Horn acoustics. Basics of acoustics for dummies: types of acoustic design of speakers Homemade horn acoustics how to make

Before a detailed consideration of the problem, let's outline the range of tasks, knowing the ultimate goal, it will be easier to choose the right direction. Making speaker systems with your own hands is an infrequent case. It is practiced by pros, novice musicians, when store options are not satisfactory. There is a task of embedding in furniture or high-quality listening to existing media. These are typical examples that are solved by a set of generally accepted methods. We will take a look at it. We do not recommend flipping the speaker device diagonally, delve into it!

Speaker system device

There is no chance of making a speaker system yourself without understanding the theory. Music lovers should be aware that the biological species Homo Sapiens hears sound vibrations of frequencies from 16-20000 Hz with the inner ear. When it comes to classic masterpieces, the spread is high. The bottom edge is 40 Hz, the top edge is 20,000 Hz (20 kHz). The physical meaning of this fact is that not all speakers are able to reproduce the full spectrum at once. Relatively slow frequencies work better with massive subwoofers, and beeping at the lower border is reproduced by smaller loudspeakers. It is clear that for most people this means nothing. And even if part of the signal is lost, will not be reproduced, no one will notice it.

We believe that those who have set the goal of self-producing a speaker system should critically evaluate the sound. It will be useful to know that a suitable speaker has two or more speakers in order to be able to reflect the sound of a wide band of the audible spectrum. But the subwoofer, even in complex systems, is one. This is due to the fact that low frequencies make the environment vibrate, penetrating even through walls. It becomes unclear where exactly the basses are coming from. Therefore, there is only one bass speaker - a subwoofer. But as for other things, the person will confidently say from which direction this or that special effect came (the ultrasound beam is blocked by the palm of your hand).

In connection with the above, we will divide the acoustic systems:

1. The sound in Mono format is unpopular, so we avoid touching on historical digressions.
2. Stereo sound is provided by two channels. Both contain low and high frequencies. Equal columns equipped with a pair of speakers (bass and squeak) are better suited.
3. Surround Sound is distinguished by the presence of a larger number of channels, creating a surround sound effect. We avoid getting carried away with subtleties, traditionally 5 speakers plus a subwoofer convey the gamut to music lovers. The structure is varied. Research is still ongoing to improve the quality of acoustic transmission. The traditional arrangement is as follows: at the four corners of the room (roughly speaking) along the column, the subwoofer is on the floor to the left or in the center, the front speaker is placed under the TV. The latter in any case is supplied with two speakers or more.

It is important to create the right enclosure for each speaker. Low frequencies will require a wooden resonator, for the upper end of the range it does not matter. In the first case, the sides of the box serve as additional emitters. You will find a video demonstrating the overall dimensions corresponding to the wavelengths of low frequencies in science, it practically remains to copy finished designs, the topic is devoid of sensible literature.

The scope of tasks is outlined, readers understand that a home-made acoustic system is built with the following elements:

• a set of frequency speakers according to the number of channels;
• plywood, veneer, hull boards;
• decorative elements, paint, varnish, stain.

Acoustic design

Initially, we select the number of columns, type, location. Obviously, to produce in a larger number than the home theater has channels is an unreasonable tactical move. A cassette recorder needs two speakers. At least six cases will be released for the home theater (there will be more speakers). According to the needs, accessories are built into furniture, the quality of bass reproduction is lame. Now the question of choosing speakers: in the publication of the authorship of Naidenko, Karpov, the nomenclature is given:

1. Bass - CA21RE (H397) 8" fit.
2. Medium range - 5" MP14RCY/P (H522) head.
3. Treble - head 27TDC (H1149) 27 mm.

They gave the basic principles for designing acoustic systems, proposed an electrical circuit for a filter that cuts the stream into two parts (a list of three subranges is given above), and gave the name of purchased speakers that solve the problem of creating two stereo speakers. We avoid repeating ourselves, readers can take the trouble to look through the section, find specific titles.

The next question is the filter. We believe that National Semiconductor will not be offended if we scan the drawing of the Ridiko translation amplifier. The figure shows an active filter powered by +15, -15 volts, 5 of the same type of microcircuits (op-amps), the cutoff frequency of the subranges is calculated by the formula shown in the image (duplicated by text):

P - Pi known to schoolchildren (3.14); R, C - ratings of the resistor, capacitance. In the figure, R \u003d 24 kOhm, C - is hushed up.

Active filter powered by electric current

Given the capabilities of the selected speakers, the reader will be able to choose a parameter. The characteristics of the column playback band are taken, the overlap junction between them is found, and the cutoff frequency is placed there. Thanks to the formula, we calculate the value of the capacitance. Avoid touching the resistance value, reason: it can (disputed fact) set the operating point of the amplifier, the transfer coefficient. On the frequency response given in the translation, which we omit, the boundary is 1 kHz. Let's calculate the capacity of the specified case:

C \u003d 1 / 2P Rf \u003d 1/2 x 3.14 x 24000 x 1000 \u003d 6.6 pF.

Not so hot what a large capacity is selected from the condition of the maximum allowable voltage. In a circuit with sources of +15 and -15 V, it is unlikely that the nominal value exceeds the total level (30 volts), take a breakdown voltage (the reference book will help) of at least 50 volts. Don't try to put in DC electrolytic capacitors, the circuit has a chance of blowing up. There is no point in looking for the original circuit of the LM833 chip because of Sisyphean labor. Some readers will find a replacement chip that is different ... we hope for understanding.

As for the relatively small capacitance of capacitors (retail and total), the description of the filter says: due to the low impedance of the heads without active components, the ratings would have to be increased. Naturally causing the appearance of distortion due to the presence of electrolytic capacitors, coils with a ferromagnetic core. Feel free to move the range division boundary, the total bandwidth remains the same.

