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post #1 of 3 Old 01-08-16, 11:06 AM Thread Starter
TEK
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Join Date: Jan 2011
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Bad measure?

Hi

I have build a couple of speakers and was measuring them to verify that they behaved as I expected.
The speakers have two bass elements (8 1/4" Wavecore elements).
To measure the elements I did a near field measurement right between the two speakers, so that room modes should not influence the measurement.
I got some strange behaviour between 20-30 hz that the theoretical models can not explain.
Then, to check, I also measured my sub near field (5-10cm from the cone). I'm getting the exact same pattern from the sub.
Please see attachments. The first picture is the speakers, the second is the sub.

This makes me believe that there are something going on between 20-30hz
I would guess the most likely reasons are
1) that room-modes influences the measuring (even it should not as they are near-field?)
2) there are something bad with my microphone, or some other part of the measuring setup

My measuring setup is: Behringer 502 mic-amp, EMM-6 microphone, the mic-amp is connected to my pc trough a asus xonar sound card. Rew generates test tones by sending signal to my receiver (Marantz SR7005) trough hdmi.

Can this be caused by room modes?
Is there something I can look at in the REW measurments to check if this is room modes or if it's likely that it is something else?
Attached Thumbnails
Bad measure?-near-field-response.jpg  

Bad measure?-sub-measurementpng.png  

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post #2 of 3 Old 01-08-16, 01:10 PM
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Location: UK
Posts: 6,707
Re: Bad measure?

Just because you are between the speakers doesn't mean you are not influenced by modal behaviour. Easiest might be to measure outside, if weather permits that. Another way to see if the effect is due to the room is to move the speaker you are measuring somewhere else (in that room or another room) and see what the nearfield looks like in the new location. Also check your calibration files, if any are loaded, to see if the features are reflecting a feature in the cal files.
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post #3 of 3 Old 01-08-16, 02:29 PM Thread Starter
TEK
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Re: Bad measure?

Quote:
JohnM wrote: View Post
Just because you are between the speakers doesn't mean you are not influenced by modal behaviour. Easiest might be to measure outside, if weather permits that. Another way to see if the effect is due to the room is to move the speaker you are measuring somewhere else (in that room or another room) and see what the nearfield looks like in the new location. Also check your calibration files, if any are loaded, to see if the features are reflecting a feature in the cal files.
Thanks for your input.
I was hoping that modal behaviour would not affect it as it was near-field measurements (10cm from the cone).
I have checked the calibration file for the mic. It seems OK in that area (just some minor corrections).
Right now it's winter here and -17 degrees Celcius
I might be able to move them, but need to get some longer cables first then.
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