Modernization of the dynamic head 20GDS-1. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers
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The mid-frequency dynamic head 20GDS-1 (formerly called 15GD-11) was widely used to complete domestic three-way speakers in the late 70s. However, a sharp drop in its frequency response at frequencies above 5 kHz did not allow obtaining good sound quality from the speakers in which it was used. In this regard, there were proposals to replace it with a broadband head 5GDSh-5. But such a replacement required a change in the values of the elements of the separation filters of the midrange and high-frequency sections of the speaker and significantly reduced the maximum power of the speaker.
Experiments carried out by the author have shown that a fairly simple modification makes it possible to expand the frequency band reproduced by the 20GDS-1 head up to 7...8 kHz.
When finalizing, the head is removed from the speaker housing. Wetting the adhesive seam of the protective cap of the voice coil with acetone using a pipette, separate the cap (prying it with a scalpel or an awl) from the diffuser. Then it is glued to the edge of the voice coil protruding (usually by 1 ... 3 mm) from the diffuser with the convex side, i.e., turning it over 180 degrees. For gluing, it is advisable to use a slightly thickened Moment glue.
The operation is performed in the following sequence. First, a strip of "Moment" glue is applied to the convex side of the cap, previously marked along the diameter of the voice coil, and briefly pressed against the edge of the voice coil. Part of the adhesive remains on the edge of the voice coil. Then the glued parts of the head are dried for 10 minutes and another 1-2 layers of glue are applied to the cap, so that the thickness of the adhesive strip increases to 1 mm. After 10 minutes, the cap is again pressed against the voice coil. At the same time, it is necessary to ensure that the glue does not get into the working gap of the voice coil.
In the described way, two 20GDS-1 heads installed in 25AS-033 acoustic systems were finalized. The sound of the speakers at medium frequencies has become more natural, the localization of the sound picture has improved, and the stereo effect zone has expanded.
It is advisable to combine the refinement of the head with its acoustic damping (installation of PAS), using one of the methods recommended by the Radio magazine in previous years (see, for example, the article by P. Popov and V. Shorov "Improving the sound quality of loudspeakers" in "Radio" , 1983, No. 6, pp. 50-53).
Author: A.Kiselev, Moscow
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