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Bass Tube Traps 101

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Tube traps work in much the same way as a typical corner bass trap, but you can place them in other locations besides corners. They’re also more aesthetically pleasing, so you can also use them in rooms not dedicated to acoustics.

Tube traps have been available since 1984, although they were originally used only in room corners. They absorb excess bass energy while minimizing flutter echo with built-in diffusers that scatter mid-to high-frequency sounds. This property minimizes flutter echo, thus providing sound with a fine-grained lateral ambiance.

What are Tube Traps?

A bass trap may be any type of acoustic panel that reduces a space’s response to low frequencies. They’re a subset of panels that absorb sound but are specifically designed for bass sounds below 250 hertz (Hz). Low-frequency sound easily passes through other types of panels and materials, since they cover less of a sound wave’s length.

This process results in an accumulation of low frequencies in the room, causing the sound to become muddy and boomy. Bass traps must therefore be made of thicker and denser material to absorb these frequencies, which is their defining characteristic.

A tube trap is a type of bass trap with a cylindrical shape, which provides the structural rigidity and internal volume needed to absorb bass frequencies. Its diameter is more crucial than its length in determining the frequency of sound it can absorb, so tube traps tend to be thicker than other bass traps.

Studio room with Stacked Tube Bass Traps
Photo via psaudio.com

Other bass traps are made of membranes and resonators that absorb sound slowly. In comparison, tube traps are also “impedance-matched,” meaning they respond very quickly to bass frequencies. This property allows tube traps to handle transient sounds just as easily as sustained sounds, providing music with articulate, dynamic bass.

A Bit of History

Acoustic engineers developed tube traps from scientific principles based on guidance from “golden ear” audiophiles. The result was the world’s first sound absorber for a wide bandwidth that has since become closely associated with quality listening and performing spaces.

Tube traps are now used in all phases of sound production, beginning with the initial creation of the audio tracks. They’re also common in mixing and mastering, where they help create the acoustically neutral environments these processes require.

Tube traps are also commonplace in listening rooms, especially those used by audio equipment manufacturers, dealers, and end-consumer audiophiles.

Tube Trap Pros & Cons

It’s important to take both the pros and cons into account when considering whether to use them in your listening space.

Pros

The biggest advantage of bass tube traps is that they work at least as well as traditional bass traps in absorbing energy from base frequencies. The higher the pressure of these frequencies, the more energy tube traps absorb from them. Bass pressure tends to accumulate in corners, where it’s typically 4 to 8 times stronger than in other parts of the room.

Each corner of a room acts as a megaphone in reverse like compressing incoming sound waves into a narrow volume focused on each corner. This compression creates a pressure zone that makes corners a perfect location for bass traps. As a result, room designers usually stack tube traps from the floor to the ceiling in all four corners of a listening room.

Furthermore, tube traps can be placed in other parts of a room beside the corners. In comparison, corner-mounted bass traps are specifically designed for corners and can’t be used anywhere else. The cylindrical design also makes it look like a piece of furniture or some other type of decoration, giving it greater versatility than corner traps.

Cons

The biggest disadvantage of a Tube Trap is its cost. The original ASC TubeTraps are particularly expensive, although all the good models have a high cost. Furthermore, the choice of manufacturers is also quite limited.

Many audiophiles and musicians decide to make their own bass tube traps, with varying degrees of success. Some of these DIYers have reported good results with this approach, although it’s highly dependent upon their expertise for these projects and the amount of time they’re willing to spend on it.

How do Bass Tube Traps Work?

Professional recording studios have had powerful bass speakers for decades. Modern speakers and subwoofers for the end consumer, are also capable of generating large amounts of bass energy, especially high-performance models.

Studios have also historically used built-in bass traps to balance a room’s acoustics since they’re dedicated to this purpose. However, residential and retail settings have previously lacked this property since they must also fulfill other functions, preventing them from absorbing excess bass frequencies.

In addition to compromising the quality of sound in the room, uncontrolled sound pressure also shakes the room’s ceilings, floors, walls, doors, and windows. The shaking surfaces act like giant speakers, but without the control of actual speakers.

This phenomenon compromises the sound quality and also disturbs neighbors, whether the room is being used for recording or playback. Bass absorption is thus critical for quality sound, no matter how good the speakers are.

A tube trap is a self-contained bass trap with an acoustical circuit that reacts to sound. It’s therefore most effective when it’s located in areas with high sound pressure. These areas are primarily the corners of the room, although sound pressures are usually high near the walls as well.

Tube traps are also known as pressure-zone bass traps since they only react to sound pressure. Alone, tube traps are broadband sound traps, meaning they respond to all frequencies. However, they’re easy to modify so that they have a narrow range of sound absorption in addition to their broadband-trapping properties.

