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Discussion Starter · #1 ·
I'm trying to figure out some strange high frequency (>800Hz) waves in my room's SPL graph. In order to rule out the speakers, I did a nearfield measurement of my front left, and my center.

I'm using a CSL calibrated U-Mik1 on a boom mic stand. Using the 0 degree narrow band cal file. The mic is about 3 inches away from the tweater of my Aperion Verus Grand.

They both came out with these waves in the upper frequencies. Can anyone explain this, or tell me where to start troubleshooting?

Thanks!
 

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Nearfield measurements shouldn't look like that .

Since you are using the UMIK-1 mic , I don't know what could be causing that .

Typically, ( due to the regularity of the spacing of those deep nulls ) that would suggest input being fed to output creating a feedback loop & the resultant cancellations ( but that shouldn't be the case when using the UMIK-1 mic ) .

What Operating System are you running ?

:sn:
 

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Discussion Starter · #3 ·
Okay, thanks for confirming that something is wrong... Is 3 inches too close for a nearfield measurement?

I'm using Windows 7 (32 bit), and the ASIO4ALL drivers. I do have a laptop with Windows 7 (64 bit) that has HDMI out...so, with a bit of work, I can do another measurement using that instead which might help rule out some things, I suppose. Any chance this could be a bad USB cable? That seems unlikely. Can I mic be "bad" in this way?

Thanks again!
 

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Perhaps the problem is related to using ( an overly long ) passive USB extension cable . Doesn't miniDSP warn against this practice ?

Beyond a certain distance of desired extension ( I forget just how many feet for the various USB types ) , one needs to use an Active USB Repeater cable ( which has an amplifying component that regenerates the USB signal ).



3 inches in front of a tweeter , is a good way to measure the tweeter's ( nearfield ) response .

2 - 3ft from the speaker , is a better way to get the fully integrated response of any speaker .

:sn:
 

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Discussion Starter · #5 ·
Perhaps the problem is related to using ( an overly long ) passive USB extension cable . Doesn't miniDSP warn against this practice ?

Beyond a certain distance of desired extension ( I forget just how many feet for the various USB types ) , one needs to use an Active USB Repeater cable ( which has an amplifying component that regenerates the USB signal ).
I did have to use an extension cable in order to get the mic close enough for the nearfield measurement. But the waviness shows up when measuring the room as well, and in that case, I'm only using the cable that came with the UMik1...So that shouldn't be considered overly-long (I hope.).
 

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The fact that you saw "waviness" from an acoustic measurement is rather meaningless ( unless the waviness matched the deep nulls ) // most users see "waviness" caused by various room interactions .

The deep notches ( of the nearfield measurement ) are clearly electronic in origin .

You are going to have to eliminate all the various possibilities .

For instance, I'd capture another nearfield sweep of your tweeter / but this time move the computer close enough to allow the UMIK-1 mic to be used without an extender cable ( or insert an active USB hub between the mic & your extender cable / or buy the active cable extender that I linked to ) .

Also, try all the USB ports found on your computer ( the UMIK-1 most likely will need to be re-recognized by the USB driver before you boot-up REW, each & every time you move the mic ) .


:sn:
 

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Discussion Starter · #7 ·
The fact that you saw "waviness" from an acoustic measurement is rather meaningless ( unless the waviness matched the deep nulls ) // most users see "waviness" caused by various room interactions .

The deep notches ( of the nearfield measurement ) are clearly electronic in origin .

You are going to have to eliminate all the various possibilities .

For instance, I'd capture another nearfield sweep of your tweeter / but this time move the computer close enough to allow the UMIK-1 mic to be used without an extender cable ( or insert an active USB hub between the mic & your extender cable / or buy the active cable extender that I linked to ) .

Also, try all the USB ports found on your computer ( the UMIK-1 most likely will need to be re-recognized by the USB driver before you boot-up REW, each & every time you move the mic ) .


:sn:
The "waviness" in the room measurements looks very similar to these...in that they are far too regular to really be there...I'm planning some troubleshooting in the next few hours.
 

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Discussion Starter · #9 · (Edited)
Make sure 'Listen to this device' is not checked on the Listen tab of the Recording device properties for the UMIK-1.
I looked, it isn't checked. At the same time I checked that my Umic is set to "2 channel, 24 bit, 48000Hz", and in REW, I'm using ASIO4ALL, set to 48kHz, so it isn't a sampling rate difference either.... ???

Also, in the ASIO control panel, I haven't made any changes (so, resample isn't checked, for example)
 

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Discussion Starter · #12 ·
I re-installed windows from scratch. All is fine now. So, it was almost certainly some setting somewhere, or some driver version or something. Either way, the waves are gone now. ;-)
 
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