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Author Topic: Reverse Polarity  (Read 2912 times)

aml25

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Reverse Polarity
« on: April 13, 2010, 11:13:14 am »

Hi, I was wondering something about reversing an audio polarity.

If I cut open a mic cable and connect wire A(red) to wire B(black) and then B to A I know that I have reversed the polarity, but will this create a waveform that is an inversion of the audio source? Or is it all relative and only actually inverted if there are 2 recording sources.

In other words, will doing this achieve the effect of "noise canceling" if you hear the sound from the microphone with switched wires and the actual sound from the source all in the same phase.

Thanks,
Adam
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Podgorny

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Re: Reverse Polarity
« Reply #1 on: April 13, 2010, 01:52:47 pm »

Adam,

You're thinking too hard about this.
Reversing the hot and cold wires simply means that a positive input on one end will result in a negative on the other, and vice versa.

As in, say a microphone on top of a drum puts out a signal whose initial transient is negative (as can be seen on the waveform display). If you swap pin2 and pin3, you will see the waveform go up (positive) instead.

Doing can be used to create positive reenforcement between two microphones that are micing the same source from opposite directions (the most common application being top and bottom snare mics).

To answer your question about noise canceling, inverting phase of one microphone can also be used to lessen bleed by using differential signaling between two microphones - but this can get messy pretty fast...
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"Nobody cares what the impedance is; all they care about is when you can walk into the room, set up a mic, turn the knobs, hit record, and make everybody go 'wow.'"

aml25

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Re: Reverse Polarity
« Reply #2 on: April 13, 2010, 02:57:47 pm »

Right, I understand that

I am still confused though about something else, let me try to explain.

Say there is a speaker producing a sine wave. For arguments sake lets say it starts at its peak at +2 and then drops to 0 then to -2 then back to 0 and so on.
If I have a microphone picking up this sound (the wires are unaltered) will it produce a wave that starts at its high (peak)? And therefore, if I switch the wires will  it then produce a wave that starts at its low, in other words the opposite polarity (or phase?) as the initial source?


I hope that is clear,

Thanks,
Adam
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Podgorny

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Re: Reverse Polarity
« Reply #3 on: April 13, 2010, 03:47:12 pm »

aml25 wrote on Tue, 13 April 2010 13:57

If I have a microphone picking up this sound (the wires are unaltered) will it produce a wave that starts at its high (peak)? And therefore, if I switch the wires will  it then produce a wave that starts at its low, in other words the opposite polarity (or phase?) as the initial source?



That is correct.


And just to clarify (or further confuse), polarity and phase are different.  What you are describing is inversion of polarity.  Phase is used to describe the relationship between multiple signals.
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"Nobody cares what the impedance is; all they care about is when you can walk into the room, set up a mic, turn the knobs, hit record, and make everybody go 'wow.'"

aml25

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Re: Reverse Polarity
« Reply #4 on: April 13, 2010, 04:04:50 pm »

Yeah I read an article on the homepage of this site, which led to me this forum, about polarity and phase but I was still confused since everywhere seems to call this phase reversal not polarity, even Bose.

Thanks a lot for your help.

- Adam
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Podgorny

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Re: Reverse Polarity
« Reply #5 on: April 13, 2010, 04:25:52 pm »

Hey Adam,

I hope what I wrote made sense.
Please stick around and check out the other forums.  There's lots of info from people much smarter than I floating around here.


Kyle
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"Nobody cares what the impedance is; all they care about is when you can walk into the room, set up a mic, turn the knobs, hit record, and make everybody go 'wow.'"

aml25

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Re: Reverse Polarity
« Reply #6 on: April 13, 2010, 04:28:41 pm »

Yeah definitely, I only found this forum today actually but I will definitely be sticking around. Thanks
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Hallams

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Re: Reverse Polarity
« Reply #7 on: April 13, 2010, 06:36:49 pm »

It can be a good idea to check the mics in your collection for their polarity to see which ones suck when they should push..... Twisted Evil
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Chris Hallam.
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Berolzheimer

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Re: Reverse Polarity
« Reply #8 on: April 15, 2010, 07:06:18 pm »

aml25 wrote on Tue, 13 April 2010 13:04

Yeah I read an article on the homepage of this site, which led to me this forum, about polarity and phase but I was still confused since everywhere seems to call this phase reversal not polarity, even Bose.

Thanks a lot for your help.

- Adam


Welcome to the forums, Adam.  I think you'll find in the world of professional audio that the Bose company is hardly ever referenced as an authoritative source of technical information or terminology.
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Josh McArdle

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Re: Reverse Polarity
« Reply #9 on: April 16, 2010, 01:27:03 am »

Quote:

 Welcome to the forums, Adam.  I think you'll find in the world of professional audio that the Bose company is hardly ever referenced as an authoritative source of technical information or terminology.



Hehehe  Very Happy
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