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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Subwoofer in combined wood and fiberglass construction. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers The "first" subwoofer in this car was made on the basis of Soviet, thoroughly forgotten 10GD30 heads - in the seventies - the workhorse of domestic electroacoustics. With a decent resonant frequency (32 Hz), they had a terrible quality factor, about 0.8 - 0.9 (according to various estimates), so they had a fair return, but a very humpbacked frequency response. Well, what's there, we need to get involved, and then we'll see (the original statement On s'engage, pius on verra belongs to Napoleon Bonaparte, to whom the author expresses his gratitude for a productive thesis). As a result, a box with a volume of about 20 liters came out, almost rectangular (the wall facing the back of the rear seat, of course, was made with a corresponding bevel), with two heads on the front wall and an amplifier tacked to the side.
This thing bassed low and willingly, but not very musically, in the sense of a clear predisposition to certain tones and a clear dislike for others, regardless of the arbitrariness of the musician who took these notes. A certain improvement came after the conversion to an isobaric design, by installing two more of the same heads (that's all, no more left). The resulting monster is in the picture. The soul, however, asked for something else - respect for musicians armed with bass instruments. After all, they think about something before they pull the string or press the mallet pedal. The new subwoofer was conceived on the basis of a 25 cm a / d / s / driver. I heard it in a branded demo car at a competition and I liked it. There were two design tasks:
The required volume turned out to be about 19 liters, from which they proceeded. The red line on the graph - for comparison, what would happen with the same head in the same volume with the box closed. Looking ahead, I will say that it was not so easy to compare it with a real design, due to some exotic forms. Now about performance. Since the car is a hatchback (antique Ford Sierra, didn't I say?), full use of the advantages of the luggage compartment is possible only on the condition that nothing prevents the seat from being folded down. In these prerequisites, the eye fell on the right rear corner of the trunk, and, since the side surface there is far from flat, this meant the need for some sophistication in the choice of materials and technology. The dark past of the author included, at some stage, fiddling with boats and motor boats, so the sight of fiberglass and the smell of unsaturated polyester resins did not frighten him (me, if you lost the thread). So we decided. So, the first and most important step. Bearing in mind the 7:1 ratio between measurement and cutting, for all flat parts that were supposed to be made from good old chipboard, hardboard templates were made, which were gradually, right in place in the trunk, adjusted to obtain maximum conformity, that is, the absence of gaping gaps .
Then, according to the templates obtained, all panels were cut out, except for the rear, facing the trunk wall, and the front (this will come later) and connected according to all the rules - glue, screws, reinforcement bars and scarves, etc. Upholstery details (two), on which the fiberglass bottom of the box was to be glued, were removed from the car and temporarily fixed on a sheet of plywood in the same relative position that they occupy in the trunk.
Now the main task is to protect them from the all-penetrating resin. An excellent material for this is polyethylene film for food packaging. It is thin and sticks to itself, which gives some confidence in the absence of places of possible resin leakage, the consequences of which are of the nature of a disaster. After everything was closed (in two or three layers - the film is thin and does not distort the shapes), the wooden part of the box was put in place, and all the joints with the upholstery on the outside were sealed with red packing tape.
The figure shows the first layers of fiberglass laid on the surface of the protected upholstery, which plays the role of a matrix in this technology. When they harden, you can tear off the tape, pull the box out of the upholstery (if you were careful with the release film. If not, then too tear off, with noticeably more damage), put the upholstery in place and work with the subwoofer cabinet as such. Subsequent layers of fiberglass are also glued from the inside of the box to leave the outer surface exactly matching the contours of the matrix. Since the main thing in the design of the subwoofer enclosure is rigidity, all the tricks to ensure it were used: stiffeners glued simultaneously with the wall surface, scarves at the junction of the side flat panels, reinforcement for installing the front panel and a powerful intermediate wall connecting the two side (chipboard) and back (fiberglass).
There is not much in this genre. After the whole structure with strength and the article begins to resemble a battleship (do not settle for less), you can calm down and, before putting the front panel, with holes already cut out for the head and tunnel (or tunnels, as in my case), cover the entire surface inside with vibration-absorbing material. Almost any anti-corrosion coating in an aerosol will do.
After the final assembly of the case, alignment of the irregularities at the joints and shells (unavoidable, alas) on fiberglass, all of the above takes on this form (from the face and from the back).
PS After the prescribed time, the car stopped its earthly life, but, interestingly, the subwoofer housing is still alive (in the author's personal museum), and the Jensen amplifier continues its combat life, and brings awards for lethal sound pressure levels on Sergey Klevtsov's car. Author: Andrey Elyutin; Publication: avtozvuk.com
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