# New Mixing Room Measurement



## colorblind80 (Aug 21, 2010)

Hi to everyone!

During this mid august I've had some time to take some measurement and do adjustment on my new (work-in-progress) mixing room.
The main speaker are 2 Adam A7X Speaker and the room dimensions are 2,48x3,46x2,71 meters. Unforunately the placement of the speaker is on the longest dimension and off-center. I know all the issues thata arises from this placement, but giving that for me mixing is not a work, it's a trade off that I must accept... :huh:

I'll start with initial measurement of the room:









and then the final after EQing:









And here there are the waterfalls:

Room Response Left Speaker







Room Response Right Speaker








Room Response EQed Left Speaker







Room Response EQed Right Speaker








The dip in the left speaker at about 87Hz is due to placement and it is relative to the height of my room.

And now, finally, the questions:
Do you think that the room after EQing is capable of delivering some consistent mix?
Considering that the treatement of the room is quite invasive in my case, do you think that can address major problems? (I cannot move speaker or forniture positions)

Thank you in advance! Luca


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## gazoink (Apr 17, 2013)

As you've already seen, that almost 20dB dip in the left is the room and you can't EQ it out. However, you might think about adding a subwoofer or two to deal with it. Subs can crossover at 100Hz, and can be more easily located. Two subs in very different locations help to smooth out bass response. You can also talk to the folks at Real Traps or GIK Acoustics about a bass trap to help kill that null.


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## colorblind80 (Aug 21, 2010)

I forgot to specify that the measurement came from a calibrated chain.


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## CFmartin (Mar 8, 2010)

The FR graph is a combination of direct and reflected sound. You have EQ:ed 500-3000Hz area trying to smooth FR, but doing so you probably make the direct sound worse. I´d be very carefull when EQ:ing above schroeder frequency.


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## gazoink (Apr 17, 2013)

colorblind80 said:


> I forgot to specify that the measurement came from a calibrated chain.


What's the chain?


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## gazoink (Apr 17, 2013)

CFmartin said:


> The FR graph is a combination of direct and reflected sound. You have EQ:ed 500-3000Hz area trying to smooth FR, but doing so you probably make the direct sound worse. I´d be very carefull when EQ:ing above schroeder frequency.


That would be true if it were made with an RTA which is time-blind and integrates all arrivals, direct and reflected. However, at least to the degree that measurement bandwidth will allow, his graphs are made with a system that is not time-blind. Each line in the waterfall represents an offset in time away from the first arrival (direct), and does in fact show to a reasonable degree direct and reflected separately. As you probably know, time and frequency resolution are linked, so there is some integration of time within a certain window, but reflections removed in time are shown in the waterfall.

The FR graph is the first arrival, first plot in the waterfall.


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## CFmartin (Mar 8, 2010)

^ Based on the FR graph resolution in the bass region I´d say impulse response was windowed with several hundred ms. Not small enough to exclude early reflections.


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## colorblind80 (Aug 21, 2010)

Thanks gazoink!
The chain is composed by:

-Calibrated ECM8000 with calibration curve used in REW (in off-axis measurement position)
-M-AUDIO FW410 with loopback calibration used in REW
-Time Alignment using a second IN/OU of the soundcard
-SPL calibrated in REW using external calibrated SPL meter
-Output to A7X Monitors using digital out of FW410 into the actual DAC used in my studio (Mytek STEREO96 DAC)

Additional note: the EQ is done in region where excess of group delay is minimum and similar to system delay. This should assure that I'm not messing with phase (right?)


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## colorblind80 (Aug 21, 2010)

CFmartin said:


> ^ Based on the FR graph resolution in the bass region I´d say impulse response was windowed with several hundred ms. Not small enough to exclude early reflections.


I'm not really an expert of the matter and excuse me if I say something wrong, but:
-The first slice of the waterfall does not seems to me much different from FR
-Apart modal resonances (that are clearly shown in waterfall) I can't see in waterfall changes in the behaviour of spectral decay, that should suggest to me the arrival of reflected sounds

I'm interested in forum opinion, this give me some new knowedge on interpreting the measurement! 

Thank you in advance!


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## CFmartin (Mar 8, 2010)

To put things in perspective, typical mixing desk reflection comes less than 1ms after direct sound. It effects FR region around 600-800Hz. If we want to window this reflection out, we are left with poor resolution and not much bass to analyze. This applies to waterfall slices as well. Waterfall window is set 500ms default and gives us 2Hz resolution.


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## gazoink (Apr 17, 2013)

CFmartin said:


> To put things in perspective, typical mixing desk reflection comes less than 1ms after direct sound. It effects FR region around 600-800Hz. If we want to window this reflection out, we are left with poor resolution and not much bass to analyze. This applies to waterfall slices as well. Waterfall window is set 500ms default and gives us 2Hz resolution.


Good point on adequate midband resolution resulting in poor bass resolution, and good catch on the desk reflecting, yes, his resolution isn't good enough to show it. However, his complaint is with the bass dip, which won't relate to that reflection anyway, and is definitely the room. The presence and contribution of a desk reflection could be confirmed by repositioning the measurement mic such that the mic is still in the direct field, but the reflection angle passes it. However, a reflection 1ms after the direct should be fully integrated with the direct from a standpoint of perception anyway so long as the spectrum is similar, and the combination of direct and reflected in that case could be valid, so long as the second arrival is only a minor factor in localization. In the case of the desk, it probably is a minor localization issue, if at all. Agree, or am I off the track?

I always suggest the desk reflection be dealt with, at least to the degree possible, by speaker positioning.


