Manufacturer: PA "Radio Engineering", Riga.

Purpose and scope : for high-quality reproduction of music and speech programs in stationary living conditions. The S-90 acoustic system, developed in 1975, is the first domestic system that meets the requirements of international documents for Hi-Fi equipment. S-90 B the later model “S90”, characterized by an expanded range of reproduced frequencies, the introduction of an indication of electrical overload of the loudspeakers and a new appearance. The recommended power of a high-quality household amplifier is 20 - 90 W.Manual on disk.

Characteristics

3-way floorstanding speaker with bass reflex

Frequency range: 25 (-14 dB) – 25000 Hz

Frequency response unevenness in the range 100 - 8000 Hz: ±4 dB

Sensitivity: 89 dB (0.56 Pa/√W)

Directivity at angles of 25±5° in the horizontal plane and 7±2.5° in the vertical plane, from the frequency response measured along the acoustic axis of the speaker:

in the vertical plane: ±3°

Horizontal: ±4°

Harmonic distortion of speakers at a sound pressure level of 90 dB at frequencies:

250 - 1000 Hz: 2%

1000 – 2000 Hz: 1.5%

2000 – 6300 Hz: 1%

Resistance: 8 ohms

Minimum impedance value: 7.6 ohms

Rated power: 35W

Maximum (nameplate) power: 90 W

Short-term power: 600 W

Installed speakers:

LF:

MF:

HF:

Dimensions (HxWxD): 710x360x285 mm

Weight: 23 kg

Design

The body is made in the form of a rectangular non-separable box made of chipboard, veneered with valuable wood veneer. The wall thickness is 16 mm, the front panel is plywood 22 mm thick. At the joints of the housing walls, elements are installed on the inside that increase the strength and rigidity of the housing.

The heads are framed by two decorative overlays, made of plastic, painted “metal” or black. One cover frames the midrange and tweeter, as well as the upper half of the front panel, the other – the woofer head and the lower half of the front panel of the speakers. The heads are protected by metal mesh. Each of the overlays is secured with six decorative screws. The midrange head is isolated on the inside from the total volume of the housing by a special plastic casing in the shape of a truncated cone. The LF, MF and HF heads are located on the front panel along the vertical axis. The nameplate at the top of the speaker shows the frequency response curve and gives the name of the speaker. In the right corner of the front panel there are speaker overload indicators by channel, and in the lower part there is a rectangular bass reflex hole, 108x35 mm in size and tuning frequency of 25 Hz. On the rear wall of the speaker there is a nameplate with the main characteristics and a block with clamps for connecting the connecting cord, as well as sound pressure level controls at medium and high frequencies.

The internal volume of the speaker is 45 liters. To reduce the influence on the frequency response of sound pressure and the sound quality of the speaker resonances of the internal volume of the housing, it is filled with a sound absorber, which is mats of technical wool, covered with gauze.

Inside the case, on one board, there are electrical filters that ensure separation of the speaker bands. The crossover frequencies between LF/MF are 750 Hz (±50 Hz), between MF/HF - 5000 Hz (±500 Hz). The design of the filters and the overload indication unit uses resistors such as BC, MLT, SP3-38B, S5-35I, PPB, capacitors such as MBGO-2, K50-12, K75-11 and inductors on plastic cast frames.

Music lovers constantly start debates about which speaker system to choose for comfortable listening to music at home. And this is no accident: the entire contingent was divided into two camps. The first believe that it is worth shelling out a tidy sum to buy a cool Hi-Fi (or better yet, Hi-End) system in order to be happy and forget about headaches about this topic for the rest of your life. But there are also those who are not ready to give up their entire life’s savings for expensive acoustics (instead of the required car or apartment), and therefore consider the best option to purchase simpler equipment or improve the good old classics to good sound.

In this article we will talk about one of the most popular audio systems produced during the USSR, which could not leave any of its owners indifferent. The S90 speakers, the technical characteristics of which can excite consciousness to this day, have become one of the highest achievements of the Soviet company Radiotekhnika.

Speaker models

The very first thing worth mentioning is the real and full name of the speaker model - 35AC-012. An important factor is that this acoustics was produced in several variations. The most popular of them are S90 and S90B. There were also S90i, S90D and S90f models, but they were not widely used and are now almost unheard of.

