Acoustic system verna 50 01.

The design uses the best modern European dynamic drivers that meet the strict requirements for building acoustic systems for the most demanding listeners. Model 100A-005, like 50A-003 "Sevina" (Demyanov A. "Acoustic system" Sevina "(Verna 50A-003)". - Radio, 2015, No. 2, p. 7-11), belongs to the highest group Verna products.

The medium-sized model 100A-005 is optimal for rooms with an area of ​​14...20 m2 (volume from 35 to 55...60 m3) when using UMZCH power 50...100 W (at 8 Ohm load). Low-frequency heads (bass reflex) - SEAS H956, 8 "(Norway), with diffusers made of aluminum alloy, a linear displacement of 7 mm and a resonant frequency of about 20 Hz. (France) with diffusers made of long-fiber oriented and impregnated cellulose, coil frames made of fiberglass-reinforced Kapton, they have external suspensions of variable thickness and antiresonant diffuser holders. HF heads - isodynamic - VISATON MHT 12/8 (Germany), which have extremely low inertia and a reproducible frequency range of up to 22 kHz with an unevenness of not more than 3 dB.

In order to somewhat expand the musical stereo base (in the case of a distance between the speakers of no more than 130 cm), the MF and HF heads of the Acoustic Systems (AS) are installed on massive stands 40 ... 50 cm high or tilted back, placing stops under the base from the side front panel (as in Fig. 1) so that the center of the midrange emitter "looks" at the listener's face. This largely allows you to get rid of early reflections in an unprepared (especially) room, which largely mask and distort the direct reproduced signal. The distance between the systems can be within 150...200 cm, their location in the room is along a long wall, the distance to the listeners is 150...250 cm.

Rice. 1. Speaker system

Main specifications

Rated resistance, Ohm .............................. 8

Sensitivity in the range of 35...18000 Hz, dB/W/m.................................84.5

Amplifier power, W.....50...100

Reproducible frequency range by level -5 dB, Hz ..................... 27 ... 22000

Maximum noise power, W .................. 100

Dimensions, mm..........760x406x270

Mass of one AC, kg, not less than .............................. 40

A brief addition to the main technical characteristics is given on the frequency response and impedance (Z-characteristics) graphs of the used heads (Fig. 2 - Fig. 5). The tables below the woofer graphs show the measured characteristics and Thiel-Small parameters. On fig. 2 shows graphs of two woofers - blue and red curves. It is important to note that very rarely the graphs provided by the manufacturer correspond to those already measured by the user in an anechoic chamber. In this case, the correspondence is almost complete. Which, in fact, along with the allowable (7 ms) impulse response, made it possible to choose these low-frequency heads for speaker system high level.

Rice. 2. Graphs of the frequency response of two woofers

Rice. 3. Graphs of frequency response

Rice. 4. Graphs of frequency response

Rice. 5. Graphs of frequency response

For a more complete representation of the behavior of the midrange head in different volumes, two graphs are presented (Fig. 3 and Fig. 4) in volumes of 5.2 and 10 liters, here the frequency response of two heads is also presented. In the described AC model, the volume of the box is 8 liters. There are PAS panels (acoustic impedance panels) installed on the windows of the diffuser holders of the heads to dampen the main resonance, which instrumentally and subjectively significantly increased the quality of reproduction in the midrange (580 ... 3800 Hz), especially low-level signals. On fig. 5 at different angles in the horizontal plane shows the graphs of the frequency response of the RF emitter and the frequency dependence of the impedance of the head (its Z-characteristic).

