Requesting help with strange REW result

[73hadd]

Hi all! My first attempt at measurements with UMIK and REW. Sorry for the graphic quality, let me know what additional data will help.

Microphone at LP, 6ft away from speakers, on axis, speakers 6ft apart:

I did bottom one first, labeled "Both Speakers" L+R measurement first and saw the huge dip at 15k and the other dip centered at around 5k. I then went back and did the Right and Left separately as noted. Since the dip was not there individually, I did the "both" again and got the same result as the "Both Speakers" as shown.

Again I am new to this so maybe this is expected due to an error in my setup/test method.

Any help is appreciated!

 

[LTig]

Hi all! My first attempt at measurements with UMIK and REW. Sorry for the graphic quality, let me know what additional data will help.

Microphone at LP, 6ft away from speakers, on axis, speakers 6ft apart:

View attachment 70885
I did bottom one first, labeled "Both Speakers" L+R measurement first and saw the huge dip at 15k and the other dip centered at around 5k. I then went back and did the Right and Left separately as noted. Since the dip was not there individually, I did the "both" again and got the same result as the "Both Speakers" as shown.

Again I am new to this so maybe this is expected due to an error in my setup/test method.

Any help is appreciated!

The dips in the green plot are the result of cancelling effects due to the microphone not being in the perfect position (slightly different distance from speaker to microphone). Just ignore it since you listen with 2 ears.

 

[Purité Audio]

First I might apply some smoothing to the plots it you go into the ‘graphs’ tab ( top of page) and select 1/12 That will make it easier to read.
Keith

 

[ernestcarl]

Hi all! My first attempt at measurements with UMIK and REW. Sorry for the graphic quality, let me know what additional data will help.

Microphone at LP, 6ft away from speakers, on axis, speakers 6ft apart:

View attachment 70885
I did bottom one first, labeled "Both Speakers" L+R measurement first and saw the huge dip at 15k and the other dip centered at around 5k. I then went back and did the Right and Left separately as noted. Since the dip was not there individually, I did the "both" again and got the same result as the "Both Speakers" as shown.

Again I am new to this so maybe this is expected due to an error in my setup/test method.

Any help is appreciated!

It's literally impossible to see the scaling numbers on your snapshots.

I suggest using the button

in REW and using a smaller width, maybe ~1,000 -- as well as some smoothing.

You can take measurements with none of the HF cancellation artifacts that you're seeing here when measuring both speakers if you used the moving microphone method (MMM). Simpler, faster, better...

 

[Ivanovich]

At 15kHz the wavelength is about 2,3 cm (I’m assuming you are in EU, 0.9-in for us here).

Sine waves cancel when they are out of phase by 180 dgs (1/2 wavelength). So, if the distance from each speaker to the mic is off by 1/2 that amount or a multiple of it, you’ll get this cancelation.

The suckout at 15 kHz tells me the there is a 1,14 cm difference in the distance of the UMIK to each speaker.

The good news is you can ignore it for FR measurements and EQ purposes, and listening! Measure one speaker at a time EQ’ing.

If you are doing nearfield monitoring (like for mixing), it is more useful to see both, so you can make slight adjustments to you speaker and listening positions. A 6-7 cm difference would be way more problematic in that case, as it would put the phase cancellation in the 2-3 kHz range. For that situation a mixing engineer wants each monitor exactly equidistant to the corresponding ear.

\m/

 

[73hadd]

Thank you. What a gift, you all, and this forum!

 

[tmtomh]

Yes, this is super-helpful information for a lot of us. Thanks!

 

[Vasr]

Measuring multiple speakers (separated by distance) together with REW provides very little benefit especially at high frequencies. Speaker+Sub crossed over at lower frequency can be useful to see what happens in the crossover region and detect phase issues even if they are apart some distance.

 

[RayDunzl]

Any help is appreciated!

I use the Acoustic Reference when measuring. I set the reference to the left speaker, then measure left and right speakers.

Observe the Impulse Response to see when the microphone is centered between the speakers.

Gross example:

Two speakers playing, using left reference, microphone about 1 foot off-center, making the right speaker "late":

Same two speakers, microphone all but perfectly centered:

Difference in observed Frequency Response due to mis-positioned single-point measure above:

 

[tmtomh]

I use the Acoustic Reference when measuring. I set the reference to the left speaker, then measure left and right speakers.

Observe the Impulse Response to see when the microphone is centered between the speakers.

Gross example:

Two speakers playing, using left reference, microphone about 1 foot off-center, making the right speaker "late":

View attachment 70959

Same two speakers, microphone all but perfectly centered:

View attachment 70960

Difference in observed Frequency Response due to mis-positioned single-point measure above:

View attachment 70962

That third graph is quite sobering - such a major difference based simply on the slight mis-positioning of the mic. Yikes.

 

[RayDunzl]

That third graph is quite sobering - such a major difference based simply on the slight mis-positioning of the mic. Yikes.

The measurement is from this: 7 positions across the sofa (where you might sit), including center:

 

[RayDunzl]

Try this:

Play pink* noise from both speakers, watch the RTA.

Very slowly move the mic left and right across the center.

You'll see waves in the frequency response, starting from the highest frequency when just off center, propagating lower and lower as the mic moves away from center.

I had a little movie, that is lost now, but might try to make it again.

*correlated pink... mono pink...