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Thursday, January 12, 2012

Build A Thumper: A Simple Way To Test Loudspeaker Polarity

A cheap and easy way to test for proper wiring inside your loudspeakers

 
If you’ve attended a HOW-TO Sound Workshop, you’ve heard me play examples of loudspeakers out of polarity.

You can lose bass response, cancel your vocals and cause general phase mayhem in your sound system.

Well, here’s a cheap and easy way to test for proper wiring inside your loudspeaker cabinets before you install them up on the wall and without running any audio signal through them. See below for Thumper, my trusted polarity signal injector.

Once you build Thumper, you just hook a loudspeaker cable from its phone jack to whatever cabinet you want to test.

A brief push on the momentary push button will inject a 9-volt positive signal into your speaker cones. You should then see all the woofers pop out just a bit.

If one loudspeaker pops in while the others pop out, you have big wiring problems inside the cabinet. If all of the loudspeakers pop in, then the input jack on the cabinet or the cable may be wired in reverse. (You already know how to solder from a previous column, so get fixing.)
 
You can build Thumper from junk parts or go to Radio Shack for a little plastic project box, quarter-inch phone jack, 9-volt battery clip and SPST (Single-Pole/Single-Throw) Normally-Open (N-O) momentary contact switch.

An exact part mounting plan isn’t critical — as long as everything fits inside the case it should work.

I usually put a small piece of foam under the battery to keep it from rattling around or sliding inside the box. But just make four solder connections, and you’re done.

The Thumper works great on loudspeakers both large and small, and the 9-volt output only dumps a 10-watt pulse into your speakers, so it’s safe to use. What’s not to like?

Mike Sokol works with the HOW-TO ASSIST Tour (Academy of Sound System Integration, Setup & Troubleshooting) which provides sound and electrical contractors and sound system installers with the best possible training on how to setup, integrate and troubleshoot live sound systems of any size. Find out more here.

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