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Do I need a backbox?
Last Updated: 06/13/2016

Yes. But not for the reason you think.

Integrators install backboxes for three reasons — to reduce sound transmission into adjacent rooms, to ‘claim the space’ in the wall or ceiling, and to protect the speaker from debris.

As a rule, backboxes do not improve the acoustic performance of good speaker systems. Inferior speakers may benefit from the ‘stiffening’ backboxes provide, but we’re not talking about inferior speakers here.

Architectural speakers need a good amount of open air space behind the drivers. Most architectural speakers use an Infinite Baffle design, with the back of the speaker playing into the wall. Infinite Baffle designs work best when there’s an infinite (you saw that coming) amount of unimpeded air space behind the speaker. When the air space is too small, the springiness of the air stiffens, which constrains the movement of the bass unit. Reduced airspace reduces driver movement, which reduces bass extension and overall output volume.

To test this, simply put an architectural speaker into a wall that’s stuffed to the brim with insulation. You’ll hear no bass and no impact. We call this overdamping, or choking.

The more bass a speaker is capable of producing, the more air it needs behind the drivers. That’s just physics. But most manufacturers (us included) size our backboxes so they fit between and are no deeper than a 2x4 stud. That means a backbox would have to be at least two feet tall to give enough breathing room to achieve bass to 60 Hz. If a speaker is capable of reaching down past 60 Hz, but it’s put into a smallish box, the speaker will lose a good deal of bass extension.

Most enclosed architectural speakers suffer from limited bass specifically because of this issue.

Reduce sound transmission
Well constructed backboxes — with plenty of absorptive material — reduce sound traveling into adjoining rooms at certain frequencies. High frequencies above 500 Hz are nicely contained within the box. But low bass notes are not, and while attenuated, escape the confines of the box, regardless of construction.

Think of it this way: when you’re at a stoplight and a car pulls up next to you with loud, heavy bass music playing, you can easily hear the music. And this is music that’s contained by two boxes — their car and yours.

Bass notes — with their very long wavelengths — easily pass through wood and metal containers. The best backboxes do reduce upper bass frequencies up to 9dB. That’s a significant reduction, to be sure (almost 65% of the sound is trapped in the box). And yet these backboxes are unable to significantly reduce low bass information, which easily pass through the walls of the house.

Again, consider a subwoofer in a dedicated theater. Even when placed in a well-insulated room, the rumble of the sub is heard throughout the house. This is the physics of sound — bass notes, with their long wavelengths travel freely. Backboxes help overall, but have their limitations.

Claim the space
During new construction, it’s important for the Integrator to protect a defined area in the walls from pipes, conduit, and excess insulation. A backbox is an inexpensive way to ensure other construction elements don’t interfere with sonic performance and speaker placement. Integrators like to be ‘first in line’ after studs are up to install backboxes, helping the electrician and plumber plan their routes.

Protect from debris
Because most architectural speakers are open behind the drivers, there’s a likelihood that construction debris and critters make contact with the back of the speaker. In-ceiling placement is particularly sensitive, since the debris rests atop the moving parts of the speaker, rattling perfectly to the beat. Backboxes keep the back of the speaker clean, while preventing critters from munching on critical components.


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