# DIY basstraps



## lglura (Aug 25, 2008)

Hi guys. I start to build bass traps, this is what I have found to use as dampening material, the lowest of the curves are for the "extra bass" with total depth of 200 mm.


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## bpape (Sep 14, 2006)

Ummm. You do realize that the lowest curves are the worst performance, right? The rolloff at the top is likely due to a facing like FSK on it. 0.45 for 200mm (8" thick) is really really bad. With that thickness and the proper density, you should be up around .8 even down into the 60's

Bryan


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## lglura (Aug 25, 2008)

bpape said:


> Ummm. You do realize that the lowest curves are the worst performance, right? The rolloff at the top is likely due to a facing like FSK on it. 0.45 for 200mm (8" thick) is really really bad. With that thickness and the proper density, you should be up around .8 even down into the 60's
> 
> Bryan


Hi Bryan. I must correct a bit, the curve is 100 mm damping material and 100 mm air behind it "A" mont.
What is proper density for a bass trap.
lglura


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## bpape (Sep 14, 2006)

That's still not all that great for 4" even flat on a wall, much less with a 4" space behind it. 

Density depends on thickness. For a 4" panel, you can go anywhere from 2.5-6lbs/cu ft.

Bryan


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## lglura (Aug 25, 2008)

bpape said:


> That's still not all that great for 4" even flat on a wall, much less with a 4" space behind it.
> 
> Density depends on thickness. For a 4" panel, you can go anywhere from 2.5-6lbs/cu ft.
> 
> Bryan


Thanks bryan, I will check with the supplier, what damping material would you recommend for bass trap

lglura


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## bpape (Sep 14, 2006)

I poked around a bit. What you've pictured is a ceiling tile product. also, the good absorption in the graph (top one) is for both the master and the xtra bass together and with a 200mm total system thickness -though they never say that I could find, how thick the absorption itself is. 

This appears to be very very similar to the mineral wool we get here in the US. 


http://www.knaufinsulation.co.uk/products/rocksilk_slabs/rocksilk_universal_slab.aspx

While they don't provide acoustic numbers, you can pretty closely follow these numbers.

Product thickness density 125hz 250hz 500hz 1000hz 2000hz 4000hz NRC 
MinWool-1200 Industrial Board 1240 1.5" (38mm) 4 pcf (64 kg/m^3) 0.13 0.48 1.02 1.08 1.02 1.01 0.90 
MinWool-1200 Industrial Board 1240 2" (51mm) 4 pcf (64 kg/m^3) 0.20 0.61 1.07 1.06 1.04 1.07 0.95 
MinWool-1200 Industrial Board 1240 4" (102mm) 4 pcf (64 kg/m^3) 0.88 1.14 1.17 1.08 1.06 1.10 1.10 
MinWool-1200 Industrial Board 1240 6" (152mm) 4 pcf (64 kg/m^3) 0.32 1.14 1.11 1.09 1.06 1.07 1.10 
MinWool-1200 Industrial Board 1260 1.5" (38mm) 6 pcf (96 kg/m^3) 0.18 0.62 1.08 1.08 1.03 1.07 0.95 
MinWool-1200 Industrial Board 1260 2" (51mm) 6 pcf (96 kg/m^3) 0.25 0.85 1.15 1.10 1.04 1.06 1.05 
MinWool-1200 Industrial Board 1260 3" (76mm) 6 pcf (96 kg/m^3) 0.80 1.07 1.11 0.99 0.98 0.96 1.05 
MinWool-1200 Industrial Board 1260 4" (102mm) 6 pcf (96 kg/m^3) 0.99 1.01 1.10 1.03 1.03 1.05 1.05 
MinWool-1200 Industrial Board 1280 1.5" (38mm) 8 pcf (128 kg/m^3) 0.13 0.64 1.08 1.08 1.04 1.07 0.95 
MinWool-1200 Industrial Board 1280 2" (51mm) 8 pcf (128 kg/m^3) 0.32 0.90 1.11 1.07 1.01 1.05 1.00 
MinWool-1200 Industrial Board 1280 4" (102mm) 8 pcf (128 kg/m^3) 1.11 0.91 1.03 1.03 1.06 1.07 1.00


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## xyrium (Jul 28, 2008)

Interesting, the numbers at 125Hz drop as the 4lb wool goes to 6".


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## bpape (Sep 14, 2006)

I believe that's a typo in the table. 6" will definitely outperform 4".

Also, all of those numbers are pure A mount, flat on the wall, no air gap.

Bryan


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## lglura (Aug 25, 2008)

bpape said:


> I poked around a bit. What you've pictured is a ceiling tile product. also, the good absorption in the graph (top one) is for both the master and the xtra bass together and with a 200mm total system thickness -though they never say that I could find, how thick the absorption itself is.
> 
> This appears to be very very similar to the mineral wool we get here in the US.
> 
> ...


Hi Bryan. If I understand correctly, a higher density in dampening material would be a better solution for a bass trap. In Norway we have a simular brand to Rocksilk Acoustic Floor Slab, but only in 50 mm thickness. How thick should I build panels, and what if i mix different material in the basstraps. how it will function as broadband bass trap?


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## bpape (Sep 14, 2006)

If you can only swing 4" thick, then the higher density would work slightly better for bass control. If you can do 6" or more thickness, you can get by with the 4lb density just fine.

Bryan


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