Resonance vs Stuffing Materials I originally decided to make comparisons between wool and polyester stuffing to gain some insight on how polyfill compared against wool. Wool was and still is a popular stuffing ingredient. I also wanted to compare various types and grades of polyfill to see if there were any differences. Most of the findings were published in Speaker Builder magazine 3/86. I decided to test the lowering of driver closed box resonance, find the attenuation characteristics inside the box, and find the propagated delay times inside my elongated box. One side was left open for the attenuation and delay tests. The driver was a 6 1/2 inch free air resonance of 46 hz. The total box volume was 1280 cubic inch. Table 1 ............................................................ Stuffing oz. Polyesters Wool Cotton Fiberglass Foam 1 2 3 4 5 6 7 4 65 64 64 65 64 64 65 8 62 63 62 62 61 62 60 12 62 62 62 62 57 58 56 16 - - - - 57 53 49 1. cheap irregular 2. Dupont, Dacron Hollofil II 3. Dupont, Dacron Quallofil 4. Long hair wool 5. Cotton balls and furnature batting 6. Radio Shack type fiberglass 7. Open cell foam bricks, medium grade, with 1/2 inch holes going through the material, matrix style. A couple of notes from the table. As can be seen, the polyester stops lowering the driver resonance rather quickly no matter how much you use, wool included. At low densities it dosn't much matter what material you use. As stuffing increases to decrease driver resonance, the impedance peak keeps flattening. Even when the resonance stops decreasing in frequency, the output amplitude continues to decrease or affecting apparent efficiency at the mesured frequency. Resonance effects were more apparent when stuffing is thicker closer to the driver. The above results were computed with even distribution however. The graphing may change a bit with different box sizes, Q's, and different drivers, but the relative merits of the stuffing material should remain about the same. No attempt was made to determine the % box size increase. New: Concerning a recent project with a 10 inch driver, Qts of about .5, in a box of about 1/4 the size projected with my program, Q-box. Stuffing the box pretty well with fiberglass, the thin log strand no-itch type, gave me pretty much a theoritical maximum of about a 40% box size increase. You can't get this kind of increase using polyfill. The rule for stuffing- stuff pretty well, but you should be able to weave your hand through the material with out too much difficulty. Be carefull not to make contact with the driver diaphram when stuffing. A layer of black polypropolyne gutter guard may help. I'm just guessing, the box must be significally smaller than recommended to achieve as much as the 40% increase in aparent size, but maybe not?? END