Effect of sofa on room measurements

[sejarzo]

What difference does it make? If that's in the room when you listen, then leave it there to measure... if you change your sofa then just remeasure

Because if I move the mic 3 inches, the minimum frequency of the dip is at a different frequency. I don't listen with my head in a vise--do you?

 

[Keith_W]

Effect of sofa on room measurements

Yesterday I decided to look at the effect of having the sofa at the listening position on measurements. This is where the sofa is located: And without sofa: These are the measurements. I applied some smoothing to make the measurements more legible: The mic was not moved from the...

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if you corrected a FDW with excess phase than you created artificial peaks where frequencies are delayed

With the amount of smoothing I applied to the upper frequencies, I don't think I have created any artificial peaks? Or am I looking in the wrong place?

I was quite aware that the measurement would be contaminated by comb filtering, which is why I applied so much smoothing.

(edit) and I also staggered the curves with the gain function so that it is more legible, so please don't think there is a whopping difference in dB between all those curves!

 

[JeremyFife]

Because if I move the mic 3 inches, the minimum frequency of the dip is at a different frequency. I don't listen with my head in a vise--do you?

No ... but my sofa doesn't move at all ...

Ah ... Sofa interferes with the mic? which messes up the measurements? Is that it - still learning!

 

[Sokel]

I also have a leather sofa (very big one) and the measurements are different on the summer where my fur rugs are missing (don't let me start with them,I have to fix them back all the time ,they slip! )
But they do get better when put something that simulates me.

(the rugs were there during the install by the way).

I don't feel the need to correct it thought,sounds ok to me.

 

[sejarzo]

To be honest, I listen on DCA headphones 95+% of the time now. Twenty years of fighting this space with room treatment and various forms of EQ now have proven to me that I will always be sensitive to comb filtering in the vocal range, an inherent problem with stereo, and headphones are the solution for me.

 

[dasdoing]

View attachment 301401

With the amount of smoothing I applied to the upper frequencies, I don't think I have created any artificial peaks? Or am I looking in the wrong place?

I was quite aware that the measurement would be contaminated by comb filtering, which is why I applied so much smoothing.

(edit) and I also staggered the curves with the gain function so that it is more legible, so please don't think there is a whopping difference in dB between all those curves!

hard to follow for me what you did.
note that you need to create minimum phase version before aplying the window. can't bring forward what has been removed.
that 38Hz-ish dip for example. it could be just delayed (or not). so by bringing 25Hz and 65Hz down to the same level there could be a peak now on the total window. just an example.

I must say that I never had the chance to use Acourate though. But I guess the FDW feature works the same as in REW.

 

[tmtomh]

but it IS problematic as allready said. we don't want sofa comb filtering in the measurements

If you include the sofa but are not sitting in it when you take measurements, then the measurements will not reflect exactly what goes on when you're sitting there listening. But if you include the sofa and sit in your listening position while taking the measurements - or if you approximate your body as noted above with a dummy or pillows or a blanket over the sofa - then you'll get quite close to actual listening conditions.

Removing the sofa makes no sense, because doing so changes the measurements. You might as well take all the furniture out of the room.

 

[tmtomh]

What concerns me more now is that a leather sofa is perhaps more reflective than absorptive in the critical range above Schroeder but below around 1kHz. As I move the mic closer to the speakers...without any dummy in place, LOL...the curve from 400-1KHz tends to flatten. The closer the mic is to where my ears would be when seated in prime listening position, the deeper the dip, and the frequency fairly well correlates to a reflection from the sofa cancelling the direct sound from the speaker.

Maybe the moral of the story is that leather seating is sub-optimal?

Or maybe the moral of the story is to consider the impact of sofa material in the context of the level of in-room response linearity we can realistically get in a typical living space.

 

[krabapple]

Did you take any repeat measures, under the same condition, to find what the natural variance of the system is? An average of n=3 would be nice.

 

[tmtomh]

I think folks might be surprised to see how the magnitude of run-to-run variations compares with the magnitude of the reflection/absorption issues they are trying to solve. And that's not even accounting for how the measurements might vary based on the normal temperature and humidity changes in a typical residential room over the course of the seasons (or a day).

 

[Keith_W]

Did you take any repeat measures, under the same condition, to find what the natural variance of the system is? An average of n=3 would be nice.

I have 4 sets of measurements, using 4 different filters, all with sofa vs. no sofa. The mic was not moved during any of these measurements. If this is what you are looking for, I can post them later?

