AV Police Squad

♪ Rock The Sound Bar: The Buzzes & Rattles Test

I think we can all agree that internal, rear-firing loudspeakers found in most LCD displays leave a lot to be desired. I see many people opting for a “sound bar,” of sorts, or program loudspeakers to get more fidelity and level in their simple systems. However, the problem with simple systems is they are often neglected. While the installers might do an excellent job securing the display to the wall, they oftentimes do a “quick” job on the loudspeaker installation, especially when the client wants the sound bar mounted as close to the display as possible.

I remember when you had to buy loudspeaker kits for plasma displays. They looked like ears for the plasma, and came with some hardware to secure the loudspeakers to the display. They also came with this foam ribbon that you were supposed to adhere along the length of the display to stop the plastic of the display from rattling against the plastic of the loudspeakers at certain resonant frequencies. I can’t tell you how often those foam ribbons were simply thrown out. It didn’t look like a big deal, but when a bad guy came on the screen and you heard some sub-200Hz frequency notes in the background music—as in, “Oh me, oh my! Stinky Pete just tied Pa to the railroad tracks and there’s a train a-comin’!” Dun-Dun-DUUUUUUUNNNNNN!— users heard a very noticeable rattle from the display.

Fast forward 10+ years, and people are butting sound bars up against displays of a different manufacturer. There is no attachment kit or foam to make sure they play nicely together. When those sub-200Hz frequencies get distributed that sound bar will be bouncing off the display like those crazy Bubble Soccer guys!

(Well, not exactly, but you get my point.)

We need to insist on a Buzzes and Rattles Test being performed on every system, even the simple ones. Basically, all that’s involved is setting the system to its maximum, useable volume level and playing a sine wave sweep from 20Hz-20kHz, with a ramp of roughly 30s. At each frequency, listen for any buzzes and rattles in the system.

Not only will this flush out sloppily installed sound bars, but it will also make any non-conforming loudspeaker very apparent. You do have to use your ears, especially in rooms with fancy lighting fixtures. They may rattle from the sound pressure, but at least you can note it and bring it to the attention of the client before it gets blamed on the sound system.

The Buzzes and Rattles Test is a quick, grass-catcher test that should be performed on any audio system, particularly the simple ones. It can be very time consuming and frustrating to everyone involved to diagnose a poorly installed, rattling loudspeaker. The user may insist that the audio is “distorting.” The technician can very easily determine that there is no clipping in the system, and never notice the real problem. Because the mechanical rattling may only present itself at specific, resonant frequencies, finding the issue may take several service calls, resulting in a loss of profits and angry clients. Both can be easily avoided by rocking the sine-wave sweep at some point in the installation. You can rest assured that the loudspeakers are all in good working order, and there is no danger of them playing bubble ball with neighboring devices.

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