Few things can affect the quality of a sound as loudspeakers being out of polarity. You can lose bass response, cancel out vocals and cause general phase mayhem in a sound system.
There are many ways to determine polarity; however, here’s a very inexpensive and easy solution to test for proper wiring inside loudspeaker cabinets before installing them, and without running any audio signal through them.
See Thumper, below. It’s my trusted polarity signal injector. Once you build Thumper, simply hook up 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 loudspeaker drivers. You should then see the woofers push out just a bit. If one pops in while the others push out, you have wiring problems inside the cabinet.
If all of the loudspeakers pop in, then the input jack—or the cable itself—may be wired in reverse.
Thumper can be built from from junk parts, or go to Radio Shack for a little plastic project box, 1/4-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. Just make four solder connections and you’re done. I usually put a small piece of foam under the battery to keep it from rattling around or sliding inside the box.
Thumper works great on loudspeakers both large and small, and the 9-volt output only dumps a 10-watt pulse into them, so it’s safe to use.
What’s not to like?