Or are you asking if I have repeated the measurements with the mic moved?

 

[ozzy9832001]

but it IS problematic as allready said. we don't want sofa comb filtering in the measurements

I disagree. Measurements should be taken with and without the sofa. You can decide whether to compensate for those differences. I personally wouldn't unless it is creating some sort of reflection in line with your ears, but it could be creating a problem for another seating position in the room. Therefore, it maybe worth adjusting for it.

 

[ozzy9832001]

What concerns me more now is that a leather sofa is perhaps more reflective than absorptive in the critical range above Schroeder but below around 1kHz. As I move the mic closer to the speakers...without any dummy in place, LOL...the curve from 400-1KHz tends to flatten. The closer the mic is to where my ears would be when seated in prime listening position, the deeper the dip, and the frequency fairly well correlates to a reflection from the sofa cancelling the direct sound from the speaker.

Maybe the moral of the story is that leather seating is sub-optimal?

At some point in time there has to be compromise. Seating, like windows, doors, closets and other furniture is a series of yings and yangs.

 

[BinkieHuckerback]

'So, what difference does it make?
So, what difference does it make?
It makes none
But now you have gone
And you must be looking very old tonight'

Couldn't resist.

 

[krabapple]

I think folks might be surprised to see how the magnitude of run-to-run variations compares with the magnitude of the reflection/absorption issues they are trying to solve. And that's not even accounting for how the measurements might vary based on the normal temperature and humidity changes in a typical residential room over the course of the seasons (or a day).

Surprising or not, it's an elementary step that must be taken for the later results to have any context..

 

[krabapple]

I have 4 sets of measurements, using 4 different filters, all with sofa vs. no sofa. The mic was not moved during any of these measurements. If this is what you are looking for, I can post them later?

Or are you asking if I have repeated the measurements with the mic moved?

No. Repeated measurements with the exact same setup.

Every measurement system has some 'run-to-run' variability. IOW you can measure the same thing twice and get nonidentical results. You need to know the extent of that non-identity before you can interpret what you see in your 'experimental' runs where you DO change stuff.

 

[tmtomh]

Surprising or not, it's an elementary step that must be taken for the later results to have any context..

Well, yes - I was agreeing with you!

 

[DWPress]

Sorry, I missed your post. I haven't tried the MMM method. What is it good for? Frequencies above Schroder? Removing comb filtering?

Google MMM (moving microphone method) for a full explanation and how-to, plenty here on ASR about it. It is exceedingly easy to do in REW. In the most basic sense it is purely a FFT measurement where you are slowly moving your mic around in a large 3D figure 8 pattern to get an idea what is going on beyond your single point measurement. There is no timing or phase information to be gathered but the results give a truer idea what is happening in the frequency domain.

 

[Keith_W]

No. Repeated measurements with the exact same setup.

Every measurement system has some 'run-to-run' variability. IOW you can measure the same thing twice and get nonidentical results. You need to know the extent of that non-identity before you can interpret what you see in your 'experimental' runs where you DO change stuff.

You mean you want me to leave the microphone in place, use the same filters, and perform the same sweep a few times with the only variable being sofa present or not? Yeah, I can do that.

Google MMM (moving microphone method) for a full explanation and how-to, plenty here on ASR about it. It is exceedingly easy to do in REW. In the most basic sense it is purely a FFT measurement where you are slowly moving your mic around in a large 3D figure 8 pattern to get an idea what is going on beyond your single point measurement. There is no timing or phase information to be gathered but the results give a truer idea what is happening in the frequency domain.

I have read links about MMM, but it has never been clear to me what they are trying to accomplish. It would seem to me that it would average out some frequency bands more than others, namely short wavelengths, and I suspect that how much averaging depends on how far you move the microphone. I guess I could resolve all these questions by performing the experiment myself and seeing what the results are.

 

[ernestcarl]

if correcting magnitude only the minimum phase version of the meassurements should be calculated before aplying the window. else, frequencies that are delayed fall out of the window.
I showcased this problem here: https://www.hometheatershack.com/th...dependent-windowing.99673/page-6#post-1619293

Good idea... But, I think this is more problematic if one uses the (usually single point) windowed version as one's sole reference for EQ.

Some auto EQ algorithms may overcompensate... yet, this should be easily avoidable if one checks manually using more than one method e.g. multi-point reference and sometimes even in tandem with spatial averaging (MMM).