The model with the postfix “B” differed from the usual “nineties” in a wider range of reproduced frequencies. Another significant difference was the introduction of an electrical overload indicator for the speakers. The recommended power of a high-quality amplifier for these speakers is in the range from 20 to 90 watts. It is also worth noting that Radiotekhnika S90, S90B (and other modifications) were the first models of speaker systems that met international requirements for Hi-Fi equipment.

Design

The case in which the S90 speakers are enclosed is, in fact, a non-demountable rectangular box made of veneered wood made of precious wood. The thickness of the speaker walls reaches 16 mm, the front panel is made of plywood 22 mm thick. The internal joints of the cabinet walls are connected by special elements that increase the rigidity and strength of the structure, but do not interfere with high-quality sound.

If you look at the device from the front, the speakers are arranged in the following order (from top to bottom): tweeter, midrange speaker and woofer. Also on the front panel of the S90 speaker you can see the frequency response (amplitude-frequency response) graph and the bass reflex hole. While the frequency response is located at the top or bottom (depending on the acoustic model), the bass reflex is always located at the bottom. This was done for reasons of proper design for better sound and giving the speakers good bass.

Speakers S90: characteristics

If we take the regular S90 as an example, they have dynamic direct radiation heads installed. More precisely, a high-frequency head 10GD-35, a mid-frequency head 15GD-11A and a low-frequency head 30GD-2 (in later models - 75GDN-1-4).

Equipped with two step playback level controls to adjust the midrange and treble in the ranges from 500 to 5000 Hz and from 5 to 20 kHz. Each regulator moves in three fixed positions. In position “0” there is no obstacle for the signal from the crossover filter, and it is fed directly to the corresponding head. When using the “-3 dB” and “-6 dB” positions, the signal is attenuated by 1.4 and 2 times, respectively, relative to the “0” position. By switching the selected control, you can change the timbre of the sound.

The rated power of the S90 speakers is 90 Watts, while the nominal power is 35 Watts. The nominal electrical resistance of this speaker system is 4 ohms, and the range of frequencies available for playback ranges from 31.5 Hz to 20 kHz. The nominal sound pressure of the S90 is 1.2 Pa. I would like to note the rather impressive dimensions of one column - 71.0 x 36.0 x 28.5 cm, and the total weight of the entire system reaches 30 kg.

Speaker circuit and connection to the sound source

In order to understand whether it is worthwhile to modify any speaker system, you need to study all the data and aspects of the equipment. Below is the electrical diagram of the S90 speakers. Anyone, even a novice radio amateur, can understand it; you just need to have at least basic knowledge.

Another important point is the correct connection of the speaker system. After all, if something goes wrong, even during connection you can, without meaning to, damage the equipment. You don't need to be a professional to figure out how to connect S90 speakers. The main thing is to have at least 20 watts with the amplifier (in this case, most likely, the sound will not be loud enough for large rooms), but not more than 90 watts. If the amplifier's permissible power value is exceeded, the user risks being left without acoustics due to its breakdown. To connect, you will need regular speaker wires, which must be connected to the terminals on each speaker and amplifier. The main condition for connection is compliance with polarity.

Revision 35AS-012

As it becomes clear from the description above, it itself has good technical characteristics and is capable of “rocking up” even small public spaces. But for home use, the most sophisticated music lover will prefer to modify the S90 speakers with his own hands. And all because the acoustic systems of the Radiotekhnika company, assembled more than twenty (or even thirty) years ago, did not already have high build quality and the materials used in those years.

Analysis

In the event that the acoustics were purchased in used condition and are currently well-worn by life, it is worth paying attention to the appearance. To do this, you need to disassemble the S90 speakers, first placing them on their “back”.

When removing the speakers, you need to take into account that the tweeter and midrange heads are attached to the housing using the same screws as the linings. The woofer is attached separately, and you need to be as careful as possible not to damage it when unscrewing it.

The HF/MF controls are much easier to dismantle than they seem. All you need to do is carefully remove the decorative plugs that are located in the center of each regulator. After this, using a screwdriver, you need to unscrew the screw that is revealed to the eye and remove the regulator handle itself. The plastic lining must be carefully lifted on both sides using flat objects and removed, and the four screws remaining under it must be unscrewed. Then you can push the S90 inside the speaker, not forgetting to unsolder it from the filter.

