NA4 – The acoustics are original in everything. The simplest design with a complex sound.

I initially did not develop these acoustic systems (hereinafter – AC) for myself and, what is pleasant, the only condition of the customer was the high-quality reproduction of Music and the color of the body that was in harmony with the interior. Thus, I was not limited either by the electrical characteristics, or by the number of bands, or by the dimensions of the speakers (the listening room was supposed to be large and free, with a small amount of furniture). In the beginning, there was an idea to make speakers on more powerful speakers (specifically 25 GDSH-102) or on dual 10 GDSH-102, but then I decided to sacrifice power for the sake of guaranteed quality and assemble the speakers on one broadband 10 GDSH-102.

The speakers 10gdsh102 of the Znamensk plant (they are, in other incarnations: 10 GD-36K, they are 10 GDSh-1-4) sound good by themselves, and at first I even wanted to make just Screens or OYa (open box), but later (for aesthetic reasons) it was decided to make a ZYa (closed box). The option is not ideal, but practical.

It was a deliberate sacrifice of the amount and depth of bass (in comparison with the PHI) for the sake of its higher quality, and no less deliberate rejection of a great-sounding screen due to its unrealistic dimensions. In addition, to reduce the influence of the edges of the front panel, it was decided to make it as large as possible, and the ZYA itself took the form of a rather flat box located behind this wide “screen”.

This idea was born quite spontaneously, I drew analogies with the old speakers, which in most cases were made with a wide front panel and did not at all engage in “licking” the front edges of the case. But earlier the speaker enclosures were designed for high-quality music reproduction (now they are being developed more and more for the interior). You can see the result of my design work in the drawing.

Figure 1 – Acoustic system NA-4, drawing

For the facade and the stand, I used pedestal covers made of laminated chipboard 25 mm thick, the box is made of 16 mm chipboard, I “laminated” it myself, with self-adhesive film. The structure is assembled on bars in the traditional way – self-tapping screws + glue, only the glue had to be chosen so that it would stick well to the laminated surface. Assembling the box and ensuring smooth mating of its parts is similar to that described in the article about the NA-3. The bottom stand is screwed from below with long thick self-tapping screws.

The bottom fixing technology is as follows: 5-6 fixing holes are outlined and drilled in it in a row, then the bottom and the facade are fastened with one extreme screw (for exact coincidence of the edges of the facade and the bottom, it is necessary to assemble on a flat, clean and flat surface), this stage should give an even connection of parts; then the parallelism of the edges of the parts relative to each other is precisely adjusted (in order to obtain a perfectly even indent from the front edge of the bottom to its mating with the front panel) and the resulting position is fixed with the second same extreme screw, the rest are twisted already when the parts are precisely fastened together; after that, the structure is disassembled and the joint is coated with glue or sealant and assembled clean.

Two ribs of stiffeners pass inside the body. Another would be ideal – two spacers between the front and rear walls of the case, but this made it difficult to attach the sound-vibration isolation cover. I decided to compensate for possible vibrations of the rear wall with good sound and vibration isolation from the inside and a leatherette lining on the outside.

In this case, there was a rubber-based carpet inside, glued with the rubberized side along the entire inner surface and a fluffed synthetic winterizer distributed throughout the volume.

The leatherette overlay also hides the only screws from the outside and gives the speakers an elegant rear view. Listening to this pair in conditions when one of the backs was not yet covered with leatherette gave the following result: the “unfinished” speaker had a sharper sound, more attached to the speaker, while the “trimmed” one sounded softer, light, open. So the use of this particular type of coating turned out to be quite justified.

To damp standing waves in the body, the following solution was used: on the bottom and roof of the box (naturally from the inside), the carpet was fixed by waves, and the waves on the bottom and the cover were directed at 90 degrees relative to each other. Carpet waves were made as follows: first, using short screws with large heads and “Moment”, one edge of the cut strip of carpet is attached, then a wave fold is made with a length and height of about 3-4 cm and is again attached to the chipboard in the same way, etc. etc. The side walls, if desired, can be finished in the same way, but I limited myself to only two surfaces.

The speakers are processed as follows: the polyurethane corrugation (suspension) is impregnated with castor oil, this must be done carefully, with small doses of oil neatly distributed in the middle of the corrugation, otherwise there is a risk of peeling it off the basket or from the diffuser.

This is done to eliminate the dip in the region of 400 Hz (this recipe for “treatment” of the speakers was used in his developments by “Doctor” Alexander Klyachin). After impregnation, the corrugations should be slightly warped – this is normal to be afraid, but excessive impregnation will lead to very strong warping and, as a result, worsen the sound of the speaker – this is no use to us.

The speaker basket windows are sealed with one layer of padding polyester (about half a centimeter thick), this allows you to reduce the quality factor of the speaker and adapt it, thereby, to the conditions of the closed cell. Alexander Klyachin also recommended sticking anti-magnets, but they had to do without them, for lack of a suitable pair of magnets.

In the photo there are speakers, the windows of which are sealed with the required layer of padding polyester. The different color of the glue lines is simply the result of using two types of glue (dark – Moment-1, light – Moment Crystal, the effect is identical).

In this design, one of the most important elements is the internal wiring cable. As an inexpensive option with a guaranteed result, you can use a homemade litz in paper insulation. Another budget option is a mono-conductor in polyethylene insulation from an old telephone cable.

The age of the cable in this case guarantees its sufficient heating and a decent quality of copper. A certain number of mono-cores (most likely in the range from 4 to 6) must be twisted into a core, the cores should be twisted together in the opposite direction with a small step (literally 2-4 turns per meter).

A more expensive option for internal wiring is to use a quality branded cable (Supra, Analysis-Plus). Naturally, when making and connecting wires, we take into account their direction. In the speaker, I did not apply any filters, the speakers are connected directly. By the way, one of them had the wrong polarity, so be sure to check it yourself (for example, with a battery: the diffuser is forward, which means + hit +). The goal was to provide good sound with minimal design complexity and light …