Passive filters will assemble with their own hands each trained in soldering, a school physics course. In an extreme case, enlist the help of Gonorovsky, the intricacies of the passage of signals through radio-electronic lines with non-linear properties are nowhere better described. The presented material interested the authors in low and high frequency filters. Those who want to divide the signal into three parts should read the works that reveal the basis of bandpass filters. The maximum allowable (or breakdown) voltage will be scanty, the value will become significant. To match the mentioned electrolytic capacitors with a nominal value of tens of microfarads (three orders of magnitude higher than those used by an active filter).

Beginners are concerned about the issue of obtaining a voltage of +15, -15 V powering speakers. Wind the transformer (an example was given, PC program Trans50Hz), supply a full-wave rectifier (diode bridge), filter, enjoy. Finally, buy an active or passive filter. This thing is called a crossover, carefully select the speakers, more accurately correlate the ranges with the filter parameters.

For passive speaker crossovers, you will find many calculators on the Internet (http://ccs.exl.info/calc_cr.html). The initial figures of the calculation program takes the input impedance of the speakers, the division frequency. Enter the data, the robot will quickly supply the capacitance and inductance values. On the given page, set the filter type (Bessel, Butterworth, Linkwitz-Riley). In our opinion, a task for the pros. The active stage shown above is formed by 2nd order Butterworth filters (frequency response reduction rate of 12 dB per octave). It concerns the frequency response (frequency response) of the system, it is clear only to professionals. When in doubt, choose the golden mean. In the literal sense, check the box on the third circle (Bessel).

Acoustics of computer speakers

I happened to watch a video on YouTube: the young man announced that he would make a speaker system with his own hands. The youth is talented: he ruined the speakers of a personal computer - well, none at all - brought into the world God's amplifier with a regulator, placed it in a matchbox (acoustic system case). Computer speakers are notorious for poor bass reproduction. The devices themselves are small, light, and secondly, the bourgeois save materials. Where does bass come from in an acoustic system? The young man took ... read on!

The most expensive component of the music center. Hi-end class acoustics bypasses a cheap apartment in cost. Repair, assembly of speakers is a good business.

The low-frequency amplifier of the speaker system will assemble an advanced radio amateur, no Kulibins are needed. A volume knob sticks out of a matchbox, input on one side, output on the other. The speakers of the old speaker system are small. The young man got hold of an old loudspeaker not of fabulous size, but solid. From a Soviet-era speaker system.

So that the sound would not disturb the air with a squeak, the clever boy knocked together inch boards in a box. The speaker of an old acoustic system was placed in the size of a mailbox, shifted, as is done by manufacturers of modern home theater subwoofers. I was too lazy to finish the speaker from the inside with a sound insulator. Those who wish can use batting or other similar material for the speaker system. Small speakers are placed inside oblong boxes, just containing the end of the loudspeaker. The proud lad connected one channel of the speaker system to two small speakers, the second to one large one. Works.

The young man is a fabulous fellow, does not drink in the alley, becoming like his peers, does not spoil future brides in his free time, is busy with business. As one acquaintance said: “The young generation is forgiven for the lack of knowledge and experience, not for the excess of arrogance reinforced by indifference.”

Improvements

We decided to improve the technique, frankly we hope that the addition will help make the speaker system a little better on its own. Problem? The concept was invented by radio engineers, the creators of acoustic systems - frequency. The vibration of the universe has a frequency. They say that even the human aura is inherent. It is not for nothing that each good speaker can accommodate several speakers. Large ones are for low frequencies, bass; others - for medium and high. Not only the size, but also the device they have is different. We have already discussed this issue and we refer those who are interested to the written reviews, where the classification of acoustic systems is given, the principles of operation of the most popular ones are revealed.

Computer scientists know the BIOS interrupt system buzzer, which seems to be capable of producing a single sound, but talented programmers have written fanciful melodies on it, even with an attempt at digital synthesis and voice reproduction. However, if desired, such a tweeter cannot produce bass.

Why this conversation ... A large speaker should not just be adapted to one of the channels, but bass specialization should be awarded. As you know, most modern compositions (we don’t take Sound Around) are designed for two channels (stereo playback). It turns out that two identical speakers (small ones) play the same notes, there is little point in this. At the same time, bass is lost from the same channel, and high frequencies die on a large speaker. How to be? We propose to introduce passive band-pass filters into the circuit, which will help to split the stream into two parts. We take the scheme of a foreign edition for the simple reason that it was the first to catch our eye. Here is a link to the original site chegdomyn.narod.ru. The radio amateur re-shot from the book, we apologize to the author for not indicating the source. This happens for the simple reason that it is not known to us.

So, picture. The words Woofer and Tweeter are immediately evident. As you might guess, this is, respectively, a subwoofer for low frequencies, and a speaker for high frequencies. The range of musical works is covered from 50-20000 Hz, and the subwoofer accounts for the low-frequency band. Radio amateurs themselves can calculate the bandwidths using well-known formulas, for comparison, for the first octave, as you know, is 440 Hz. We believe that such a division is suitable for our case. I would just like to find two large speakers, one for each channel. Let's see the diagram...

Not quite a musical scheme. In the position occupied by the system, the voice is being filtered. Range 300-3000 Hz. The switch is signed Narrow, translated as a stripe. To get Wide (wide) playback, omit the terminals. Music fans can throw out the Narrow bandpass filter, and skype surfers are advised to avoid a hasty decision. The circuit will completely exclude the microphone loop effect, known everywhere: a shrill buzz due to overamplification (positive feedback). A valuable effect, even the military knows the difficulties of using a speakerphone. The owner of the laptop is aware...

To eliminate the feedback effect, study the question, find at what frequency the system resonates, cut off the excess with a filter. Very comfortably. Regarding popular music, we turn off the microphone, take it away from the speakers (the case of karaoke), and start singing. We will leave the high and low pass filters unchanged, the products were calculated by unknown Western friends. For those who have difficulty reading foreign drawings, we explain, the diagram depicts (the Narrow band-pass filter is discarded):

1. Capacitance 4 uF.
2. Non-inductive resistances R1, R2 with a nominal value of 2.4 ohms, 20 ohms.
3. Inductance (coil) 0.27 mH.
4. Resistance R3 8 Ohm.
5. Capacitor C4 17 uF.

