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Room mode at 700hz and 850 hz

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Re: Room mode at 700hz and 850 hz

Postby Hugh Robjohns » Fri Nov 01, 2019 8:38 pm

Measurements are only as good as (a) the equipment, (b) using it correctly and (c) nderatanding and interpreting the realts accurately.

REW is great, but it relies entirely on the accuracy of the measurement mic and/or it's calibration file.

...and then using it correctly and understanding what it's telling you are far from trivial... And as a result it is incredibly easy to chase ghosts...
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Re: Room mode at 700hz and 850 hz

Postby jodaki » Fri Nov 01, 2019 8:45 pm

Wonks wrote: Because (in theory) its the EQ curve you'd need to apply to the DAW output to get a flat measurement response . If you've got a 3dB peak at one frequency then it will counter it with a -3dB dip.
In reality you can't counter room mode dips with just EQ boosts.

I got the wrong end of that too then. The sound card is calibrated prior to measurements so I assumed the sound card calibration was an offset used by REW when drawing measurement graphs to compensate for the imperfections/biases of the card.

I accept what you say but if I’m being honest then if the sound card calibration is simply an inverse of the measurement then I dont really understand the point of calibrating my soundcard, surely REW can just invert the response reading to generate an eq ’recommendation’.

I dont have a device or much of a desire to fix the room modes by eq so I’d prefer to get as far as I can by altering the space characteristics - by which I mean my position in the space and the response characteristics of the space.
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Re: Room mode at 700hz and 850 hz

Postby Hugh Robjohns » Fri Nov 01, 2019 8:49 pm

I fear there's some major misunderstandings here...

If the sound card is anything other than ruler flat from 20Hz to 20kHz it's broken.

The calibration is a correction for the measurement microphone, and any inaccuracies will obviously give false room measurements.
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Re: Room mode at 700hz and 850 hz

Postby jodaki » Fri Nov 01, 2019 10:11 pm

Hugh Robjohns wrote:I If the sound card is anything other than ruler flat from 20Hz to 20kHz it's broken.

Are you talking about REW’s soundcard cal graph? As in the SPL plus phase graph IO posted?

As you can see mine is clearly an inverse of the measurement. So it is not flat, but as far as I can tell my 18i20 works perfectly.

Are there any other possibilities?
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Re: Room mode at 700hz and 850 hz

Postby jodaki » Tue Nov 12, 2019 2:30 pm

Hugh Robjohns wrote:Measurements are only as good as (a) the equipment, (b) using it correctly and (c) nderatanding and interpreting the realts accurately. REW is great, but it relies entirely on the accuracy of the measurement mic and/or it's calibration file.

I read an article last week somewhere on the pointlessness of using an ECM8000 with a generic calibration file as the response of those mics varies wildly. In particular noting that the example mic in the article displayed a set of peaks culminating around 800Hz.

After which I ditched the behringer and bought a UMM-6 and Dayton Audio gave me the calibration file for it.

Since then Ive spent the last week moving speakers and mic around my room measuring the spots Im willing to work in.

This is what I had as a bare measurement (mic and speakers, no other gear) in my favourite spot.

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Not knowing what a good REW SPL graph looks like I'm not in a position to judge this reading, though it looks more even than some Ive had.

Looks like some problems at 163Hz and 370Hz but more absorbers didn't seem to help.

And I don't know whether I have 2 peaks at 50Hz and 63Hz, or whether I have a cancellation at 56Hz. The un-smoothed graph is almost identical sub 100Hz to the 1/24 smoothed graph. I don't pretend to understand but I think the waterfall graph shows peaks so Im guessing these are peaks at 50 & 63Hz.

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Adding more mass to the bass traps (pushing them up to nearly 200kg with extra bales, 140kg/m3 RW6 rockwool and techsound 5.8mm MLV) makes little to no difference to the sub 100Hz region. Not sure what else I can try to reduce the bass there. Perhaps the problem is leakage into the room or reflections from the ceiling or the floor.

Then I added my desk and gear back in, resulting in this measurement. This is a real world example of the response at my listening position:

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My desk seems to have solved the problems at 163 and 370Hz. I don't know why or how.

But has it in turn created a new problem around 97Hz?
Is that mid-range dampening between 600 and 1.6kHz or is that an improvement?
And what do I make of what look like periodic high range resonances from 3.25kHz upwards?
Help understanding these readings would be appreciated..

And perhaps most importantly I don't know whether this is a good result. And what should I try and do from here?
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