be expensive.

I would like to bring to your attention my free translation of the article by Martin J. King “Designing a Passive Two Way Open Baffle Speaker System”. I think the problems raised and their solutions will be interesting.

--
Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine

Source site (En): by Martin J. King

My comment to the article

Of course, the opinion of the author of the article is not an immutable truth and does not claim to be a final and complete solution to the problem, however, it is of interest to amateurs interested in acoustics. I do not guarantee the complete accuracy of the translation, but I hope that I have presented the main provisions correctly.

The lack of measurements using a microphone and specifically at home causes skepticism. It would be interesting to know the impressions of independent listeners-experts who have not “processed” the constructions by the author. But these are just my dreams.

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The main resonance frequency is the frequency at which the total electrical resistance of the coil increases to its peak maximum;

Quality factor of the electromechanical loudspeaker system. This is a very important characteristic. It shows the degree of inertia of the system - both mechanical and electrical, and determines the rate of attenuation of free oscillations of the monitor;

Nominal frequency range, i.e. frequency region in which the loudspeaker operates to the standard;

Average sound pressure is the pressure developed in a certain frequency range and at a certain point in the sound field when a certain electrical power is supplied;

Characteristic sensitivity;

Frequency response unevenness is the difference between the maximum and minimum pressure in the nominal (or, if necessary, in any other) frequency range. For good loudspeakers it does not exceed 3-4 dB;

Frequency response - graphical representation of the previous parameter;

Directionality - a change in pressure when deviating from the working axis by a certain angle at a constant distance from the center;

Harmonic distortion (usually the 3rd harmonic and higher) - the level of harmonics, expressed as a percentage, that appears when a pure sinusoidal signal is fed to the loudspeaker, in which there are no harmonics;

Intermodulation distortion factor. We need to say more about this parameter. Suppose a signal containing two frequencies, 100 and 1000 Hz, is applied to a loudspeaker. As a result of the interaction of these frequencies, combination frequencies arise (sometimes incorrectly called combination harmonics) with frequencies corresponding to the difference or sum of the upper frequency and a multiple of the lower frequency - in our case, 800, 1200, 600, 1400 Hz, etc. The lower the overall level of these frequencies, the better. An ideal loudspeaker should not generate these frequencies at all, or any others not present in the original signal.

Of the several power parameters, the most important are the following:

Rated power - power at which nonlinear distortions do not exceed a specified limit;

“musical power”, also called “nameplate”, “maximum noise”, “continuous”, etc. - power in a certain frequency range that a loudspeaker can withstand a real or broadband noise signal without damage for some time;

Peak (maximum short-term) power - the power that a loudspeaker can withstand a noise signal for a short pulse (from 0.01 to 1n) without damage;

Horn emitters. The main disadvantage of direct radiating loudspeakers is their extremely low efficiency. The reason for this is the mismatch between the resistances of the mechanical system and the environment. To increase the radiation resistance, it is necessary to increase the size of the emitter, but this will entail an increase in the mechanical resistance of the emitter mass and will not provide a gain in efficiency. Since the diffuser performs two functions: converting mechanical vibrations into acoustic ones and radiating these vibrations into the environment, such a contradiction can only be resolved by separating these functions, which is carried out in horn loudspeakers. The horn also serves to match the resistance of the mechanical system and the environment. A horn is a pipe with a variable cross-section. The inlet of the radiating horn (throat) is smaller than the outlet (mouth). The output hole is the emitter, and the input hole is the load for the mechanical system. Thus, the emitter can be made as large as desired, and the mechanical system can be made small and therefore lightweight.

Types of horns: a - dual; b - sectioned.

Horns are used with different laws of change in cross-section. The most common horns are exponential; Conical ones are used less frequently, since they have a much less uniform amplitude-frequency response. For sharp directivity and a lower limit of the transmitted frequency range, the output aperture of the horn should be increased and a horn of greater length should be selected. To increase the length, the horn is often rolled or folded. We encounter similar phenomena in wind musical instruments: the lower the register of the instrument, the longer its horn.