Speakers must match. Suggestions for this site. The subwoofer will be MSM 1853, the tweeter (the word was not written off) will be PE 270-175. You can calculate the bandwidth yourself. The capital letter Ω means ohms - there's nothing to worry about, change the denomination. Remember, the capacitances of capacitors connected in parallel add up like series-connected resistors. In case it is difficult to get suitable denominations. It is unlikely that it will be possible to make speakers with your own hands, it is realistic to dial small resistance values. Do not use coils, we cut out plates of nichrome, similar alloys. After manufacturing, the resistor is varnished, no high current is planned, the element should not be protected.

Inductors are easier to wind on your own. It is logical to use the online calculator, by setting the capacitance, we will get the parameters: number of turns, diameter, core material, core thickness. Let's give an example, avoiding being unfounded. We visit Yandex, we type something like "online inductance calculator". We get a number of issuance responses. We choose the site you like, we start thinking about how to wind the inductance of the speaker system with a nominal value of 0.27 mH. We liked the site coil32.narod.ru, let's get started.

Initial information: inductance 0.27 mH, frame diameter 15 mm, PEL wire 0.2, winding length 40 millimeters.

The question immediately arises, seeing the calculator, where to get the nominal diameter of the insulated wire ... We worked hard, found on the site servomotors.ru a table taken from the reference book, which is given in the review, consider it to your health. The diameter of copper is 0.2 mm, the insulated core is 0.225 mm. We boldly feed the values ​​\u200b\u200bof the calculator, calculating the required values.

It turned out a two-layer coil, the number of turns is 226. The length of the wire was 10.88 meters with a resistance of about 6 ohms. The main parameters are found, we begin to wind. A home-made speaker system is made in a hand-made case, there is a place to fit the filter. We connect a tweeter to one output, a subwoofer to the other. A few words about amplification. It may be that the amplifier stage will not pull four speakers. Each scheme is characterized by a certain load capacity, you cannot jump higher. The loudspeaker design is designed with a fixed headroom to match the load, often with an emitter follower. The cascade that makes the circuit work, full return on any speaker.

Parting words to novice designers

We believe they helped readers understand how to properly design a speaker system. Passive elements (capacitors, resistors, inductors) can be obtained and made by everyone. It remains to assemble the speaker cabinet with your own hands. And for this, we believe, it will not. It is important to understand that music is shaped by a range of frequencies cut off by improper device manufacturing. If you are going to make a speaker system, think about it, look for components. It is important to convey the splendor of the melody, there will be firm confidence: the work was not in vain. The acoustic system will last a long time, it will give joy.

We believe that readers will enjoy making speaker systems with their own hands. The coming time is unique. Believe me, at the beginning of the 20th century it was impossible to draw tons of information every day. Training resulted in hard painstaking work. I had to rummage through the dusty shelves of the libraries. Rejoice in the internet. Stradivari impregnated the wood of violins with a unique composition. Violinists of today continue to choose Italian specimens. Think about it, 30 years have passed, the cart is left behind.

The current generation knows the brands of adhesives, the names of materials. Necessary is sold by shops. The USSR deprived people of abundance, providing them with relative stability. Today, the advantage is described by the possibility of inventing unique ways to earn money. A self-taught professional cuts down cabbages everywhere.

A. Bogomolov, Israel

On WEB pages devoted to the acoustic design of loudspeakers, horn systems are sometimes found. They are distinguished by their unusual appearance and exorbitant price. The complexity of manufacturing a horn and the use of expensive full-range speakers put these systems at a height unattainable for designers and music lovers. And those lucky few who managed to listen to high-quality horn acoustics say: "Whoever heard it at least once will never forget it."

How to listen to this miracle? For homemakers, this question takes on a special meaning. Let's make our own horn!

My first speaker

The following relationships between the resonant frequency and the total quality factor are known, according to which the heads are classified.

1.Fj/Qb< 30 (F, - резонансная частота, Q B - полная добротность). Головки этого типа имеют низкую добротность и лучше всего работают в открытом корпусе и экране. К этому типу относится большинство бытовых головок для магнитофонов и другой носимой техники. Добротность их довольно высока, Q B > 1,2.

2. FJQ a< 50. Это так называемые компрессионные головки с тяжелыми диффузорами и мягким подвесом. В закрытом ящике такие головки обеспечивают наименьшую неравномерность АЧХ. Оптимальная добротность головки для такого применения Q B = 0,7.

P,/0 V< 85. По виду они выглядят практически так же, как и го ловки для закрытых ящиков, но оптимальным оформлением является фазоинверторное. Наименьшую неравномерность АЧХ обеспечивают головки с Qb = 0,39. (

3. F^Qb<105. Это головки для полосовых резонаторов, бандпаов. Так обычно оформляются сабвуферы.

Heads for use in horn systems are specially designed. Low-Q electrodynamic heads, Q B< 0,4.

A horn is a pipe with a variable cross section and rigid walls.

In practice, two types of horn loudspeakers are used: wide-mouthed and narrow-mouthed. The inlet has an area close to the area of ​​the head cone base. That is why they are called wide-mouthed. There are also narrow-necked horns, they are connected to the head through a chamber that plays the role of an acoustic transformer. The use of a horn that loads the movable loudspeaker system very strongly (by a good ten times) improves the efficiency of the latter and thus makes it possible to obtain a sufficient sound pressure value and volume at a relatively low amplifier power. For those to whom the word "horn" resembles an aluminum funnel into which the captain shouts, we will offer a more concise word - bugle. In the future, we will use this term, which is accepted among manufacturers of acoustic systems.

