# Use multimeter to determine polarity on speakers while playing?



## onefstfoknv6 (Dec 18, 2019)

Can you use a multimeter to determine polarity on wire that is unlabeled (potentially while music on)? Wires were connected to factory rears to run to amp high level in. Those bare wires will power a test 5x7, just unsure of polarity when wiring my high level adapter.


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## gijoe (Mar 25, 2008)

If it's a woofer (doesn't really work with tweeters) you can touch the wires to a battery and see which way the cone moves. Don't leave it connected, you just need to quickly touch the wires to the battery.


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## onefstfoknv6 (Dec 18, 2019)

Thanks for the input. I've seen that suggestion, but I am looking for wire polarity, not the speaker polarity.

This is what I've got:

wire loom along floorboard was tapped for left rear and right rear speakers to be used as high level inputs

the wires that I added are run under the carpet to the amp location

those wires are unlabeled 

the rear door speakers still work, and when I connect a test speaker direct those those wires I've run to the amp, it plays just as the door speakers do (polarity is not an issue here)

however, I need to connect the left and right rear +/- to the appropriate polarity on the high level harness provided with amp

can I use a multimeter to check those bare wires, prior to splicing to the high level input plug, potentially while music is playing (or otherwise)?


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## Holmz (Jul 12, 2017)

Maybe using a diode would help whole an amp is running?

But usually one just a uses a DMM lead near at amp, and then test each side at the speaker...
On the correct side with the wire is 0 ohms And the wrong side is 2, 4 or 8 ohms.


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## gijoe (Mar 25, 2008)

Oh, I misread. 

Do either of the wires have a stripe? A striped wire is typically negative.


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## onefstfoknv6 (Dec 18, 2019)

These wires are not labeled at all, I soldered to L/R rears on the loom and fed wires under carpet. Idiot/lazy move using these wires, they were just what I had.

Imagine these bare leads coming out of carpet, they are live rear speaker wires run in parallel with rears for the purpose of connecting to high level amp input. Can I not read AC voltage on the bare end while they are hot? I am just afraid to fry something checking with multimeter...


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## onefstfoknv6 (Dec 18, 2019)

This is best I've found...

Q1. Can a conventional voltmeter be used to check the unit's speaker output?
A1. Yes, set voltmeter to its AC (alternating current) selection and use that 15-volt scale you mention your meter having. Run the head unit's volume level fairly high and watch for variable meter pointer movement (or indication if the meter is a digital type) corresponding with the audio program material. The output from a head unit's speaker output is audio, that's AC voltage, so it matters not reversal of the meter's connection leads to the two wires from each of the head unit's audio channels. When wiring connection errors are a possibility it's far best to disconnect all the car's speaker wiring from the head unit so meter indications don't get confused with audio outputs for other speaker channels. 

credit Jeff Anderson: 
https://forum.miata.net/vb/archive/index.php/t-207624.html


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## gijoe (Mar 25, 2008)

onefstfoknv6 said:


> This is best I've found...
> 
> Q1. Can a conventional voltmeter be used to check the unit's speaker output?
> A1. Yes, set voltmeter to its AC (alternating current) selection and use that 15-volt scale you mention your meter having. Run the head unit's volume level fairly high and watch for variable meter pointer movement (or indication if the meter is a digital type) corresponding with the audio program material. The output from a head unit's speaker output is audio, that's AC voltage, so it matters not reversal of the meter's connection leads to the two wires from each of the head unit's audio channels. When wiring connection errors are a possibility it's far best to disconnect all the car's speaker wiring from the head unit so meter indications don't get confused with audio outputs for other speaker channels.
> ...


This will not tell you anything about the wiring polarity. Did I read correctly that these wires will be the high level inputs for an amp?


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## onefstfoknv6 (Dec 18, 2019)

gijoe said:


> This will not tell you anything about the wiring polarity. Did I read correctly that these wires will be the high level inputs for an amp?


Yes you did. Should I just wire the high level input adapter to the bare leads and try it? Is polarity important in wiring the adapter? Or, do I just need to match the polarity orientation between channels? 

Image from amp manual:


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## gijoe (Mar 25, 2008)

If you are feeding those wires into the high level inputs of an amp, you don’t really need to worry about polarity. If one speaker ends up wired in reverse polarity then you can just swap the speaker wires and put it back into the same polarity as the other speaker. 

