Loudspeaker polarity checker? - Page 1
Forum section: electronics / testgear

author: cvanc
author_rank: Frequent Contributor
timestamp: September 29, 2015, 03:25:57 pm
content: 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; and3- Walk around with a microphone on a stick, probing the nearfield of each speaker in turn, and deriving a polarity indicationSo 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.

author: Delta
author_rank: Super Contributor
timestamp: September 29, 2015, 03:33:41 pm
content: 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...

author: Jeroen3
author_rank: Super Contributor
timestamp: September 29, 2015, 03:59:12 pm
content: The problem has to do with cancellation, right?Maybe there is a method to measure the phase of the audio signal between two speakers.

author: Electro Fan
author_rank: Super Contributor
timestamp: September 29, 2015, 04:05:47 pm
content: If you don't find the answer here try the speaker forums at:www.audioasylum.comwww.audiogon.com

author: zapta
author_rank: Super Contributor
timestamp: September 29, 2015, 04:11:21 pm
content: 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 wavehttp://newt.phys.unsw.edu.au/jw/sound.spectrum.html

author: Fungus
author_rank: Super Contributor
timestamp: September 29, 2015, 04:12:30 pm
content: Quote from: Delta on September 29, 2015, 03:33:41 pmWhy? 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...

author: electr_peter
author_rank: Unknown
timestamp: September 29, 2015, 04:41:22 pm
content: 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.

author: davorin
author_rank: Unknown
timestamp: September 29, 2015, 05:11:00 pm
content: 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;

author: hayatepilot
author_rank: Frequent Contributor
timestamp: September 29, 2015, 05:27:28 pm
content: 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

author: _Wim_
author_rank: Super Contributor
timestamp: September 29, 2015, 06:00:19 pm
content: 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.

author: nfmax
author_rank: Super Contributor
timestamp: September 29, 2015, 06:09:33 pm
content: Quote from: hayatepilot on September 29, 2015, 05:27:28 pmI 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.

author: kripton2035
author_rank: Super Contributor
timestamp: September 29, 2015, 06:27:00 pm
content: my denon avr 19xx or 21xx video power amplifier has a measurment microphone that adjusts the frequency response to the room it is installedI 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...

author: Fungus
author_rank: Super Contributor
timestamp: September 29, 2015, 07:00:35 pm
content: Quote from: zapta on September 29, 2015, 04:11:21 pmSawtooth works too. Use Audacity to create a wav file with a half hour long sawtooth wave.

author: MattFL
author_rank: Contributor
timestamp: September 29, 2015, 07:25:55 pm
content: 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.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 29, 2015, 07:36:41 pm
content: 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.

author: necessaryevil
author_rank: Regular Contributor
timestamp: September 29, 2015, 07:50:55 pm
content: 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

author: SL4P
author_rank: Super Contributor
timestamp: September 29, 2015, 09:51:25 pm
content: 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?

author: SL4P
author_rank: Super Contributor
timestamp: September 29, 2015, 10:55:16 pm
content: Exactly.That's why it occurred to me at the end of the first post!Thx

author: verbatone
author_rank: Contributor
timestamp: September 30, 2015, 01:43:58 am
content: I don't get it....red to red and black to black, right?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2015, 02:06:22 am
content: 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.

author: SL4P
author_rank: Super Contributor
timestamp: September 30, 2015, 03:09:45 am
content: Quote from: verbatone on September 30, 2015, 01:43:58 amAlmost.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!

author: forrestc
author_rank: Unknown
timestamp: September 30, 2015, 04:04:43 am
content: Quote from: cvanc on September 29, 2015, 03:25:57 pmIs 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.

author: andtfoot
author_rank: Unknown
timestamp: September 30, 2015, 04:46:09 am
content: Quote from: forrestc on September 30, 2015, 04:04:43 amReversed 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.

author: verbatone
author_rank: Contributor
timestamp: September 30, 2015, 05:24:36 am
content: Quote from: SL4P on September 30, 2015, 03:09:45 amI 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2015, 05:32:54 am
content: Quote from: verbatone on September 30, 2015, 05:24:36 amIt 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.

author: Mr.B
author_rank: Unknown
timestamp: September 30, 2015, 05:41:21 am
content: Quote from: Richard Crowley on September 30, 2015, 05:32:54 amI have often wondered about this... Perhaps should have Googled it...Thank you for the education Richard.

author: pickle9000
author_rank: Super Contributor
timestamp: September 30, 2015, 09:07:22 am
content: Set up another speaker (correctly wired as a reference) and mic, and record both mic's in stereo, just look at it on a scope.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: September 30, 2015, 09:33:12 am
content: Quote from: Richard Crowley on September 30, 2015, 02:06:22 amI did this plenty of times but I looked for phase cancellation at low freq!?? Typo?Quote from: forrestc on September 30, 2015, 04:04:43 amThis is right but assuming it's all about single driver 110v line speakers, yes you may as well be sure they are all in phase.The reason they sound shit (inaudible if it is a PA) is that the differing delays to each spot from multiple sound sources ie. multipathing.Best, if possible to minimise the number of sources and make them louder, so less null zones.The other one to fix inaudibles is to minimise hard surfaces and also somehow also minimise the resonances of each room.

author: commongrounder
author_rank: Frequent Contributor
timestamp: September 30, 2015, 01:24:15 pm
content: I believe the OP is talking about a distributed sound system with a large number of tranformer coupled, ceiling mounted, speakers. It is important that they be in phase with each other, or there will be "suck-outs" as a listener passes between the acoustic overlap points between them. In my installation business, I used a Sencore/Terrasonde SoundPro/Audiotoolbox. These units have a phase checker that uses a special waveform (like what EricTheNorwegian mentioned) that is triangle on the positive side and sine on the negative, with a 1khz frequency. With these units, one just walked around the room, with the acoustic measurement microphone on a boom, and hold it in front of each speaker. The toolbox would give you the polarity, along with the certainty of correctness, instantly. You could do a room full of speakers in minutes. One can still find these units on auction sites for very little money.Another thing about 70 or 100 volt distributed systems. They are often wired in a daisy chain fashion, so it is very difficult to electrically isolate one speaker without pulling it (What the OP is trying to avoid). Getting close with a microphone acoustically isolates the speaker, and is usually the easier way to check out a finished install.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 30, 2015, 01:34:03 pm
content: MY former employer used a Rolls PT102, and the schematic is out there on the web..Or just buy a Phase-It...However, there is an easy way, and its what I use.Holm Impulse is free, does more then just phase, and just needs a laptop with a sound card that can send and record at the same time. You'll of course need a appropriate mic and cabling.http://www.holmacoustics.com/holmimpulse.phpWhile a cheap microphone will give you your phase vs frequency with Holm Impulse, for commercial work you usually want something known to be calibrated.Reference mics with reasonably flat response:Home Made:http://www.johncon.com/john/wm61a/Commercial :http://www.parts-express.com/dayton-audio-emm-6-electret-measurement-microphone--390-801http://www.guitarcenter.com/dbx/RTA-M-Reference-Microphone-for-DriveRack-PA.gcNote that commercial reference mics need Phantom power. I usually use a 44$ 2 channel mixer to get Phantom Power with my RTA-M

author: LaserSteve
author_rank: Super Contributor
timestamp: September 30, 2015, 02:08:41 pm
content: Mobile Solutions has This:http://www.mobilesolutions-usa.com/store/p839/PT-9A_Kit.htmlSteve