The excerpt you are about to read comes from what may be the most definitive story of the evolution of small-room acoustic conditioning ever written. The full paper explains the history of the TubeTrap, from its origins and refinement, through its sudden emergence and domination of the HiFi acoustics market. Then you learn exactly how a TubeTrap imparts such a profound improvement upon your listening experience, along with the most appropriate metrics to quantify this improvement. Further explanation follows of the parameters that make an audio room excellent, concluding with advanced room construction techniques.

If an audiophile was stranded on a desert island with a 16’x26’x10′ shack and a pair of loudspeakers, this is the one book they should bring.

This issue we’ll jump right into the heart of the paper, exploring the benefits of TubeTraps and starting to explain how they happen. Enjoy!

Read the entire paper

We Know TubeTraps Work. But Why?

Most people who have listening rooms do not also have access to as many TubeTraps at they want. They find themselves very happy with the results derived from a few stacks of traps, starting in the two front corners of the room. I kept trying to measure what they were being pleased about. The basic setup was always the same: Put a set of traps in the two front corners of the room, the corners behind the speakers, rotate the reflectors in towards the speakers and step back and let the Traps do their magic. It always worked and no one had to know more than to be able to find the corner behind the speaker, to become an acoustic guru

Corner Bounce Control

At first I thought the reason TubeTraps were working was the original reason the TubeTrap was used which was to kill the phase add and cancel distortion effects due to the corner bounce out from behind the speaker. The Traps certainly reduced the comb filter action in the frequency responses curve of the speaker. Measurements confirmed that the comb filter effect was minimized by putting the bass trap in the corner and I published this in my first AES paper. But comb filter correction didn’t correlate with what the HiFi buffs who bought the Traps said when they and called in with a thank you and the list of their observations.

Audiophiles who bought TubeTraps said they liked the improved bass smoothness which was expected because the phase add and cancel effect had been addressed. But then they continued, saying they also enjoyed the bass extension, punch, dynamics, and the surprising absence of a one note or drone tone bass being replaced with a musical bass line. All of these notable improvements were in the bass range although I was hard pressed to account all these improvements to correcting a comb filter reflection out of the corner behind the speaker.

If that wasn’t perplexing enough, they went on into the treble range, describing their amazement as to how could a bass trap could improve imaging, musicality and sound stage, all of which are aspects of listening that belong to the treble range. Certainly the treble diffuser of the TubeTrap is nice for ambience and some spatial detailing but it couldn’t be that good. Most all of their observations couldn’t be accounted for by absorbing a bass bounce and adding a treble splash out of the corner. So the search for an explanation about how they did what they did was not over.

Reverb Decay Control

Adding bass traps in a room changes the decay rate, speeds it up. Absorption causes sound to die out faster in a room. When a sound is made in a room, we first hear the sound and then we hear the echoes and then the reverberation, which dies out over a relatively long time. If we make a continuous set of sounds the reverb of the first sound is added to the reverb of the second sound which adds to the reverb of the third sound and so on until a fairly continuous din of background noise builds up. This din of noise keeps people from hearing quiet sounds being made or quiet parts of louder sounds being made. Trying to have a conversation across an empty gym is a good example of how sound masking this din of reverb noise can be.

Audio playback rooms “work best” if their RT60 (time it takes for reverb sound to drop 60 dB) is not very long, maybe about 0.75 seconds. Most fairly bare rooms in homes have reverb times in the range of 5 seconds. Acoustics have to be added into these rooms to get their RT60 rates corrected. In the bass range, stacking TubeTraps floor to ceiling in all 4 corners usually does the trick.

The recommended RT60 is not the same for all frequency ranges. In the midrange it is about 0.75 seconds, while in the high frequency range it might be 0.9 seconds and in the low frequency range up to 1.2 seconds. By measuring the RT60 in different frequency ranges and adding the right amount of absorption to the room in these different frequency ranges, the recommended RT60 can be achieved.

Notice that EQ was not mentioned. EQ does not change the decay rate in a room, it only changes how much sound is being put into the room at various frequencies, compared to other frequencies. EQ is a volume control, not a reverb control. So we added TubeTraps to the room with sound panels and achieved the recommended specification. This plus comb filtering the corner reflection must be the magic combination that makes rooms sound great….it must be what TubeTraps are doing right…

Well, these rooms did sound a little better but actually not as much as expected. Definitely there is more involved with room acoustics and TubeTraps besides RT60 adjustment. I had to continue to broaden my search for the answer.