The size of the bugle is closely related to the lower reproducible frequency. You should not even think about making a bugle at home with a lower frequency of 20 or 30 Hz. The wavelength at the lower end of the sound range exceeds 10 meters, and the dimensions of the bugle must be even larger. The choice of the lower frequency is a crucial design moment. In this case, you need to take into account many factors, ranging from your own technological capabilities, the dimensions of the listening room, the parameters of the head, and ending with the overall concept of the system.

A great influence on the sensitivity and euphony of the bugle is its shape. Conical, hyperbolic, parabolic and exponential constructions are currently known. All of them have their advantages and disadvantages, but the latter are considered the most musical. In 1926, the English engineer Peter Voigt found a curve, later called the tractrix.

Traktrisa (novolat. tractrix, from lat. tractus - elongated) - a flat transcendental curve, for which the length of the segment MP of the tangent from the point of contact M to the point P of intersection with a given line (axis) is a constant value. Being a kind of exponential and retaining all its advantages, the tractrix made it possible to reduce the length of the speaker and make the speakers more compact with virtually no deterioration in parameters. We owe it to Voight that this technology is still being successfully implemented in models for home use.

However, despite this discovery, the columns still turn out to be more bulky, difficult to manufacture and significantly more expensive than traditional closed boxes and. The high cost is also due to the fact that the calculation of the hearth is extremely complicated. All existing methods give approximate results, and besides, it is impossible to choose the right parameters from the first time, which are included in the formulas for computer programs. Many of them are determined experimentally, almost on the finished product. You can imagine what it would cost, such a method, when each time you have to make an extremely complex wooden structure, changing only one element in it. Any, even the most insignificant deviation can radically change or even completely “kill” the sound.

The program with which we will make calculations is called Tractrixl2. It can be easily found on the Internet. vybi-

Table 2.1

300 Hz low horn frequency and 3 inch inlet. In table. 2.1 shows the radii of the sections of the hearth at various distances from the outlet.

Accuracy 0.1 mm - for those who have a lathe. It is rather inconvenient to make measurements during the manufacture of a forge, therefore, during manual processing, an error will occur, which you will have to put up with.

The length of the hearth, as can be seen from the table, is 250 mm. The horn inlet corresponds to a three-inch speaker, that is, one with a cone diameter of about 75 mm. It does not even have a name, there is an inscription on the end of the magnet, 4 ohm, 5 W. Such heads are installed in computer speakers. The type or name does not really matter, the main thing is that it be broadband. The cross section and possible types of design are shown in the drawings (Fig. 2.1, a, b).

The material for making a forge can be wood or plastic; in the literature there were photographs of forges hollowed out in stone or cast from concrete. If there is no suitable log, another manufacturing method can be suggested.

For the manufacture of the hearth frame, we need foam with a density of at least 30 kg / m 3. Of all the varieties of foam, you need

Rice. 2.1. Possible execution options

Rice. 2.2. Using an electric drill as a lathe, you should choose the most durable one. It should have a finely porous structure, not crumble when pressed on the edge. Bubbles in the structure of the foam should be no more than 3 ... 5 mm. When cutting with a knife, a flat and smooth surface should remain. It is convenient to use an electric drill with adjustable speed as a lathe (Fig. 2.2, a, b).

We take a workpiece with a thickness of 250 mm, on it we draw a circle with a diameter of 380 mm. Using a hacksaw blade, cut out the cylinder. This is our pig. We cut out two washers with a diameter of 60 mm from plywood. In the center of the blank and washers we drill a hole with a diameter

10.. .12 mm for the stud on which the part will be machined. Washers are needed so that the foam does not deform and does not scroll on the Hairpin. We collect the entire workpiece, tighten it with nuts and clamp it into the drill chuck. As a cutter, you can use a knife, a file, sandpaper wrapped around a wooden block or a broken hacksaw blade. Slowly increase the speed, center and select the best clamping point. We increase the speed and process the workpiece according to the size of the drawing.

When sanding the foam frame, we start with sandpaper No. 2, then No. 1, and finally finish with “zero”. In the place where the speaker is attached, we glue the plywood ring with epoxy. You can attach a speaker and even try to turn it on and listen. Changes and unusual sound can be heard on such a semi-finished product.

Curiously, frequencies below 600 Hz become "floating". They appear and disappear depending on the location of the forge and its orientation relative to the surrounding surfaces. For example, in the corner of the room or against the wall there are “bottoms”, but if you hold the horn in your hand in the center of the room, they are not. The secret is simple. Styrofoam, due to its low density, has a low sound reflection coefficient. For low frequencies it is transparent. It is necessary to reinforce the inner surface of the hearth with a denser material. Choose self-adhesive aluminum foil. According to the catalogs of companies in online stores, it is called Aluminum-Foil Tare (aluminum foil tape). The thickness of the foil on the paper backing is 30 microns. Roll length 45 meters, width 50 mm. This roll costs $5. If it is not possible to purchase this very convenient material, you will have to look for another foil and glue it with a non-detachable foam compound. The foil should be cut into trapezoidal shreds and glued, carefully ironing its surface (Fig. 2.3, a, b).

One way to increase the return is to use horns. Remember the old gramophones: thanks to the horn, small vibrations of the needle connected to the membrane created a very loud sound. In gramophones, part of the horn is folded and "hidden" inside the case. The open lid serves as a sound reflector. Horn loudspeakers are used for scoring open areas. A professional horn loudspeaker can be up to 25-35% efficient. A good horn loudspeaker is hardly available to radio amateurs, but something can be made from ordinary heads.

Of the author's available, good results were shown by a small-sized commercially manufactured speaker in a narrow and deep plastic case with a single head 1GD-40. Its return, quite large and without additional measures, was significantly increased by a folding horn (Fig. 3.4), made from cardboard folders for papers. Radiation from the back of the cone of the head, leaving the open back of the speakers, is reflected from the middle part of the horn speaker system and directed by its expanding side walls towards the listener. From above and below the system is also closed with cardboard covers.

