TubeTrap (Original)

The original portable bass trap, the TubeTrap is a highly modified version of Harry F Olson’s “functional sound absorber” and operates far more efficiently and to a lower frequency than its size would suggest. By including an integral treble range polycylindrical diffuser with each unit, Art Noxon (ASC founder, president, engineer) created a broadband acoustic control device able to maximize the sound quality in any space.


Their cylinder shape provides the structural rigidity and internal air cavity necessary to absorb sound in the low frequency range. It’s their diameter, not length, that determines how deep into the bass range they can absorb. Because TubeTraps are “impedance-matched” to sound, they are fast-acting bass traps. Unlike slow acting membrane and resonator bass traps, TubeTraps handle musical transients just as easily as they handle sustains. TubeTraps transform room acoustics into an unforgettably articulate and dynamic musical bass line.


  • The original TubeTrap line is now a CUSTOM ORDER product.

TubeTraps, the original, archetypal bass trap, dating back to 1984, are set up in the corners of the room where they act like sonic shock absorbers. TubeTraps eliminate excessive build-up of bass energy in the room while their built-in diffusers minimize flutter echo by horizontally scattering mid-high frequency sounds to provide fine grained lateral ambience.

The TubeTrap was developed using acoustical engineering principles and voiced by the consensus of “golden ear” audiophiles and engineers.  It was the first full bandwidth sound absorber/diffuser (abfuser) and has become synonymous with quality listening and performing spaces.  TubeTraps quickly became the worldwide defining icon of high performance audio room acoustics, and remain so to this day.

TubeTraps are used to make music from the beginning to the end of the audio chain.  In the recording studio, TubeTraps are used to control the acoustics that surround the talent and mic during the creation of audio tracks.  Next in the process, TubeTraps work to create crystal clear mixing environments.  After that, TubeTraps are used to create the perfectly translatable acoustic environment needed for song and album mastering.

Finally, TubeTraps are used to create reference listening rooms for the manufacturers of audio equipment, great demo rooms for the equipment dealers and fantastic playback rooms for the audiophile listener…amazing rooms which help audio gear turn great recordings into great sounding music. TubeTraps are involved with music from creation to consumption.

TubeTraps are very busy at work, from the making of music to the playback of music…or as we like to say…..from music to music.

Room Acoustics & TubeTrap Bass Traps

The loudspeakers and subwoofers in today’s high performance audio playback settings produce tremendous amounts of bass energy.  Professional recording studios have long used speakers powerful in the bass range, and traditionally have used built-in bass traps to balance the sound in the room and prevent unwanted buildup.  On the other hand, rooms constructed for residential or retail demonstration use have no accommodation to handle the build-up of excess bass energy. And so the uncontrolled sound pressure builds up inside the room, which not only is unpleasant for the listener, but it additionally shakes the walls, floor and ceiling, windows and doors of the room.

These shaking surfaces act like giant uncontrolled loudspeakers that bother the neighbors and additionally ruin the quality of sound in the room. High power audio playback at home or in commercial spaces is no different than what goes on in recording studios. Bass trapping, combined with treble range absorption/ diffusion, is needed for quality sound to be heard, regardless of how expensive the speakers and amps may be. The TubeTrap is a self-contained, broadband bass trap, utilizing a reactive acoustical circuit that is energized by and works off of the presence of sound pressure.  It performs best when placed at locations in the room where the sound pressure is the highest, which are typically in the corners and against the walls of the room.

Because the TubeTrap only reacts to sound pressure it is sometimes referred to as a pressure-zone bass trap. Although the TubeTrap is a broadband sound trap, it can be modified by adding additional acoustic circuitry to give it an enhanced narrow band range of sound absorption in addition to its broadband bass trap properties. However, this is not to be confused with a “tuned bass trap” which is exclusively a narrow band bass trap and has no broad band properties.