The cotton wool bags located inside the case must be removed. Again, if the previous owner of the speakers did not forget to return them to their place in case of disassembly.

You should first unsolder the panel with filters from the output on the rear side of the speaker, and then you need to dismantle it by unscrewing the screws. Now you can remove the panel with the terminals attached to it.

Appearance and body

If the grilles and decorative covers of the speakers are “tired,” then it is worth straightening them and painting them, having previously sanded and degreased them. This will give the speakers a fresh look. The body of the S90 speaker becomes loose over time and can be strengthened if desired. This will result in a better sounding woofer.

This can be done in various ways, including installing spacers and additional corners inside. It is also necessary to pay attention to sealing all joints and seams using conventional plumbing sealant. In addition, you can glue the inner walls of the case with foam rubber (except for the front), which will increase the volume of the latter.

Terminals and filter

Knowledgeable radio amateurs advise replacing the standard speaker terminals with universal type terminals with gold-plated connectors. The installation location must be lubricated with sealant and the panel with terminals must be put in place.

Considerable attention should be paid to the sound filter. If it was attached to the body with metal screws, then the filter settings will be lost. There are cases where the filter was assembled on a metal plate. This can be corrected by transferring all nodes to a plywood panel. The circuit of the filter itself may have been changed at the manufacturer due to different parameters of the speakers, so you should make sure that everything is assembled in accordance with GOST. If there are jumpers in the filter, then they must be removed and replaced, for example, with an oxygen-free copper cable with a cross-sectional area of ​​4 mm 2. It is worth removing the attenuator from the circuit, as it simply distorts the sound, and replacing the wires used to connect the speakers to the filter.

For low-frequency speakers, a wire with a cross-section of 4 mm 2 is suitable, for mid-range speakers - with an area of ​​2.5 mm 2, for high-frequency speakers - with an area of ​​2 mm 2. After these simple steps, the filter must be returned to its place and covered with foam rubber.

Speakers and other "trifles"

New seals should be cut for the speakers. This can be done using cheap or simply outdated computer mouse pads. This is the simplest option. After this, it is worth returning them to their seats and installing decorative overlays and nets.

Before installing the regulators in place, you will have to remove all resistance from them. When installing them in place, it is imperative to use sealant, as when installing a bass reflex.

Through such simple manipulations, the S90 speakers acquire new life. The sound quality becomes an order of magnitude higher, despite the low costs. As a result, we can say that if you don’t have the money for expensive 2.0 format acoustics, you can use a similar option and become the happy owner of the time-tested Radiotekhnika S90 speaker. If it happens that only half of the speakers are available, do not be upset. After all, it is remarkable that the S90 speaker, a photo of which can be found on almost any site for acoustics lovers from the times of the USSR, can work alone and give good results.

1. Small housing volume for woofer. The consequence is a muttering of low frequencies.
2. The bass reflex is designed for a frequency of 20 Hz. The consequence is large low-frequency distortion.
3. Worst midrange speaker. The consequences are disgusting midrange and overtones.
4. Low resonance frequency of the tweeter. Consequences - "quacking", hissing.
5. The filter is designed taking into account the previous shortcomings. The consequence is that when modifying any unit, the filter must be changed.
6. The body is not rigid enough and is not “damped”. Consequences - vibrations, overtones, "barrel".
7. Etc. and so on. ...

We study and dare

While drinking beer, we reach three truths. There are three ways:

1. Lightweight and effective.
2. Medium difficulty. More shamanism and snobbery. Some sound improvements compared to point 1.
3. Super complex, time consuming and super efficient. In reality, you are trying to make new speakers. It all depends on the quality of workmanship and musical flair. If nothing works out, then no one promised you anything.

Attention! Attention! Attention!

1. When carrying out all work, ensure that the phasing of the speakers is correct. If you have not encountered this yourself, invite a specialist - electronics!
2. Remaking the speaker 15 GD - 11A is an irreversible process. If you are not careful, the speaker has one path - to the trash can, and you have another - to the market.

The first way. Lightweight and effective.

