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post #1 of 8 Old 02-04-13, 12:58 PM Thread Starter
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Same setting different responses

Hi all,
I finally got my system to work, did some first measurements today. I set everything up, did the calibrations and ran about ten tests with the EC8000 at the listening position. To my surprise about 5 of the measured responses were more or less the same (see fig.1 ) but the others had serious dips in the upper range (fig. 2), all at different spots. Is there any obvious reason for this? Should i just ignore those measurements?
Thanks for looking!

Same setting different responses-04-02-2013-closely-together.jpg
fig. 1
Same setting different responses-04-02-2013-dips.jpg
fig. 2
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post #2 of 8 Old 02-04-13, 01:16 PM Thread Starter
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Re: Same setting different responses

Also, here's on waterfall i made. It seems like there is something wrong, too much noise in the room? It looks like the spl never drops 60db? The only thing i had on that makes some noise is the power supply of my mixer. Can that be it? Or can it be that the speakers are on the meter bridge? And that this makes the meter bridge sort of ring in the low end?
here's the waterfall:

Same setting different responses-waterfall-04-02-13-too-much-noise-.jpg

too much noise?

Last edited by hbjans; 02-04-13 at 04:03 PM.
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post #3 of 8 Old 02-04-13, 02:38 PM
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Re: Same setting different responses

Best read this sticky to get the graph scalings right: Please read: Posting a Graph

The dips do look odd, would need to post some of the measurements (the .mdat files) to look more closely at what is going on there.

Are you using a single sweep or multiple sweeps (single is recommended)?
Does the sweep always sound smooth and continuous, no drop-outs?
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post #4 of 8 Old 02-04-13, 02:57 PM Thread Starter
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Re: Same setting different responses

Hi John,
Thanks for your help! I accidentally threw away that first large set of measurements. But i made some new. Two of the were ok, one had the strange dips. The (single) sweeps sounded ok, no audible dips. Please notice that the dips (as you can see in the old graphs) were at different locations in the different measurements.
here's the new plot, for the new file. I also attached the (zipped) file.
Same setting different responses-04-02-13-right-scaling-new-meaurements-.jpg

Here's the file:
cntrl rm 4-2-13 2xpsi mixer long side.mdat.zip

Regards!
Jan
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post #5 of 8 Old 02-04-13, 03:15 PM
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Re: Same setting different responses

Unfortunately only the 2nd measurement of those 4 looks correct, here is its impulse response, which is typical of how it should look:
Same setting different responses-good-ir.jpg

This is the 1st measurement, it is almost right but shows some odd behaviour:
Same setting different responses-dodgy-ir.jpg

This is from the 3rd measurement with the dips, it has almost a repeat of the entire impulse but after about 500ms. The 4th measurement is similar, both are incorrect:
Same setting different responses-bad-ir.jpg

I guess you are on OS X? And using a Firewire card? Firewire inputs did not work in the past for Java under OS X, though there were 1 or 2 people that managed to get good results. Your soundcard calibration result looks fine though. You could just keep measuring, check the impulse response for each measurement and ignore/delete any that do not look correct, or try changing the buffer settings in the REW soundcard preferences to see if that has any beneficial effect.
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post #6 of 8 Old 02-04-13, 03:38 PM Thread Starter
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Re: Same setting different responses

Ok, thank you very much. I use OS X with a usb, Focusrite Scarlett 2i2. If you don't mind i have two more questions.
1 - interpreting is quite hard: in that correct IR, where do you see the reflections?
2 - i adjusted the scale in a waterfall for that correct measurement, does it look right now? It seems very long, more than 3 s for the lowest modes. And in that time the level drops only 20 db? How does this relate to the RT60 (the time to drop 60 db?)

I would understand it if this is too much to answer here.

thank you again!

Jan

Same setting different responses-waterfall-correct-measurement-.jpg

and the RT60:

Same setting different responses-rt-60-measurement-2.jpg
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post #7 of 8 Old 02-04-13, 03:55 PM
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Re: Same setting different responses

Quote:
hbjans wrote: View Post
1 - interpreting is quite hard: in that correct IR, where do you see the reflections?
I zoomed out on the impulse response time axis to see the overall shape, for more detail of individual reflections you would use a much narrower time span, and look at the ETC trace rather than the Impulse Response itself.

Quote:
2 - i adjusted the scale in a waterfall for that correct measurement, does it look right now? It seems very long, more than 3 s for the lowest modes. And in that time the level drops only 20 db? How does this relate to the RT60 (the time to drop 60 db?)
The time span of that graph is 300ms (0.3s). RT60 is valid for large rooms/listening spaces over a span of frequencies, it isn't right to treat the decay of an individual room resonance as an 'RT60' figure, but it does have a time to decay by 60dB - around 700ms for the resonance(s) at about 44Hz, for example.

You can get better waterfalls with the latest version of REW by the way, V5.01 beta 13.
Same setting different responses-waterfall.png
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post #8 of 8 Old 02-04-13, 04:32 PM Thread Starter
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Re: Same setting different responses

Thank you John, i am on the new version now. I like this stuff, takes some effort to get into it though!
Jan
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