Technical Papers

BassTrap Sound-Off: FuzzBalls vs TubeTraps

Is a bass trap nothing more than just a container of fuzz, building insulation? Many budget bass traps are essentially just that; foam blocks, containers of building insulation. TubeTraps are different, they have a complicated mechanical structure inside, But are the complications worth the added cost?

In the late 1980's we also wondered about this same thing. We looked into the difference between the TubeTrap and an otherwise equivalent bag of fuzz. Our testing in a reverb chamber first confirmed that a bag of fuzz does provide the services of a mild-mannered bass trap. And secondly, the good news was that standard TubeTraps deliver 2 to 3 times more absorbing power than the mild-mannered bag of fuzz.

We weighed the amount of fiber in a 16x2 TubeTrap. We placed the same amount of fiber evenly distributed in an empty 16x2 container. We tested the empty reverb chamber RT60 at 1/3 octaves between 20 and 200 Hz. It was around 11 seconds which meant the reverb chamber had about 11 Sabines of wall friction.

Then we placed 2 units of fuzz into two corners of the chamber and tested the RT60 again, it ranged around 8 seconds. This meant the chamber plus two corners with fuzz in them provided about 15 Sabines, 4 more Sabins of acoustic friction than the walls of the empty chamber.

Then we removed the fuzz traps and replaced them with standard TubeTraps, which included the built-in reflector, crossed over at around 600 Hz. The 2 TubeTrap had exactly the same amount of fuzz in the same overall volume and shape as the 2 bags of fuzz and they were placed in the same two corners of the reverb chamber. The RT60s measured in the range of 6 seconds which meant the room had a little over 20 Sabins, 9 Sabins more than the wall friction of the empty room.

The ball of fuzz delivered 4 Sabines of absorption while the original style TubeTrap delivered 9 Sabines which is 2.25 times more absorption than the otherwise equivalent ball of fuzz. The only difference between these two tests was that the same amount of fiberglass was compressed into a cylindrical shell which left an empty air cavity instead of a cylinder uniformly filled with light density fiberglass.

The above gave the average result of the testing between 20 and 200 Hz. In the actual testing, the absorption varied with the frequency. For example, at 100 Hz the 2 TubeTraps produced nearly 32 Sabins of absorption at 100 Hz while the cylinders of fluff produced around 12 Sabins of absorption. TubeTrap configuration of the same amount of fiber produces 2.7 times the absorbing power at 100 Hz compared to an otherwise equivalent bag of fluff.

Today, our IsoThermal TubeTrap literally doubles the sub-bass absorbing power of the original TubeTrap in the sub-bass frequency below 60 Hz and by 30% above 200 Hz. This means it is 5 times more absorbing in the sub-bass range than a ball of fuzz and in the octave above 100 Hz, the muddy bass range, the IsoThermal is about 3.5 times more power absorbing than a ball of fuzz.

Arthur Noxon
Acoustical Engineer
President of ASC TubeTraps
Sept 2018
