SpeakerTalk

[Lee in Montreal]

Butyl rubber vs foam

1984 - The revolutionary KEF 104/2 is introduced. The first version of the 104/2 (the one with the crossover in the midrange module) had Butyl rubber suspension and dust cap on the B200 woofers. Then the dust cap changed to another material : Foam

The first production with rubber suspension and dust cap remains mysterious. I could not find a part #.
Woofer is part # SP1188 for rubber suspension / foam dust cap


1988 - KEF 107's B250 woofers have foam suspension and dust cap - Considering that the 107 was KEF's top of the line home speakers, then the KEF engineers must have considered foam to be the better material...
Woofer is part # SP1215

1990 - KEF introduces the updated bi-wire 104/2 with both suspension and dust cap made from Foam.
Woofer is part # SP1256

1989/1994 - KEF introduces the 105/3 with the same woofers as the late 104/2. FOAM suspension and dust cap.
Woofer is still part # SP1256

1994/1999 - KEF introduces the Reference Model 4. Woofers returns to rubber suspension and NO dust caps. Just a dome.

1996 - The Raymond Cook version of the 107/2 has ceased production.

What triggered this change of material from rubber and foam, and then back to rubber? And then both versions overlapping? Does the new Chinese ownership have anything to do with that?

And at the end, which material is best?
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[audiolabtower]

Well it took some years for the foam deterioration to become apparent. Then I guessed Kef did not use it for quality reasons. Foam can probably give a low resonance with little weight to the cone thus better efficiency. Rubber is probably a little heavier but since B200s are still going strong rubber/neoprene/ pvc or whatever are probaly better materials if you don't have to rebuild the cones every 10 years !

[speakerguru]

I thought I'd answered this way back but I can't find it atm.

Coupled cavity alignments work best with lighter moving parts for the same cutoff compared to closed box and reflex systems. Foam surrounds are lighter than anything else. Unfortunately, they have a limited life, especially in hot humid environments.

Feedback to Marketing Dept from overseas agents resulted in pressure being put on Engineering Dept to abandon foam surrounds and specify an alternative despite sub-optimal CC alignment. I'm a bit hazy on the models affected and the order and timing of these changes. Sorry.

I've also made this replay a "sticky"