The drawing of the AC case is shown in fig. 6. To minimize (almost completely eliminate) body vibrations at a total sound pressure developed of 90 dB (and the presence of signals and overtones up to 25 Hz), the body is assembled from two layers of FK-1 plywood 12 mm thick (outside) and an inner layer of medium-density MDF with a thickness 16 mm. This inner layer has milled cavities for the installation of baffle frames and panels that form the MF-HF box. To reduce the pressure of the walls of the case on the bottom panel inside, along all perimeters, bars made of solid beech with a section of 30x30 mm are glued. Also, to reduce deformations (shifts) in the corners of the cases, the connected panels are fixed with beech dowels (10 mm in diameter and 60 mm long) every 50 mm. When assembling the cases, adhesives with a hardener and fillers were used. All these measures fully ensured the necessary rigidity of the structure with sufficient mass and the overall (main) mechanical resonance of the cases at a frequency of about 1000 Hz (more on this can be found in the author's article "Acoustic system "Sevina" (Verna 50A-003)" in "Radio" No. 2 for 2015 on pp. 7-11). It is also worth noting here that such a "rigidly inert" cabinet allows you to maximize the high sound potential of the used heads, primarily low-frequency ones, which are the main source of vibrations. Exclusion of uneven (in amplitude and frequency) overtones of the body, strongly distorting musical material, made it possible to obtain sound with an abundance of low-level signals of the second and third plans. In other words, it is more realistic to reproduce the recorded material in the first place - piano and acoustic musical instruments, as the richest wideband overtones, as well as the sound of classical vocals.

Rice. 6. Drawing of the speaker cabinet

The AS cases were assembled at a specialized enterprise by experienced craftsmen within 38 days. When assembling, special attention was paid to the quality of all work performed. During gluing, blanks for panels were kept under pressure for 100 hours until the adhesives were completely polymerized, after which they were milled to size. The inner surfaces of the LF and MF volumes are covered with a PVA layer (Finland) 2 mm thick. After polymerization, a sound absorber was installed on these surfaces - a three-layer (stitched asymmetrically with thick threads) artificial felt with a density of 0.31 kg / m 2 and a total thickness of 18 mm. Cotton wool bags and specially treated VISATON wool (Germany) were used as additional sound absorption. The entire volume of the MF-HF box (8 l) is densely filled with this wool.

The front panel of the housings is painted gray color under "shagreen", the rest are covered with calibrated "Makore" veneer, covered with three layers of semi-gloss varnish and polished. On the bottom panel, at the corners, there are four steel cones, their height - 45 mm, diameter - 30 mm, flange diameter 65 mm. On the rear panel, in the lower part, there is a panel with AVC-link acoustic terminals, the connection material is brass 63. The phase inverter pipe is VISATON BR19.24, extended by 40 mm.

The AS diagram is shown in fig. 7. Filters for the low-frequency link - the third order (18 dB / oct.), excluding the resonances of the emitters at frequencies above 700 Hz. In the mid-range (580...3800 Hz), a first-order band-pass filter (6 dB/oct.) is used. At the same time, the mid-frequency head's work area "enters" the woofer's work area, providing in some way a more solid sound. The whole nature of reproduction, its sound production, musicality, microdynamics are determined mainly by the sound of the AUDAX AM130G0 head, which is connected without a sound seam to a HF head connected through a third-order filter (18 dB / oct.). Therefore, the minimum distance from the listener to the line connecting the acoustic systems is one meter (with a distance between channels within 1.2 ... 1.6 m).

Rice. 7. AC diagram

The filters use ERSE inductors (USA), wound with copper wire 1.3 mm in diameter on magnetic cores (L1, L2), the rest - with wire 1 mm in diameter with frameless winding. All capacitors - K73-11 (Russia) for a rated voltage of 250 V, resistors - MUNDORF (Germany). The filter is installed without connecting wires. The remaining connections are stranded copper (purity 99.99%) wires with a cross section of 1 mm 2 (Russia). The parameters of the filter elements are selected with an accuracy of 0.5%.

In the woofer, you can use modern heads SEAS H1208. In the midrange, no change acoustic design and filter elements, AUDAX HM130G14 or AUDAX HM130G0 can be installed.

The sound of acoustic systems makes it easy to distinguish the change of elements of the rest of the audio path.

Expert A. Avatinyan (Moscow) noted "the high musicality of the sound with a multifaceted (in depth) reproduction of musical programs of the classical and jazz repertoire, their realism, as well as a wide frequency range of acoustic systems."

