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Funky measurement results with UMIK-1 7 years 11 months ago #17907

  • Amnes
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Dear tech support,

I've got my second ever UMIK-1 and I'm kind of scratching my head with the results. I keep getting a steep notch on the plots.

I'm using a macbook with the latest OSX into a echo audiofire 4 firewire soundcard as the source and UMIK-1 as the mic + cal file. I tried a few power amplifiers, so these are definately not at fault. Attached are measurements of a JBL 2425H driver mounted to a 2307 horn and 2308 diffuser and a JBL 2405 tweeter. The measurement made at lower signal is of a Yamaha NS1000M running fullrange.

It seems to me something is funky. Of course up front I'm suspicious of the UMIK-1 being faulty. I had a nearly identical setup a year ago but with a different UMIK-1 and I do not remember such results. I'm open to find that some software/hardware setup is incorrectly set.

My only idea is that somehow I'm measuring with the laptops inbuilt mic, but I assume that would produce much more alarming results. The UMIK-1 was definately selected in the sound input preferences.

I'll be grateful for pointers.
Maciej
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Last edit: by Amnes.

Funky measurement results with UMIK-1 7 years 11 months ago #17920

  • john.reekie
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Hi, you have a cancellation notch caused by interference of two signals with a slight delay (71 usec if I worked it out right). See in your green plot you have the notch at 7 kHz, and then another at 21 khz (OK off the plot but you see it).

I'd try as a first step removing the echo (ominous name ;) ) soundcard from the loop and just take analog out from your macbook. Also, do you have any other kind of audio processing software running - just check that you have a "straight" audio path.

[Edit] If that makes no difference, make sure it's not a driver interference issue (does seem unlikely but it never hurts to eliminate possibilities( by doing a close-range measurement on the tweeter.
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Last edit: by john.reekie.

Funky measurement results with UMIK-1 7 years 11 months ago #17923

  • Amnes
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Many thanks John. I will try the analogue output of the macbook first up - it sounds like a smart move to exclude the soundcard/drivers out of the equasion. I did perform a loopback measurement on this card in the setup, and it came out dead flat from 2-20,000Hz IIRC, but who knows how these mistakes happen (I don't).

The attached measurements had 24db/octave smoothing applied. It's fairly interesting that various smaller peaks and notches from completely different speakers seem to resemble one another.

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