To concentrate or distance sound waves, acoustic lenses are used, based on the refraction of sound rays when passing from one medium to another with different propagation speeds (for example, the speed of propagation of sound waves in porous materials or in grilles and louvers of plates differs from the speed of propagation in open space) . The disadvantages of the horn include nonlinear distortions caused by the large magnitude and sharp change in the amplitude of sound pressure within one wavelength in the throat of the horn, as well as frequency distortions in conical horns. Horn electrodynamic loudspeakers have two design options: narrow-neck and wide-neck. The area of ​​the horn inlet in narrow-neck loudspeakers is several times smaller than the area of ​​the piston diaphragm; in wide-neck loudspeakers, these areas are either the same or close to each other.

These are the main technical parameters of loudspeakers. It should be noted that passport data should be handled with caution. Some manufacturers sometimes name, for example, the range of reproduced frequencies without indicating the unevenness of the characteristics; in this case, it may turn out that the declared lower threshold of 25-30 Hz is ensured only when the pressure drops by 10 dB or more, which is actually a falsification.

I would like to note that in the 80 years since the invention of the dynamic, the task of conveying the sound of a symphony orchestra, ensemble, voice, etc., one can only be surprised and admire the genius of the design of the loudspeaker itself, audio technology has come a long way: from the phonograph to the DVD - and the loudspeaker is structurally fundamental did not change. Only the technology of its manufacture and materials have changed radically. Considering that such a simple design (consisting of just a few elements: a diaphragm, a coil and a magnetic circuit) faces a huge mass-produced acoustic product, billions of which are used all over the world.

Acustic systems

From the characteristics of loudspeakers, let's move on to the acoustic systems made up of them. Unfortunately, domestic terminology has not yet been established and does not correspond to foreign ones. So, in fact, “speakers” in our terminology, especially in old GOSTs, are called “heads”, and acoustic systems are called “loudspeakers”. In modern professional and commercial environments, the term “acoustic system” is used, and household acoustic systems are commonly called “speakers”, and professional studio acoustic systems “monitors”. Some, confused, simply switched to transliteration from English - “speaker”, in their mouths not the chairman of the Duma at all, but the speaker “in general”. At the same time, a low-frequency “speaker” is a “woofer” or “subwoofer”, a mid-frequency one is a “driver”, and a high-frequency one is a “twitter”, but there is also a Russian definition for it: “tweeter” (by the way, the exact translation of the word tweeter).

An ideal speaker system should have only one full-range loudspeaker that reproduces the full frequency range of 20-20,000 Hz. However, since different and often mutually exclusive requirements are placed on a loudspeaker when operating in different frequency bands, it is almost impossible to make such an ideal loudspeaker, at least at an affordable price. Therefore, the vast majority of modern acoustic systems have two or more heads operating in different frequency bands. A low-frequency loudspeaker is always a diffuser speaker, a mid-frequency loudspeaker too, but sometimes there are mid-frequency horn-type ones. High-frequency loudspeakers are produced as diffuser, horn and dome (dome, bullet). The two-way system is usually used for so-called “near-field monitors”, i.e. located directly near the sound engineer's head. One speaker in such a system reproduces low and medium frequencies, the other - high frequencies. To separate frequencies, there is a separating filter inside the housing (in foreign terminology, crossover). In this case, the frequency of separation of the input electrical signal for supply to the low-frequency and high-frequency speakers is selected slightly higher than the lower limit of the range of the high-frequency loudspeaker. The RF loudspeaker power rating is also taken into account. 3-band systems consisting of a low-frequency loudspeaker (woofer), mid-frequency (mid-driver), and high-frequency (tweeter) reproduce the audible frequency range much better. Working in a limited range of “own” frequencies improves the sound of low- and mid-frequency speakers and reduces distortion, because The high-order harmonics generated by these speakers are higher than the cutoff frequency of the filter and are correspondingly suppressed.

Acoustic design

P
The front and rear surfaces of the oscillating piston emit oscillations in antiphase: when the front surface at time t 1 creates compression of the medium, then the opposite surface of the piston, at the same moment t 1, creates a vacuum.

Compression and rarefaction spread in different directions (Fig. 18.6). Under certain conditions, bending around the piston, the waves interfere with oscillations arising from the opposite side (phase) and their sum tends to zero. This phenomenon is called acoustic short h short circuit (AKZ). The occurrence of a short circuit reduces the output of the acoustic power of the emitter (piston) in the region of those frequencies at which the emitted wavelength is large compared to the size of the piston (diffraction conditions). This phenomenon occurs at low frequencies of LF sound waves.

