• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Incorporating environmental factors for DRC

How many environmental factors do you incorporate in room correction?

  • SPS with no sofa (room incorporated only)

    Votes: 2 13.3%
  • SPS with sofa (room and sofa incorporated)

    Votes: 11 73.3%
  • MMM whilst sitting (room, sofa, and body incorporated)

    Votes: 2 13.3%
  • Binaural mics (room, sofa, body, head, and pinna incorporated)

    Votes: 0 0.0%

  • Total voters
    15

Keith_W

Major Contributor
Joined
Jun 26, 2016
Messages
2,939
Likes
6,821
Location
Melbourne, Australia
After reading a bit about BACCH ORC, which uses binaural mics to capture the HRTF, it struck me that there are many different ways you could take measurements for room correction. The difference is how many environmental factors you want to incorporate in your measurement. In a nutshell:

- SPS (single point sweep with omni mic) with no obstructions: Move the sofa, coffee table, and anything obstructing line of sight to the speakers away, and place the mic at MLP and do a sweep. Use that to generate room correction. This is the usual recommendation for Acourate and Audiolense, and is also recommended by @mitchco in his book.
- SPS with sofa: Leave the sofa and all the usual furniture in situ, place the mic at MLP, and do a sweep. The idea is to do a correction with the normal configuration of furniture when listening.
- MMM: this time you sit at the MLP and move the mic around your head. This not only incorporates the furniture, but also your body in the measurement.
- Binaural: This is at the other extreme. The effect of the sofa, body, and HRTF are incorporated into the measurement.

As you can see, strategies for taking measurements for room correction range from one extreme to the other. At one extreme, environmental factors are minimized, and only the room is corrected. At the other extreme, the effect of room, furniture, body, and head, and pinna are incorporated into the measurement and therefore corrected. Yes, I know that MMM and Binaural can not capture phase and timing information. Let us ignore that for the moment and focus only on FR correction.

Now obviously, accounting for body/head/pinna means shorter wavelengths are also incorporated. Because of the small size of the head compared to the wavelength, the head does not even begin to affect the measurement until 1kHz and up, and the pinnas from 5-6kHz and up. Here is an image I found online of the HRTF of three individuals:

40857_2019_169_Fig2_HTML.png


What you can see is that everything <1kHz is broadly the same. Above this, there is quite marked variation. So I can see that depending on whether you believe that full frequency correction vs. correction below Schroder only should be done, as we discussed in another thread I started ("should we correct to Schroder or full range"), it will influence the way you take your measurement. If you believe in correcting below Schroder only, there is no benefit of incorporating the HRTF into your measurement. So for the purpose of this discussion, let us assume that you are correcting full range.

I do not own a binaural mic, but I have done experiments comparing sweeps of sofa vs. no sofa vs. MMM. About the only thing I haven't done is duct tape the mic to my balding head although I am considering doing that as an experiment! As you would expect, the results are markedly different. I can't find my MMM measurement, but here is a comparison of the FR of my system with/without sofa, before DRC:

1711342718015.png


You can see that the sofa boosts the bass frequencies and especially the high frequencies. If I were to make a correction, the result would be markedly different. The MMM looked different again, from my recollection there was even more of a treble boost.

It has also occurred to me that headphone guys want to incorporate as many environmental factors as possible. The importance of the HRTF is emphasized when generating headphone corrections, with some (like Griesinger) advocating tailoring the FR to the actual subjective response in your brain. No crappy binaural mics here, it's either deep insert mics, or better still, using test tones. This works by adjusting the volume of a test tone until it subjectively matches the reference tone, and this generates an extremely personalized transfer function which incorporates ear canal, the tension of the eardrum, movement of the ossicles, fluid pressure in the Organ of Corti, hearing loss, and so on. I have tried this, and it generates a horrible sounding correction. I am unsure if it is the method which is at fault, or my inability to volume match the tones. But that is a separate discussion.

Given that different authorities advocate different methods of obtaining a raw curve for room correction, some advocating for minimal environmental factors, and some others advocating for incorporating everything including the head and pinna, the only way for me to make a decision was to try them all. I took measurements with/without sofa and MMM, used those measurements to make filters, and listen for what I subjectively preferred the best. For me, I liked the sound of "SPS without sofa" the best. I felt that the other two methods knocked back the bass and treble too much and gave the music less impact and clarity.

