Polarity mystery: Can you help me solve it?


THE BACKGROUND: My speakers are Focal 1007be. They have a Linkwitz-Riley crossover with a 36 dB per octave slope. Because of that, the two drivers are wired with opposite polarity: the woofers are positive, the tweeters are negative.

WHAT I DID: At the advice of a friend with the same speakers, I inverted the polarity of the drivers, by simply reversing the red and black speaker wire leads to the terminals of both speakers, so that the speakers are still in phase with each other, but now the woofers are negative polarity and the tweeters are positive polarity.

WHAT HAPPENED: To my surprise, the sound improved! Specifically, image focus improved. The improvement can't be attributed to the preservation of the absolute phase of the recording, since the improvement was the same for many different recordings (some of which, presumably, preserve absolute phase, while others do not). And the improvement can't be attributed to the speakers being wired incorrectly at the factory, since the friend who suggested that I try this experiment owns the same speakers and experienced the exact same result. So I don't know what to attribute the improvement to.

Can anyone help with this mystery?
bryoncunningham

Showing 2 responses by eldartford

Jea48...Some driver manufacturers (JBL for example) use the oposite polarity definition (cone pulls in).
Both the woofer and tweeter are connected through a crossover which causes phase shift as a function of frequency (and order of the crossover). At the crossover frequency both drivers are equally loud. You want them to be in phase at this frequency or else they will counteract each other. If the phase difference is 180 degrees you will need to connect the two drivers with oposite polarity. If the phase difference is something other than 180 degrees neither wiring polarity is perfect. Try it both ways and pick what sounds or measures best.

Relative position of the two drivers also affects the acoustic phase. It is easy to tell when driver polarity is wrong: there will be a deep notch at the crossover frequency