H To avoid AKZ at low frequencies, it is necessary to install a screen so that vibrations from the compression area do not bend around the piston and eliminate the phenomenon of interference. The screen is installed in combination with the emitter. This technique is called acoustic screen design (design). The simplest type of design is a shield (Fig. 18.7). To completely eliminate the short circuit, it is necessary to install a shield whose linear dimensions of the plane were greater than half the length of the LF sound wave λ:

d > λ/2;( 6.1.1)

A standard acoustic screen according to GOST 16122-84 has a size of 1350 x 1650 m.

A closed box (CL, Closed Box) is a second-order design (Fig. 6.1.3 A and Fig. 6.1.4). Compared to other types of loaded design, it is less sensitive to deviations in characteristics. Its main advantages: excellent impulse response. This theoretically allows you to obtain a flat frequency response. Disadvantage = low efficiency, which requires increased amplifier power, and increased level of even harmonics due to the asymmetrical load of the diffuser.

A – closed box, B – bass reflex, C – passive radiator

H
The resonance frequency and total quality factor of the head when installed in a closed box with a volume Vc commensurate with the equivalent Vas increase. Thus, when installing a head in a cell with a volume equal to an equivalent one, its resonant frequency and quality factor increase by 1.41 times, in a box with a volume of 0.5Vas = by 1.73 times, and so on.

The next most common type of acoustic design is a bass reflex. Speakers with an Fs/Qts value of 90 or more are suitable for use in a bass reflex. Of all the possible designs of double-action systems, the bass reflex is the most widely used (FI, Vented Box, Ported Box, Bass Reflex). This is a resonant system. The mass of air contained in the FI at its tuning frequency behaves like a diffuser, being a source of sound vibrations. A passive radiator is a type of FI in which the mass of air in the tunnel is replaced by the mass of the moving system of the passive radiator. A conventional dynamic head is most often used as a passive radiator, sometimes with a remote magnetic system.

Structurally, it is made in the form of a closed box with two holes

The emitter (piston) is placed in one hole, the other hole is free, and has a design in the form of a small pipe with a volume V. The bass reflex frequency is ƒ f, (Fig. 18.10).

With slow oscillations (8Hz - 10Hz) spring C in (Fig. 18.10). connecting both masses m does not have time to deform, since it has a large elastic resistance z:

z=1/(ω·С in) ; (18.1)

As a result, both masses m p and m b move with the same phase. In this case, the wave emitted by the hole is shifted by 180 o in phase compared to the wave emitted by the piston. An increase in frequency leads to a decrease in the elastic resistance of the air in the box and the spring C in begins to deform. As a result, a phase shift occurs between the oscillations of both masses m p and m b, increasing with increasing frequency and reaching 180 o at the box resonance frequency. Thus, the air in the hole and the piston oscillate in antiphase, and the waves emitted by them will be in phase and interfering and reinforcing each other. The bass reflex resonance frequency ƒ f is, as a rule, chosen equal to the resonance frequency ƒ 0 of the head (piston), i.e. in the low-frequency operating range (Fig. 18.10). With a further increase in frequency, sound emission from the hole does not occur, since the inertial resistance of the air in the hole ω·m in becomes extremely large. At these frequencies, the bass reflex is similar to a closed box. The internal surfaces of the bass reflex, as well as the box, are covered with sound-absorbing material.

Figure 18.11

In the diagram fig. 18.11 power amplifier, which is a signal source for a loudspeaker, with open circuit voltage and the output resistance is converted into a voltage generator that simulates a generator with an output value of acoustic pressure, after the generator there is a total resistance, which is the sum of the active resistance of the voice coil and the output resistance of the amplifier. M as is the acoustic mass of the moving system, the attached air mass from the front and back sides of the diaphragm. C a s - acoustic flexibility of suspensions. R as - acoustic resistance of the moving system. M av is the acoustic mass of air in the phase-inverted tube.

Acoustic load. The diffuser of a dynamic head in a closed design experiences significantly different resistance when moving forward and backward. Load asymmetry is a potential source of nonlinear distortion. Therefore, back in the mid-70s, acoustic systems appeared in the design of which this drawback was eliminated by introducing an additional acoustic load on the front surface of the diffuser. Similar solutions can be used to limit the amplitude of diffuser oscillations in double-acting systems. There are no reliable methods for calculating acoustic load; experimentation is necessary.

