NA3 – Modest 50 liter shelf units. Maximum quality at minimum cost


Created on 27.12.2010 18:28.

Updated 10.17.2019 09:17.

Author: Naumov Maxim.

The idea to create acoustics based on broadband 4GD-35 was born a long time ago, because, having heard them once as part of the Rigonda radio, I could no longer forget their sound. Of course, not only speakers provided the characteristic sound of the legendary Soviet radio, but nevertheless …

Initially, screens were either OY (open box) with a frontal size of about 50×100 cm with mini subwoofers, on which these screens would be attached … But! These speakers provide adequate sounding with a screen size of 100×150 cm, and even the “calculated” 50 cm width of the OY did not fit into the size of the room.

This project remained a project and was archived under the name NA-2. Until now, I am of the opinion that the NA-2 model is absolutely viable, the only question is in the exact calculation of the OP that serves the mid-high-frequency section. As a low-frequency link, 50 liter subwoofers based on the common 25GD26 speakers may well be suitable.

Rice. 1. General design of the NA2 speaker system

Since the desire to make an acoustic system on these speakers has not diminished at all, I was not too lazy to stick the PAS baskets (Acoustic Resistance Panel) on the windows and put the whole thing in the cases from my first NA-1 speakers (50 liters of FI with dimensions of about 22 * ​​30 * 100 w * d * h). PAS was used to adapt a high-quality speaker to the conditions of a closed case, without which the sound was jammed and uninteresting.

First of all, I was surprised that with a passport range of 60-12500 Hz, these speakers reproduce music very completely and completely, provide a sufficiently high resolution, sound emotional, expressive and lively. Having experimented with the options for the FI (Phase Inverter) and even the ZY (Closed Box), I came to the conclusion that the available section of the FI pipes is clearly not enough, and I did not want to use the cases from the old speakers. This is how the blueprint for the NA-3 was born.

Rice. 2. Drawing of the NA-3 acoustics model

Part two. Rationale and design features of the NA-3

In the new speakers, it was decided to use walls made of natural wood, followed by varnishing, as well as to pay more attention to sound and vibration isolation of the enclosures. The volume of the case was supposed to be about 50 liters, FI is slotted, originally calculated for speakers 10 GD 36 (which, in fact, are deeply modernized 4 GD 35) L = 21cm, S = 67cm2 later the length of the FI was changed to 20.8 cm – the size indicated by Alexander Klyachin in the sketch of the case for 10 GD 36 – the action was completely ill-considered, but it seemed to me extremely wise at that time (after all, in which case it would be possible to attach the same 10 GD 36 , for which the phase inverter was calculated).

The decision to organize the FI, and even calculated for, albeit a similar, but different dynamics, was, to put it mildly, naive. The depth of the bass reproduced by 10 GD 36 and 4 GD 35 differ markedly from each other, so at least this should have stopped me. But, it did not stop … The result was appropriate – the FI provided a slight rise in the bass due to its noticeable blur. As a result, I use these speakers in the ZYA mode (I just plugged the phase inverters with rags). Now I would make the hulls according to this drawing.

Rice. 3. Drawing of the NA-3 acoustics case

I left the assembly description unchanged – as it was originally written for a FI-type case. There are two reasons for this: firstly, the new corpus is trite, and having understood how the FI is done, it will not be a problem to assemble the PS; secondly, in the process of assembling a case with a slotted type FI, several specific problems arise, the own solution of which was explained in the original text. So I leave everything as it was before. Comments on the new corpus will appear in parallel with the old text.

The size and shape of the speaker finally determined the size of the available material: furniture boards measuring 100x40x1.5 cm, which were cut in half with an electric jigsaw (in the direction across the fibers, at high speed, the cut of the tree is quite neat) and used as side walls. The design was originally developed in such a way that the thickness of the side walls can be arbitrary, so the material for the side walls could be taken of any thickness.

After cutting the furniture board, I was discouraged by the shape and size of the resulting blanks – it turned out that initially the boards were made with noticeable deviations from the declared dimensions, both in length and in width, the deviations reached +/- 3-5 mm. As they say, it is unpleasant, but in fact, I had to carefully level the ends with improvised carpentry tools … The rest of the parts were cut from veneered chipboard 16 mm thick – in my case, these were different parts from old cabinets.

Since not all of the material was of high quality (and I am not a good carpenter), it was decided to stick to the “antique” style. The speakers were supposed to turn out initially shabby and “beaten by life” and look like the speakers, some of which turned out to be older than myself. In order not to spoil the veneered surfaces with unaesthetic screw caps, I assembled the AC on bars, i.e. all the walls were attached to the bars with screws (with preliminary coating of the surfaces with glue) in such a way that all the screws were twisted exclusively from the inside.

The only wall bolted from the outside is the bezel. The drawing shows that it is surrounded by walls on all sides, and during assembly, the seat for it is made so that it is slightly recessed into the body (by 2-3 mm), in order to hide the ends of the decorative cover covering the screw heads. The fact that the bar also falls into the FI lumen prompted a recalculation of its cross-section. Taking into account the timber, its dimensions were 27×3 cm.

Pay attention to the relative position of the speaker cabinet walls: the sidewalls cover a larger number of ends of the remaining parts (only two ends remain in sight – the bottom and the cover, the rest are located on the back side), the front wall is completely recessed, and the parts surrounding it hide the ends of the facing surface ( leatherette, cork, etc.). That is, such a layout is the most win-win, especially for a novice column carpenter.

Part three. Assembly order

First, all the blanks were cut. At the side panels, the outer vertical edges were slightly rounded with the help of a bar with coarse sandpaper. Further, the blanks were selected among themselves and their most suitable combination was marked – thus, it was possible to compensate for the deviations of their sizes from the calculated ones.

The next step is cutting and fastening the timber (item 8, Fig. 3) to the side panels using 3 – 4 screws and PVA glue. The most accurate positioning of the bar was obtained by simply applying the appropriate wall (for which I marked their best mutual combination), for greater accuracy, it is necessary to drill holes in the bar with a diameter slightly larger than the screw diameter and use screws with flat (not countersunk conical) heads. First, I smeared with glue and lightly screwed the bar with screws, so that it could be moved with difficulty (as far as the enlarged holes in the bar allow), and then, attaching the appropriate wall like …