Speaker phase meter: any idea?

Hi all,

it's possible to create one audio phase tester instr with arduino, like http://www.rolandhigham.co.uk/phcheck1.html ?

There is already some project?

thanks again


That should be possible.

Just make sure you [u]bias[/u] the Arduino's input because the Arduino can't read negative voltages (and it can be damaged by negative voltages). Or, the SparkFun microphone breakout board has a biased output (but it doesn't have variable gain). And, you'll need a preamp if you're not using an amplified breakout board.

I scanned the article, but I didn't study it. Here's what I think is tricky -

  • The polarity of microphones & speakers isn't always consistent, nor is the polarity through amplifiers or other audio equipment. Most of the time that's not a problem since audio is AC, as long as both (or all) channels pass-through the same equipment and the relative phase/polarity is the same through both (all) speakers.

If there is a polarity reversal somewhere in your system, you may want to leave it that way (a long as everything matches). ...If you "fix it" by reversing the polarity of your speakers that might cause confusion in the future when someone "fixes" your reversed speakers

  • In speakers, the speaker polarity of the tweeter in a 2-way system is usually flipped, or the midrange in a 3-way system, etc. That's because the crossover introduces a phase-lag in the lower frequency driver and phase-lead in the higher-frequency driver... And by flipping the polarity, you can bring them back into-phase at the crossover point.

So... If you send a pulse into a speaker some of the frequency components will be phase-shifted and/or inverted. And, speakers/microphones are not great with pulses anyway, so you're analyzing a messed-up waveform.

And if you mix-and-match different speaker systems, they may be in-phase at some frequencies and out-of-phase at other frequencies (and you have to decide which polarity is best by-ear).

P.S. The bottom line is, if you put a positive pulse into your system, the microphone will put-out a voltage that goes positive and negative. The question is, does it go more positive than negative or is there a way to get the polarity from this signal...

A very simple phase tester is a battery. Watch the direction the speakers move. Step all the way through the system. I know a guy who said he could hear absolute polarity. Never tested to see if he could.