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Discussion Starter · #1 ·
Hi there,

I have spent every night this week until 1am trying to sort out my EQing using REW. I can get my graph nice and flat no problems but when I produce a waterfall graph it all goes wrong.

I have run two measurements using the same bfd filters and the waterfall graphs are completely different.

Any ideas as I am starting to get really frustrated. Probably due to lack of sleep.

Need help!

cheers

graham
 

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Discussion Starter · #2 ·
I just changed the spl meter to 70 db and re checked the levels at 75db and calibrated the spl meter to REW. Re run new measurements x3 and they came out the same. Still not sure they look that great.

Your thoughts guys

cheers

graham
 

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Discussion Starter · #3 ·
One thing I have just noticed is that when you lower the volume and calibrate the spl meter again I then get less ringing and the waterfall graph looks better. Is that normal.

This was measured at 68db.

cheers

graham
 

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You have to calibrate your measurements to 75dB. Most of the waterfall graphs indicate that you aren't calibrated to 75dB. If you want to see the response graph, simple dial the waterfall slice count from 30 down to 0 slices. That's the response graph. Move the slider to 1 slices. That's the signal in the room 10msec later if you're using a 300msec time variable (300msec/30=10msec), and so on.

The first slice (or the response graph should be showing a 75dBSPL level. Yours looks to be about 90dBSPL.

brucek
 

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Discussion Starter · #5 ·
Bruce,

Thats really wierd as I went to check levels and set them so that the spl meter read 75db. I could increase the levels with the input to raise to -18db as it was already on max so I had to leave it as that. I then calibrated the spl meter which was fine at 75db. Then did a measure and they are the result of that. The only way I could reduce it was to turn down the master volume on the av amp but then when I check levels it was lower than 75db so I just calibrated the spl meter and typed in what was reading on the spl meter. Clicked ok and then measured until it said 75db in the filename under the waterfall graph. That was the only way I could do it.

Is there something I am doing wrong?

Silly question, does it matter what input you use on the av amp. Is there a particular one that has a hight input level? I am using the right channel to do the levels as well.


cheers
graham
 

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One thing I have just noticed is that when you lower the volume and calibrate the spl meter again I then get less ringing and the waterfall graph looks better. Is that normal.
You don't have less ringing, you have just moved the whole plot downwards so more of the ringing is below the floor of the plot. If you use the scroll bars you can move the plot back up again.

When you refer to "Check Levels" do you mean the button on the measurement panel (i.e. before you click "Start Measuring"? That is only a confidence check to make sure the sweep range chosen is not inappropriate for the measurement (e.g., having a sweep to 20kHz selected when measuring a subwoofer). You should not need to make adjustments to levels before each measurement, just get the levels right once using the "Check Levels" routine on the soundcard settings panel then you can leave them alone. You also do not need to calibrate your SPL meter reading every time, once should be enough - it only needs to be redone if you change volume settings for your soundcard input or change your SPL meter sensitivity setting.
 

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Graham, have you tried moving the sub ( or the mic if you cant ) to see how that affects the ringing. There is always a chance the mic is picking up something close to your sitting position, of one of those drivers (perhaps the one firing into the wall) is causing the issue.
 

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Discussion Starter · #10 ·
Dan

One driver is quite close to the wall but I cant really do much about that. I will pull it away from the wall as a test to see if there is less ringing but I would guess that this was the same with the PB13 I had.

cheers

Graham
 
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