# Use a double-wall as Bass-Trapp?



## charles_b (May 10, 2010)

Hello!

my listening room is about 5,7 m long, 4,2 m wide and 2,2 m high.

I ran the HEW measurment of the low-f resonances and found a prominante peak at arount 27 Hz. Using the room simulation this brings me to a lenght of about 6 meters of the room.

Indeed, there is a double-wall, consisting of a light material construction, shortining the room from earlier 6 m to the 5,7 m. 

If I listen to music with a larger bass content the whole double-wall construction starts to vibrate.

I think about tearing out this whole garbage, but then I remember that one can build bass trapps to eliminate unwanted bass frequencies.

Should I keep the wall (no idea what expect me BEHIND that wall...) and just go for some well calculated hole diameters or is this all nonsense and a big cleanup would be best....?


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## bpape (Sep 14, 2006)

Unless you build a panel that's literally 24" thick, you'll not even think about touching 27Hz. Even our Soffit Trap at 17" square will only do mid 30's. You could tear the wall out OR you could just beef it up with additional layers of drywall to stop it from resonating so bad as long as the framing structure is halfway decent.

Bryan


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## charles_b (May 10, 2010)

bpape said:


> Unless you build a panel that's literally 24" thick, you'll not even think about touching 27Hz. Even our Soffit Trap at 17" square will only do mid 30's. You could tear the wall out OR you could just beef it up with additional layers of drywall to stop it from resonating so bad as long as the framing structure is halfway decent.
> 
> Bryan


Thank you for the correct technical word "drywall" is the same in German. I remember these large bass-trapps they were showing on the High End Fair last weekend here in Munich, assuming that f res is given by the volume of the trapp. The hidden room would be something like 4,4*2,2*0,3 m³.

What do you mean by building a 24" panel? Is the smallest dimension the one which sets the low frequency?


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## NBPk402 (Feb 21, 2012)

charles_b said:


> Thank you for the correct technical word "drywall" is the same in German. I remember these large bass-trapps they were showing on the High End Fair last weekend here in Munich, assuming that f res is given by the volume of the trapp. The hidden room would be something like 4,4*2,2*0,3 m³.
> 
> What do you mean by building a 24" panel? Is the smallest dimension the one which sets the low frequency?


I believe he is saying that a 24" thick bass trap will go deeper than a 17" thick bass trap.


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## bpape (Sep 14, 2006)

Yes - exactly.


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## NBPk402 (Feb 21, 2012)

bpape said:


> Yes - exactly.


I guess I have retained something in my brain from you so far. :T


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## charles_b (May 10, 2010)

My problem is now that I dont know what you mean with "24" thick". Is the thickness of the dry wall supposed to be 24"? Or should the air behind the dry wall have 24" in depth until the concrete wall is reached?


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## bpape (Sep 14, 2006)

I'm saying if you want to address that low a frequency, you'll need a 24" thick absorber. That can be the space you have after removing the drywall, or taking 24" out of the room that is now in place to form the cavity.


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## dennisfoley (May 14, 2014)

charles_b said:


> Hello!
> 
> my listening room is about 5,7 m long, 4,2 m wide and 2,2 m high.
> 
> ...



If you are having issues with 27 Hz. you are also having issues with 54, 71, etc which are the harmonics of that fundamental. 

You can achieve the absorption rates and levels you require in a much smaller space requirement than 24". Research the process of diaphragmatic absorption. With this process, you can control level or how low the absorber will go and rate, how quickly it will absorb from that level, by using a ratio of cabinet depth, cabinet fill type, and construction material density.

Dennis


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## bpape (Sep 14, 2006)

Yes - you can do membrane absorbers - but even those with any sort of reasonably efficient membrane are going to be very thick. Our Scopus tuned to 40 using a relatively efficient membrane is still 12" thick.

Bryan


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