I'm not not sure what that warning is getting at. If you have speakers wired in opposite polarity, they will be 180 degrees out of phase. This does not result in "complete loss of signal" but it will reduce the bass, because there will be destructive interference with the sound waves. Wire it however you want, then once you've connect the speakers flip the wires on one of the speakers. Do that back and forth a couple of times, and whichever configuration gives the best bass will be the configuration that is wired correctly in phase.


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## onefstfoknv6 (Dec 18, 2019)

gijoe said:


> If you are feeding those wires into the high level inputs of an amp, you don’t really need to worry about polarity. If one speaker ends up wired in reverse polarity then you can just swap the speaker wires and put it back into the same polarity as the other speaker.
> 
> I'm not not sure what that warning is getting at. If you have speakers wired in opposite polarity, they will be 180 degrees out of phase. This does not result in "complete loss of signal" but it will reduce the bass, because there will be destructive interference with the sound waves. Wire it however you want, then once you've connect the speakers flip the wires on one of the speakers. Do that back and forth a couple of times, and whichever configuration gives the best bass will be the configuration that is wired correctly in phase.


Kind of what I was hoping you would say. I'll report back.


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## F150Man (Apr 14, 2017)

Can you not see the color of the wires you connected to ? Are you sure the rear output of the stock headunit is full range ? If it is for a sub amp, may not have a full bass signal. If it is for a full range amp, you might get a bandpassed signal.


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## onefstfoknv6 (Dec 18, 2019)

Makin' music now! Hooked it up properly the first time. Took it apart and tried an alternate config, got worse. 

Thanks to all that provided input.


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## gijoe (Mar 25, 2008)

onefstfoknv6 said:


> Makin' music now! Hooked it up properly the first time. Took it apart and tried an alternate config, got worse.
> 
> Thanks to all that provided input.


Just to clarify, either way will make music, and the difference won't likely be obvious expect for in the lower frequencies. As long as you are certain with the results of your A B test, you're good, but be aware that the differences will really only be obvious in the low frequencies, so make sure you've tested thoroughly before deciding on the correct polarity.


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## onefstfoknv6 (Dec 18, 2019)

F150Man said:


> Can you not see the color of the wires you connected to ? Are you sure the rear output of the stock headunit is full range ? If it is for a sub amp, may not have a full bass signal. If it is for a full range amp, you might get a bandpassed signal.


When I soldered yes. Wrapped the + in tape. When I pulled under carpet I lost tape, didn't realize until I buttoned everything up. Just too lazy/stubborn to pull those wires back through and check it. Also, was genuinely curious if there was a method to verify with multimeter.


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## Shadow_419 (Aug 1, 2018)

You could use meter to check for continuity, and if you have the car harness wiring chart determine which is + or -


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## gijoe (Mar 25, 2008)

Shadow_419 said:


> You could use meter to check for continuity, and if you have the car harness wiring chart determine which is + or -


The problem is that he doesn't have access to the OEM wires. He soldered his own onto the OEM wires, then buried them under the carpet, leaving only the unmarked add on wires exposed. Continuity doesn't help determine the polarity.


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## Shadow_419 (Aug 1, 2018)

Just a way. Not the easiest but if he has wiring diagram it would be correct. Tbh he could check continuity from the radio harness back if there isn't a factory amp/processor involved. Just not the easiest way


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## gijoe (Mar 25, 2008)

Shadow_419 said:


> Just a way. Not the easiest but if he has wiring diagram it would be correct


But, what good will the wiring diagram do if he doesn't know which wire is which? He'd still have 2 un-labeled wires to work with. Am I missing something?


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## Shadow_419 (Aug 1, 2018)

gijoe said:


> But, what good will the wiring diagram do if he doesn't know which wire is which? He'd still have 2 un-labeled wires to work with. Am I missing something?


It's not like he can't check for continuity. Like I said it's just not as easy as labeled wires. Another alternative is an o-scope but that's way harder than wiring diagram and continuity


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## gijoe (Mar 25, 2008)

We don't need to take this too far off the rails, because it sounds like he's got the problem resolved, but I'm just trying to figure out if I'm totally missing something. Both wires will be the same, wouldn't they? The audio signal is AC, not DC, so you can't just put a meter on and get a positive or negative voltage reading. If there is a way to figure out the polarity using your recommendation it would be really helpful for some people, I just don't understand how measuring continuity and using a diagram will help.


