# Best to average multiple readings for room correction?



## Nonlinear (Jun 9, 2012)

Simply moving the measurement microphone a few inches causes the measurement nulls and peaks to move around, especially at the higher frequencies.

So, for overall room correction via REW filters, is it best to take an average of numerous readings at different points in the room - or at least multiple points near the intended "sweet spot"?

If so, should one use very little smoothing in that case prior to generating the correction filters?


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## Phillips (Aug 12, 2011)

Averaging is mainly used for multiple listening positions (seats for Hometheatres).

When moving around these things do tend to happen.

By all means average a couple of measurements in 1 x seat and listen to the result.

Post some measurements if you can?


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## natehansen66 (Feb 20, 2011)

Ask 10 different people and get 11 different answers.  

Currently what I do is a series of 12 measurements in a roughly 2' box around the lp. Below the Schroeder freq (about 200 hz) I use 24dB/octave smoothing and a 500ms gate after 0, which is the stock setting. They all tend to follow the same curve below 200hz. I use a combination of 6dB/octave and 24dB smoothing from 200 to about 600. Above 600 I use a 20ms gate centered on 0 and 6dB/octave smoothing. A variable window that changes from a 500ms gate in the bottom octave to a very short gate at 20khz would be ideal IMO. Hopefully one day REW will be able to do this  

If you're interested enough in room correction you might find yourself falling down a rabbit hole.......


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## Wayne A. Pflughaupt (Apr 13, 2006)

Nonlinear said:


> Simply moving the measurement microphone a few inches causes the measurement nulls and peaks to move around, especially at the higher frequencies.
> 
> So, for overall room correction via REW filters, is it best to take an average of numerous readings at different points in the room - or at least multiple points near the intended "sweet spot"?


There’s no reason to worry about the differences in response you see at different close-by locations, unless they are severe. Keeping in mind that the unsmoothed measurement is a combination of the speaker’s direct response and the room’s reflections, what’s happen with a measurement at a different location is that the reflections are (naturally) a bit different, so when the graph has some smoothing applied the response looks somewhat different as well. 

It’s nothing to be concerned with: If you physically put yourself in the places where the mic was located during the different measurements, can you tell any audible difference with program material? Chances are you can’t. The reason is that the ear is much less sensitive than the measurement mic. 

Then there is the fact that if you take additional measurements in say, six months, you'll likely get response graphs that look different than the earlier ones. The temperature and humidity will be different on the date the latter measurements are taken, and that has an effect on the physical - and hence electrical - properties of the mic element. And as a consequence, any measurements it produces will be different too, even if everything sounds the same to you as it did when the first measurements were taken. 

To re-iterate, the ear is much more forgiving of these things than a measurement mic is. As such, you can get satisfactory results simply by equalizing for the sweet spot - say, the center position of a couch - and they’ll be heard at the adjacent locations (naturally this can’t be an “absolute” rule given that every residential room is different). 




> If so, should one use very little smoothing in that case prior to generating the correction filters?


I’d use just enough to eliminate the comb filtering and let you see a consistent measurement trace.




natehansen66 said:


> Currently what I do is a series of 12 measurements in a roughly 2' box around the lp. Below the Schroeder freq (about 200 hz) I use 24dB/octave smoothing and a 500ms gate after 0, which is the stock setting. They all tend to follow the same curve below 200hz. I use a combination of 6dB/octave and 24dB smoothing from 200 to about 600. Above 600 I use a 20ms gate centered on 0 and 6dB/octave smoothing.


Personally I’m not fond of gating a measurement - perhaps for a FYI reading, but not for the purposes of equalizing: If room reflections happen to be effecting a measurement at certain frequencies enough to be audible, then that’s what I want to address, since that's what I’m hearing. Gating is most definitely not the same as smoothing. It removes the room reflections from the measurement, and as such is a useless measurement for equalizing and/or acoustical treatment.

Regards, 
Wayne


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## natehansen66 (Feb 20, 2011)

Wayne A. Pflughaupt said:


> There’s no reason to worry about the differences in response you see at different close-by locations, unless they are severe. Keeping in mind that the unsmoothed measurement is a combination of the speaker’s direct response and the room’s reflections, what’s happen with a measurement at a different location is that the reflections are (naturally) a bit different, so when the graph has some smoothing applied the response looks somewhat different as well.


To me that's exactly why I want to use multiple measurements. If at position A I have a 5dB suckout, I might have a 6dB peak at position B. That would tell me to leave it alone, but with one measurement I wouldn't know that.



Wayne A. Pflughaupt said:


> Personally I’m not fond of gating a measurement - perhaps for a FYI reading, but not for the purposes of equalizing: If room reflections happen to be effecting a measurement at certain frequencies enough to be audible, then that’s what I want to address, since that's what I’m hearing. Gating is most definitely not the same as smoothing. It removes the room reflections from the measurement, and as such is a useless measurement for equalizing and/or acoustical treatment.
> 
> Regards,
> Wayne


I'm far, far from an expert at psychoacoustics. As far as I understand it above the room transition freq the direct arrival of sound dominates. Looking at a measurement that includes all the reflections doesn't account for the fact that the brain can differentiate the direct arrival from some of the reflections. IMO eq'ing for all the reflections could change the speaker response for the worse. I like to look at a series of measurements and different gate lengths to get an idea of what I should and what I shouldn't be eq'ing. This is a _very_ tedious process but I enjoy it, and so far the results are promising. I've only recently gotten serious about drc, I'm still learning :dontknow:

I'm also getting into time domain correction and being able to see different "slices" of the response in time is critical to getting good results and not overdoing it. Same goes for freq correction IMO.

This thread: http://www.hometheatershack.com/forums/rew-forum/64094-psychoacoustically-correct-room-correction.html#axzz2La0aS9w1 has some good info and links to how we perceive sound and methods for measurement and room eq based on our hearing.


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