Loudspeaker polarity checker?

[cvanc]

Hi all-

I need the check the polarity of a large number of installed speakers.  Almost all of them are ceiling mounted, so pulling each one down and hand-checking the wiring is not practical.  Ideally I can find a way to:

1- Inject a test signal at the central equipment rack;
2- Route the test signal to all rooms; and
3- Walk around with a microphone on a stick, probing the nearfield of each speaker in turn, and deriving a polarity indication

So I'm looking for both a test signal source (ideally just a CD with the signal burned onto it), and a receiving/analyzing mic setup.  Does such a thing exist?

Thanks for any hints you can provide.

[Delta]

I'm not an expert in this field, but I would say: Not a chance mate. 

The only ways I know to check the polarity of a speaker require that you can actually watch the driver move...

[Jeroen3]

The problem has to do with cancellation, right?

Maybe there is a method to measure the phase of the audio signal between two speakers.

[Electro Fan]

If you don't find the answer here try the speaker forums at:

www.audioasylum.com

www.audiogon.com

[zapta]

I would think that a signal that is non symmetric for inversion and a mic + oscilloscope will allow you to tell polarity. Anything wrong with that approach?

Edit: for example an approximation of a saw wave

http://newt.phys.unsw.edu.au/jw/sound.spectrum.html

[Fungus]

I'm not an expert in this field, but I would say: Not a chance mate. 

Why? Microphones respond to positive/negative pressure waves.

Maybe you could play a binary pattern into the speaker and look at the microphone output on a 'scope. See if the signal is inverted.

Something like : 10101010 11110000 (repeat endlessly)

Maybe just: 1001001001001001001001...

[electr_peter]

The simplest way to measure speaker polarity: stick a battery on speaker wires and watch the movement direction.

Other methods could work, it all depends on the circumstances. All I know is that there are more than 10 ways to accidentally switch speaker polarity in wiring, amplifiers, software, etc. so that I do not bother about this until final installation.

[davorin]

Hmm...are those loudspeakers cabled individually?

I would go the other way around...use them as microphones....and connect the speakers to a portable DSO...clap in the hands and look at the waves (o;

[hayatepilot]

Are there multiple speakers in a room?
If not, then the polarity doesn't matter. You can't hear the absolute phase of a signal.

If there are multiple speakers one can hear if one is out of phase when you have some experience.

Greetings

[_Wim_]

If you run a swept sine like done in ARTA (farina method), and convert it to an impulse (arta does this automatically), you can see the phase of the loadspeaker by direction of the first peak/dip (see pictures). So if you first record the test signal that ARTA generates, and then play this in a loop, you should be able to record this and convert to an impulse again (I know ARTA can work with external trigger, but never used that).

So in essense I think you can do it with a laptop and the free ARTA package, together with a CD-player.

[nfmax]

Are there multiple speakers in a room?
If not, then the polarity doesn't matter. You can't hear the absolute phase of a signal.

If there are multiple speakers one can hear if one is out of phase when you have some experience.

Greetings

I used to work at Quad, the audio firm. Final test for the ESL-63 loudspeaker involved feeding a tone burst to the UUT and a reference unit, out of phase. The output from a microphone, on the axis between the two speakers, had to be nulled on a scope by adjusting only the signal level to one speaker, within a range of a dB or so. Very impressive, the first time you see it.

[kripton2035]

my denon avr 19xx or 21xx video power amplifier has a measurment microphone that adjusts the frequency response to the room it is installed
I remember this thing told me one speaker was reversed when I made the settings in my home.
so yes this is feasible, but this may require an audio DSP box which may not be so simple...

[Fungus]

I would think that a signal that is non symmetric for inversion and a mic + oscilloscope will allow you to tell polarity. Anything wrong with that approach?

Edit: for example an approximation of a saw wave

Sawtooth works too. Use Audacity to create a wav file with a half hour long sawtooth wave.

[MattFL]

Easy way;  if you can get a long wire back to the amplifier, then put a similar speaker wired properly in a sealed box with an on/off switch, to carry with you.  Walk next to a speaker you want to test playing the same tone from the same amplifier through both the ceiling speaker and the speaker in the box.  With your head about half way between them, turn the box speaker on and off.  If both speakers on is louder, the ceiling speaker is wired properly.  If both speakers on gets really quiet, the ceiling speaker is wired backwards. 

If you want to get complicated; I can't remember what it's called, but a company used to make speakers with a coil on top to sense cone movement.  This was connected back to the amplifier for feedback.  The amplifier would compare the feedback to its input signal and try to adjust its output so the feedback would more closely match the input signal, for more accurate sound.  I can't remember the product name or the company, maybe Alphasonik?  Anyway, maybe you could come up with something similar.  A little coil you could hold up to the center of the speaker (over the voice coil) while a tone is playing. On a scope compare the feedback from your coil to the input signal to the amplifier to see if they're in our out of phase. 