I would like to opinions on:

- whether you believe in maximizing or minimizing the effect of environmental factors when designing your room correction,
- using binaural mics for room correction,
- which sounds best to you
- your reasoning behind your decision.

I also welcome any criticism of any flaws in my methods and reasoning.
 
Last edited:
None of above choices :) , I usually apply MMM while removing or covering with absorbers if possible objects close to the LP like chair/sofa as their close reflections alter the sound field above bass, a recommendation I actually got from Dr. Ulrich Brüggemann from Acourate. If correcting only bass they can stay but on the other hand the differences are not high and in the end what which result personally sounds best to us matters.
 
  • Like
Reactions: MAB
I use MMM, multi point sweep, single point sweep.
I always leave the furniture in place.
I don't measure while sitting in the MLP. I don't worry since there isn't much I can do about me in the MLP, and my occasional attempts to quantify the effect of me and the furniture I am sitting show it isn't a big difference. And, the difference wouldn't lead to new EQ settings in my small experience.
The only rule I have on furniture is no high-backed chairs! But what I have tends to stay in place.
 
About the only thing I haven't done is duct tape the mic to my balding head although I am considering doing that as an experiment!
There's got to be a cartoon of this somewhere!
 
My partner constantly moves furniture and furnishings around. I would probably need to remeasure and adapt the configuration at least monthly, or live with a compromise (my current approach).
 
I don't see any point in doing room correction if everything in the room is not exactly as it will be when listening, including furniture, people or large fluffy pets etc. ...
 
None of above choices :) , I usually apply MMM while removing or covering with absorbers if possible objects close to the LP like chair/sofa as their close reflections alter the sound field above bass, a recommendation I actually got from Dr. Ulrich Brüggemann from Acourate. If correcting only bass they can stay but on the other hand the differences are not high and in the end what which result personally sounds best to us matters.

He doesn't recommend that though. He recommends moving the sofa out of the way so that the mic has direct line of sight to the speakers with no reflective surfaces nearby. There must be a reason why he recommended this for you. Perhaps your furniture is too large or too inconvenient to move?

Anyway, the responses so far have been interesting. We have:

- 1 person leaving furniture in place and attenuating reflections (you),
- 1 person leaving furniture in place and doing MMM, SPS, MPS, etc (MAB)
- 1 person removing the sofa and not redoing DSP every time his wife moves the furniture (MaxwellsEq)

@bluefuzz those are my sentiments exactly, it makes no sense to me doing room correction if the room is not left exactly as it should be for listening. However, in my experience it does generate nicer sounding filters.

BTW, maybe I missed it in my reading, but Toole does not seem to say anything about it.
 
SPS (single point sweep with omni mic) with no obstructions: Move the sofa, coffee table, and anything obstructing line of sight to the speakers away, and place the mic at MLP and do a sweep. Use that to generate room correction. This is the usual recommendation for Acourate and Audiolense, and is also recommended by @mitchco in his book.

I didn't even know about this recommendation. Do you know the reasoning behind it? Can it be we're interpreting it wrong, meaning the idea is not to remove the sofa you sit on while listening but just to clean up your space ("move anything obstructing line of sight to the speakers").
 
I usually apply MMM while removing or covering with absorbers if possible objects close to the LP like chair/sofa as their close reflections alter the sound field above bass, a recommendation I actually got from Dr. Ulrich Brüggemann from Acourate. If correcting only bass they can stay

Might this be because Acourate attempts to find the anechoic response (quasi-anechoic measurement) and correct for that (above Schroeder freq.)?
 
Last edited:
Might this be because Acourate attempts to find the anechoic response (quasi-anechoic measurement) and correct for that (above Schroeder freq.)?
Yes, not only in Acourate you want to correct more the direct sound above room transition frequency.

He doesn't recommend that though. He recommends moving the sofa out of the way so that the mic has direct line of sight to the speakers with no reflective surfaces nearby. There must be a reason why he recommended this for you. Perhaps your furniture is too large or too inconvenient to move?
I don't see a contradiction to what I wrote above?
 