1. Mid frequencies are the main emphasis. By reworking the speaker, we will make it work in piston mode, increase the upper limit frequency, remove overtones, increase sensitivity, improve directivity, and dampen it.
2. Let's move the speaker to the range of 31.5 Hz, instead of 20 Hz. There will be less muttering.
3. Let's suppress the resonance of the high-frequency head.
4. Let's quiet the sounds of the building

We buy a Soviet tennis ball from a store. Chinese and others are not suitable. They have different material. The ball should be exactly the same as in distant childhood for 8 kopecks. As a last resort, you can take it from friends or in the tennis sports section. We buy epoxy resin (a little, maybe 1cm cube), glue (Supercement, Mars, Argo, etc. - hard after hardening), a couple of simple pencils, any medical bandage and cotton wool.

Let's get creative. We saw the ball in half along the seam. The seam is visible to light. It is overlapped and 1 - 2 mm wide. You need to cut in the middle of the seam. I sawed with a Nev blade, having previously made notches on it with a sharpening stone. After sawing, align the cut line on sandpaper and sand the outer surface of the ball with fine sandpaper. If there are large deposits inside the seam area, then they also need to be removed. When working, the ball must be secured with plasticine on a Mars battery (a film case, a jar of fish food, etc., according to your imagination) at three points. It's enough. Plasticine is removed later either with a dry cloth or by wiping with gasoline. Once the surface of the ball has been treated, do not touch it with your hands. Grind the pencil leads on sandpaper.

Dilute epoxy resin with double the amount of hardener. Cover the surface of the ball with the thinnest layer. If necessary, excess glue can be removed with newsprint. Sprinkle with graphite and shake off excess. It is necessary to ensure that the white plastic of the ball does not show through the graphite. If it shows through, it means the layer of epoxy resin was small. Need to add. Once everything is done, let it harden.

Assembling a 3 KHz filter. To do this, we take a 4.7 Mf capacitor and a 0.6 mH inductor. You can take a capacitor from 4 to 7 mF and adjust the inductor to it. In order not to bother your head with unnecessary formulas, the simplest thing is that the product of the capacitor capacitance in microfarads and the inductance of the inductor in mH should be equal to 2.82. Let's say the capacitance of the filter capacitor is 6.6 μF (MBGO and MBM with a permissible deviation from the nominal value of ±10%), then the inductance of the coil is 2.82: 6.6 = 0.43 mH, (the winding contains 150 turns of PEV-1 0.8 wire , wound on a frame with a diameter of 22 and a length of 22 mm with a cheek diameter of 44 mm). Using these data, it is possible to assemble a circuit without an LC meter, since it is not the exact value that is important, but the “capture” of the resonant frequency, which has a certain spread. We attach the capacitor and inductor to a piece of fiberboard and solder one terminal of the coil to the terminal of the capacitor. We solder wires 40-50 cm long to the free terminals.

Let's disassemble the column. We remove the low-frequency speaker, the mid-frequency speaker, take out the glass from it, remove the high-frequency speaker, remove the decorative trim, remove the phase reflex (on some speakers you will have to unscrew the filter). We take half of the dried ball, polish it on the outside with suede or newsprint and glue it over the dust cap of the mid-range speaker head with hard glue. You must ensure that there are no un-glued gaps between the edge of the ball and the cap and that the ball is glued exactly in the center. We do the same with the second midrange driver. Leave to dry.

We screw a homemade filter onto the back wall of the speaker (inside) opposite the tweeter. Solder the wires from the filter to the output of the high-frequency speaker. Which one goes where does not matter. We remove the connectors from the back wall of the speakers and solder the wire going from the amplifier directly to the filter. We saw off 10 cm from the phase reflex pipe with a hacksaw along the center line. We wrap the phase reflex pipe and the mid-frequency speaker glass with a layer of gauze and bandage it. It is necessary to check whether they will enter their nests after this procedure. If they do not fit, then reduce the layer of cotton wool and gauze. We check if there is cotton wool and gauze in the glass. Add if it’s not enough until it’s full. We dampen the mid-frequency speakers. To do this, we additionally cover their diffuser holders with foam rings made from 10x27x355 mm blanks. the ends of which are glued end-to-end with Moment glue. We cover the bottom and ceiling of the column from the inside with felt (batting, padding polyester, etc.). We wrap the wires with a bandage.

We place the bandage along the wire and twist it, wrapping it around the wire. It is convenient to secure the bandage with threads. Assembling the column. We coat all the perimeters of all speakers with plasticine. There is no need to wear protective nets, but only on the condition that there are no small children, the wife will not come in with a mop or vacuum cleaner, and that the speakers will not be transported. Turn on the speakers. We don't know right. We call our friends. Please bring your favorite recordings. Let's listen. We calm our friends down with beer. We note with mockery how useful the bucks spent on purchasing foreign rubbish would be to them.

