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If room modes can cloak the FR/phase plot effect of inserting a sub vs mains path length difference, I guess an anechoic test would be needed to properly investigate.

In a typical living room, does it help at all if you keep the test SPL very low, or do room modes excite to an equal extent for low vs high SPLs ?

 

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42 minutes ago, marten said:

do room modes excite to an equal extent for low vs high SPLs ?

In general.   Yes.

 

... that being said, you usually need to run relatively high SPL to get a high SNR.    Testing should typically be just loud enough that being in the room is uncomfortable.

 

Quote

I guess an anechoic test would be needed to properly investigate.

Yes - although due to the extreme measurement errors possible.... it is better to simulate these things.     Or at least simulate AND measure (to ensure your measurement isn't too far different from what is expected).

 

You can still test in room .... the modes just may make it more difficult to observe what is happening.

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Thanks Dave, instructive as always.

 

On the "simulate things" - what options do we have for simulating sound arrival at the listening position from two non-coincident sources (mains plus sub) ?

Edited by marten

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10 hours ago, almikel said:

single sub is about 1m closer to LP than left main speaker

 

I would expect to see some ripples in the FR and phase response, but maybe room modes are too dominant...I can try it tonight...with a bit of luck the mic may even be in the same spot still

 

Mike

mic was moved :( but as Dave said, @50Hz the wavelength is long - and too late in the evening to pull out the calculator to work out % of wavelength for differing delays in the DEQX...

...the FR and phase was pretty good without adding delay to mains or sub for the crossover at 50Hz - I'll leave it as is.

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1 hour ago, marten said:

On the "simulate things" - what options do we have for simulating sound arrival at the listening position from two non-coincident sources (mains plus sub) ?

In a DEQX context I still think the first major peak of the impulse of sub and woofer is the guide.

If your sub lags your woofer, then treat the difference in the peaks as the maximum time delay for the woofer.

Start at 0 sub (edit) mains delay and looking at FR and phase in REW, slowly increase delay on the woofer in DEQX to get a smooth FR and phase in REW.

 

If the sub leads the woofer in the impulse response (likely sub is much closer to the LP than the mains), same process, but add delay slowly to the sub and monitor FR and phase in REW

 

You could probably do it all in REW (but adjusting delay in DEQX) - I'm just more used to using the DEQX for finding the impulse response peaks.

 

 

REW is better to see how drivers are combining and looking at phase.

 

Mike

 

Edited by almikel
typo

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Thanks for the explanation and your procedure for setting electronic delay Mike.

1 hour ago, almikel said:

In a DEQX context I still think the first major peak of the impulse of sub and woofer is the guide.

When using an Impulse as opposed to Sine Wave sweeps, does it make a difference to the extent room modes are excited - i.e. less effect on FR and phase plots ?

 

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You’re always using sine wave sweeps with both rew and Deqx
The impulse response is calculated from that

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