Figure 18.12

Acoustic loading can be implemented in various ways. In the simplest case (Fig. 18.12 A), a reflective surface (Reflex Body) is placed in front of the diffuser. However, this solution worsens the sensitivity of the speaker and its frequency response at medium frequencies. In some modern designs, a lenticular-shaped body of rotation is used to improve the frequency response and directivity pattern (Fig. 18.12 B). For the same purpose, you can use a reflective surface located at an angle (Fig. 18.12 B). The wedge load partly acts as a short horn, which contributes to the acoustic amplification of a certain frequency range. As a further development of this idea, acoustic systems with a resonator appeared (Fig. 18.12 D). After this, there was only one step left to take in the design of bandpass loudspeakers.

P
voice loudspeakers. A common feature of all bandpass speaker designs is the presence of one or more resonant chambers and the installation of a dynamic head inside the housing. Since these systems are no longer direct radiation systems, their design and manufacture are very complex. Therefore, mainly fourth-order designs have become widespread (Fig. 18.13 A). Bandpass loudspeakers of the sixth (Fig. 18.13.B, C) and eighth (Fig. 18.13.D, E) orders are less common.

Figure 18.13

Bandpass loudspeakers: A – closed box resonator, B – double-acting bass reflex, C – sequential bass reflex, D – sequential double-acting bass reflex, D – sequential double-acting bass reflex

Bandpass acoustic design is used exclusively for subwoofers. The advantage of a bandpass loudspeaker is its high efficiency, but the pulse and phase characteristics are very mediocre and deteriorate with increasing order. For all designs, except for a closed resonator box, it is desirable to use an infra-low-pass filter (as for a classic bass reflex).

In addition to the considered designs of bandpass loudspeakers with one dynamic head, speakers with two heads are also known. The design is obtained by combining two identical strip systems. One of the chambers becomes common, its volume doubles. (Fig. 18.14 A, B) shows two design options of the fourth order, and Fig. 18.14 B - the sixth.

ABOUT
One of the advantages of such designs is that they do not require a special monophonic amplification channel: each head can be connected to its own channel of a stereo UMZCH.

Figure 18.14

Twin heads. In almost all of the designs considered, dual dynamic heads can be used. To do this, heads of the same type are installed using one of the methods shown in Fig. 18.15. The resulting design can be considered as a new low-frequency dynamic head with completely different properties. The theoretical values ​​of the total quality factor and the frequency of the main mechanical resonance of the resulting system are calculated as the geometric mean of the corresponding values ​​of the original heads. Since when doubling, heads of the same type with fairly similar parameters are usually used, we can assume that these parameters will remain virtually unchanged. However, the bound volume of air enclosed between the diffusers of the heads increases the effective mass of the moving system, lowering the frequency of the main mechanical resonance of large heads to 80% of the original.

Figure 18.15 Installation of double heads: A - face to face, B - back to back, C - in the back of the head, D - with associated volume

Until now, wood remains the main material for the manufacture of speaker cabinets. It is taken into account that wood has its own acoustic properties, and the introduction of its own overtones by the body is undesirable. They are combated both by special damping structures and by using chipboard (chipboard), which we so dislike in furniture, instead of solid “clean” wood. Chipboard does not have any structure (which is the linear fibers of wood), therefore it is less susceptible to resonances. The outside of the chipboard is finished with various coatings, including those imitating wood (veneer), but this finishing is purely decorative.

Along with the traditional use of wood, attempts to use other materials - plastic, metal, stone - continue. There are quite a large number of plastic acoustic systems, usually small in size (near field), which sound quite acceptable and are cheap due to the manufacturability of the housings. However, attempts to create plastic enclosures for large-sized speaker systems have not yet been successful (from the point of view of acoustics, of course, and not “box construction”). The fact is that a large case must also have a large mass, otherwise such resonances begin to “walk” in it that their suppression is much more expensive than, for example, in a wooden case.

Metal speaker enclosures have been quite effective and have become popular lately. This is due, in particular, to the widespread use in studio practice of computers with traditional cathode-ray picture tube monitors, which are adversely affected by speaker magnets if they are too close. The metal body of the speaker system is in this case a screen. In addition, the metal is easy to manufacture and provides the necessary rigidity for acoustic requirements.

