Feltmetal is a brand name for metal matrix filters used in foundries for filtering inpurities in molten metal. Because these filters have wide band flow resistance properties, they can be used in acoustics as well.
An alternative is ceramic sponge filters, also used in foundries.
I've experimented with them to give structural rigidity to thin cabinet walls, and to increase the apparent volume of an enclosure. They are also quite effective for damping the rear reflection of a cone driver, because they attenuate over a wider bandwidth than traditional cabinet lining meterials. Also, if you want to attenuate on the back of an open back cabinet, these materials are more linear. Conventional materials such as felt, foam and fibreglass deform as a result of the pressure wave and are therefore non-linear.
For more info on feltmetal see:
http://www.techneticsfl.com/Acoustic_Media/acoustic_media.html
An alternative is ceramic sponge filters, also used in foundries.
I've experimented with them to give structural rigidity to thin cabinet walls, and to increase the apparent volume of an enclosure. They are also quite effective for damping the rear reflection of a cone driver, because they attenuate over a wider bandwidth than traditional cabinet lining meterials. Also, if you want to attenuate on the back of an open back cabinet, these materials are more linear. Conventional materials such as felt, foam and fibreglass deform as a result of the pressure wave and are therefore non-linear.
For more info on feltmetal see:
http://www.techneticsfl.com/Acoustic_Media/acoustic_media.html
Baki,
Yes, initially I had some difficulty too. But I got some samples from distributors eventually. Maybe search the net to see if there is a distributor in your country. There may be an equivalent product. These filters are widely used in the foundry industry.
As a last thought : I found the ceramic foams the most useful, They are available in different bulk densities and flow resistances, and different ceramic materials. The low bulk density types were the most useful, some types were too dense. I still want too do some follow up work in this area, because I had some interesting results.
Yes, initially I had some difficulty too. But I got some samples from distributors eventually. Maybe search the net to see if there is a distributor in your country. There may be an equivalent product. These filters are widely used in the foundry industry.
As a last thought : I found the ceramic foams the most useful, They are available in different bulk densities and flow resistances, and different ceramic materials. The low bulk density types were the most useful, some types were too dense. I still want too do some follow up work in this area, because I had some interesting results.
In a previous job I sold feltmetal in the aerospace industry. As the name implies it is short metal fibers randomly arranged and sintered together, much like regular wool felt.
Even for aerospace it was expensive and labor intensive alternatives were frequently used as they were more cost effective. If you can find it, you'll be hard pressed to justify its cost in a DIY application.
For acoustic applications you'd choose felt metal where you need a lot of attenuation over a fairly narrow band and the environmetn is harsh - hot jet exhaust, turbine APU mufflers, etc.
Compared to using perforated sheet over honeycomb to create helmholtz resonators, felt metal gives a little better attenuation over a broader band, although still not broadband. Perforated metal with a thin layer of metal scrim (long metal fibers in a random screen arrangement) proved at least as effective on an intake silencer for a lot less money at one customer.
Even for aerospace it was expensive and labor intensive alternatives were frequently used as they were more cost effective. If you can find it, you'll be hard pressed to justify its cost in a DIY application.
For acoustic applications you'd choose felt metal where you need a lot of attenuation over a fairly narrow band and the environmetn is harsh - hot jet exhaust, turbine APU mufflers, etc.
Compared to using perforated sheet over honeycomb to create helmholtz resonators, felt metal gives a little better attenuation over a broader band, although still not broadband. Perforated metal with a thin layer of metal scrim (long metal fibers in a random screen arrangement) proved at least as effective on an intake silencer for a lot less money at one customer.
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