# Trouble With Stereo Image



## ske (Mar 3, 2013)

I have been matching my subs to the mains by matching the impulse responses from 60-80 hz (crossing over at 70 hz, 24dB slope). The results for the bass are great at the crossover region. But I lose the stereo image. I'm thinking that matching the mains to each other at 70-90 hz may be the root of the problem, as they may now be out of phase in the mid-range frequencies.
So this morning I'm going to concentrate on phase matching vs impulse response matching for subs, but I'm unsure of how to treat the mains in relation to the subs and each other.
I'm having a rain-delay at the moment, so any help while I set up would be most appreciated (flat, foam roof plus hard rain is NOISY!)

Thanks


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## AudiocRaver (Jun 6, 2012)

Getting good stereo imaging strictly from measurements is rather difficult. I always recommend starting out by ear because you can get close fairly quickly, then can use measurements to see what areas need improvement.

But to answer your question:

Frequency response should match very closely above 250 Hz or so, +/- 2 dB will be good, +/- 1 dB will be very good.
Phase response should match closely from 250 Hz to 2 kHz, +/- 30 degrees or so.
Impulse responses should match to about 20 us (1/4 inch).
You will not get perfection, but if you get anywhere close to these measurements, it should sound really good.


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## ske (Mar 3, 2013)

Frequency and impulse are great. But I'm having trouble determining phase on REW. Can you tell me how to determine that? It seems that every move I make in REW yields wildly different results off my measurements. I looked in the main panel, tried Shift IR, looked in the overlay panel, etc...Thanks


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## AudiocRaver (Jun 6, 2012)

First, you have to be using a non-USB mic with a 2-input audio interface so you can use a loopback channel as the timing reference. Are you doing that? It locks down a timing reference so various measurements can be related to each other.

Then for each measurement, you can _Generate Minimum Phase_ but do NOT _Estimate IR Delay_ or correct for it or add any time offsets.

Go to Overlays > Phase > select the two plots to compare. The farther the mic is from the speaker, the more phase rotation there is and it becomes less usable. Also look at Overlays > GD (Group Delay - you must generate minimum phase for it to work), with some smoothing (1/6 octave). It is an easier view.


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## ske (Mar 3, 2013)

Yes, I'm using a non-usb with loopback.
So I checked the previous measurements in question, and the left/right were off by 72 degrees. My current measurements are only off by 7 degrees, and sound better (I moved the speakers away about a foot).
I also need to play with the toe-in. I have noticed the sweet spot is in front of me by a couple of feet, though I didn't think my toe-in was too severe. But these are new speakers to me, so I'll have to play with that.
Thanks for the help with the phase in REW. Everything was just "off" last time around.


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