The use of stone also produces interesting results. There is no need to talk about the manufacturability of the enclosures, but the acoustic results are excellent. However, the problem is solved by a compromise - the use of synthetic material, which makes it possible to combine the ease of production of the body with the massiveness and rigidity of the stone.

However, despite the active search for new materials, the “good old” wood remains the main one.

For a long time, the traditional arrangement of speakers on the front wall of the case in the form of a “snowman” (low-frequency loudspeaker at the bottom, mid-frequency loudspeaker in the middle, and high-frequency loudspeaker at the top) suited users. However, it has been noted that the distance from the centers of different speakers to the listener is often different, and the sounds from them do not reach the listener strictly in phase. The amount of non-synchrony is extremely small, but the problem exists. The solution was found in various types of so-called coaxial loudspeakers. In the simplest cases, the high-frequency speaker was fixed in front of the center of the cone of the low-frequency diffuser, but, naturally, without physical contact with it. Another, more complex, but also more elegant way of creating a point emitter was proposed by the famous English company Tannoy. In their now classic system, the tweeter diaphragm is located behind the woofer magnet. The core of the low-frequency loudspeaker has channels through which air pressure from the high-frequency membrane passes in the direction of radiation of the low-frequency diffuser, which is also a horn for high frequencies. This way, ideal pinpoint radiation is achieved.

It was previously mentioned that at high frequencies diffusers, especially large ones, vibrate mainly in the central part adjacent to the coil. This property was used to create wideband loudspeakers, popular in professional equipment two or three decades ago and still found today. In these loudspeakers, an additional micro-diffuser was glued into the central part of the diffuser, which worked as a coaxial high-frequency loudspeaker. Of course, the result was far from the quality of real coaxial systems, but the high-frequency response of these full-range speakers did improve significantly.

Modern production is extremely standardized. Standards have also emerged for the size of loudspeakers - from small to large. Modern speakers are usually measured in inches, and this is convenient: it gives not only the size, but also, as it were, the “product number”.

Even for powerful acoustics, speakers larger than 21" are not used, and eighteen-inch ones are not often seen. Next in order are 15", 12", 10" and 8".

Mid-frequency - 8", 6.5" and 5". High-frequency - 4", 2.5" and 1.5". However, the dimensions of the diffuser are important mainly for low-frequency loudspeakers, directly affecting the lower limit of the range and the sound pressure level.

The real sound picture can only be presented by large acoustic systems (control monitors) of the “far field”, sounding evenly over the entire frequency range and not overloading at the recommended listening level (about 90 dB).

Directivity characteristics

As follows from the theory of acoustics, the ideal source of sound is a “point” emitter, that is, an emitter whose dimensions, compared to the length of the sound wave emitted by it, can be neglected. Unfortunately, real acoustic systems are very far from such an ideal emitter and, moreover, have different radiation patterns for different frequencies of the sound signal. The width of a loudspeaker's radiation pattern is determined by the ratio of the wavelength of the sound signal emitted by it and the geometric size (diameter) of the loudspeaker cone. In addition, the radiation pattern in the region of the joint action of radiation from two loudspeakers depends on the mutual phase shift of their signals, determined by the separating filter circuit of the speaker system.

Today in “speaker building” there are two approaches related to the directionality of acoustic systems. Adherents of the first of them argue: the system must be highly directional in order to eliminate harmful sound reflections. According to this logic, highly directional speakers are required to deliver sound information exactly to the listening area without unwanted “impurities” in the form of reflections from walls and various objects. Well-known examples are speakers built on highly directional coaxial drivers (Tannoy, KEF). Coaxial two-way radiators are mid-frequency and high-frequency loudspeakers assembled on a single magnetic system. The dome “tweeter” is assembled on the internal core of the magnetic system and is located inside the cone diffuser of the mid-frequency loudspeaker, which is a kind of horn-sound guide for sound waves emitted by the “tweeter”. Such radiators have a number of unique features that significantly distinguish them from the mass of other loudspeakers. Firstly, thanks to the design used, the emission centers of the HF and midrange loudspeakers are located practically at the same point, which eliminates the occurrence of phase and time distortions of the signals emitted by them. Secondly, since the radiation of medium and high frequencies is physically carried out from one point in space (conditionally), Uni-Q type emitters have a good radiation pattern at these frequencies due to these serious advantages, the sound of speaker systems with coaxial emitters is characterized by excellent localization of sound sources in space. In European speakers, there are D "Appolito schemes, in which the tweeter is located between two identical low-frequency/mid-range heads - this sharpens the directivity at a number of frequencies, reducing the number of sound reflections from the floor and ceiling. In expensive speakers, sometimes there are entire garlands of tweeters designed for jewelry focus high frequencies A diametrically opposed approach is omnidirectional loudspeakers, or omnidirectional loudspeakers. Such loudspeakers, by virtue of their design, are completely