This type of bass trap shouldn’t be confused with a tuned bass trap, which is just a bass trap with an unusually narrow absorption range. Tuning a bass trap typically involves its placement within the room rather than making any changes to the trap itself.

The reason for this approach to tuning a bass trap is that the sound pressure in a room is highest when that room’s resonance is stimulated. Furthermore, the trap’s sound absorption efficiency increases with sound pressure.

On the other hand, frequencies that don’t match any of the room’s resonance frequencies distribute themselves evenly throughout the room. This behavior means that placing tube traps properly will damp loud, lingering sounds more effectively than sounds that decay quickly. They are thus able to completely balance a room.

Tube Traps vs Corner Bass Traps

The effectiveness of tube traps in absorbing bass frequencies at room corners as compared to standard bass traps primarily depends on the diameter of the trap. The round shape of a tube trap generally means that it has to be quite large to present the surface area needed to trap bass frequencies effectively.

In general, a tube trap should have a diameter of at least 20 inches to compete with a corner bass trap, which is typically a rectangular panel measuring two feet by four feet.

Fractional Tube Traps

The most common shape is a cylinder, but they’re also available in fractional shapes such as half and quarter circles. These fractional shapes are most useful for corners that aren’t right angles, which occur in some modern room designs.

Fractional tubes can also be installed so that their end caps align at the angles needed to match a wall with an irregular shape. Tube traps can thus create acoustic panels of virtually any shape, allowing you to install them in any location with high sound pressure.

Tube Trap Placement & Layouts

You can place tube traps in many ways to improve the sound quality in a room. The shape of the room is one of the biggest factors affecting this process, although the type of music may also be significant.

Tube Bass Traps arranged in a basement studio.

Corner Trapping

The most common plan for placing bass traps in a listening room is to place them in all four corners of the room. These should generally be very close to the walls, and they can even touch the wall without compromising their bass absorption.

Even if the walls have molding at the base, tube traps should still be within one inch of them in most cases. For nightclubs or studios that play many genres of music, tube traps should be placed as tightly into the corners possible.

For music played by an orchestra, they should be a few inches out of the corner to make the bass more reverberant.

Secondary Reflections

Once the corners of the room have been properly bass trapped, you can take additional steps to damp secondary reflections and make the sound as clean as possible. For example, speakers that are near a wall can also benefit from tube traps next to the wall in line with the speakers to damp and diffuse the sound that bounces off that wall.

A center imaging stack on the back wall can also help achieve this goal, along with arrays to the left and right at the mid-sidewalls. These placements can help damp secondary reflections, providing the music with greater detail and clarity.

Lateral Reflections

Lateral reflections are caused by sound bouncing off the sidewalls, often after initially reflecting off the rear wall. The primary goal in this situation is to absorb early sidewall reflections, which will help sharpen the sound image. It’s also important to scatter late reflections from the rear walls, creating greater ambiance.

Advanced acoustic control frequently involves the use of bass traps with built-in treble diffusers, which helps improve a time-delayed lateral ambiance. You can address this issue by placing the traps next to any speakers located in the front of the room, which will enhance the ambiance and deepen the soundstage.

Placing small tube traps near the sides in the back of the room can also help with lateral reflections.

V-shaped Room

A V-shaped room requires additional attention to trap sound that accumulates in a corner with an acute angle. These steps include bass traps for speakers pointed towards that corner as well as bass traps for left and right speakers at the front of the room. All these bass traps need built-in treble diffusion.

Challenging Rooms

Some rooms can be particularly difficult to treat with bass trapping, typically due to an odd shape or an unusually large number of acoustic obstacles like bookcases or windows. The general solution to this problem is to closely flank these obstacles with bass traps to absorb the reflected sound that would otherwise cause excessive reverberation.

Speakers Too Close to a Wall

You should normally place speakers some distance away from walls to prevent too much sound from bouncing off the near wall. However, this isn’t always practical, especially for small rooms. Use bass traps with built-in treble diffusion to soften near-wall bounce. Fractional tube traps are also a common solution to this problem.

Off-balance Room

A room that’s open on one side will be acoustically off-balance since the open side won’t reflect sound. Address these problems by adding bass tube traps to the opposite side, providing the room with greater acoustic symmetry.

Self-resonating Speakers

Powerful speakers can cause their enclosure to “self-resonate,” meaning the enclosure itself vibrates in response to the sounds coming from the speaker. Self-resonance causes the back of the enclosure to act like another speaker, which can muddy the sound. Damp out this unwanted sound pressure by placing a tube directly behind a self-resonating speaker

Rear Wall is Too Close

A listening position that’s too close to the rear wall can often result in an excessive bounce off that wall. Place a series of smaller half-round tube traps along the rear wall to resolve this issue.