# identifying driver polarity



## kev (Mar 28, 2010)

how do we know the driver has invert polarity or not from the graph? what should i see? the phase in the spl and phase graph?

thanks a lot


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## JohnM (Apr 11, 2006)

Easiest is to look at the impulse response in % FS mode to see if the peak is positive or negative. That assumes you are measuring a single driver, or if measuring a multiple drive unit speaker you restrict the sweep range to the crossover range of the driver you are interested in.


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## kev (Mar 28, 2010)

Thank you very much John,another question that i want to ask,if we build the stereo 2 channel system,the loudspeakers are 3ways and we use active x over such behringer dcx,and we use multi channel amp.we need to get the proper center image,say the vocalist located in the middle between the 2 loudspeakers.what should we do?,allign the impulse response each speaker driver's left and right or any other way that should we do?.

once more thank you very much for the help


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## Moonfly (Aug 1, 2008)

Just our of interest Kev, why would you use REW to check polarity rather than say, a 9v battery?


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## kev (Mar 28, 2010)

Moonfly said:


> Just our of interest Kev, why would you use REW to check polarity rather than say, a 9v battery?




Hi Moonfly,i'm using accuton C50 for midrange driver,they have very small execursion,so i can't see their cone movement.
and also i build full active 3ways loudspeaker for my stereo system,and REW help me much for tuning :bigsmile:


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## JohnM (Apr 11, 2006)

kev said:


> another question that i want to ask,if we build the stereo 2 channel system,the loudspeakers are 3ways and we use active x over such behringer dcx,and we use multi channel amp.we need to get the proper center image,say the vocalist located in the middle between the 2 loudspeakers.what should we do?,allign the impulse response each speaker driver's left and right or any other way that should we do?.


You could do that, but you would first have to check the box in the Analysis preferences to use a loopback connection as a timing reference so your measurements have an absolute time reference (and connect a loopback of course). In practice though you would probably be just as successful adjusting channel delays by ear or according to the measured distances (if you are trying to compensate for unequal distances).


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## Moonfly (Aug 1, 2008)

kev said:


> Hi Moonfly,i'm using accuton C50 for midrange driver,they have very small execursion,so i can't see their cone movement.
> and also i build full active 3ways loudspeaker for my stereo system,and REW help me much for tuning :bigsmile:


Ah that makes sense, sometimes I find it difficult to think outside of the (subwoofer) box.


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## kev (Mar 28, 2010)

JohnM said:


> You could do that, but you would first have to check the box in the Analysis preferences to use a loopback connection as a timing reference so your measurements have an absolute time reference (and connect a loopback of course). In practice though you would probably be just as successful adjusting channel delays by ear or according to the measured distances (if you are trying to compensate for unequal distances).



Thank you very much John


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## kev (Mar 28, 2010)

JohnM said:


> Easiest is to look at the impulse response in % FS mode to see if the peak is positive or negative. That assumes you are measuring a single driver, or if measuring a multiple drive unit speaker you restrict the sweep range to the crossover range of the driver you are interested in.



i'm sorry for ask again,which peak is to see?,the highest peak or the first peak?,can you give me an example?.
because some time the graph show a little deep at first and then the go peak.
thank you very much


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## JohnM (Apr 11, 2006)

kev said:


> the highest peak or the first peak?


The highest.


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## kev (Mar 28, 2010)

thank you John


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## kev (Mar 28, 2010)

would you please to give me a little bit information about ETC?, what is the function and how to interpreting them?

thank you


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## JohnM (Apr 11, 2006)

The ETC shows the _envelope_ of the impulse response, this wikipedia article has some good images showing what is meant by a signal's envelope: http://en.wikipedia.org/wiki/Envelope_detector

Viewing the envelope rather than the raw impulse makes reflections easier to identify and makes following the decay of the impulse level easier.


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