SpeakerTalk

clubsport911 · Posted: Thu Aug 30, 2012 8:45 am Post subject: Rubber vs Foam surround

An obvious "upgrade" for the KEF 105/3's would be to take the units with the rubber surround from the 104/2's and use in place.

Of course, the compliance will be different but then again, I'm wondering how significant this would be ?

Put it another way, what was the thought process behind foam speaker surrounds in the first place ? Compliance ? easy (cheap?) to manufacturer ?

It seems at odds with the (then) SOTA device like the 105/3

Thoughts welcome.

proffski · Posted: Thu Aug 30, 2012 9:35 am Post subject: Re: Rubber vs Foam surround

By changing the surround to a less compliant material the 1st thing that would change most I guess is the Fs.
There may be additional mass added to the cone, that too would be taken into account.
The importance would therefore be to preserve the compliance of the original as much as possible and aim for 'nearly' correct parameters.
Unforseen side-effects like a sharper resonance peak at Fs (Q) are another stumbling block, all will affect ultimate performance.
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

clubsport911 · Posted: Thu Aug 30, 2012 9:54 am Post subject:

Thanks

Kef must have had a good reason why 104/2's were rubber and 105/3's (from the same era) were foam surround. Essentially the same unit, but in a different cabinet volume. the 105's reach a little deeper, but not massively so (from what I understand).

Ps - Where in GL ?

proffski · Posted: Thu Aug 30, 2012 10:48 am Post subject:

Different magnets, voice coil length, and so on...
I'll swear that my 104/2s have foam surrounds! Shocked

(10 miles from you, look under my outdated picture for clue!) Smile

_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

clubsport911 · Posted: Thu Aug 30, 2012 12:25 pm Post subject:

This guy here

http://www.youtube.com/watch?v=GRaQDPBBSIo

Seems to have rubber (interesting video BTW)

Also, I'm actually in "Chuksberry" now - where I work (Moog). Small world....

proffski · Posted: Thu Aug 30, 2012 12:28 pm Post subject:

I hate YouTube films with inane inappropriate "music" I had to turn sound off before I kicked the computer to death! Smile

Video is ok though...
...and the world is getting smaller than you may think. If I stood on my roof I could probably see MOOG!

You have PM!
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

clubsport911 · Posted: Thu Aug 30, 2012 1:49 pm Post subject:

Agree. that music is naff, but you see the rubber surround.

I'm not an expert on the 104/2's.. late model perhaps ? Again, perhaps someone (you ?) might know the internal thoughts KEF had to move from foam to rubber... and then why they didn't then transfer this "upgrade" to the 105/3's. (same but bigger).

I'm sure there is an answer. My interest is to avoid changing another set of foams if at all possible.

I get that the life of the foam is variable but no longer than 10-15 yrs, but
perhaps a move to rubber solves this. I only then have the issue of how to fashion a centre "do-nut" in rubber and then it's done for good.

proffski · Posted: Thu Aug 30, 2012 1:57 pm Post subject:

Mine seem to be on almost permanent loan to my sister a few miles away.
The foam is just getting tack now but not yet breaking down completely.

When the day comes I shall either risk using a "modern foam compound" or go against my own preaching and possibly go well chosen butyl rubber or whatever I can find that is deemed not too different.

I did the same for a friends Tannoy Arden's 15" drivers, he insisted using foam like the originals.
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

clubsport911 · Posted: Fri Sep 07, 2012 9:46 am Post subject:

I found this resource... very interesting

http://www.goodhifi.com/FAQ/Speaker%20repair%20FAQ.htm

proffski · Posted: Fri Sep 07, 2012 10:18 am Post subject:

vistisen · Posted: Wed Sep 12, 2012 5:49 pm Post subject: Re: Rubber vs Foam surround

speakerguru · Posted: Wed Sep 12, 2012 6:42 pm Post subject:

I don't recall any 104|2 bass units ever being made with rubber surrounds.

All KEF coupled cavity designs required a low moving mass woofers. Foam is much lighter than rubber. I know, shame it rots with age under certain conditions.

clubsport911 · Posted: Thu Sep 13, 2012 3:26 am Post subject:

Hi speakerguru and thanks. So why does cavity coupled designs demand such a woofer ?

speakerguru · Posted: Thu Sep 13, 2012 11:19 am Post subject:

You tune the woofer in the first box to the centre of the required bandpass then the ratio of the volumes sets the bandwidth. See the Fincham paper elsewhere on this site.

clubsport911 · Posted: Fri Sep 14, 2012 12:51 pm Post subject:

So another question in my mind, is why the upper and lower boxes aren't tuned to a low frequency with a port. ? Why are they IB ?

Thanks