Bass Buildup

Bass build-up creates a sluggish bottom line, where the bass dynamics that define tempo and strident aspect of the musical line become lost in a wash of bass reverberation. To minimize unwanted bass build-up, bass traps are put to work in the audio room. ASC developed the world’s first factory built and shippable bass traps, the TubeTrap back in 1984 and continues to supply the original model TubeTrap along with the many upgraded modified versions of the TubeTrap that have been developed over the years.

The classic location for bass traps is in the corner, because that’s where the bass pressures are higher than elsewhere in the room, and also, in the corners of the room are found a “pressure zone” for any and all room modes and corner bass traps dramatically dampen the decay of the bass reverberation once it has been built-up in the room.

At ASC, we’ve analyzed how the bass build-up process takes place. It takes place in three stages. The first is what we call “head-end ringing” which is the rapid build-up of vertical and lateral bass reverberation in the plane of the speaker. Then we have the more familiar front to back build-up of reverberation end to end in the room. Finally, we have the “tangential and oblique” type of build-up where the sound is not bouncing between parallel surfaces but careening around the room, bouncing at angles off the various surfaces of the room.

What we do in room design is to aggressively damp the buildup of vertical and lateral reverberation in the plane of the speakers by adding bass traps alongside and above the speakers. The sound is very loud at this location and huge amounts of the off-axis bass wave front is attenuated, which removes about 2/3rds of the total bass build up energy (5- dB) from the room, long before it actually ever actually builds up in the room.

Then we add traps into the front and rear corners and along the front and rear walls to damp down the end to end build-up. And then, the careening parts of the wavefront are rapidly attenuated because of the friction created when a segment of wavefront impacts at an angle, the surfaces of the room, and as well, when they impact the various Bass Traps in the room.

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