This article offers readers a description of the acoustic system "VERNA 50-01". It uses available Russian-made loudspeaker heads 25GDN-3-4, 5GDSH-5-4 and 10GDV-2-16, which allows radio amateurs to build speakers with good quality sound.

Main technical characteristics of speakers.

• Rated (maximum) power - 25 (50) W.
• Rated electrical resistance- 8 ohm.
• Playable range audio frequencies- 50...20000 Hz.
• Frequency response unevenness in the range of 100...8000 Hz - +/-3 dB.
• The level of characteristic sensitivity - 85 dB / W / m.
• Total harmonic distortion at a sound pressure level of 90 dB in the range:
  • 63...500 Hz - 3%.
  • 500...10000 Hz - 1.5%.
  • 1000...15000 Hz - 1%.
• Dimensions - 220x700x270 mm.
• Weight - 15 kg.

The manufacture of speakers begins with a pairwise selection of low-frequency loudspeaker heads after their 10 ... 30 hour run, which makes it possible to stabilize the characteristics of the head diffuser suspension. When running the 25GDN-3-4 heads, they are connected in turn to a sound generator and a signal with a frequency of 65 Hz and an amplitude of 18 V is applied to them. The real sensitivity and quality factors of the heads installed in the same housing should not differ from each other by more than 10 and 5 % respectively. It is also recommended to use heads with different (within 10...15 Hz) resonant frequencies. This favorably affects the frequency response of the sound pressure and reduces the even harmonics of the reproduced signal by half, and this is very important for small speakers.

circuit diagram AC is shown in Fig.1. The 5GDSh-5-4 broadband head with a mastic-impregnated suspension and PAS panels installed on the diffuser windows works in the midrange link. This head can be replaced with 6GDSh-5-4, but since the level of its characteristic sensitivity is lower than that of 5GDSh-5-4, then the resistor R2 must be taken with a lower resistance.

When selecting a HF head, you should choose specimens with the lowest resonance frequency. Then you should disassemble the heads in order to replace the sound absorber in them. To do this, unscrew the screws securing the acoustic lens, then remove the lens itself and the head dome. As a new sound absorber, it is recommended to use 0.5 g of eye (fine) cotton wool. It should be fluffed evenly and put under the dome. Then the HF head must be assembled in the reverse order. The fastening screws of the acoustic lens are fixed with NC varnish.

Briefly about the filter. In the low-frequency section, a third-order filter L1C1L2C2R1 with a cutoff frequency of 550 Hz and an attenuation of 18 dB / oct. is used, in the mid-frequency section - a first-order bandpass filter R2, C2, L3 and in the high-frequency section - a third-order filter R3C4L4C5.

Coils L1 and L2 are wound on flat magnetic cores made of 2000NM ferrite with dimensions of 8x15x80 mm; L1 contains 200, and L2 - 72 turns of PEL-2 wire 1.12 mm. Winding - turn to turn. Coils L3, L4 consist of 140 and 147 turns of PEL-1 0.56 wire, respectively. They are wound on plastic frames with a diameter of 20 and a height of 25 mm. The filters use capacitors K73-16 (C1-C3) and K73-21, K73-17 (C4, C5), resistor R1 - PEV, R2, R3 consist of four MLT-2 resistors connected in parallel with a resistance of 16 ohms. All filter elements are mounted on a fiberglass board, which is screwed through rubber washers to the rear panel of the speaker cabinet.

