Strange measurement response

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Primoz Vozelj

Freshman
Apr 21, 2014
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Here's measurement of 15" driver from 3way vented speaker. There's strange notch in amplitude response, phase shift and notch in coherence at around 320Hz. What could be reason for such a response? At first I thought there's something wrong with driver, but we have 4 same speakers and they all have same response. 15.png
 
Driver is mounted in the speaker. External height is 814mm, so internal dimension must be around 78cm, which is close to your result. Should I add absorptive material inside the box?
 
hey

Yeah just what I was gonna say, room response would be my first guess, either a reflection from the wall or from the floor.

As Mark says try sitting the cabinet on the floor (and away from all other walls etc of course) and putting the measurement mic a meter away from the cab, and as close to the floor as the stand will hold it without touching. You won't get a true measurement of the low end, as you'll be in half space now and be getting a boost in response from the ground, but it will at least let you eliminate a room reflection as the cancellation.

If that doesn't work then yeah it could well be an internal reflection. Even if the overall cab is 814mm high, the 15" section could be in its own closed off chamber inside who's dimensions may be a little closer to the size needed to create an internal standing wave at that frequency.

K
 
As you said, there is a coherence and phase anomaly right there at the dip. This is highly suggestive of a measurement issue. All sound advice from the previous posters. In addition, if possible, do your measurement outdoors in an open space for better accuracy.
 
Hi..as per my knowledge it is the reflection in the cabinet. Wavelength approx. 1m, so halve wavelength approx. 0.5m. If there currently is none, then adding absorptive material might help in decreasing the dip.

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