Another folding horn speaker system is easy to make from an old “diplomat” with hard fiber walls (soft ones absorb sound). The design (side view) is clear from fig. 3.5. Two elliptical heads 1 (for example, 1GD-40) are fixed in one line on a narrow reflective board 2 located in the front of the suitcase. The horn system is formed by the bottom and a slightly curved plastic panel 3. The slots formed at the side walls must be closed. Coming out of a wide rectangular hole, the sound is reflected by the open cover of the suitcase 4, going towards the listener, and adding up with the sound emitted by the front side of the diffusers. For better reflection, “acoustic mirrors” 5 made of plastic are installed near the loops. In the "diplomat" there is enough space to accommodate the output transformer, receiver and other useful things.

A wide-mouthed phase inverter is sometimes made in the form of a "horseshoe", which was described above, or a "maze". Both designs are shown in Fig. 3.6, and the front view (along A) is almost the same for them - at the top there is a hole for the head, at the bottom - the outlet hole of the horn. The side walls can be made vertical, but better - expanding towards the opening of the horn. We do not give dimensions, since they are not critical. With a sound wave path length inside the "horseshoe" or "maze" of the order of a meter, one should expect reproduction of low frequencies up to 70-100 Hz. Of course, these speakers can also be placed horizontally, aligning them, for example, with a bookshelf.

Matching transformers have already been mentioned in the previous section. Where to install it, in the receiver or in the speakers? The answer is unequivocal - only in the acoustic system, otherwise the losses in the connecting wires can significantly reduce the efficiency. For example, with a wire resistance from the receiver to a four-ohm speaker of only 1 ohm, the efficiency will be 80%. By increasing the input impedance of the AC to 4-10 kOhm with a transformer, we get an efficiency of 100% and the ability to use thin wires. But the blocking capacitor must be installed in the receiver, since it closes the high-frequency currents of the detector. If the size of the speakers is still large, it is better to use "solid" transformers - they have less loss. Well suited TVK and TVZ from old TVs. Their approximate data: core cross-section 2.5-3 cm 2, primary winding - 3000 turns of PEL 0.15, secondary - 100 turns of PEL 0.7. You can also use "siloviki" - network transformers of power supplies with a transformation ratio of 220/6-12.

ACTIVE SPEAKER

WITH INCREASED RESPONSE AT LOW FREQUENCIES

The birth of this description was preceded by a number of calculations, the manufacture of prototypes, successful and not very successful. In the end, it was precisely these dimensions of the universal case of an economy-class active speaker system that fit under the MOST acoustic heads. During the construction of this acoustic system, the task was not set to reach the NIGHT-END class, it should be an acoustic system that is competitive with the average price category of variety equipment, reliable and maintainable even in "field" conditions.
When creating this speaker system, four tasks were set:
Don't sacrifice much on sound quality
Don't spend a lot of money on building
Get increased low frequency response as the speaker was designed for large rooms and open spaces
Do not "sharpen" the case for a specific set of dynamic heads
These tasks have been solved and before you is a description of how to make an acoustic system yourself, without using any scarce and expensive components.

Several options were tested - a closed case, cases with phase inverters, bandpasses and horn cases. I liked the latter the most, but the CORRECT horn body is rather laborious in calculations and manufacturing. Therefore, we decided to make some kind of arithmetic mean similarity of the horn, since for almost all types of speakers included in the calculations, one trend was clearly traced - the length of the horn is about 3 meters and the horn should have a more or less constant expansion plus a bell at the end. You can roll the horn in different ways, for example, take the Hitchcock horn system and the length of the horn itself depends on the desired resonant frequency. The length of the horn can be calculated using the formula L = 344 / F, where 344 is the speed of sound, F is the resonance frequency. Since the dynamic head is facing the listener, it is necessary to receive a signal at the output of the horn in antiphase, because the rear side of the diffuser will act as the exciter of air vibrations for the horn. Therefore, the resulting length of the horn is divided in half, i.e. the radiation of sound waves is obtained shifted in phase relative to the front side of the diffuser by exactly 180 degrees.
In fact, this is how the SOUND BARREL turned out. In other words, this is a fairly versatile enclosure for almost ANY low-frequency link and the output power depends only on the power amplifier and speakers used.
The most affordable and not very expensive speaker systems designed for the car, the so-called car speakers. Based on this, the choice was made on this acoustics. A 400 W subwoofer speaker (normal W) was taken and a set of two 13 cm two-way dynamic heads for playing the mid-high range. It’s worth mentioning right away - 2 x 40 W, which were initially selected for MF-HF, turned out to be not enough when applying 500 W to the assembled set (a slight overload for reliability texting). Both dynamics ordered a long life. Therefore, for the MF-HF range, it is necessary to take a set with a power of at least 60 W, and round dimanic heads of such power are not less than 16 cm.
Therefore, the actual final set of dynamic drivers for a power of 400 W looked like this: a woofer - a subwoofer for open speaker systems with a diameter of 31 cm with a power of 400 W maximum long-term and a set of two 16 cm two-way dynamic heads for midrange-high frequencies with a power of 100 W maximum short-term.
However, it should be noted here that this design of the speaker system is quite suitable for lower powers, which actually caused the appearance of completely ready-to-install modules for 150 W, 300 W and its m modified version, 550 W and stereo version, 150 W each channel. The modules contain the entire set of necessary devices - a switching power supply, AC protection against DC voltage, some are also equipped with output power indicators and overheat protection, as well as systems for smoothly increasing the volume at the time of switching on. The main difference for acoustic systems of different powers lies in the materials used - for power up to 150-180 W, chipboard 18 mm thick is used, for powers up to 300 W - chipboard 22 mm thick or plywood 18 mm thick, for power up to 600 W plywood 22 mm thick . The cutting of blanks is made in such a way that the thickness of the material is taken into account only in the manufacture of the rear wall, while the rest of the dimensions do not change.
When choosing a material, it is necessary to make an allowance for the fact that, depending on the year of manufacture, the quality of chipboard differs markedly, therefore, for powers over 150 W, we strongly recommend that you go through relatives and friends and ask about the presence of old wardrobes, bookcases and sideboards. Chipboard up to the year 90 has a much higher density, it is more difficult to process, since the adhesive components used at that time were much stronger and the sawdust material was compressed much more strongly. If you're lucky, you may stumble upon a very old chiffonier with chipboard thickness. 22 mm. This can be considered a gift of fate, since even 800 W speakers were made of such material only by installing a spacer cross inside the woofer box. You can advertise in the local newspaper to buy old furniture, in any case it will be much cheaper than buying new, rather loose chipboard and much cheaper than buying plywood.