The AC case (Fig. 2) is made of chipboard plates 16 mm thick and bars with a section of 20x20 mm, installed in the corners of the panels to be joined. MF and HF heads are located in a compartment separated from the main body. The low-frequency unit has a volume of about 17 cubic dm, which allows you to tune the phase inverter, consisting of two tubes with an inner diameter of 30 and a length of 150 mm, to a frequency close to resonant frequency LF heads - 50 Hz. At the same time, the sound pressure level at this frequency is 5 dB lower than the level of the average characteristic sensitivity. The frequency response unevenness when using two 25GDN-3-4 heads in a given volume in the range of 50 ... 500 Hz does not exceed +/-3 dB. Soft felt 15 mm thick is used as a sound and vibration absorber in the woofer unit, which is tightly glued with Moment glue to all its internal surfaces. At the joints of the body panels, gauze bags with batting are fixed over the felt. The bass reflex tubes are made of steel and fixed in the holes with epoxy glue. To increase the rigidity and vibration losses of the case, beech bars are glued with PVA glue between the holes of the woofers and phase inverters.

The MF-HF block is formed by two partitions made of plywood 12 mm thick (they are installed in a mounted speaker cabinet without a rear panel). Its volume allows you to freely reproduce a signal with a frequency of 300 Hz. Inside the box, cotton wool weighing about 200 g is evenly laid. MF and HF heads are fixed outside through felt rings 3 mm thick.

The woofers are also installed on the outside through 3...4 mm porous rubber pads.

Outside, the speaker cabinet is covered with oak veneer and water-resistant colorless varnish. The front panels of the speakers are covered from the outside with a frame with an acoustically transparent fabric. On the rear panel there are clamps for connecting speakers to a power amplifier.

A comparative subjective analysis of the speaker sound quality showed that "VERNA 50-01" sounds no worse than such imported speakers as MATRIX 805, JBL L-20, TDL NFM-2, KEF K160, K140, with much lower manufacturing and tuning costs.

Readers are offered a description of another acoustic system by our regular author A. Demyanov. It is made on the basis of domestic loudspeaker heads: 25GDN-3-4, 5GDSH-5-4 and 6GDV-4-8 and has good technical characteristics. So, thanks to the panels of "soft" acoustic impedance (PMAS) installed in the woofer compartment of the loudspeakers, it was possible to significantly improve the reproduction of lower sound frequencies, and the refinement of the midrange head according to the method of V. Shorov made it possible to obtain a light and clear sound.

Despite the wide choice of speakers on Russian market, this did not reduce interest in their independent production. The main reasons for this phenomenon, according to the author, are the dissatisfaction of sound recording enthusiasts with the real sound quality of foreign-made speakers, especially the average price category; a poor choice of domestic industrial systems, and their rather high cost.

The main thing is the desire of radio amateur designers to build an AU, designed to work in a particular room and as part of the sound amplifying path available to the listener. A huge market of component parts also contributes to independent creativity: loudspeaker heads, finishing materials, all kinds of accessories, etc. An important role, of course, is played by the fact that a self-made speaker system will cost its creator two to three times cheaper than an industrial one.

When developing the proposed design of a home-made speaker, the task was to create it on the basis of domestic loudspeaker heads that are constantly on sale and well known to a wide range of consumers. As a result, AS "VERNA 50A" was developed (Fig. 1). designed for installation on stands 40...50 cm high. With its help, you can sound a room up to 25 m 2 and play a wide variety of musical works.

Its technical characteristics: nominal electrical resistance - 8 ohms; nominal range of reproducible frequencies - 50 ... 20 LLC Hz with uneven frequency response of 2%: level of characteristic sensitivity - 85.5 dB / W / m; nominal (maximum noise) power - 50 (75) W; dimensions - 215x315x600 mm; weight of one AC loudspeaker - 25 kg.

Each AC loudspeaker is a three-way phase inverter with two woofers 25GDN-3-4. located in the lower compartment with a volume of 17 dm3, medium-frequency head 5GDSh-5-4. placed in a special box, and HF head 6GDV-4-8. installed at the top of the case.

The front panel of the loudspeaker (Fig. 2) is made of solid birch and has a thickness of 40 mm. Its shape and location of the heads on it are chosen taking into account their real electro-acoustic characteristics and directivity patterns in the frequency range of 300 ... 20,000 Hz.