The second way. Medium difficulty.

We do everything indicated in path 1, but do not collect the columns.

1. Let's improve the properties of the body and kill overtones and the "barrel"
2. Let's achieve better signal transmission
3. Housing sealing. Removing the influence of the body

So, let's go. Strengthen the rear wall of the case by placing two slats with a cross-section of 3x2cm. vertically along the entire length at a distance of 15-20 cm from each other symmetrically, and attaching them with screws to the back wall. Pre-treat the mounting area with epoxy. It is necessary to take into account the possibility of installing a phase reflex later. Between the rear and front walls we install a spacer rail at the level of the midrange head, taking into account the possibility of installing a glass. We coat all wall joints and corners from the inside with silicone glue such as "Bison" or plumbing silicone putty. We cover the entire body inside with felt (batting, padding polyester, etc.). It should not be thicker than 1.5 cm, so as not to greatly reduce the internal volume of the case.

We reject all proposals to replace 15 GD-11A with 6 GDSH-5. Ours is already “cool”, and such a replacement will lead to a loss of power, a decrease in the dynamic range (very dangerous) and you will have to greatly change the filter. So, when replacing 15 GD - 11A with 6 GDSh-5 for 35AS - 212, you will have to replace the following parts: L1 - 0.22mH, C2 - 1.0mF, C8 - 0.5mF, L4 - 0.1mH. New parameters have been specified. When using 6 GDSH - 5 - 4, you will also have to install an additional resistance in the circuit of this head at 4 Ohms. The appearance of the column also changes. Well, if you really want to, then you can. Further. Removing tone switches. Remove unnecessary resistors R (1, 2, 4, 5, 7, 8, 9, 11, 12). We replace the wires on the filter mounting with a copper wire with a diameter of 1.2 mm. We replace the wires going from the speakers to the filter with more traveling ones. For the low-frequency speaker - multi-core - with a cross-section of 2.5 - 3 mm square, for the mid-frequency - 2.5 mm square. For high frequency - 2 mm square. - single-core. All wires are soldered to the filter directly, rather than passing through previous speakers. The filter is installed at the bottom of the column. All wires are laid under a layer of felt. On the side walls.

The filter regulators are removed. In their place, we make wooden (chipboard, plywood) plugs according to the thickness of the body. We pour them onto the epoxy and sand them down. We cover the front panel with self-adhesive wood-look film to match the veneer of the speakers. Installing speakers. Low-frequency and mid-frequency through rubber gaskets. Suitable rubber from window insulation, thin rubber medical hoses, silicone hoses (worse). We treat the installed speakers around the perimeter with plasticine or non-hardening window putty (it resembles a bar of laundry soap and is cheap). Checking the sound. We're just fooling around. We push aside all sorts of “Pioner”, “Technics”, JAMO and ...

The third way. Super complex, time consuming and super efficient.

It’s a good idea to have the following instruments: an oscilloscope, an audio frequency generator, a digital multimeter, an LC meter. A person who doesn’t do repairs and assembly at home, of course, doesn’t have all this, but there is a way out - go to the workshop and ask to try on what you need, taking filters, heads, etc. with you. If they ask for payment for this, it will be purely symbolic. You can even order a filter. This, of course, will be more expensive. Let's begin. We take as a basis 35AC-212 with dimensions 710x360x285. It is desirable that the case be made of plywood, a woofer with a rubber surround, and a high-frequency speaker with a fiberglass dome. Let's sort everything out. We no longer need the midrange speaker. The housing needs to be increased for a woofer with a rubber surround to 100 liters. If the suspension is polyurethane foam, then up to 120 -130 liters. Our body is 70 liters.

There are two options:

1. Remove the front wall from the case, in order to later use it for a matrix for the holes for the speakers in the newly manufactured case for 100 liters. The remains of the buildings make good boxes for potatoes and markoshka in the cellar.
2. You can try to build up the old body.

