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Enclosure damping

 
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iso
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Location: Finland

PostPosted: Sat May 26, 2012 5:20 pm    Post subject: Enclosure damping Reply with quote

Referring to Harwoods BBC RD 1977/3 report, I hope you have information about bitumen damping pads. In this report, self adhesive damping pads were considered best way to damp enclosures.

Does anybody know if these pads were 100% bitumen or bitumen impregnated felt. It would also be interesting to know, how well self adhesive pads do adhere to plywood or other materials. This bond seems have considerable effect on damping properties of pads, like Harwood explains when different adhesives were used to bond roofing felt.

At least here, Bostik brand of pads are unavailable. Auto parts stores are most likely sources for this material. Does anybody have any idea, if there is any reason to think that their products are inferior to Bostik brand.

As these pads have been used for 40 years, your experience how well self adhesive bond has lasted, would be nice to share. Or... is there any reason to use different adhesives or maybe add staples after the glue has dried.

On my recent Cantata project, it seemed to be good idea to finish inside surfaces to be coated with pads with thinned urethane laquer. This seems to be only easy way to get rid of dusty surface of MDF.

Best Regards

Kimmo
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dsmith
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PostPosted: Sun May 27, 2012 12:19 pm    Post subject: Reply with quote

Most of the pads I've seen are automotive self adhesive pads. They are intended for sticking to body panels to damp the metalic ring. The materials seem pretty standard as a generic tar substance.

Sticking is a real issue and I have frequently seen the pads peel off. Heat seems to make them curl and come off. Loss of contact will diminish damping effect. The best approach would be to staple them every few inches with a heavy duty staple gun. Sealing the surface sounds like a good idea too.

I owned a pair of LS 5/1ac monitors for a while and they used a more felt like (rather than tar like) material with fairly thin plywood walls. They sounded very dead to the "nuckle rap" test. Still, I think a felt needs to be pretty dense to offer any wall damping and tar or rubber materials would be better.
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iso
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PostPosted: Sun May 27, 2012 3:54 pm    Post subject: Felt like material Reply with quote

When I added brace in Tannoy LR Monitors from mid 80`s, I found that Tannoy used also some kind 2-3 mm bitumen impregnated felt to damp cabinets.

Cabinets were made of 18 mm chipboard, they sounded also quite dead when I made the usual knuckle rap test. This must be more virtue of self damping properties of board used than damping pads, as pad thickness was so small compared to board.

Only fibreboards Harwood examined were 15 and 18 mm three layer 0,600 density chipboards. MDF and HDF were not generally available in 1977. Kef specified several other fibreboards in CS series bulletin, but no reports about their properties in cabinet construction seems to exist.

Best Regards

Kimmo
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ColinR
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PostPosted: Sun May 27, 2012 4:00 pm    Post subject: Reply with quote

Evode is now owned by Bostik so bitumen based automotive products now fall under the Supaglue brand.

Dupont is the other big player but requres large volumes so Falcon Acoustics has stopped doing Dedshete as the minimum order requirement is for an uneconomic ~500kg with only a potentially very small retail market and financial return.

Multiple layers of roofing felt and mastic appear to provide good results according to the paper; so if you don't already have a "man-shed" buy one Smile .

10mm bitumen loaded felt from my experience of "poking about" was only ever used in "high end" or bespoke designs from the 70/80s.
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iso
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PostPosted: Mon May 28, 2012 10:35 am    Post subject: Antiphon A-13 Reply with quote

Vance Dickason mentioned Antiphon A-13 from Sweden to be extremely effective. Willmslow Audio has also sold this product. Dickason mentioned that 2 layers of A-13 applied to 50% of wall area is quite effective.

Thickness of A-13 is less than 2 mm, it is self adhesive bituminous felt/clay composite used by automobile industry to damp roof panels of cars. One can figure that it must stick on good surface and withstand varying temperatures quite well.

One thing about these other than 100% bitumen products have puzzled me. Is felt or clay mixed to bitumen to improve properties of bitumen or just to make this product more economical to manufacture.

Best Regards

Kimmo
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ColinR
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PostPosted: Mon May 28, 2012 11:07 am    Post subject: Reply with quote

Quote:
Is felt or clay mixed to bitumen to improve properties of bitumen


Back to Newton's Laws and moments of inertia Very Happy, adding mass to a damping material will lower its resonant frequency and therefore reduce a panelís ability for flexure for a measurable given range of constant amplitude frequencies of vibration.
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