Audio Polarity Test

This is a demonstration showing that it's not difficult to hear the effect of inverting the polarity of an audio signal.  Some argue that the polarity doesn't matter as long as phase between channels is maintained.  Here's your chance to find out if you can hear a difference.

The test consists of a 16-bit, 44.1 kHz mono WAV file about ten seconds long.  It was created using the waveform generator function of Cool Edit.  I inverted the polarity after about five seconds to simulate the effect of reversing the polarity of a mic (switching pins 2 and 3 of an XLR connector) or reversing the leads to both speakers.   Here's what it looks like:
 
 

      Original polarity                    Reversed polarity
 
During the original polarity portion, for a properly wired system,  the speaker cone will move outward very quickly (the vertical line), then move slowly back to its original position (the slanted line).  When the polarity switches, the cone moves outward slowly and moves back quickly.

Thinking about it this way, it's not surprising that the sound changes when the polarity is inverted, yet this is no different than swapping speaker wires, something that's usually thought to not matter.

Here's the test file.  Download a copy, load it into any WAV file player or editor, and play it through any speakers you can reach with the signal.  On three speakers here, including the Radio Shack Minimus 7's I have on my surfin' computer, the original polarity signal sounds more "bassy" than the inverted signal.

 poltest.wav for MS-DOS systems

 poltest.au for Sun systems

This (the master) site has been accessed times since the beginning of this year.

Drop me a note and let me know what you hear
 
 

Mike Rivers

Mike Rivers (mrivers@d-and-d.com)