The appearance of the acoustic system with increased efficiency at low frequencies. Right without back wall

You should start with the manufacture of a block of heads in the MF-HF range. To do this, you need to cut out 4 parts, the dimensions of which are shown in Figure 1. After that, a U-shaped structure is assembled from parts 2-4 using 3.5x45 self-tapping screws. Before screwing under each self-tapping screw, it is necessary to drill a hole with a drill with a diameter of 3 mm. The drill must be elongated, i.e. so that the resulting hole is longer than the self-tapping screw. Preliminary drilling of holes for self-tapping screws completely eliminates delamination of the material during screwing in of self-tapping screws, and a slightly smaller diameter of the holes does not in any way reduce the mechanical strength of the connection. Before screwing in the self-tapping screws, the contact points of the chipboard with each other must be smeared with mounting foam.

Perhaps a few words should be said separately about the foam. Mounting foam is primarily good because it has very good adhesive properties. In addition, expanding in all directions, it completely fills all the existing voids and cracks. Getting a different density of foam in a frozen state is also quite simple - the slower it leaves the balloon, the less it will increase in size and will have a much higher density. And the opposite effect - the more you press on the exhaust valve, the faster it will leave the balloon, respectively, it will swell and increase in size more. In addition, the hardened foam has good mechanical properties and is not a bad sound-absorbing material. For greater clarity, we introduce three concepts of density - DENSE when the foam is released from the balloon at the lowest possible speed and is more like sour cream or cake cream and increases in size barely noticeably, AVERAGE- when the foam is released from the balloon at an average speed, it immediately begins to increase, LOOSE- when the foam from the balloon is released at the maximum speed, it immediately becomes a lot and it begins to increase in size more tightly.

But let's get back to the assembly of the MF-HF box. Parts 2 and 3 are fastened with their ends to part 4 with four 3.5x45 self-tapping screws, the contact points of the parts are smeared with mounting foam of a dense composition, then part 1 is attached to the resulting structure in such a way that the upper part of part 1 coincides in height with the upper part of part 2. Contact points are also smeared with mounting foam of a dense composition.

Figure 1 Patterns for the manufacture of MF-HF boss of an active speaker system.

After that, after allowing the foam to harden and cutting off the protruding foam from the outer seams, holes are cut in part 1 for dynamic heads and forced cooling fans. The forced cooling system was chosen based on economic considerations - even a pair of fans is much cheaper than increasing the heat sink area to the required size, especially since the output power of the amplifier exceeds 100 watts. For clarity, let's say that one radiator from an old 50 W amplifier (Lort), installed on a sheet of aluminum 5 mm thick and 300x150 mm in size, is quite enough for the SOUND BARREL 150 amplifier in the presence of two computer fans with a diameter of 80 mm and a consumption of 0.12 A ( current is indicated on the fan and determines the performance of the fan).
The diameters of the holes for the fans are 80 mm, by the way, sometimes fans with a diameter of 90 mm and a consumption of 0.24 A come across on sale, these are ideal for the SOUND BARREL 550 amplifier. There are also fans with a diameter of 80 mm with a current consumption of more than 0.12 A These fans are best used for SOUND BARREL 300, SOUND BARREL 300M and SOUND BARREL 2x150 amplifiers. It is better to cut the holes for the dynamic heads according to the available templates, which are ALWAYS drawn on the packaging boxes of car speakers.
The result is the design shown in Figure 2.

Figure 2 External view of the MF-HF box for an active speaker system.

A few words about making round holes. There are quite a few ways, but the most preferred is still a jigsaw. Stepping back from the edge, inside the marking circle of about 10 mm, drill a hole with a diameter for a jigsaw file and starting to saw through in a spiral, the file is brought out to the markup. It should be noted that for cutting round holes there are special files for electric jigsaws. You can even tell them apart by their appearance. files for cutting round blanks have additional fine teeth on the back side, which, cutting the material, do not allow the file to break. Sawing out a round part with an ordinary saw, the shape of the resulting hole has a cone-shaped shape, since the file bends when turning.
After cutting the holes, the box must be wiped with a damp cloth and all sawdust carefully removed, since when marking the mounting and mounting holes of the dynamic heads, the sawdust can get inside the speaker system, which is highly undesirable. After marking ALL the required holes for mounting the speakers and mounting the amplifier with a heatsink, the dynamic heads should be repackaged in plastic and packing box, and only then the required holes should be drilled.
Now you need to cut out 4 parts, the dimensions of which are shown in figures 3 and 4. They will serve to create the inside of the horn.

Figure 3 Top, bottom and technological blanks for the inside of the horn.

Figure 4 Bearing wall and horn interior assembly

After assembling and receiving the workpiece shown in Figure 4 on the right (it is assembled in the same way as the box of midrange-high-frequency heads - with a 3.5x55 self-tapping screw and dense foam at the chipboard contacts), it is not worth filling the area shown in the figure with foam until it is worth it - a little bit later. Item 8 will be installed approximately in the middle.
Next, four blanks are made, shown in Figure 5. In fact, they will serve as sidewalls, upper and lower parts of the active acoustic system case.

