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In Reply to: is this BS? - the inner foam ring on KEF 104/2 woofers is important? posted by centaurus3200 on March 1, 2007 at 16:57:00:
I thought it was also there to break up some of the output of the woofers. Pure guess it damps some higher frequency(above woofer pass band) standing waves. I suspect it helps a bit but isn't critical.
Follow Ups:
I can attest .. it's a fact that the foam dust caps are indeed an important part of the system. Having just been through doing it I'll be glad to share the "how to's" and a good source of the materials to any one who asks.
Rob
Well, look at it this way: are you going to believe the people who MAKE the thing, or someone who's trying to SELL you the thing? :)Have a good day,
although, the people at KEF are not the "old school crew" that have been there for years. the company was sold to a chinese conglomerate in the mid 1990's. so, who knows if the current people know enough about the classic designs.but, with that said, simple logic says that it looks like a foam dustcap that keeps crap out of the VC around the force canceling rod.
and being mine still put a smile on my face, i'll just leave well enough alone ;-)
but, i am no expert.
As one of the engineers form the "old school" KEF I can confirm that the inner roll is indeed important. It is not there to simply keep crud out of the gap, though it does serve that purpose too.
Because of the use of the force cancelling rod, used to reduce vibrations in the cabinet, we had to eliminate the conventional dustcap in order that the rod could connect to the magnet. This not only opened up the voice coil gap to contaminants but also lost the seal between front and back of the cone. There is an air leakage path around the voice coil. Coupled cavity loading is sensitive to leakage between the front and rear chamber, causing shifts in the requency response away from optimum and allowing air to chuff at large displacements of the cone. We therefore developed a rolling seal to overcome these problems.
So, the short answer is "yes, you need the dustcap". Could you get away without it and not notice? Perhaps, but it would not be performing to the fullest level to which it was designed.Regards
mine aren't torn, look good, but i'm sure the foam is brittle from age. i'll look into replaceing them, but that ebay place is insane for wanting $95 per speaker to replace ONLY THE ANULUS. puleez. and i'd have to remove the woof woofs to send to them.i think there's a link to where you can buy them and do it yourself though.
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