  • Like
Reactions: MAB
If you were correcting for HRTF (I don't) then shouldn't it be treated as per linearisation given that your head doesn't change with the room?

Moving furniture seems to me to be just another step towards approximating a quasi anechoic measurement without actually taking one.
 
I think that you cannot determine a significantly better or worse measurement method if you do not have a significantly precise target (understood as magnitude, phase, reflections amount, etc.).
To date it seems to me that a target of magnitude is still not universally defined, nor definable.
Even less if we consider the phase and amount of reflections...
So, A sufficiently adequate measurement technique is only subjectively determinable, but here the usual known problems open up.
 
I used to have two sets of filter one with the door to adjacent room open and one with the door closed . but the Meridian DRC only operated below 300Hz so i never bothered moving furniture around .
 
Yes, not only in Acourate you want to correct more the direct sound above room transition frequency.

Of course, but it means removing furniture doesn't matter if you're not interested in correcting above the Schroeder frequency via a measurement on the listening position. Personally I use a near field measurement to make corrections above Schroeder.
 
Of course, but it means removing furniture doesn't matter if you're not interested in correcting above the Schroeder frequency via a measurement on the listening position.
That's what I had also written above:

If correcting only bass they can stay but on the other hand the differences are not high and in the end what which result personally sounds best to us matters.
 
I would only move furniture away if it is readily mobile -- e.g. chair for a desk ~vs~ calibration microphone and its floor stand.

I have speakers directly facing beds in bedrooms... am I supposed to dismantle and move queen-sized bed furniture outside first? How about the chairs inside the cabin space of a passenger vehicle?

Regardless, single-point log sweeps at the MLP should still be referenced alongside other data sources as additional checks as much as possible: the anechoic (e.g. spinorama), quasi-anechoic (e.g. nearfield/gated), on- and off axis dispersion, directivity index or vertical and horizontal beamwidth, and spatial averaged MMM curves in-room.

*Oh, yeah, I would never ever measure speakers with my head/body in the way if it can be helped -- with MMM, you can't really do that completely unless you use some kind of extension arm boom.
 
Last edited:
I don't see a contradiction to what I wrote above?

I am sorry, I misread your post.

I didn't even know about this recommendation. Do you know the reasoning behind it? Can it be we're interpreting it wrong, meaning the idea is not to remove the sofa you sit on while listening but just to clean up your space ("move anything obstructing line of sight to the speakers").

If it made sense to me, I wouldn't question it :) What makes sense to me: everything that is present when you are listening should be accounted for. This includes your body and your head, which is why I find the idea of binaural mics attractive. However, my own experiments suggests that the sound is subjectively more pleasing when the initial measurement is taken with the sofa removed.

This is one data point only, and I acknowledge that it is a particularly useless data point because subjectivism is involved. However, I do wonder if I am over-thinking it. After all, 99.9% of the speaker market involves people buying speakers and plonking them in their rooms and not bothering with any room correction at all, and they get good sound. I have a tendency to be overzealous when it comes to correction, and I have certainly produced filters that measure beautifully but sound awful. I am still inexperienced when it comes to correlating what measures good with what sounds good, I only have experience with my own system and not with others. This is why I ask ASR whether it's just me!
 
Don't worry, you are not the only one, I have been seriously experimenting with DRC since now more than 10 years (my first EQ with pink noise generator and RTA was even 30 years and my first car with EQ which I corrected based on miving mic measurements 20 years ago) and I have come to similar conclusions, a reason why for example although I own Acourate too I just use nowadays simple IIR REW based correction.
 
I've been using REW and other tools for over a decade now myself for my active XO 3 way + 2 subs and room correction. My listening room is my work studio though, office and book bindery (presses in the other room) so all measurements over the years have been as the room evolved. I use both fixed point for timing information and MMM for just dialing thing in first. Also way down the rabbit hole with individual driver correction, going crazy in rePhase and loving every minute of it.

Now, using @mitchco 's cool HLC app I can directly compare my efforts with other things like DLBC (which I trialed and purchased), Sonarworks stuff, Home Audio Fidelity and anything else I could trial and use on Mac.

I'm rambling. To sum it up - not enough choices. You can't get all the information you need from single sweep or MMM.
 
Back
Top Bottom