While struggling to remove my Blaupunkt “Frankfort: AM/FM radio from the console in my BMW 2002 to replace the dial bulb, it suddenly seemed inappropriate, after so much work, to simply put everything back.
Being something of a hi-fi freak and a serious student of music, an old truism floated out of the ether. It’s not the hi in your fi that counts, it’s really the clarity or lack of distortion that creates good sound reproduction. The radio and speaker were both of good quality and the console provided a reasonable amount of space for speaker wave rear baffling. In any speaker set-up, the transducer should do the sound reproduction, not the cabinet. While the console is constructed of a soft vinyl-covered hardboard that is essentially inert, the radio and speaker are mounted on a live plastic moulding with a sheet metal baffle under the grill. If the plastic mounting board could be deadened and the metal baffle be insulated voila instant and cheap sound improvement.
So, I cut two 1/2″ by 4” strips of carpet and glued them alongside the speaker, in a vertical fashion on the inside surface of the grill. The lower metal baffle posed an interesting problem. Because of bending and stamping requirements, there are two square openings alongside the plastic grill. These act as ports for the rear wave from the speaker. But since the console is arranged in bass-reflex fashion that is, with a port at the rear of the console shelf, one wall formed by this metal plate chances are that the sound waves meet, creating a situation involving sonic wave cancellations or just plain muddy sound. I cut a piece of carpet to the exact size of the inner surface of the metal baffle, covering the two square ports. Then noticing how close the carpet came to the speaker frame, I Cut a semi-rectangular relief for the speaker. This relief allows the sound to flow from the rear of the speaker with equal pressure all around. Using 3M 8031 Fast Tack Adhesive, the pieces of carpet should be glued nap side up, so the wooly bits can deaden the sound waves. Fiberglas insulation is an excellent alternative, since that is what is used in hi-fi speaker cabinets.
After re-assembly, don’t be too disappointed. We didn’t create a new radio, but the clarity of your radio sound should be enhanced, being particularly apparent in the bass ranges. Listen to the drum beats or crescendo/diminuendo passages they should be crisper. In fact the overall effect should be one of, “Hey, where did all the bass response go to?” Keep your tone control in the middle or normal position. You will get used to it just as you got used to your first good hi-fi set at home,
Author: David J. Rivkin
77-37 Kew Forest Lane, Forest Hills, NY 1 1375.