The remaining panels of the loudspeaker case (Fig. 3) are two-layer: on the inside - chipboard 16 mm thick. from the outside - furniture plywood 15 mm thick. When gluing with PVA-E glue, these materials were kept under load (about 120 kg) for three days. This helped to obtain panels with a damping factor of about 0.9 and good damping properties. In the side panels, a part of the chipboard layer is cut out (Fig. 4), which is necessary for the unhindered installation of the plates that form the phase inverter passages.

As can be seen from fig. 3. at the joints of the panels have a selected "quarter", which provides maximum vibration damping and the necessary rigidity of the loudspeaker case. Its weight without heads and filter board is 20 kg.

It should be noted that the use of a powerful front panel and a two-layer construction of the rest of the materials with different damping ratios is not accidental. The fact. that with small sizes of low-frequency heads, their large mass (2 kg) and a resonant frequency of 50 Hz, it is possible to obtain good sounding of low sound frequencies only with careful damping of the acoustic design. This is exactly what was implemented, taking into account the above design features of the AC loudspeaker enclosure. Its walls do not vibrate even during the playback of a musical signal with a high content of low-frequency components with a power of up to 70 watts.

The loudspeaker heads are fixed in the front case panels. The low-frequency heads are mounted on damping sealing rings made of natural felt 8 mm thick, and the mid-frequency and high-frequency heads are mounted on rings made of felt 6 and 3 mm thick, respectively.

Additional rigidity of the loudspeaker of the speaker cabinet. and hence, its greater damping is provided by panels of "soft" acoustic resistance 1 - 4 (see Fig. 3 and Fig. 5). All of them are made of plywood and glued into the body. The number and area of ​​holes in the panels were determined empirically. The panels dampen the main resonant frequencies of the woofers and reduce the displacement amplitude of their diffusers, as a result of which non-linear distortions are reduced and the linearity of the frequency response in the region of 45 ... 600 Hz is improved.

To achieve the monolithic design of the AC loudspeakers, 30 (on each side) oak dowels with a diameter of 8 and a length of 50 mm are inserted into the ends of their front panels (not shown in Fig. 3). The same dowels are installed in the ends of the upper, lower and rear panels respectively 13. 13 and 30 pieces. All of them are fixed with glue. The ends of all perforated panels are also reinforced with dowels 6 mm in diameter and 40 mm long.

The 5GDSh-5-4 mid-frequency head was installed in a standard industrial plastic box with an internal volume of 2.8 dm3 (Fig. 6). The box is attached to the inner surface of the front panel with four screws fixed with epoxy glue. Inside the midrange box is pasted over with natural soft felt 12 mm thick. About 1 dm 3 of the box volume is filled with cotton batting weighing 120 g, and the rest of it is filled with cotton wool at the rate of 100 g/dm 3 . Such sound damping almost completely eliminated the influence of internal resonances on the midrange head cone and ensured the uneven frequency response of the speakers in the range of 500 ... 5000 Hz no more than ±2 dB.

The passages (slots) of the phase inverters are formed by the side panels of the housing (Fig. 6) and metal plates made of D16T aluminum alloy (Fig. 7). The plates are fastened with screws to a wooden block (Fig. 8) which is glued to the front panel of the loudspeaker housing. The variable section of the passage prevents the occurrence of standing waves and. as a result, it prevents the appearance of mumbling during the operation of the phase inverter. Hole areas and penetration depth are set to 47 Hz. The location of the phase inverter slots along the edges of the front panel helps to reduce the reflections of sound waves from its surface.

From the inside, the loudspeaker case is pasted over with soft natural felt 17 mm thick. on top of which are glued rollers of cotton batting with a diameter of 50 and a length of 150 mm. The inner surface of the front panel is pre-filled with a mixture of PVA-E glue with beech sawdust, the thickness of the dried layer is 5 mm.

On the lower and upper edges of the back panel, beech triangular corner bars with a side of 30 mm are glued. The same bar is installed between the bottom and front panels. The bars relieve longitudinal stresses that occur when the case is deformed and when speakers are installed on insufficiently massive and rigid stands.