For the most part, the “tuning” of the TubeTrap is actually not done with internal circuitry, but done by the room itself.  When a room resonance is stimulated, the sound pressure is always the highest in the corners of the room and in select locations along the walls.  Placing TubeTraps in the corners and at certain wall locations puts them in the high pressure zones of the room modes. The higher the pressure, the more efficiently the TubeTrap absorbs energy.  For tones that are not room modes, the energy in the room is diffuse and sound pressure is more uniformly distributed.   Properly placed TubeTraps ensure that loud, long lingering modes will be more highly damped than the more quickly decaying diffuse sounds in the room.  This gives any room in which TubeTraps are used a much more tonally balanced reverberant field.


The History of ASC Bass Traps: a TubeTrap is Born (Original from 1985)


TubeTraps are the original corner-loaded bass trap, taking inspiration from Harry Olson, the prolific RCA engineer who nearly invented modern acoustics.  A young engineer/physicist named Arthur Noxon took Olson’s “functional sound absorber” to the next level by increasing the size and modifying the frequency response to allow adjustable treble levels in the room.  The TubeTrap was thus born, and 40+ years later continues to be built by hand in ASC’s factory in Eugene, Oregon.

Our original TubeTrap bass trap, back in 1985, was 9″ diameter and 3′ long. Our current standard TubeTrap product line includes 9”, 11”, 13”, 16” 20” and 24” diameter models. They all utilize the same patented RC-circuit bass trapping technology and treble range diffuser panel as our original model. The larger diameter units provide more sound absorbing power because of their larger surface area and a lower roll off frequency because of their increased internal volume.  As of 2018, new production TubeTraps all contain Isothermal interior air volumes unless otherwise specified.

Specialized TubeTrap Bass Traps

In addition to the wide variety of standard TubeTraps available we provide an even wider variety of customized TubeTraps

In addition to the wide variety of standard TubeTraps available, we provide an even wider variety of modified TubeTraps. Some modifications are superficial, belonging only to the appearance of the TubeTrap. Other modifications are internal, in which case they are fit with some sort of performance enhancing feature.

It is not unusual for a room corner to be acute or obtuse. QuarterRound TubeTraps can be altered to accommodate such situations.  Fractional TubeTrap (HalfRound and QuarterRound) end caps can also be installed at various angles so the units can be butted together to follow an irregular wall shape.  TubeTrap technology can be used to create “black acoustics” of nearly any shape, to be hidden behind stretch fabric, furnishings, or any other out-of-sight location which is also a high sound pressure zone.

We often add absorption enhancing elements inside what appears to be an ordinary TubeTrap.  The most common upgrade along this line is the SuperTrap,  where the operational volume of the TubeTrap is increased by 33%. This modification extends the roll off frequency of the TubeTrap ½ octave lower, and is available in all diameter models of TubeTraps.

We also make Helmholtz Traps.  These units are specifically tuned for powerful absorption at a particular frequency, without affecting the broadband performance of the TubeTrap.  Helmholtz Traps act like SuperTraps in the lowest register, but at the resonant frequency the backpressure buildup inside the TubeTrap goes to zero due to the sound canceling effects of the Helmholtz resonator inside the TubeTrap.  These options are available in most  standard diameter and length TubeTraps.

Customized TubeTraps include modifications to standard traps and specialty bass traps. Examples of modifications might include a hole running through a TubeTrap so a stiff power cord can be lugged and unplugged into a power socket without having to move the TubeTrap setup. Another modification might to notch out part of the side of a TubeTrap so that it fits close up to and around some obstruction. It is not unusual to modify a TubeTrap so that it holds a TV monitor or some other piece of artwork.

We also make true custom bass traps, usually for acoustic designers or architects with particular needs. All our bass traps still utilize our patented RC circuit bass trap principles, but not all include our treble range diffuser. We collaborate with the designer to design and manufacture a short run of special products which meet the specifications of the job.

One example of our custom bass traps is the VentTrap.  These are basically acoustic friction elements located in one room, with a duct connecting their back side to an acoustic volume that is some number of feet away, even perhaps in a basement.  Most of our stand-alone bass traps have the acoustic resistor wrapped around the acoustic capacitor forming an integral self contained bass trap package; VentTraps are shipped without the capacitive volume, which the customer or builder provides.  This is similar to what we see in electronics, where an electronic resistor is connected to a capacitor with a wire, except in this case, the acoustic resistor is connected to the acoustic capacitor with a pipe of air.

