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Old 24th February 2011, 12:17 AM   #1
MCPete is offline MCPete  United States
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Default making the cloth surround of a speaker less lossy

In building a closed-box system with a Selenium 12PW5-SLF 12" woofer, I discovered that the cloth surround of the woofer is very lossy. I know that because I tried attaching some 3/8" dia. poly foam caulk saver in front of the surround next to the woofer's frame with (what else?) duct tape. As soon as I did that, my maximum impedance reading for the woofer (at Fc, of course) increased dramatically. As mechanical Q of the box system relates inversely to the system losses, and impedance at resonance is according to the ratio of Qmc to Qec, the max. Z reading gives me a quick indicator of box losses.

What I'm wondering is if any one here has found a way to permanently reduce leaking (losses) of a cloth surround without significantly raising free air resonance Fs? I would like to permanently reduce the leaking of the Selenium woofer's surround.

My thought was to apply rubber-based contact cement, but I don't know if this would work or really ruin the woofer.

Why do I want to do this? The Selenium woofer has a very high Qms/ Qes that I would like to preserve as much as possible in a closed-box system partly to prevent Qtc from being significantly less than Qec. Qts of this woofer equals 0.31, and I don't want a really small box in order to get Qtc equal to about 0.7.

Come on, if nowhere else, there must be someone here who has treated a cloth surround to stop the leaks, I guess.

Thanks if you can share your experience,
Pete
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Old 24th February 2011, 12:24 AM   #2
CLS is offline CLS  Taiwan
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There's a kind of glue, which seems never dry, remain wet-looking and actually sticky for decades...

You may find it in speaker driver repair shops.

In case it fails (well, anything can happen), you've found the shop, so.... Foam surronnd would be a good choice. (I like how it sounds )
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Old 24th February 2011, 12:59 AM   #3
kevinkr is offline kevinkr  United States
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It sounds to me like this driver was designed for a ported box? Perhaps another driver with a foam or butyl rubber surround would be a more appropriate choice? Just wondering about the longevity of any treatment you come up with and whether the surround would stiffen over time.
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Old 24th February 2011, 01:35 AM   #4
MCPete is offline MCPete  United States
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Quote:
It sounds to me like this driver was designed for a ported box? Perhaps another driver with a foam or butyl rubber surround would be a more appropriate choice? Just wondering about the longevity of any treatment you come up with and whether the surround would stiffen over time.
I selected the Selenium driver for its extraordinarily high ratio of Qms to Qes. You are certainly right, this driver was designed for a vented alignment- Qts = 0.31 is very low for a closed-box system. I also worry about whatever treatment I might think would work; that's why I'm asking for advice.

Quote:
There's a kind of glue, which seems never dry, remain wet-looking and actually sticky for decades...
CLS,
By any chance are you referring to PVA glue? By looking at other similar threads here at diyaudio.com ( I missed them before starting this thread), I discovered "PVA speaker foam edge sealer" from simplyspeakers.com, their part # MI-1291FG. Their "part" is a very high-priced 1 OZ. of the stuff.

From Wikipedia, PVA is polyvinyl acetate, a rubbery synthetic polymer. Further PVA is a component of widely used glues such as white glue, carpenter's glue, school glue and PVA glue.

Simplyspeakers.com is selling PVA for sealing foam surrounds (CLS's favorite), but it maybe would do a good job making a cloth surround less air-leaky.

Thanks for the replies, hope that this is of interest,
Pete
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Old 24th February 2011, 01:59 AM   #5
CLS is offline CLS  Taiwan
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Sorry, I don't know the exact ingredient of that (sticky) glue I described above. I'm not sure if any combination including PVA would work or not.

What I know about PVA glue is the white stuff commonly used in woodworking. I've been using it (diluted) on paper cones, not surround. It stiffens and damps the cones when dried. I don't think its the right property you need.

Have you search here? ADHESIVE SPRAYS & CEMENTS from Parts Express ship same day and come with 45 day money back guarantee. Free Shipping Available. Order free 10,000 product catalog.

Or this might be a reference, too: Wharfedale Super 8
(scroll it down) It doesn't say what the coating is, though. You might try to contact the web page owner.

And, you know, almost all such mods on driver are not reversible, so you got to take the risk. If I were you, I'll search for any glue that remains soft when cured, and find the right solvent to dilute it a little, apply as thin as possible...

--------

BTW, why does a foam surround need sealing? It should be close-cell, no?

Last edited by CLS; 24th February 2011 at 02:05 AM.
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Old 24th February 2011, 02:24 AM   #6
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Find someone called 'vintage-AR' on ebay. He sells what has been found thru much trial and error, the best fabric surround sealer - better than the EVA stuff used on pro woofers.
You may have to leave him a PM. The item is not showing up on his ebay store list.
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Old 24th February 2011, 04:07 AM   #7
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What's the forever sticky stuff that Altec used on their surrounds?
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Old 24th February 2011, 05:50 PM   #8
MCPete is offline MCPete  United States
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CLS,

Simply Speakers (Simply Speakers - Official Speaker Repair Page - Speaker Parts and Repair Service) claim that the foam edge sealer slows down the process of bacterial attack on the foam. Go to their website to get the full description of their product part #MI-1291FG. The company location is Florida, US.

Speakerdoctor,

Thanks for the tip to contact an Ebay seller about a sealer.

Just now I read an email reply from Simply Speakers saying that their foam edge sealer will also prevent air leakage of a cloth surround.

Best Regards,
Pete
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Old 24th February 2011, 06:05 PM   #9
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I haven't tried the SS sealer, but do know a guy who's tried just about everything to seal vintage KLH and AR woofer surrounds. He developed a non-hardening sealer which he shared with Vintage-AR. I've tried it and tested it with aging studies and know it works. FWIW.
If you want to preserve the bass extension of your woofer you must get something that doesn't stiffen up over time. Most of the white sealers sold and watered down silicone bathtub stuff will stiffen with age and it's measureable as elevated resonant frequency.

good luck!
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Old 24th February 2011, 07:07 PM   #10
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You want "speaker dope".

There are compounds made for the industry that are designed for "doping" cloth surrounds.

There are two main types, the older solvent based and the newer "water" based. They come in a variety of viscosities. Finding them is another matter. They will prevent the air from getting through the cloth.

The "Altec" stuff is one of the solvent based ones.

Most speaker recone shops will have some on hand, and the PE offerings may include some, not sure.
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