The outer surface of the front panel of each loudspeaker is tinted "mahogany", and the rest are finished with mahogany veneer. The front panel has a removable frame covered with an acoustically transparent fabric.

Schematic diagram of separation filters is shown. in fig. 9. LF and MF heads are included through the filters L1R1C1 (6 dB / oct) and R2C2-C6L2 (6 dB / oct), respectively, and the tweeter - through the filter (18 dB / oct) R3C7C8L3C9-C11. The filter parts are placed on a 10 mm thick plywood board with dimensions of 100-55 mm. The installation was carried out without the use of connecting wires, their functions are performed by the conclusions of the parts. When assembling, resistors were used: PEV-8 (R1) and S5-16MV-5V (R2. R3). All capacitors K73-16 for operating voltage 63 (CI, C2) and 160 V (others).

Coil L1 is wound on a magnetic core measuring 8x15x85 mm from 2000NM ferrite. Its winding consists of 240 turns of wire PEL-1 1.12. Winding coil to coil in three layers.

The windings of the coils L2, L3 are placed on cylindrical frames of industrial production with a diameter of 18 and a height of 20 mm. The first of them contains 212. and the second - 120 turns of wire PEL-1 0.56. The windings of the finished coils are impregnated with BF-4 glue and tied with PVC tape.

The crossover filter board is installed at the bottom of the rear panel of the loudspeaker box. In the immediate vicinity of it there is a panel with clamps for connecting the loudspeaker to the power amplifier.

Click on the image to enlarge (opens in a new window)

To connect filters with midrange and bass heads and input jacks, two stranded (17 cores) silver-plated wires with a cross-sectional area of ​​1.8 mm (Fig. 9) in fluoroplastic insulation were used.

For loudspeakers, the main specifications have been carefully checked for the following main specifications: nominal electrical impedance direct current, the fundamental resonance frequency, the level of characteristic sensitivity and the modulus of electrical impedance in the reproducible frequency range. The verification was carried out in accordance with GOST 16122 - 67 "Loudspeakers. Methods of electroacoustic testing" [1].

The woofers selected for operation in loudspeakers had a DC resistance of 3.53 (two) and 3.58 (two) ohms. main resonance frequencies 47 (two) and 50 (two) Hz. characteristic sensitivity level 85.4 dB/W/m.

Specimens with voice coil resistances of 3.68 and 3.66 ohms were taken as midrange heads. with fundamental resonant frequencies of 173 and 171 Hz and a characteristic sensitivity level of 92 dB/W/m.

The midrange heads were modified according to the method proposed by V. Shoroey. involving the impregnation of their diffusers with gerlen-based mastic and the installation of PAS diffuser holders on the windows. consisting of two or three layers of synthetic material, made in accordance with TU 17 of the RSFSR 35-3941 - 81.

The tweeters selected for the speakers had a DC resistance of 6.24 and 6.3 ohms. the main resonant frequencies are 2510 and 2530 Hz. characteristic sensitivity 92 dB/W/m.

The HF heads have also undergone a slight revision. To do this, they were dismantled, the voice coils were re-centered, and the amount of sound absorber inside their domes was tripled.

The following measuring equipment was used for measurements and tuning: sound generator GZ-34. universal voltmeter V7-26. oscilloscope C1 -91. high-frequency meter E7-9. multimeter F4800. as well as reference inductors and capacitors.

At self-manufacturing construction, the following assembly sequence should be followed.

First, choose your materials carefully. Treat surfaces to be glued with coarse-grained emery paper. Glue PVA-9 is used for gluing two-layer body panels. In other cases, a mixture of PVA-E and small chipboard (beech, oak) sawdust in a ratio of 10:3 is used as an adhesive.

Then, from the prepared panels, you should assemble the frame - without the front and back panels and fix its "right" corners with the help of metal corners and clamps - until the adhesive mixture dries completely (two to three days).