The potential variety of custom bass traps is limitless, held back only by the imagination of the acoustic designer, architect,  or customer.  Every once in a while, we build a custom bass trap that ends up having a wider application than the one it was developed for.  If people like it, this new bass traps joins our standard product line.

Sonic Benefits of TubeTraps

The TubeTrap bass trap is designed to absorb sound energy when in the presence of bass range sound pressure.  The higher the pressure, the more energy is absorbed. Bass pressure is 4 to 8 times stronger in the corners of the room than away from the corners.  TubeTraps are usually stacked floor-to-ceiling in columns in all four corners of the typical audio room. Each corner acts like a giant megaphone in reverse, compressing incoming sound waves into the narrow volume at the root of each corner of the room. This corner compression of bass waves creates the perfect location for a pressure zone bass trap: the TubeTrap.

Unlike any other bass trap, the physics behind the TubeTrap are based on a capacitive-resistive circuit. The acoustic capacitor (C) is the air chamber inside. The bigger it is, the more efficient the TubeTrap is at low frequencies. The acoustic resistance (R) is DC impedance matched to the radiation (LC) impedance of a freely radiating soundwave. Because of this design feature, the TubeTrap is more than 100% efficient.

Another unique feature is the adjustable diffusion grid built into the TubeTrap. The specular diffusion panel that covers half of the TubeTrap is an acoustic choke (L) which is sized, ported and mass loaded to backscatter the treble range.

Absorption In Sabines Per Tube
63Hz 125Hz 250Hz 500Hz 1KHz 2KHz 4KHz NRC
9″ x 3′ 7.13 8.41 12.93 12.04 11.81 9.08 10.36 1.62
9″ x 2′ 5.40 6.64 6.59 8.74 7.71 6,77 5.54 1.59
11″ x 3′ 10.18 10.47 16.29 16.42 13.47 11.42 11.69 1.67
11″ x 2′ 10.01 9.08 10.32 8.51 9.06 7.42 10.21 1.54
16″ x 3′ 14.58 17.04 14.85 17.75 13.62 16.35 15.39 1.24
16″ x 2′ 10.37 15.03 11.15 12.06 8.03 7.64 7.40 1.16
9″ x 3′ 1/2 Rnd 1.44 2.17 4.13 3.07 4.14 3.37 3.23 1.10
11″ x 3′ 1/2 Rnd 2.66 2.65 4.93 6.29 5.14 4.95 2.75 1.23
Conditions: Results are an average of at least 8 samples at each center frequency using 1/3 octave, band limited pink noise. Tests were performed in a reverberant environment using a B & K 4165 microphone, a B & K 2309 sound level meter and a B & K chart recorder. Specifications assume tubes are concentrated at the tri-corners of the room. At 90 degree intersections other than tri-corners, multiply absorption ratings by .78.



Design Rolloff & Crossover Frequencies
Diameter Rolloff Frequency Crossover Frequency
9″ 110Hz 400Hz
11″ 90Hz 400Hz
13″ 70Hz 400Hz
16″ 55Hz 400Hz
20″ 40Hz 400Hz

TubeTraps (all variations)


  • All of our TubeTrap products are also ~3/8″ oversize in diameter.

Standard Height

  • Standard TubeTraps products are built taller than the nominal listed height by 1/2″ to 3/4″
  • Maximum available single height for any full-round product is 48 1/2″
  • Custom Sizes under 4′ available

Custom Heights

These are built within 1/8″ tolerance.

  • A 13 x 3ft TubeTrap will have a diameter of 13 3/8″ and a length of approximately 36 5/8″
  • A 16 x 46″ Custom made TubeTrap, which will have a diameter of 16 3/8″ and a length of 46″ +/- 1/8″

This includes but is not limited to:

  • TubeTraps
  • IsoThermal TubeTraps
  • Quarter Rounds
  • Half Rounds
  • TowerTraps (all variants)
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