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## Shadow_419 (Aug 1, 2018)

The wiring diagram will give you the + and - designation of the signal. Continuity will let you know which wire is which. ie if wiring harness color red is + and you have continuity from red to whatever unmarked wire in the trunk, that is the +.


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## gijoe (Mar 25, 2008)

Both wires will have the same signal, and since he can’t see which one is red, I don’t see how that will work. When you say measure continuity, what do you mean? Measure the resistance? Or voltage? Either way, both wires will be the same. And, if he could see the color of the wire to match it to the diagram he would already know which one was positive and which was negative


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## Shadow_419 (Aug 1, 2018)

Continuity mode on a multi meter emits a voltage on one probe and if picked up on the other probe you get a tone or beep. This let's you know you have a continuous circuit. If red is + and is connected to unmarked cable, continuity will let you know which wire it is on the other end.


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## gijoe (Mar 25, 2008)

Shadow_419 said:


> Continuity mode on a multi meter emits a voltage on one probe and if picked up on the other probe you get a tone or beep. This let's you know you have a continuous circuit. If red is + and is connected to unmarked cable, continuity will let you know which wire it is on the other end.


Both wires will have continuity. We already know it’s a continuous circuit, we just don’t know which wite is + and which is -. Both will measure the same. 
Tht test will yield the same results on both wires.


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## Shadow_419 (Aug 1, 2018)

gijoe said:


> Both wires will have continuity. We already know it’s a continuous circuit, we just don’t know which wite is + and which is -. Both will measure the same.
> Tht test will yield the same results on both wires.


Disconnect your speaker wire from your amp and speakers. Will you still have a continuous circuit? Put a voltage on one of the wires, will you get continuity on both?


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## gijoe (Mar 25, 2008)

Shadow_419 said:


> Disconnect your speaker wire from your amp and speakers. Will you still have a continuous circuit? Put a voltage on one of the wires, will you get continuity on both?


Disconnect the speaker/amp/dsp and put a meter on wire A and you’ll get the same result that you’ll get with wire B.


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## gijoe (Mar 25, 2008)

I guess the question is, what difference will you see between the two wires that will tell you which is positive and which is negative?


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## Shadow_419 (Aug 1, 2018)

You're not understanding how continuity mode works. Two conductor wire. If you put voltage on wire 1, wire 2 will have no signal on it. When you put a meter on continuity mode you will not get a signal on both wires.


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## gijoe (Mar 25, 2008)

Shadow_419 said:


> You're not understanding how continuity mode works. Two conductor wire. If you put voltage on wire 1, wire 2 will have no signal on it. When you put a meter on continuity mode you will not get a signal on both wires.


But that requires you to have access to the wire further up the path. If we had access to that we wouldn’t need to have this conversation.


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## Shadow_419 (Aug 1, 2018)

Like I said it isn't the easiest way. But you can always pull the wiring harness from the head unit. Can't get more upstream than that


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## Sine Swept (Sep 3, 2010)

I think one of the first posts said to use a battery. Take the leads you have created and with the system all turned off, tap the speaker wire to a 9 volt battery. Observe the movement of the speaker that is tied into your speaker wire. When tapping + to + and - to - the cone of the speaker will move forward towards you. This will show you polarity. I have a 9 volt battery in a plastic case with a momentary switch and leads for doing just this.


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## Holmz (Jul 12, 2017)

Shadow_419 said:


> You're not understanding how continuity mode works. Two conductor wire. If you put voltage on wire 1, wire 2 will have no signal on it. When you put a meter on continuity mode you will not get a signal on both wires.


If the OP was talking about the amp to speaker I mentioned in post #4 there about to check resistence between the + at the amp and the speaker.
The plus side will have zero ohms on a wire with continuity.
If he tests the other post he will be testing the wire's zero ohms, and the speaker's 4 ohms... and he will see 4 ohms...

Then he grabs a some tape and a pen, or swaps the wires at the amp.



gijoe said:


> ...
> 
> .... If you have speakers wired in opposite polarity, they will be 180 degrees out of phase. This does not result in "complete loss of signal" but it will reduce the bass, because there will be destructive interference with the sound waves...


The mid bass and tweeters will have a dry and airy sound like the music is inside of one's head.


