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Ed Zeppeli
01-13-2017, 03:46 PM
...without some kind of notch filter?

75383


I did close measurement (3") centred on the dustcap to see how my cabinet was performing. Looks pretty good I must say until the 50DB DROP @ 795 HZ!

So is this even possible without some sort of notch filter engaged? Bad woofer? Odd mic anomaly? Something else I'm missing here? I'd bypassed all EQ and any feedback elimination within the driverack is off.


I will continue troubleshooting and checking the other side etc but any suggestions would be appreciated.


Thanks,

Warren

srm51555
01-13-2017, 04:15 PM
I just read today that if you have a dip at the crossover frequency you may need to invert the phase of one the drivers. But I am very new at this so others may chime in with a better answer.

See step four in the link below.

https://www.minidsp.com/applications/digital-crossovers/stereo-2-way-xover

Ed Zeppeli
01-13-2017, 04:27 PM
That's the thing. I changed the crossover to about 1k and this is a single close range measurement of the 2234H driver. All other drivers muted.

grumpy
01-13-2017, 04:35 PM
That's deep and narrow, even for an intentional passive notch filter or driver cancellation.
This is in-box? and no crossover? I'd try moving the mic ... but that looks suspicious.

1audiohack
01-13-2017, 05:14 PM
That's deep and narrow,...

Yeah if you don't have a hard reflection with a path length of about 8.5" like the back of an uninsulated box or a box buzz, thats a mystery.

My measurements of standing wave notches reveal that they are only several Hz wide and deep indeed.

Swap drivers?

Barry.

Ed Zeppeli
01-13-2017, 05:14 PM
That's deep and narrow, even for an intentional passive notch filter or driver cancellation.
This is in-box? and no crossover? I'd try moving the mic ... but that looks suspicious.

Suspicious.

My thoughts exactly. This is in-box, no passive crossover but it's running through the dbx Venu360, which is why I suspected some sort of feedback eliminating notch. That's what I looked for first but as mentioned I've disabled all EQs, moved the crossover point on the dbx to +1000hz and made sure no other filters were active in the dbx.

I could try moving the mic and testing the other side under the same circumstances.


Warren

tjm001
01-13-2017, 05:21 PM
...without some kind of notch filter?

75383


I did close measurement (3") centred on the dustcap to see how my cabinet was performing. Looks pretty good I must say until the 50DB DROP @ 795 HZ!

So is this even possible without some sort of notch filter engaged? Bad woofer? Odd mic anomaly? Something else I'm missing here? I'd bypassed all EQ and any feedback elimination within the driverack is off.


I will continue troubleshooting and checking the other side etc but any suggestions would be appreciated.


Thanks,

Warren
Well, it's been a long, long time since I did this kind of thing back in my apartment in Alexandria Virginia back in 1965 or so. But it's pretty much the same thing I experienced back then. There are null areas all over the place that are unexplained. The shape of the room, the shape of the dust cap, the shape of the mike. Who knows. Reality is different than theory is all I can say.

bldozier
01-14-2017, 01:39 AM
Could be an electronic condition 😐:dont-know:

Ed Zeppeli
01-14-2017, 07:19 AM
I'll run some more sweeps today and report back.

Mr. Widget
01-14-2017, 12:13 PM
Suspicious.

My thoughts exactly. This is in-box, no passive crossover but it's running through the dbx Venu360, which is why I suspected some sort of feedback eliminating notch. That's what I looked for first but as mentioned I've disabled all EQs, moved the crossover point on the dbx to +1000hz and made sure no other filters were active in the dbx.

I could try moving the mic and testing the other side under the same circumstances.


WarrenIf you suspect that the DBX is doing something odd… Try it without the DBX.


Widget

Ed Zeppeli
01-14-2017, 12:44 PM
If you suspect that the DBX is doing something odd… Try it without the DBX.


Widget

That...

...would have been my next step. Today I moved the mic over to the other cabinet at the same position on the cone and got a strikingly similar dip at 786hz. I tried a bunch of other things and then moved the mic a foot further back. Dip gone, back to smooth response.

I was thinking there may be some oddities by measuring so close to the cone but wasn't suspecting such a steep notch.

Lesson learned....audio is weird.

sebackman
01-15-2017, 11:08 PM
Hi Warren,

Try moving the tip of the mic closer to the cone.

3" is not close enough for "near field" and not far enough for "far field". That is probably why you get some weird cancellations. Maybe from the mic it selves or from the mic stat.

When I do near field I set the mic only 5mm from the center of the woofer cone, dustcap. To get "far field" you normally need to be at least about 20" out.

Kind regards
//Rob

yggdrasil
01-16-2017, 12:02 AM
If my memory serves me right nearfield measurements should be taken at 1/2 inch (1cm).

Lee in Montreal
01-16-2017, 11:53 AM
Looks like a phase cancellation... What happens if you reverse the polarity of one of the drivers?

grumpy
01-16-2017, 01:25 PM
I believe only one driver is operating (post #3).

Ed Zeppeli
01-16-2017, 01:37 PM
Hi Warren,

Try moving the tip of the mic closer to the cone.

3" is not close enough for "near field" and not far enough for "far field". That is probably why you get some weird cancellations. Maybe from the mic it selves or from the mic stat.

When I do near field I set the mic only 5mm from the center of the woofer cone, dustcap. To get "far field" you normally need to be at least about 20" out.

Kind regards
//Rob


If my memory serves me right nearfield measurements should be taken at 1/2 inch (1cm).

Thanks fellas. I didn't realize it had to be that close. That's damn-near Xmax! (no, i'm not measuring that loudly)


I believe only one driver is operating (post #3).

Yes. Thanks