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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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First, thanks to DJK for this tip a few months ago.
I have some some speakers I built a number of years ago with Audio Concepts AC7 woofers, an OEM version of the Vifa C-17, long out of production. While the grey foam surrounds showed no sign yet of rotting or becoming brittle, I was worried about this happening eventually.
Weld-bond is a water-based adhesive (smells a lot like Elmer's) which remains flexible after curing. DJK suggested that a light application, thinned with water, could extend the lifespan of foam surrounds. I watered some down to about the consistency of whole milk, and applied a couple of light coats, a couple of hours apart, to the surrounds with a small foam wedge brush, and let them cure for about 48 hours.
The post-treatment surrounds felt just a little stiffer than before to a gentle finger-push, and when I hooked the speakers up and played some familiar recordings, I noticed just a slight loss of bass response compared to pre-treatment. Since I had a good set of pre-treatment measurements, I set up the test mic and measured again. The results showed an across-the-board sensitivity loss of a little less than one dB, and the loss of some bass extension: the f3 in the sealed box moved up from 68Hz to 75Hz.
Not horrible, and not surprising. The added stiffness to the surrounds is bound to affect the Qms and other parameters a bit. I needed to alter the L-padding on the tweeters just slightly to drop the output to match the slightly lower midrange sensitivity, but overall I find the sound slightly improved from before. As you can see from the manufacturer's graph, these woofers have built-in BSC, so you can use a near-textbook lowpass filter on them. That LF "blump" levels out on an actual baffle measured in free air, but was still a little prominent in my 8.5" wide enclosures. Post-treatment, it flattened out a bit more, and the overall response now measures more neutral and sounds more pleasing.
So if you have some irreplaceable woofers with foam surrounds that are not yet decaying, this treatment may be worth considering. Just err on the side of stinginess (maybe test and listen between cured coats) when applying the watered-down Weld-bond, and expect to sacrifice a little sensitivity and LF extension.
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Topic - Report: Weld-bond as foam surround preservative - Brian H P 15:41:38 07/21/15 (1)
- Yes! I have used that stuff on many a damaged bass guitar speaker in my day. nt - Dman 16:31:22 07/21/15 (0)
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