Acoustic systems (AS) with dual heads at one time attracted the interest of many radio amateurs. Many of them chose these speakers and, judging by the reviews, are satisfied with their sound. Some foreign companies have also shown interest in dual heads. For example, in 1985, the Jarho company advertised a number of new speakers, claiming in the advertising brochure that their high power and high fidelity with relatively small dimensions were achieved through the use of dual heads. However, the lack of in-depth analysis and, most importantly, practical recommendations for the design of speakers with such heads, as well as the appearance on sale of modern low-frequency compression emitters, have somewhat reduced the interest of radio amateurs in dual dynamic heads. Research in recent years has revealed new advantages of this type of emitter. By the way, it turned out that its optimal design is one in which the heads face each other with diffusers, so in the future we will only talk about this option. The main advantages of a dual head (compared to a single one) are a smoother frequency response, less nonlinear distortion and a smaller required volume of the acoustic design box. The frequency response is smoothed out due to the mutual damping of the heads that make up the dual one. Each single head, within the limits of permissible deviations, has its own uneven frequency response due to production technology, so the frequencies of peaks and dips in their frequency response do not coincide. In a dual head, some of these peaks and dips are mutually compensated. Nonlinear distortions are reduced due to the fact that the dual head (unlike a single head) is a symmetrical electro-mechanoacoustic system. For this reason, the air resistance on both sides is almost the same; due to the design features and properties of the material, there is no difference in the flexibility of the suspension for some types of heads when the diffuser moves forward and backward. Finally, the asymmetry of the distribution of magnetic induction in the gap of the magnetic system, which negatively affects the level of the second harmonic, does not appear in the dual head.

Fig.1. Dual head location

Of course, there are other ways to reduce speaker nonlinear distortion. To reduce even-numbered harmonics, the Swedish company Audio-Pro, for example, installs two (out of four) low-frequency heads with magnetic systems facing outward in the AC B4-2000 low-frequency unit. However, the dispersion of the emitters generates interference of sound waves and narrows the directional pattern of the speakers. Jamo has found a more advanced solution. In the low-frequency section, she used one powerful dual head, placing it on a horizontal board (see Fig. 1, a), under which there is a horn that directs the sound towards the listener and matches the mechanical resistance of the moving head system with the air environment. As for the volume of the box, it is reduced due to the fact that the resulting flexibility of the suspension of a double head compared to a single head is halved. The mass of the movable system of the double head increases by the same amount, so the frequency of the main mechanical resonance does not change.

To maintain the calculated resonant frequency of a double head in an acoustic design, a box with a volume half that of a single head of the same type is required, as can be seen from the following relationships: f i / f r = \/?c g / c i + 1; c i = 1.14V / D 4 eff, where: f i and f r are the resonant frequencies of the head in the box and open air space, respectively, c g and c i are the flexibility of the suspension of the head and the air in the box, V is the volume of the box, D 4 eff is the effective diameter of the diffuser. Since the value of D 4 eff of a double head is the same as that of a single head, in order to fulfill the above relations when reducing flexibility c r by 2 times, it is necessary to reduce flexibility c i, and therefore the volume V by the same amount (compared to two heads installed separately, the volume will decrease by 4 times).

It would seem that by increasing the number of heads working per hole of the speaker, it is possible to further reduce its dimensions. However, in practice, the heads cannot be brought together so close that their geometric dimensions do not affect the phase shifts of sound waves emitted by the outermost heads. In this case, the length of the propagation path of sound waves from the innermost head to the outermost one becomes commensurate with the lengths of the emitted waves, which ultimately counting leads to subtraction and distortion of audio signals (which is why you can’t double mid- and high-frequency heads). In addition, the decrease in efficiency in this case will become noticeable.