Figure 5 Sidewalls, top and bottom of the acoustic system

Then the inner part of the horn is mounted between the sidewalls. The main condition during installation is that part 5 should be exactly the width of parts 13 and 14 from the edge of the sidewall, in this case it is 100 mm. Suorka is made with self-tapping screws. Do not forget to drill holes, and for greater rigidity in the material through which the self-tapping screw passes through, it is better to drill a hole with a diameter of 4.2 mm, but where the self-tapping screw will only be twisted with a drill with a diameter of 3 mm. In Figure 6 on the right, ALL holes in part 9 are 4.2 mm in diameter, and in the ends of the workpieces 11, 12, 6, 5, 7, 16 ALL holes are 3 mm in diameter. We coat the places where the chipboard is connected with each other with dense foam.
After fixing the inner part of the horn to the sidewalls of the active acoustic system, installing the upper part 11 and the lower part 12, installing additional overlays 16 and 17, proceed to assemble the horn itself. This will require parts 13 and 14 (Figure 6), as well as the back wall (Figure 7).
After assembling the inner part of the horn and sidewalls, installing part 15, the angle between part 5 and part 6 is filled with foam, and starting from the junction of parts 5 and 6, the foam is dense, then the middle and upper layers are made of loose foam. Thus, the heterogeneity of the foam completely eliminates the resonant effects of the "visor" 6 and more tightly connects it to the part 5.
Before installing part 11 (top cover), the resulting container between parts 9, 15, 5 (Fig. 8) is half filled with loose foam and only after that part 11 is installed. As its volume increases, the foam will either completely or almost completely fill this box.
In the same way, the box that has turned out between parts 7, 5 and 12 is filled - from the corner they are shed with dense foam, the second layer - the middle and top - is as loose as possible. The resulting sags and irregularities should not be cut off, they are quite smooth and will not give whistling overtones, but irregularities completely exclude the possibility of standing waves.

Figure 6 Horn baffles (13, 14) and additional linings (16,17), upper bell (17) and mounting of the inner part of the horn to the sidewalls.

Figure 7 Rear wall of the acoustic system.

Next, parts 13 and 14 are installed with fastening, but before that it is necessary to round off the end of the upper part of part 13 and the lower part 14 (in the figure they are angular, but they should be round. This one is not very important for a horn, but it is better to do it all the same. This can be done with a special grinding wheel for the "grinder" - a lot of strips of sandpaper are glued onto the circle, and there are both large sandpaper and fine sandpaper.It is better to take it with a large one - at high speeds, without pressing hard, you can get a fairly smooth rounding surface.
Parts 13 and 14 are attached to part 5 using self-tapping screws 3.5x55. Further, the back cover (Fig. 7) is wrapped with cellophane in such a way that the cellophane turned out on the inside of the cover and the cover is attached to the case using self-tapping screws 3.5x55, but not completely, but only the upper and lower parts of the case. As soon as all the holes are drilled, the cover is removed and the corners of the horn are filled with dense foam with the first layer, then with medium foam.
First, it is better to fill in the lower part, the corners between the parts 13-12-10, attach the back cover and let the foam harden, then turn the speaker cabinet over, remove the back cover and fill in the corners between the parts 9-11-14 and close the back cover again. After the foam has hardened, the back cover is removed again and the kisser is removed from it, which protected the cover from sticking to the foam poured into the corners of the horn. With the help of a clerical cutter, the frozen foam is given an approximate shape of a quarter of a circle, i.e. cut off the excess foam until you get the look in figure 8.
Next, drill holes in the back wall for installing the line-in connector and the 220 network connection connector and the line-in wire connector and the network wire. Figure 9 shows an example of attaching the line-in wire, which should have a braided shield, the tighter the better.

Figure 8 Fabrication of horn baffles and fillets.

After that, you should fix the back wall by smearing the ends of the body parts in contact with it with dense foam. And now the back wall is fully fixed - along the perimeter and to the partitions of the horn (Figure 9, left)
Further, a sheet of 410x430 mm in size is cut out either from a denser chipboard or plywood, which will serve to fasten the low-frequency dynamic head of the acoustic system. In the middle, a circle is cut out with a jigsaw according to the template available on the packing box of the dynamic head and the mounting holes for self-tapping screws are matched.
After that, the column is finally assembled and all the irregularities and inconsistencies between the parts are lifted up with a circle of sandpaper installed in the grinder. You should also drill holes in the sidewalls of the case for mounting the midrange-high box. After that, the box under the midrange-high frequency and the sheet under the low-frequency head are removed and the case is pasted over with acoustic fabric, and the inner part of the horn is also pasted over with the cloth, special attention should be paid to pasting the sidewalls from the inside, since this material will serve as an insulator of sound vibrations inside the box.
After gluing and drying the acoustic fabric, a power amplifier unit with a power source is installed on the back wall of the box in the MF-HF range; inside the box, a decoupling capacitor of about 50 microfarads can be attached in any way, preferably MBM, but they are quite rare now, so 10 pieces can be connected in parallel capacitors at 4.7 microfarads, or 5 pieces of 10 microfarads. The voltage must be at least 100 V.
At the bottom of the woofer box, a separating inductance wound on a mandrel with a diameter of 20 mm and containing a layer of 20 turns of wire with a diameter of 1 mm for a power of 150 W, 1.5 mm for a power of up to 300 W and 2 mm for a power of up to 600 W is attached in any way. The wire is best used in mica or fiberglass insulation. After winding, the coil must be "painted" with epoxy glue.

Figure 9 Final assembly of the active speaker cabinet.

Next, the circuit diagram shown in Figure 10 is assembled. The "ROOM-STREET" mode switch, the output power indicator, if any, and the power switch are installed on any sheet material - fiberglass, plywood, fiberboard, plastic. It is only necessary to firmly fix this panel to the box of MF-HF heads, so that when this box is dismantled, these controls and indications remain connected to the amplifier unit and do not block more than half of the resulting window between the horn bell and the box of MF-HF speakers, since this will impede air circulation and cause the heatsink of the power amplifier to overheat.