In the first case, you need to focus on the dimensions - 1100x360x350 and production in a furniture workshop according to your drawings, with abuse and quibbles about quality. We will consider the second way. So, you can try to get by with a little blood. We make it ourselves, or we order two boxes with tightly fitting walls and lids made of double 10-layer plywood with external dimensions - 380x360x285. We cut out identical holes approximately 270x210 in the bottom of the column and in the lid of the box. We cover the inside of the box with felt. After assembly it will be impossible to do this. We drill holes in the lid of the box and in the bottom of the column through which we fasten them together with bolts. The bolt heads should sink into the countersunk area. Add a little bit of shot - 10 kilograms of shot won't hurt, throw a gauze bag with cotton wool on top. We pre-fill the joint with epoxy with a normal content of hardener. We cover the joint with felt. The rest of the body movements are the same as in paths 1 and 2. Let’s take the mid-frequency head 30 GDS-1. You just need to check them - there are a lot of defects. Purely mechanical properties. Further. We measure f resonance of all speakers. You can use a felt-tip pen to sign directly on the magnets so you don’t get confused and try everything on again.

It would be good if the resonance frequency of paired speakers did not differ greatly. If the speaker produces extraneous sounds at any of the sound frequencies, then it must either be cleaned or replaced if cleaning did not achieve normal operation. We calculate and make filters for our case. The fewer inductances, the better. We continue to work with the body. Remove excess resin at the joint. Let's polish it. We make two wooden boxes for filters. We will mount them on the back wall from the outside. We solder the wires from the amplifier directly to the filters. And we will drag the wires to the speakers through the fastenings of the speaker connectors. All wires are branded audiophile ones. Choose your own price category. There’s just no point in taking very expensive ones. It is better to convert the bass reflex to a frequency of 31.5 - 40 Hz. If the dome of the high-frequency head is made of lavsan, then, after removing the crosspiece, you need to coat the suspension and the outer third of the dome with perchlorovinyl. We cover the entire body with self-adhesive film. For the rest, see path 1 and path 2. With mandatory step-by-step verification - better - worse. The best method, if there is no obvious result, is blind listening.

Literature

1. Zhagirnovsky M., Shorov 8. Improving the sound of 35AC-1 and its modifications. - Radio, 1987, No. 8, p. 29, 30.
2. Shorov V. Improvement of loudspeaker heads. - Radio. 1986, no. 4, p. 39-41.
3. Aldoshina I., Voishvillo A. High-quality acoustic systems and emitters. - M.; Radio and communications. 1985.
4. Zhbanov V. Mechanical damping of diffusers. - Radio, 1988, No. 5, p. 41-43.
5. Maslov A. Once again about the modification of the loudspeaker 35AC-212 (S-90). - Radio, 1985. No. 1, P. 59.
6. Zhbanov V. About damping of dynamic heads. - Radio, 1987, No. 8, p. 31-34.
7. Gennady and Karen Arzumanov. On the issue of modernizing acoustic systems. Bulletin of A.R.F. No. 6" 2000

February 5, 2010 at 00:45

Refinement of the S90 or how to make them “sing” at minimal cost

• DIY or Do It Yourself

How it started

I have long had a dream - to buy the legendary S90 and modify them with a file, in order to make a budget solution that will be the envy of everyone. After monitoring various flea markets for a long time, I finally bought a 35AC-212 “Radio Engineering” S90 from 1981 on one speaker (my peers;)).
The condition on the outside is a solid 4, no one has tampered with the inside with crooked paws. There was only one minus - the bass driver from one speaker was killed, which was honestly reported to me, and I really didn’t like the fact that both woofers were painted silver (it’s good that the paint is not deep paint, i.e. the mass of the diffuser has not increased much).
For 1000 rub. I bought a set for creativity.
We will improve it.
Oh, I feel strong polemics between supporters of improvements to Soviet acoustics and supporters of burying it completely and without turning.
I immediately apologize for the quality of the photos, because at the time of revision, and even now I do not have a digital camera other than a phone.

Let's climb inside

After listening, I decided to disassemble each speaker to see if the insides matched the speakers' passports. As it turned out, the HF quality is 10GD-35, MF 15GD-11A, and LF 35GD (something) I don’t remember, but with a rubber suspension that hasn’t dried out.
The first thing I did was rewind the woofer.
Restoring the speaker was no problem for me, since I did this very often in my youth for little money. Unfortunately, I didn’t have a mandrel of a suitable diameter, but I have a need for invention and I went to the nearest construction store with a caliper in my pocket. As a mandrel, I bought some kind of plumbing pipe for what seemed like 20 rubles. I sawed it lengthwise (this is necessary since after winding it would be practically impossible to remove the coil from the mandrel).
Let's add another 20 minutes for winding and centering and a day to dry the speaker. That's it, the speaker started playing without any extraneous sounds and as if untouched.