Now, according to the actual external and internal dimensions, you need to make the front and rear panels (see Fig. 2 and 3). On the inner surface of the front panel, along the output holes of the phase inverters. install the plates (Fig. 7) attached with screws to the bars (Fig. 8).

After that, the midrange box is fixed with screws on the inside of the front panel of the loudspeaker case. Then, with the help of glue, the front panel is installed in its place in the frame and kept for four days under a load of 50 ... 100 kg. After that, wooden dowels are inserted into the ends of the front panel.

Inside the case, according to Fig. 3, glue the PMAS panels (Fig. 5) and keep them for two or three days. In this case, panel 1 (see Fig. 5) is installed at the end of the body assembly, i.e. after the rear panel is installed.

On the side panels, along the curved part of the bass reflex plates. 12 mm thick plywood panels are glued close to them with epoxy glue so that passages form.

The woofer compartments of the loudspeakers are pasted over with soft natural felt 17 mm thick. Rollers made of cotton batting 40 mm in diameter and 100 mm long are glued into all their corners. In order to avoid overdamping, batting rollers are not installed near the input of phase inverters closer than 60 ... 70 mm.

And the last. To maintain the value of the characteristic sensitivity, it is recommended to use a stranded wire with a large cross section to connect the speakers to the amplifier.

For subjective listening to speakers, the PIONEER PDS502 and DFNON 1015m CD players and the PJONEER PL640 vinyl record player were used as signal sources.

In addition to assessing the sound of AC "VERNA 50A", it was compared with the sound of speakers of medium and above average cost groups: "Status S50" by AR (USA) and "AE 520" by Acoustic Energy (England).

Listeners were offered phonograph records with recordings of classical music by Russian and foreign composers ("All-Night Vigil" by S. Rachmaninov, "Scheherazade" by Rimsky-Korsakov, "Twenty-Four Caprices" by N. Paganini) and CDs with pop recordings ("Cadavrexguis" - Amanda Lear. "Na Na Hey Hey" - Donna Summer. "All That Jazz" compilation), as well as national Japanese, Indian and Chinese music("Tai Chi Too". "Shaman", "Seven Times Seven" - Oliver Shanti).

Listening was carried out in several stages over four days. There were lovers of sound recording with great experience, speakers developers. students of the Moscow Conservatory.

All listeners noted the clear, undistorted sound of AC "VERNA 50A" at minimum (1 ... 4 Vg) and medium (20 ... 30 W) power. None of the experts experienced fatigue, even with prolonged listening, while the sound of AC "Status S50" and "AE 520" began to tire them after 20 ... 30 minutes.

LITERATURE
1. I. A. Aldoshina, A. G. Voishvillo.
High-quality acoustic systems and emitters - M. Radio and communication. 1985.
2. V. Shorov, P. Popov. Improving the sound quality of your speakers -

