SpeakerTalk Forum Index SpeakerTalk
This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Rubber vs Foam surround
Goto page 1, 2  Next
 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Thu Aug 30, 2012 8:45 am    Post subject: Rubber vs Foam surround Reply with quote

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.
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Thu Aug 30, 2012 9:35 am    Post subject: Re: Rubber vs Foam surround Reply with quote

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
Back to top
View user's profile Send private message Send e-mail
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Thu Aug 30, 2012 9:54 am    Post subject: Reply with quote

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 ?
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Thu Aug 30, 2012 10:48 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Send e-mail
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Thu Aug 30, 2012 12:25 pm    Post subject: Reply with quote

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....
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Thu Aug 30, 2012 12:28 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Send e-mail
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Thu Aug 30, 2012 1:49 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Thu Aug 30, 2012 1:57 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message Send e-mail
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Fri Sep 07, 2012 9:46 am    Post subject: Reply with quote

I found this resource... very interesting

http://www.goodhifi.com/FAQ/Speaker%20repair%20FAQ.htm
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Fri Sep 07, 2012 10:18 am    Post subject: Reply with quote

clubsport911 wrote:
I found this resource... very interesting

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


Fascinating, I shall give this more time when I'm at home.
Thank you for the link! Very Happy
_________________
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
Back to top
View user's profile Send private message Send e-mail
vistisen
Intermediate Contributor 50+


Joined: 01 Sep 2006
Posts: 57
Location: Denmark

PostPosted: Wed Sep 12, 2012 5:49 pm    Post subject: Re: Rubber vs Foam surround Reply with quote

clubsport911 wrote:
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.


Be very careful. I bought a pair of 107,s that had been repaired with rubber, While there was plenty of deep base there seemed to be a hole at about 60-80 HZ. I ended up getting rid of the kef kube and using a DEQX PDC2.6 as a digital crossover. this measured a trough that was -8 db down. But the PDC can flatten that out, and do wonderful things to phase variance in the process. But it did cost twice as much as the speakers! Twisted Evil
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Wed Sep 12, 2012 6:42 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Thu Sep 13, 2012 3:26 am    Post subject: Reply with quote

Hi speakerguru and thanks. So why does cavity coupled designs demand such a woofer ?
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Thu Sep 13, 2012 11:19 am    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
clubsport911
Senior Contributor 100+


Joined: 26 Aug 2012
Posts: 157
Location: Cheltenham, UK

PostPosted: Fri Sep 14, 2012 12:51 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers All times are GMT + 1 Hour
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group