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Discussion Starter #1
I noticed something very odd. When I do a measurement of both my speakers at once, I noticed the measurements from 6khz and up is wildly inconsistent. Sometimes the measurement for both speakers will be lower than the measurement for the individual speakers! Other times it will look the way I expect it too with the combined response being higher than those of the individual speakers. If I just pick up the mic then place it down in the exact same place (I know its exactly the same place because I have it marked), the high freq measurement will again change. When I measure each speaker by itself, the high freq measurement is very consistent.

I have spent many hours moving my speakers around trying to get a good high freq response but now I am beginning to think I've been wasting my time.

Anyone else experience this?
 

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If I understand, you’re getting different results from one measurement to the next, both when you measure the speakers separately, and when both are measured simultaneously? And the speakers and mic remain in the exact same location during the measurement session?

It might be helpful to know if you point the mic at the ceiling or at the speakers, and if you’re using a 0° or 90° calibration file.

Regards,
Wayne

 

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Discussion Starter #3 (Edited)
Thank you Wayne. Yes, if I measure both my speakers together without changing anything the freq response from 6khz up is inconsistent. Everywhere else looks very much the same. I am using the Umik pointed straight ahead and the 0 deg calibration file.

Just now, I took a measurement, moved the mic forward by 1", took another measurement, moved it back to the exact same spot as before, took another measurement and the high freq response was lower by around 3db. Everywhere else the graph was exactly the same.
 

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If you run two speakers at the same time you will see comb filtering due to any difference in the distance from the mic to each speaker (that difference in distance corresponds to a phase shift, at frequencies where the phase shift reaches 180 degrees the signals from the two speakers cancel each other). In that circumstance even very small movements of the mic can give very different results at high frequencies. If you get consistent results when measuring a single speaker then there's nothing to worry about.
 

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Discussion Starter #6
If you run two speakers at the same time you will see comb filtering due to any difference in the distance from the mic to each speaker (that difference in distance corresponds to a phase shift, at frequencies where the phase shift reaches 180 degrees the signals from the two speakers cancel each other). In that circumstance even very small movements of the mic can give very different results at high frequencies. If you get consistent results when measuring a single speaker then there's nothing to worry about.
Thank you John. Yes, when measuring both speakers at the same time I limit it to 5K where it seems the results are more less susceptible to small changes to the mic. For higher freq, I actually now use the signal generator and spl meter to manually measure the range from 5k-20k.
 

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Measuring high frequency response with more than one speaker playing tells you nothing of any use, don't take any account of such measurements. It is not at all representative of what you would hear with your head where the mic is.
 
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