Let's start with the tweeters

After listening to the result and reading the great Internet, I began to think further about how to make the sound even better. Basically, all types of modifications come down to replacing the HF, replacing the midrange and damping the body.
The highs really don't sound very good. There are unpleasant overtones in the high frequencies and a lack of ringing in the midrange. The HF section uses speakers with domes made of some kind of plastic/polyethylene. For comparison, I installed 10 W speakers with silk domes, the high-frequency sound became much more transparent and the overtones that simply grated the ear disappeared. As a result, these rootless speakers for about 500 rubles per pair remained in them. I bought them a long time ago and the markings on them are unreadable, and I don’t remember what was written on the price tag. You can also use 10GDV speakers with silk domes.

I note that I first made one speaker and compared the sound from the test discs with the sound of the original speaker. After listening, I decide to leave the rework or return everything back. Everything was done according to my favorite ear, which never seemed to let me down.

Refinement of the body

Next I decided to work on the low frequencies, i.e. modification of the body. Batting was bought for ridiculous money - 38 rubles per meter of length and 2-something meters wide. Having also looked at the manufactured filters, I heeded the advice to change all the wiring in the speakers.
I removed all the speakers from the speakers. I took out the filter and switches. The wires can be safely cut since they will need to be replaced anyway.
Next, I cut out the required piece of batting, borrowed a furniture stapler from a friend, and began sheathing them inside in 2 layers.

We put the bass reflex pipe on the sealant and also cover it with batting.

The next thing you need to do is modify the filter.

The filter circuit is simple

I turned off the switches completely, since they are completely unnecessary. We remove unnecessary elements from the filter board.
We replace all the thin conductors in the filter with normal copper wire.
Here is the filter before modification.

And this is a copper wire about 4 squares used for almost all connections

As a result, rebuilt with removed dividers and regulators


Next we install it in the body and cover it with batting.
We also cover the entire midrange box from the outside with batting.

midrange link

In principle, after such modifications, the sound changed for the better, the bass became clearer, the upper frequencies became “more transparent” and “lighter”, but I still didn’t like the mids, the upper mids were not enough. There was not enough ringing in the vocals.
After rummaging through my supplies I found two 4GD-8Es in excellent condition. I installed one speaker and spent a long time comparing the results. I liked the result. In one blues recording I heard brushes hitting the main drum. Before that I didn't distinguish them.
But these speakers did not last long in acoustics.
After listening to the modified speakers for a week, I came to the conclusion that the sound began to tire me.
Probably all this is caused by the fact that the 4GD-8E dynamic heads have a very high quality factor and, in a closed box, have a very jagged frequency response. Unfortunately, there is no normal microphone to take measurements. Yes, the midrange speakers were equipped with a foam pad covering the rear holes in the speakers. The midrange box itself is filled with fluffy “eye” cotton.

On the Internet they often wrote about 5GDSH-5-4 and 6-GDSH-5, about the fact that after installing the PAS they produce excellent midrange frequencies. Walking through neighboring radio stores, I bought a pair of 6-GDSH-5 4 Ohms for 110 rubles. As far as I understand, they are installed in household electronic equipment. I sealed the windows in the diffuser holder basket with thin batting and installed them instead of 15GD-11A, fortunately their installation dimensions are completely the same. There is another way to refine the midrange speakers - impregnating the suspension with mystical guerlain mixed with the blood of the orchestra conductor with acetone and applying a thin layer to the back side of the diffuser. But as far as I understand, this is quite rare and in construction stores they just shrug their shoulders. It would be worth taking for an experiment, because 110 rubles for a pair of new speakers is not a pity.

After all operations, we completely assemble the acoustics and enjoy the new sound. I tested the sound on Sukhoi’s homemade high-fidelity amplifier (I’m afraid that true Hi-Fi connoisseurs will spew rays of diarrhea in my direction). By the way, I also assembled the amplifier myself, with minor modifications to the power supply, and it has been playing for exactly more than a decade, but that’s how it works in the same form as an engineering sample. I connected it all to Sb Live! Playing flac of special discs such as audio doctor. And just wav and flac discs that are specifically recommended for testing the audio path.

