# Why FRK only on room face of bass trap?



## bkspero (Apr 3, 2008)

I'm going to be assembling some 4" bass traps from 2" panels of OC705 FRK, and some 6" traps from 2" panels of OC703 FRK. From my reading here and elsewhere (thank you Ethan Winer and Bryan), the recommendation is to leave the FRK on only 1 of the panels in each bass trap, and have the FRK on the surface facing the center of the room (unless trapping of high frequencies is desired). The others should be stripped of their FRK. The reason for leaving on the FRK is that it is a membrane that helps couple bass frequencies to the fiberglass so that the fiberglass can more effectively dissipate the energy.

My main question is why not leave the FRK on both of the panels and face the FRK towards the center of the room on the panel nearer the center of the room, and towards the corner for the panel closer to the corner? Wouldn't it function to improve bass absorption of sound passing into and out of the back side of the panel as well as sound entering by the front face? Plus it would help limit exposure of the fiberglass to the outside world.

Some related questions are:

1) Would the recommendation be different if the corner space behind the panel contained foam wedges that would absorb much of the higher frequencies in that space? Would it then be ok to leave the FRK on the back face?

2) In cases where high and mid frequency reflection is not wanted, what is the downside of leaving on the FRK and orienting it into the center of the bass trap? With one panel? With both of the panels? I would have guessed that the high and mids would be attenuated by the first 2" of 705 anyway. What would happen if the panel nearer the wall had its FRK toward the wall, and the panel towards the center of the room had its FRK in the center of the bass trap?

3) The same issues as above, but with 3 layers of 2" 703 FRK for the 6" trap.

I apologize in advance if this has been explained elsewhere, but I've looked for several hours and not found it.

Thanks for all the information that everyone has provided here and elsewhere on this topic. If only I had read it before buying the foam products. Looking forward to improving things.


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## bkspero (Apr 3, 2008)

Isn't this the way it always works. Right after posting this note I tried one more Google search and was directed to the GearSlutz website. Rooting around there the questions were answered. At least on whether or not I had to tear off the FRK from the other panels (yes). If I understood correctly, Ethan & his partner tested panels with both front and back covering and his partner's report was that the result was poorer than just a covering towards the room. With this information, combined with the principal that if it hasn't been tested it could be terrible, the recommendation is to just leave the FRK on the one panel.

Any alternate opinions? What about for 1st reflection 2" panels....is it reasonable to leave the foil on but orient it towards the wall? Even though the panels will be mounted on stands a foot or so away from the wall?

Thanks again for all the information.


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## bpape (Sep 14, 2006)

Definitely pull the FSK off of everthing except the one side facing the room (assuming you want broadband bass through midrange only from these).

Bryan


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