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Old 30th March 2009, 06:55 PM   #1
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Default strange mesured dips

Hi,

Mainly two strange 2dbs dips at 155 and 277hz on my filtered C220NT6, here measured near-field (approx 1" from cone); no matter where the speaker placement in the room and/or the measurement distance...IYO where do they come from?

Thanks

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Old 30th March 2009, 08:14 PM   #2
Taco is offline Taco  Netherlands
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It could be standing waves in the cabinet which are transmitted through the "thin" speaker diaphragm. The length for a 1/2 wavelength at 155 Hz equates to appr. 1.1 m; 277 Hz is appr. 0.62 m.

What are your cabinet dimensions?
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Old 30th March 2009, 09:21 PM   #3
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Quote:
Originally posted by Taco
It could be standing waves in the cabinet which are transmitted through the "thin" speaker diaphragm. The length for a 1/2 wavelength at 155 Hz equates to appr. 1.1 m; 277 Hz is appr. 0.62 m.

What are your cabinet dimensions?
Hi Taco,

Usually standing waves are peaks, not dips...Furthermore my cabs are filled with partitions which allow the biggest internal dimension to be the box width it's to say 19cm (7.5"). I thought about some antiphase nuls but I cannot rely them to any of the inner nor outer dimensions...Precision: my cabs are ported, rear bottom firing vent.

Speaker on the right:

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The squeleton:

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Old 31st March 2009, 06:49 AM   #4
Taco is offline Taco  Netherlands
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Large wavelengths are not much hampered by your partitions (these compartments are still connected)

Did you sum the port output to these nearfield measurements? Did you use filtering or gating techniques other than the 1/24 octave smoothing?

Which resolution do you have in the measurements, i.e. <20 Hz. is needed for reliable measurement of the low frequency response.
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Old 31st March 2009, 08:20 AM   #5
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How do they appear in a waterfall plot ?

Regards

Charles
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Old 31st March 2009, 08:07 PM   #6
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Guys, I'm a newbie in measurements!

Taco:
No I didn't sum the port output ; no gating or filtering techs other than the needed gated length;
resolution<20Hz: what does that mean?

Phase_accurate:
some screen-shots, all made nier-field (1" from cone):
Click the image to open in full size.

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Click the image to open in full size.
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