Figure 10 Schematic diagram of an active acoustic system and an approximate appearance.

Well, actually, that's all - you yourself assembled the case of a horn active acoustic system, the power of which depends only on the material used and the installed power amplifier.

ALL DRAWINGS IN SPL FORMAT ARE POSSIBLE. OPEN WITH THE SPLAN 6 PROGRAM, WHICH IS POSSIBLE. WHEN PRINTING THE DRAWINGS FROM THIS PROGRAM, THE DRAWINGS ARE 1:10 SCALE. So you can measure with a ruler and transfer to the material, in case of any misunderstandings with the dimensions.

NOTE.
When installing fans directly on radiators, they should not be installed parallel to the radiator, but using washers, racks, etc. slightly tilt them in the vertical plane, by 10...15°, so that the air flow passing through the radiator fins goes up. Thus, air circulation will occur inside the system and air heating will be excluded (Fig. 11).

Figure 11 - Orientation of the fan relative to the heatsink of the power amplifier.

It is better to make the lower holes of part 1, intended for installing fans, not round, but to make one rectangular 80 mm high and 200 ... 250 mm wide.

If you don't understand something, see

DID NOT FIND WHAT YOU WERE LOOKING FOR? GOOGLED:

Case acoustics is actually a box with speakers. It can be of different sizes, shapes, have any external finish - the essence of this does not change. The speakers installed in it are loaded with a certain volume with their inner side, and radiate towards the listener with their outer side.

Cabinet acoustics have obvious advantages over other types of acoustic design:

• Price. A box made of wood or MDF is inexpensive, even if it is finished on the outside with exotic veneer or piano lacquer. What loudspeaker manufacturers really like is that they make a good profit by selling "box" designs.
• Simplicity. The column actually consists of three interconnected elements: the case, dynamic heads and crossover filters.
• Dimensions. They can be very different - from the size of a shoe box to the dimensions of a wardrobe. (In an era of general economy, indulging the requirements of fashion and the worldwide desire for the miniaturization of electronics, the dimensions of acoustics are getting smaller and smaller.)

In order to get normal bass from small speakers, acoustic engineers use a lot of tricks - these are all kinds of labyrinths and phase inverters, heavy speaker cones, super-rigid cabinets, etc. All this, in all honesty - the sound quality does not improve.

Firms still achieve relatively good low-frequency reproduction from speakers that have modest dimensions. Because buyers often prefer small speakers.

Horn columns

With horn acoustics, everything is much more complicated. The horn is a transducer - which matches the radiation resistance of the head with the resistance of the air space.

Its dimensions are rigidly tied to the lower emitted frequency and cannot be reduced in any way - otherwise the horn simply will not work. Horn structures designed to reproduce both the voice range and bass have very large dimensions. The length of the horn in them reaches 1 - 5 meters, and the exit area "opened" 2 - 4 square meters. meters.

It is clear that one out of a hundred people will decide to put speakers with such dimensions in the house.

To reduce the dimensions of horn columns, several methods are used:

• By folding the horn into a spiral, or “snake”, you can reduce the external dimensions, while maintaining the required length and opening
• The body of the horn is carried out beyond the dimensions of the room under the floor, into the ceiling or another room, leaving only its outlet in the visible zone.
• The columns are combined. To reproduce low frequencies, a bass module with a conventional dynamic head is installed in them. Medium and high frequencies (the most informative for music playback) are left horn.

In the last configuration, the columns are of acceptable dimensions for a living space. Such designs are most popular among lovers of jazz, classical music and vocals. Despite the slightly “torn off bass”, they have a unique horn sound.

(The horn increases the efficiency of the speaker dozens of times. This is a kind of “gearbox” that matches the high-speed motor - the “speaker” with the wheels that require a lot of torque - the “airspace”. No matter how powerful the car’s motor is, if it does not have a gearbox , the car drives very badly.Ordinary speakers in the form of a box with speakers is just a car without a gearbox)

To power horn speakers, low-power amplifiers are required, which obviously have less distortion than powerful ones. And most importantly, horn designs are in perfect harmony with tube amplifiers, which are considered the standard for music reproduction around the world.

The ideal kit for an advanced music lover is horn speakers with a tube amplifier. Horn acoustics are "aerobatics", "Bugatti Veyron", "Faberge eggs", or something similar. People who are passionate about music go to it for years.

The best systems in the world with the most natural sound - HORN ...

Which columns to choose

The choice is easy enough to make. If you need to "close the position" - install a home theater in the living room or a dedicated room, assemble a high-quality system of acceptable dimensions and at the same time not really bother with "the energy of Ella Fitzgerald's voice at a concert in Boston in 1968" - you need to install traditional acoustics.

But if you need:

• To make the hair move on the head from the voice of Vladimir Vysotsky ...
• Friends said that “In their 40 years of life, they had not heard anything like this, and had no idea at all - that Vysotsky should sing exactly - SO ...”, and then they were silent for a long time ...
• Goosebumps ran down the skin from the energy of Rammstein ... from the Show Must Go He - Freddie Mercury ...

You need - HORN acoustics

(Speakers tear a person out of everyday life, give sensations akin to narcotic ones. They completely disinhibit the human psyche and allow you to convey to your ears exactly the energy of the performer's voice - which was originally conceived by the sound engineer.)

P.S. Unfortunately, sound in the world over the past 20 years, since the birth of video, has been degrading - and at a rapid pace. The "media" industry purposefully shifts attention from sound to a beautiful picture on the screen. The ears suffer from this, and people do not understand why they are uncomfortable in cafes, clubs, restaurants and even at concerts of stars.

The mouthpiece for the ears is Leonardo da Vinci's "Madonna" for the eyes.