Which Materials Reflect Low-Frequency Sound in AC/Heating Systems?

[leka]

hi everyone,
I am currently working on a project to reduce noise in AC/Heating systems in airplanes. As reference am using some literature in Engineering Noise Control and some research papers on Active/Passive noise control. I am currently searching for some information on; if there are materials that are good reflectors of sound at low frequencies, between 500Hz and 1KHz. The current aplication that have in mind calls for a sort of a muffler(closed ends pipe, from outside). Geometry and other parameters are not defined yet.
If anyone has any sources or knows any information related to mechanisms for noise reduction or have any ideas feel free to elaborate.

cheers

 

[leka]

hmmm,
guess no one is involved with this aspect of engineering...
cheers

 

[red_fox77]

I would google 'quiet steel' which is some Ford gimic. I think it is just a rubber coating with a speherical rubber filler which is pasted onto the firewall to absorbe engine noise.

Wouldn'd be suprised if you couldn't tune it to your frequencies.

 

[leka]

thanks for the info...