The main technical characteristics of the speakers. nominal (maximum) power - 25 (50) W; nominal electrical resistance - 8 Ohm; reproducible audio frequency range - 50 ... 20000 Hz; uneven frequency response in the range of 100 ... 8000 Hz - +/- 3 dB; level of characteristic sensitivity - 85 dB / W / m; total harmonic distortion at a sound pressure level of 90 dB in the range: 63 ... 500 Hz - 3%; 500 ... 10000 Hz - 1.5%; 1000 .. .15000 Hz - 1%; dimensions - 220x700x270 mm; weight - 15 kg. The manufacture of speakers begins with a pairwise selection of low-frequency loudspeaker heads after their 10 ... 30-hour run, which makes it possible to stabilize the characteristics of the head diffuser suspension. When running the 25GDN-3-4 heads, they are connected in turn to a sound generator and a signal with a frequency of 65 Hz and an amplitude of 18 V is applied to them. The real sensitivity and quality factors of the heads installed in the same housing should not differ from each other by more than 10 and 5 %, respectively. It is also recommended to use heads with different (within 10...15 Hz) resonant frequencies. This favorably affects the frequency response of the sound pressure and reduces the even harmonics of the reproduced signal by half, and this is very important for small speakers. Schematic diagram of the AU is shown in Fig.1. The 5GDSh-5-4 broadband head with a mastic-impregnated suspension and PAS panels installed on the diffuser windows works in the midrange. This head can be replaced with 6GDSh-5-4, but since the level of its characteristic sensitivity is lower than that of 5GDSh-5-4, then the resistor R2 must be taken with a lower resistance. When selecting a HF head, you should choose specimens with the lowest resonance frequency. Then you should disassemble the heads in order to replace the sound absorber in them. To do this, unscrew the screws securing the acoustic lens, then remove the lens itself and the head dome. As a new sound absorber, it is recommended to use 0.5 g of eye (fine) cotton wool. It should be fluffed evenly and put under the dome. Then the HF head must be assembled in the reverse order. The fastening screws of the acoustic lens are fixed with NC varnish. Briefly about the filter. In the low-frequency section, a third-order L1C1L2C2R1 filter with a cutoff frequency of 550 Hz and attenuation of 18 dB / oct is used, in the mid-frequency section - a first-order band-pass filter R2C2L3 and in the high-frequency section - a third-order filter R3C4L4C5. Coils L1 and L2 are wound on flat magnetic cores made of 2000NM ferrite with dimensions of 8x15x80 mm; L1 contains 200, and L2 - 72 turns of PEL-2 1.12 wire. Winding - turn to turn. Coils L3, L4 consist of 140 and 147 turns of PEL-1 0.56 wire, respectively. They are wound on plastic caracas with a diameter of 20 and a height of 25 mm. The filters use capacitors K73-16 (C1-C3) and K73-21, K73-17 (C4, C5), resistor R1 - PEV, R2, R3 consist of four MLT-2 resistors connected in parallel with a resistance of 16 ohms. All filter elements are mounted on a fiberglass board, which is screwed through rubber washers to the rear panel of the speaker cabinet.
The AC case (Fig. 2) is made of chipboard plates 16 mm thick and bars with a section of 20x20 mm, installed in the corners of the panels to be joined. MF and HF heads are located in a compartment separated from the main body. The woofer unit has a volume of about 17 dm3, which allows you to tune the phase inverter, consisting of two tubes with an inner diameter of 30 and a length of 150 mm, to a frequency close to the resonant frequency of the woofers - 50 Hz. At the same time, the sound pressure level at this frequency is 5 dB lower than the level of the average characteristic sensitivity. The frequency response unevenness when using two 25GDN-3-4 heads in a given volume in the range of 50 ... 500 Hz does not exceed +/-3 dB. Soft felt 15 mm thick is used as a sound and vibration absorber in the woofer unit, which is tightly glued with Moment glue to all its internal surfaces. At the joints of the body panels, gauze bags with batting are fixed over the felt. The bass reflex tubes are made of steel and fixed in the holes with epoxy glue. To increase the rigidity and vibration losses of the case, beech bars are glued with PVA glue between the holes of the woofers and phase inverters. The MF-HF block is formed by two partitions made of plywood 12 mm thick (they are installed in a mounted speaker cabinet without a rear panel). Its volume allows you to freely reproduce a signal with a frequency of 300 Hz. Inside the box, cotton wool weighing about 200 g is evenly laid. MF and HF heads are fixed outside through felt rings 3 mm thick. The woofers are also installed on the outside through 3...4 mm porous rubber pads. Outside, the speaker cabinet is covered with oak veneer and water-resistant colorless varnish. The front panels of the speakers are covered from the outside with a frame with an acoustically transparent fabric. On the rear panel there are clamps for connecting speakers to a power amplifier. A comparative subjective analysis of the speaker sound quality showed that "VERNA 50-01" sounds no worse than such imported speakers as MATRIX 805, JBL L-20, TDL NFM-2, KEF K160, K140, with much lower manufacturing and tuning costs. Consultation on the manufacture, configuration and calculation of the speakers can be obtained by calling (095) 145-09-90. Chapter: