Effect of old woofer foam surrounds

Hi guys,

I bought a pair of old Dali AXS8000 some time ago. They are fitted with Vifa C20WJ-66-08 woofers with foam surround. The foam surrounds looks to be original and in very good condition.

The problem is the bass, which is really really bad. I have Dali 104 and Qln 929 speakers using Vifa C17, and they are lightyears ahead of them in the bass department.

I had a suspicion that the woofers were out of spec, and got them measured. They are all consistent with a Qts of 0,9 – 1.0 and fs 58 – 60 Hz.

I just shook my head and stuffed the speakers far away in the back of my garage, thinking both the Vifa engineers and Dali engineers must have had a real drinking party while designing this speaker.

I would have thought they would have fs 35-40Hz and Qts 0,3-0,4.
But then while surfing the net I came to read this:

"I recently refoamed a Model EIII (Vifa M21WN-07) woofer with foam from Audio Note (AN) in the UK.
WT2 testing of the recent refoam compared to a prior refoam with one of my 'standard' 8 inch foams showed the AN foam's results very close to original compared to st'd foam which were not.

The AN foams are very expensive at 15 lbs sterling each plus shipping. However, I don't know of another source of similar quality foam, let alone a lower price. The standard foam resonant frequency (Fs) was 39 hz vs 26 for the AN foam that was yet to be broken in. Qts for AN = 0.23 vs 0.53 for st'd foam.

The roll measures 11/16 wide on top which is quite wide for an 8 inch foam. The general feel of the foam is quite supple. It's easy to tell it will yield a very low resonant frequency for its size.

IMO, the bottom line is if you want to maintain the performance of your Snell speaker which utilizes the Vifa woofer, you should consider the AN foams. Visit their web site's support page for contact information.

Also IMO, the Snell Model E speakers are very worthy of the AN foams."

And then it hit me, that maybe the foam surrounds could be out of spec. Do you guys have any experience with this kind of problem before?

I know that the speakers had been stored and not used for several years when I bought them...

Cbarth
 
My advice would be not to patronise any further the silly use of re foaming speakers
Even the manufacturers of these parts, say they last just 2 years. The problem
being foam rots. No wonder there are so many businesses have their doors open
doing this, because they are pretty sure you will be back again and again

Viable long lasting alternatives are to use rubber surrounds. Another would be
to learn how AR did their cloth material surrounds, as they from personal experience,
are still good after an amazing 40 years.
 

Lojzek

Member
2012-02-10 12:12 pm
Croatia
Plug the ports with something and you will effectively solve the problem.
You can additionally put extra wadding inside the box to further lower the
Qtc if desired. I have refoamed my Dynaudios myself and the original
Qts value of 0,88 went to 1,2 which I compensated with wadding and
remeasuring. What's interesting is that the new surrounds were truly
stiffer than the original ones which made the speakers sound more dry
or I should say I like these better now. The Fs is higher now as a result
of surround stifness.
 
Last edited:
Plug the ports with something and you will effectively solve the problem.
You can additionally put extra wadding inside the box to further lower the
Qtc if desired. I have refoamed my Dynaudios myself and the original
Qts value of 0,88 went to 1,2 which I compensated with wadding and
remeasuring. What's interesting is that the new surrounds were truly
stiffer than the original ones which made the speakers sound more dry
or I should say I like these better now. The Fs is higher now as a result
of surround stifness.


I still would have too much midbass and no bass below 50hz...