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## CFmartin (Mar 8, 2010)

Gazoink, I agree with you mostly. Desk reflections have some minor effects on timbre and can be best dealed with speaker positioning. This desk reflection thing has been just guesing all along as I don't know much about the room.

But what it comes to the resolution on the graps they have indeed very good frequency resolution especially in the mid and hi bands. That means long windowing was used when impulse response was analyzed. That also means all the early reflection are included in the frequency responses with their comb filter effects.

The way single microphone hears steady state test tone is totally different from human hearing music or speech which are transient in nature. REW is a very good tool for analyzing rooms and showing comb filter effect, but final EQ:ing desisions above schroeder frequency should be made with great understanding.


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## colorblind80 (Aug 21, 2010)

It's not very clear to me (but it's my poor knowledge) what you intend, but I've done a waterfall with 20ms slicing and 4s window (resolution 0,2Hz). It seems to me that I cannot see the reflections in mid range.









I'm missing something?

The graph refers to left speaker without EQ correction


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## colorblind80 (Aug 21, 2010)

And furthermore ETC in this case:

Left Speaker:







Right Speaker







Left Speaker EQed:







Right Speaker EQed:


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## CFmartin (Mar 8, 2010)

Zoom closer so we can see the first 10-20ms in 0-60dB range.


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## colorblind80 (Aug 21, 2010)

Left:







Right:







Left EQed:







Right EQed:


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## CFmartin (Mar 8, 2010)

Looks pretty clean for the first 10ms exept for the very first reflection in 0.5ms, the rest are under -20dB.

...and some reflection on R-channel at 1ms or so.


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## colorblind80 (Aug 21, 2010)

Thanks CFmartin!

So the potential improvement to be done in my case could be:
-Bass trapping to smooth modal resonances at low-freq and to improve reverberation time at low freq
or
-Subwoofer (or to) with correct placment to deal with peaks and dip (but I suspect that the sweet spot could be very narrow)

In my opinion, reflection identified in ETC could be improved, but the final result is much less evident than low-end issues 

Do you agree?
And furthermore: do you think that EQing I've performed over schroeder freq shows major issues on the plot that I've upload?

Another theme is the asimmetry in stereo field, but I as I said before I cannot reposition the speakers (so I have to deal with)


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## gazoink (Apr 17, 2013)

CFmartin said:


> Gazoink, I agree with you mostly. Desk reflections have some minor effects on timbre and can be best dealed with speaker positioning. This desk reflection thing has been just guesing all along as I don't know much about the room.
> 
> But what it comes to the resolution on the graps they have indeed very good frequency resolution especially in the mid and hi bands. That means long windowing was used when impulse response was analyzed. That also means all the early reflection are included in the frequency responses with their comb filter effects.


Very true.


CFmartin said:


> The way single microphone hears steady state test tone is totally different from human hearing music or speech which are transient in nature. REW is a very good tool for analyzing rooms and showing comb filter effect, but final EQ:ing desisions above schroeder frequency should be made with great understanding.


EQing below the Schroeder frequency should be made with great understanding too! ;-)

One of the problems here is a single measurement at a single point. Really, it produces too much data, and a lot is actually a bit random. What he should do is take several measurements in a small cluster and average them, particularly the ETC, and that reflection should start to pop out. I never base an EQ decision on a single measurement, much less a single point, there's just too much random detail to respond to.


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## gazoink (Apr 17, 2013)

colorblind80 said:


> Thanks CFmartin!
> 
> So the potential improvement to be done in my case could be:
> -Bass trapping to smooth modal resonances at low-freq and to improve reverberation time at low freq


Yes


colorblind80 said:


> -Subwoofer (or to) with correct placment to deal with peaks and dip (but I suspect that the sweet spot could be very narrow)


Multiple subs are your friends.


colorblind80 said:


> In my opinion, reflection identified in ETC could be improved, but the final result is much less evident than low-end issues


Well, take a few more measurements in a small head-sized cluster at the mix position and average them, see what you get first. 

For the desk reflection, place a mirror on the desk, try to orient the speakers so you can only see them with your head far away from the mix position. The farther the better. Usually, lower to the desk gives a glancing reflection into the engineers stomach, which, depending on the engineer, could be either diffusive or absorptive, depending on diet and exercise. But angle of incidence equals angle of reflection, so work with the geometry to reduce the desk splash.


colorblind80 said:


> And furthermore: do you think that EQing I've performed over schroeder freq shows major issues on the plot that I've upload?


Hard to say for sure without more averaged measurements, but it looks like you're on the right track.


colorblind80 said:


> Another theme is the asimmetry in stereo field, but I as I said before I cannot reposition the speakers (so I have to deal with)


If this means one is closer to a side wall, might need to fuzz the side wall. You can use the mirror technique again to find the first reflection, but it's pretty hard to figure out second and third reflections as it bounces around the room, so even if you can't see the speaker in the mirror on the wall very well, you should probably fuzz a large area. Thick fuzz, the lowest frequency at which absorption works is related to thickness. I don't have much use for 2" fuzz, minimum is 4".


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## colorblind80 (Aug 21, 2010)

Here what's happening using Left speaker EQed and taking three points:

Theorical Head Position







30cm LEFT from theoretical head position







30cm RIGHT from theoretical head position








I don't know how to average multiple measurement in REW, but just watching at the pics I see some reflection arising in 1ms area and about 7ms area. The wall corner is on the left of this speaker.
I also note that the peak of these reflection is about 12 dB lower than main signal.

It seem to me that actual status could be considered consistent but do you think that performing more measurement in different position with respect to head theoretical position will give much more information ? (but in this case I have to know how to average the measurement)

I continue to thank you for the support!


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