Bottom line

Costs 1000 rub. the acoustics themselves
500 RUR HF speakers
110 RUR Midrange speakers
RUB 150 batting, glue, staples, screws and other small items
Total 1760 rub.
What did we get?

Such nice acoustics

What follows is only my opinion and the opinion of my friends who have experienced it.
A friend who owns jbl floorstanding speakers, I don’t remember the model, but they cost about 20,000 for one and a Yamaha receiver, he definitely agreed that after the S90 modifications, his set is being replayed.
I'm completely satisfied with the sound. Walking around different salons with acoustics and listening to them, I understand that such sound is cheaper than 15,000 rubles. You can't buy one speaker.

PS Now they are playing together with Gumel's Simple amplifier and Sukhoi's BB pre-amplifier. Everything is connected to the same sound system SB Live! and works as a front to 4.0 sound for watching movies on a 37" LCD panel. There is more than enough realism in disaster films. I don’t even think about adding a subwoofer.

Video

Description

Speaker system Radiotehnika S-90F

Radiotehnika S-90F - 3-way speaker system with bass reflex.
Production since 1980 at the Riga plant "Radiotehnika"

Designed for high-quality sound playback in standard living conditions.
"S-90F" is a speaker that meets the requirements of international documents for Hi-Fi category equipment. The difference between this modification of the speaker and the S-90 is: an expanded frequency range, the introduction of an indication of electrical overload of the loudspeakers and a new appearance. The recommended power of the amplifier used is 20-90 W.

The enclosures of all modifications of the speakers are made in the form of a rectangular non-dismountable box made of chipboard veneered with valuable wood veneer. The wall thickness of the case is 16 mm, the front panel is plywood with a thickness of 22 mm. At the joints of the housing walls, elements are installed on the inside that increase the strength and rigidity of the housing.

The speaker uses the following set of heads produced by "Radiotehnika" software:

The heads included in the "S-90F" are each framed with decorative overlays and protected by a mesh; The arrangement of the heads is similar to that in the "S-90". On the front panel, in addition, there are: indicators of overload of the loudspeaker heads, regulators of the sound pressure level of the MF and HF loudspeaker heads, and a nameplate with the name of the speaker. At the bottom of the front panel there is a rectangular outlet 95x75 mm. bass reflex, the tuning frequency of which is 31 Hz.
The internal volume of all modifications of the speaker is 45 dm3. To reduce the influence of the frequency response of sound pressure and the sound quality of the AC resonances of the internal volume of the housing, it is filled with a sound absorber, which is mats made of technical wool, covered with gauze. The mats are located and fixed on the inner surfaces of the housing walls.
Electrical filters are mounted inside the housing walls on one board, providing electrical separation of the bass, midrange, and high-frequency speaker bands. Electrical filters of all modifications of speakers have the same design and electrical circuit diagrams.
Crossover frequencies provided by filters: between LF and MF - 750±50 Hz, between MF and HF - 5000±500 Hz.
Resistors of the BC, MLT, SP3-38B, S5-35V, PPB types are used in the design of the filters and the overload indication unit; capacitors such as MBG0-2, K50-12, K-75-11 and inductors on plastic cast frames.
The removable decorative frame included in the “S-90” kit, “S-90D” is covered with knitted fabric with high acoustic transparency.
The delivery set includes 4 plastic feet, which can be attached to the base of the case if necessary.

Technical data:

Frequency range - 25 (-14 dB) – 25000 Hz;
- Sensitivity - 89 dB (0.56 Pa/? W);
- Frequency response unevenness in the frequency range 100 – 8000 Hz: ±4 dB;
- Directional characteristics of the speakers, measured by the deviation of the frequency response of sound pressure at angles to the acoustic axis:
vertical +2°: -4 dB
horizontal +4°: -3 dB
- Harmonic distortion at 90 dB sound pressure in the frequency range:
250 – 1000 Hz: 2%
1000 – 2000 Hz: 1.5%
2000 – 6300 Hz: 1%
- Resistance - 8 Ohms;
- Minimum impedance value -7 Ohm;
- Rated power - 90 W;