The speaker presented to our readers is a bass reflex loudspeaker with a useful internal volume of 50 liters. A dual head composed of 6GD-2 was used as a low-frequency emitter, and 15GD-11 and 6GD-13 were used as a mid- and high-frequency emitter, respectively. The dual head is installed on an inclined board (see Fig. 1, b), which, together with the side and bottom walls of the box, forms a horn, which, in the author’s opinion, is more successfully directed at the listener than in speakers from the Jamo company (Fig. 1, a ). In addition, with this arrangement of the board with a double head, the volume of the box is used more efficiently, which made it possible to reduce the dimensions and weight of the speakers.

Main technical characteristics of the speakers:

Rated power, W……………………………………… 12

Rated power, W, not less than …………………………. thirty

Nominal electrical resistance, Ohm……….. 4

Nominal frequency range, Hz……………………….30…18000

Thanks to the use of highly efficient 6GD-2 low-frequency drivers, the sound volume at a relatively low rated power (12 W) is not inferior to industrial speakers of the S-90 type with a power supplied to them of 30 W. As for sound quality, most listeners prefer the speakers described below.

The circuit diagram of the speaker system (based on the separation filter described in) is shown in Fig. 2, the design is shown in Fig. 3. The AC 3 box is made of 20 mm thick particle board, covered with paper imitating valuable wood species. The double head 17 is fixed on the board 10, the mid-frequency (12) and high-frequency (16) heads are on the front wall 4. The rear wall 15 is removable. The mid-frequency head is isolated from the rest of the box by box 13, made of 10 mm thick plywood and fixed to wall 4 using corners 11 and screws. The bass reflex tunnel 14 with an internal diameter of 50 and a length of 100 mm is glued together from four layers of electrical cardboard 0.5 mm thick. It is secured in the hole in the front wall 4 with glue. The output hole of the horn of the dual head 17 is closed by a grille (parts 1, 2), the holes opposite the mid- and high-frequency heads are covered, respectively, by convex metal grids 6 and 8 with ring decorative frames 5 and 7. Frame 1 is bent from a strip with a cross-section of 5X20 mm made of aluminum alloy , 2 rods with a diameter of 4 mm are made of stainless steel and glued into holes drilled in 20 mm increments in the upper and lower sides of the frame. The ring frames of the holes for the remaining heads, as well as the holes for the bass reflex tunnel, are bent from a strip with a cross section of 5X10 mm made of the same material. To fasten the frame of the mid-frequency head 5, four studs with M3 threads are provided, inserted with glue into holes with a diameter of 3.2 and a depth of 7 mm, drilled in the end of the ring on the side facing panel 4. Before cutting a hole for the head 12 in the front wall along the outer With a frame diameter of 5, using a round cutter with a cutter and a chisel, you need to select a groove 20 mm wide and 2...3 mm deep. During assembly, the head 12 is first secured, then the mesh 6 is secured using wire brackets or nails, and finally the frame 5 is installed in place, which additionally presses the mesh to the panel 4. The frame 7 of the high-frequency head 16 is secured in the groove of the front panel with glue. To give the speakers the appropriate appearance, the outer ends of frame 1 and frames 5, 7 and 9 must be polished to a mirror finish, and their side surfaces (both internal and external) must be painted with black paint. The same color should be used to paint the metal grids 6 and 8, the internal surfaces of the bass reflex tunnel, the horn of the double head and the entire area of ​​the circle under the grid 6, the diffuser holder of the lower head 6GD-2, the part of the diffuser holder of the head 12 facing the listener and the heads of the screws securing it.

LITERATURE:

1. Zhurenkov A. Dual dynamic heads. - Radio, 1979, No. 5, p. 48.

2. Prospectus of the company “Jamo”. Zurich, 1985,

3. Aldoshina I. A., Voishvillo A. G. High-quality acoustic systems and emitters. - M: Radio and Communications, 1985.

4. Ephrussi M. M. Loudspeakers and their application. Ed. 2nd, revised and additional - M.: Energy, 1976.

5. Zhbanov V. Ways to reduce the size of acoustic systems. - Radio, 1987, No.?, p. 29-31.

6. Raikin L. First, take out the low-frequency speakers. - Inventor and innovator, 1985, No. 7, p. 40.

7. Raikin L. Both the wheel and the circle cutter. - Inventor and innovator, 1986, No. 2, p. 29.

A. ZHURENKOV, Zaporozhye