I've got a pair of B&W DM640 - I really like them except one of the 4 woofers and developed some voice coil problem and causes terrible distortion around the 200-400 hz frequencies.
I've set up a test lab using REW to chart the performance of multiple woofer replacements (The original part is ZZ 8915 and is no longer available).
I'm thinking that if I can match performance in terms of Phase and Frequency response that I would have found a good replacement. But wanted to get some expert opinions.
I've tested my first replacement candidate and it looks good (except for the fact it is 2mm larger around and doesn't quite fit the case).
Take a look at these charts - does anyone see a reason not to use this element as a replacement? I have also compared the phasing and both are exactly alike. The only thing I think I lose is that really low end performance - but I just picked up a pair of PSA XV15 so don't really excercise my mains down to 30 anymore.
dm640 tests.txt 651k .txt file
Here is the frequency chart, blue is the original, green is the replacement. And the Crossover point is 300hz