I'm in the process of finishing off my bass traps finally. I read somewhere in this forum that it might be a good idea to place something like craft paper in front of the insulation to block out the high frequencies. Does anyone know if this is true? Has anyone tried this? Any feedback would be great.
Bass Trap Question
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Depends. If you leave off the paper, the trap will absorb mid- and high-frequencies as well as bass. If you put it on, it will reflect the higher frequencies. The choice depends on whether your room's acoustical situation needs HF absorption or whether it has enough. You want it neither too live nor too dead.
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for LF absorption, if you're limited to porous-only (velocity-based) absorbers, they'll need to be sufficiently thick and sufficiently large to be effective (with respect to wavelength). porous insulation is broadband, so if you're generating large surface area coverage for LF absorption, you will inadvertently absorb the indirect specular region energies as well that are incident at your LF absorbers. this can quickly lead to a highly damped/dead space - is this a design goal?
6mil plastic membrane can be applied to the outer (room facing) boundaries of the LF porous absorbers, and will reflect ~500hz+ specular energies back into the room. you can also apply any other diffusive or scattering treatments (reflection phase grating diffuser, binary amplitude diffuser (or MLS/slat/etc) as well to provide more mixed returns vs simple specular reflections via the plastic membrane.
6mil plastic membrane can be applied to the outer (room facing) boundaries of the LF porous absorbers, and will reflect ~500hz+ specular energies back into the room. you can also apply any other diffusive or scattering treatments (reflection phase grating diffuser, binary amplitude diffuser (or MLS/slat/etc) as well to provide more mixed returns vs simple specular reflections via the plastic membrane.
Thanks Kal and localhost127 for your input. My bass traps will be filled with Roxul Safe n' Sound and will fill 3 of the 4 corners in my room. My goal is to retain the high and mid frequencies and to absorb the LF's for a tighter bass. I definitely do not want a "dead" room. Does it matter if I use paper or plastic?
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Bpape often specs kraft paper for his rear wall treatments. One such build is Bacon Race in my signature. I've built a few Dennis Erskine designs where he specified 3mil plastic (Self adhesive carpet runner) over portions of the side walls (Back of room) and the back wall so that the room didn't become too dead. So to answer your question yes it is true.
If you have your traps in all four corners you should consider it for the ones in the rear.
Bpape often specs kraft paper for his rear wall treatments. One such build is Bacon Race in my signature. I've built a few Dennis Erskine designs where he specified 3mil plastic (Self adhesive carpet runner) over portions of the side walls (Back of room) and the back wall so that the room didn't become too dead. So to answer your question yes it is true.
If you have your traps in all four corners you should consider it for the ones in the rear.
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Be careful on this. As in the real estate industry, placing type of treatment is all about location, location, location. Reflecting high frequencies in line with the center channel is not the best approach considering most voices are near or higher than 500Hz. We are not interested in that because we do not want interference with speech intelligibility. As with anything, cookie cutter approach does not work or apply here. The best thing to do is know what frequencies are bouncing where, understand what affect that has on the listeners, and is it desirable or not. Generally speaking, speech intelligibility is a pretty important thing in your theater.
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