[AndyC_772]

Could you have both a small speaker and a mic on the same stick?

The mic normally picks up the sound from the speaker, which plays a continuous test tone. As you bring the pair near a particular ceiling speaker, the level picked up by the mic should simply get louder, monotonically with distance.

If, however, it gets quieter before it gets louder, then the two speakers are interfering destructively. There will be a quiet spot where the sounds cancel out, which you should be able to detect.

[necessaryevil]

Try the phone app in the link below. I don't know if it will work, try it out on speakers with known polarity first.
https://play.google.com/store/apps/details?id=com.dwa_ict.polaritychecker

[SL4P]

I'm surprised that nobody responded to the earlier post of using the individual speakers as a microphone, and looking at the waveform on e cable...?
Also, are these on a 70V or 100v PA speaker line, or simple point to point wiring?

[SL4P]

Exactly.
That's why it occurred to me at the end of the first post!
Thx

[verbatone]

I don't get it....red to red and black to black, right?

[Richard Crowley]

If these speakers are in the same room, you can play a high frequency tone through the system and walk between the speakers to hear if there is a zone of cancellation.
If they are in different rooms, it makes no difference, and you can get on with your life.

If you still really want to know the absolute polarity of the speakers, you can create a saw-tooth wave signal on your computer and play it back through the system. Then look at the microphone output waveform to see if it is inverted or right-side up.

[SL4P]

I don't get it....red to red and black to black, right?

Almost.
True if the drivers are physically on or near the same axis, but if - for example - the drivers are back-to-back in some mounting scenarios, they may be wired out of phase with each other!

[forrestc]

I need the check the polarity of a large number of installed speakers.  Almost all of them are ceiling mounted, so pulling each one down and hand-checking the wiring is not practical.

Is there a reason why you believe this is necessary?

In the situation you seem to be describing, phase may not be necessary to match at all, and an out of phase signal may actually be  more correct than an in phase one.   The reason being that the wavelength of sound traveling through the air is very short..  For instance a 1 kHz tone has a wavelength of just over a foot in room temperature air.  That means the phase reverses every 6 inches or so.   Unless your listener is going to be in a specific spot, being this picky about phase isn't really worth it.

From personal experience often the best performance out of a multiple speaker system installed in a building is obtained simply by a trained ear walking the site and reversing speakers where there seems to be a phasing issue which might be removed by flipping the speaker phase.

In large live sound systems such as those used in a concert, multiple speaker locations are used, and the signal to each speaker is actually intentionally delayed such that the signal is exactly in phase with the main speakers on or near the stage. 

[andtfoot]

I need the check the polarity of a large number of installed speakers.  Almost all of them are ceiling mounted, so pulling each one down and hand-checking the wiring is not practical.

Is there a reason why you believe this is necessary?

In the situation you seem to be describing, phase may not be necessary to match at all, and an out of phase signal may actually be  more correct than an in phase one.   The reason being that the wavelength of sound traveling through the air is very short..  For instance a 1 kHz tone has a wavelength of just over a foot in room temperature air.  That means the phase reverses every 6 inches or so.   Unless your listener is going to be in a specific spot, being this picky about phase isn't really worth it.

From personal experience often the best performance out of a multiple speaker system installed in a building is obtained simply by a trained ear walking the site and reversing speakers where there seems to be a phasing issue which might be removed by flipping the speaker phase.

In large live sound systems such as those used in a concert, multiple speaker locations are used, and the signal to each speaker is actually intentionally delayed such that the signal is exactly in phase with the main speakers on or near the stage.

Reversed polarity isn't the same as being 180° out of phase; think what happens with asymmetrical signals, such as the sawtooth mentioned a few times so far, when it's delayed vs. when it's flipped.

[verbatone]

I don't get it....red to red and black to black, right?

Almost.
True if the drivers are physically on or near the same axis, but if - for example - the drivers are back-to-back in some mounting scenarios, they may be wired out of phase with each other!

I was joking, of course.  JBL in the 60s (maybe even 70s) used red for the negative terminal of their speakers...why?, i don't know. There are a hundred ways to measure phase response of a speaker, but if you just want to know the polarity of the speaker coil windings, just use a small DC source as others have suggested.  But really this is one of those discussion where everyone is an expert, so I'll stay out of the discussion from now on.

[Richard Crowley]

JBL in the 60s (maybe even 70s) used red for the negative terminal of their speakers...why?,

It was not uncommon to find woofers and tweeters connected anti-polarity vs. each other.
The reason being that certain kinds of crossovers produced a phase shift that amounted to 180 degrees at the crossover frequency.
So connecting the drivers anti-polarity produced phase-coherent response through the critical crossover frequency.