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## gijoe (Mar 25, 2008)

Holmz said:


> If the OP was talking about the amp to speaker I mentioned in post #4 there about to check resistence between the + at the amp and the speaker.
> The plus side will have zero ohms on a wire with continuity.
> If he tests the other post he will be testing the wire's zero ohms, and the speaker's 4 ohms... and he will see 4 ohms...
> 
> ...


Maybe, but typically an out of phase speaker will only show issues in the lower frequencies. In the high frequencies that the tweeters are playing we don't hear phase well, so a tweeter that is out of phase is much more difficult to hear than a midbass that is out of phase. 

Focal has some demo discs with "in phase" and "out of phase" tracks that can be used to check to ensure that speakers are in phase. 

I don't see it being possible to use a mutimeter to determine the polarity in the OP's case.


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## Holmz (Jul 12, 2017)

gijoe said:


> Maybe, but typically an out of phase speaker will only show issues in the lower frequencies. In the high frequencies that the tweeters are playing we don't hear phase well, so a tweeter that is out of phase is much more difficult to hear than a midbass that is out of phase.
> 
> Focal has some demo discs with "in phase" and "out of phase" tracks that can be used to check to ensure that speakers are in phase.
> 
> I don't see it being possible to use a mutimeter to determine the polarity in the OP's case.


Well one normally use a 2 channel oscilloscope... 

If he cannot hear it out of phase, then the one could argue that the phase does not matter.


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## sqshoestring (Jun 19, 2007)

Don't make this harder than it is. Out of phase only affects when other speakers are playing the same frequency. So overlap in xover range will be cancelled out partially. Sometimes you want this, sometimes you don't, sometimes you only run one tweeter or mid out of phase. With subs and mids play a tone in the xover range and out of phase will weaken response, same with two subs or mids. To check wires you can put a battery on the speaker to see what wire is positive, or battery on the wires to amp, assuming you can see the speaker cone. Don't do this with small speakers or tweets of course, is my recommendation. I like to use a 9v battery. Changing phase on tweets is a tuning issue and more complex, for mid to sub it is a cancellation issue. If you have a peak at your xover of say 50Hz you could run subs out of phase to kill it for example. If you want it full output at 50 you run them all in phase. Assuming you can't fix it with xover and EQ adjustments. If you play a bass tone at a set volume level you should easily hear the difference of output from in to out of phase.

Yes you need a scope to see it with tones or music, a meter will not work. You can test a wire easily with a meter on ohms. 0 ohms is dead short, or close to it as some meters don't like zero. If you have a 4 ohm speaker and see something around 4 ohms then it is going through the voice coil too and you are testing to the other side of the speaker.

I generally check phase when I wire, but I don't worry about it that much. Swapping phase and listening is easy to do and you might find a better tune for your system. Use the fade and balance you can isolate a speaker out of phase by listening. Playing the right tone makes it easy.


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## gijoe (Mar 25, 2008)

The OP resolved the issue. But to summarize and compile everyone's input:

The problem- OP needed to check polarity of the wires carrying the signal, and he didn't have access to the OEM wire upstream to check for markings. He had 2 wires, with no labels, and needed to know which was positive, and which was negative.

Testing polarity in this case cannot be done with a multimeter. It can be done with an o-scope, but not many people have those (and for car audio, I think they are totally unnecessary).

If he was checking the polarity of the speaker (like I thought after reading the first post), a battery can be used. This will show which terminal on the speaker is positive and which is negative, and not helpful to the OP in this case.

The solution is to wire the speakers (I'm assuming here that the OP had 2 speakers that he was dealing with, left and right, and that both sides had 2 unlabeled wires) then swap the wires on one of the speakers and listen for a difference in the low end response. This is easier with a woofer, since phase issues are easier to hear. This cannot be done by only wiring 1 speaker because phase is relative, a single speaker wired in correct or reverse polarity will sound exactly the same. Polarity/phase is only an issue with 2 or more speakers playing the same frequencies.

There are some good tips in the thread, some helpful to the OP, some not helpful to the OP, but potentially helpful to someone else.


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## Holmz (Jul 12, 2017)

gijoe said:


> The OP resolved the issue. But to summarize and compile everyone's input:
> 
> ...
> 
> ...


You're a good man for helping him... The grinch types also abound around now.

However *totally* seems a bit strong, now that a good case has been identified.


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