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Using this for inside Speaker walls for damping

zeprok123

zeprok123

AK Subscriber
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So I found some recycled polyester on front rubber backed floor mats at the local home improvement store and I'm wondering if this would work for damping the cabinets of a set of ported speakers? It's much cheaper than
100% wool felt and looks easy to work with. Thoughts?
 
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It may help if you told us what the speakers were. I always recommend whatever was in them originally, just my 2 cents.
 
I read on the internet (which means it’s absolutely true.) that the small particles of fiberglass can get in to the gap between voice coil and magnet and basically act like sandpaper against the voice coil, which can then potentially grind through the coil’s enamel coating causing a short. Any truth to this? Or is it bogus internet theory?
 
mccuskerkt said:
...the small particles of fiberglass can get in to the gap between voice coil and magnet...
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I don't know if that's true or not but the toxic dust issue with fibreglass and rockwool does make me think twice about using it. It's probably not really a problem because without any force to disturb the material there should be no loose particles generated. But... there's still a niggling doubt.

As to the OP's question, you have to be careful with any damping material in ported speakers. The damping shouldn't be doing anything at low frequencies which would alter the port's tuning - it should only be working at higher frequencies to suppress internal reflections which can be heard as midrange colouration.
If the material you have in mind is cheap and can be easily removed it's worth trying out.
 
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doctorolds said:
It may help if you told us what the speakers were. I always recommend whatever was in them originally, just my 2 cents.
Click to expand...
Klipsch KLF 20s. I'm rebuilding all of cabinets with full 1 inch Baltic birch ply except motor board. They had a sponge type material behind all drivers except bottom woofer.
 

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mccuskerkt said:
I read on the internet (which means it’s absolutely true.) that the small particles of fiberglass can get in to the gap between voice coil and magnet and basically act like sandpaper against the voice coil, which can then potentially grind through the coil’s enamel coating causing a short. Any truth to this? Or is it bogus internet theory?
Click to expand...

Bogus internet theory. If this were even remotely true, then there would be no market for vintage speakers because they would have all been damaged from the small particles flying around inside old speaker cabinets. Unfortunately, now it is posted on AK and others may believe that this nonsense is true. :eek:
 
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Sorry @zeprok123 for hijacking your thread! Maybe the fiberglass discussion is a good topic for another thread, and some more research and testing.
I agree that if they are cheap, try them! See what you think.
 
mccuskerkt said:
Sorry @zeprok123 for hijacking your thread! Maybe the fiberglass discussion is a good topic for another thread, and some more research and testing.
I agree that if they are cheap, try them! See what you think.
Click to expand...
No problem, at 5 bucks a piece I should be able to A and B them and if it doesn't work I'll take the other back. Kinda concerned about the rubber backing though
 
I don’t remember where it was, it was a while ago. I have tried using polyfill and was never happy with it. I got some scraps of sound damping fluff from work and was very happy with it in a sealed three way floor speaker build. No idea what the product is called, it’s similar to fiberglass but not itchy or prone to particularization and has black fabric on one side.
 
In a ported speaker-a piece of 2" acoustic foam behind the woofer should be sufficient.
In a sealed enclosure, as Vance Dickason points out-fiberglass is still the best choice, because it tames the woofer impedance peak, lower the Q, as well as F3, better then poly, per given weight. The new fiberglass is long stranded and has round ends.
If you put it in a pillow case (for use behind the woofer), or linen if lining the walls, it's pretty much self contained.
Poly works best in small enclosures. You fully stuff them.
The issues with larger enclosure are best suited using fiberglass, because even fully stuffing the enclosure with poly, won't work as well as fiberglass. And when you fully stuff a enclosure, you start encountering friction losses very quickly.
You just have to use common sense when dealing with, and handling fiberglass-nothing to freak out about.
Roughly a lb per cubic foot works. The least amount to do the job is best, because even if not fully stuffed-friction losses do make a difference.
Tune by ear, or measure the woofer Q, or build a simple damping tester.
Dickason Damping.jpg
If a enclosure is built correctly-and to size-it should just need enough to deal with standing waves. 1" fiberglass batting behind the woofer.
 
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