How would you calculate that, e.g. using simplifications like sound rays, angle of incidence = angle of reflection and sound power from the reflection equals sound power of incidence minus sound power absorbed (let’s assume sound power absorbed equals sound power transmitted and sound power really absorbed here 
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I have the impression that what is going on in the room is prety much chaotic so not calculatable, only by approximation. Acoustics can be modelled, but that is what it is, a model. Problem with models is.. garbage in, garbage out. And it has only mediocre capabilities to predict how a room will sound. Of course, acoustic professionals come to a great length but the proof is in the pudding and experience in the field is vey important for predictions regarding room acoustics.
I would prefer the common acoustical terms of "direct/ reverb field" to "near/far field" since they are different concepts and the one that you are referring to are "direct/reverb". They can never be the same, but the direct field can be negligable, in which case there is only the reverb field.
You second statement is quit correct - reverb measures are only exact when the field is diffuse/random.
What happens is this:
In a small room the early reflections will indeed be stronger than the early reflections in a large room, because they will have spread less. But then they dissipate very quickly in comparison to the more gradual fall in a large room. Also a large room will have a large offset from the direct sound and the reverb and there won't be any perceivable singular reflections (except this can happen in a poorly design auditorium.) This difference is the essence of the small room large room differences in the timing and the level of the Very Early Reflections (VER.) That's why they are so problematic.
A high DI will both minimize the VER (especially is placed and pointed correctly) as well as increase the time offset from the direct sound to the onset of reverb. This is an essential aspect of good imaging.
These days, no competent acoustician would ever design a room without modeling it first. Of course it's not perfect, but it's still a very good start.
Well, that is not my experience.
Seen this from first hand since I worked for some quite some well known companies here.
Like @markbakk mentioned in another topic, the field of acoustics and studios is a very conservative one.
Most still rely on just old "experience", "because they have been doing it for 30 years this way".
It's all extremely empirical and made with many rules of thumb.
Even approximation is a bit of a stretch sometimes.
I can say with very big confidence, that the majority never touched modeling software and don't even know what it is.
It is slightly different for very big and expensive projects.
The "modelling" software I have seen and worked with, is also all based on just empirical ballpark numbers.
I personally would never call that modelling software in the first place, more like a cheat sheet.
As about before with near-field/far-field etc.
That is a bit lost in translation thing for me.
Certain words and definitions are still stuck in my head with my native language, which can be translated in different ways to English, depending on context.
Also some of the jargon and terminology of acousticians sometimes seem to be every so slightly different than loudspeaker people, weirdly enough.....
IIRC the reverb field isn’t 100% diffuse (no dominant vector) while Sabine derived his famous equation presuming a diffuse field. So something like (R)T60 in a reverberant field isn’t constant, while it is (or should be)in a diffuse field. Hairsplitting I know and my acoustics is a bit rusty, but reverberant field is only defined by that space where indirect sound is louder than direct sound. So don’t even use T60 for reverberant field conditions, I’m inclined to say. It doesn’t add that much for music reproduction.
In the academic field and probably in automotive and aerospace industries (I’m not at home there) auralization of spaces does emerge. Everest and Kutruff to name a few describe simulation tools for this in their standard works. And I recall some article about the faculty I attended my courses long ago developing software for this quite recently. So who knows these instruments will become available to us mere mortals eventually… but still: garbage in equals garbage out.
Well, that is not my experience.
Seen this from first hand since I worked for some quite some well known companies here.
Like @markbakk mentioned in another topic, the field of acoustics and studios is a very conservative one.
Most still rely on just old "experience", "because they have been doing it for 30 years this way".
It's all extremely empirical and made with many rules of thumb.
Even approximation is a bit of a stretch sometimes.
I can say with very big confidence, that the majority never touched modeling software and don't even know what it is.
It is slightly different for very big and expensive projects.
The "modelling" software I have seen and worked with, is also all based on just empirical ballpark numbers.
I personally would never call that modelling software in the first place, more like a cheat sheet.
As about before with near-field/far-field etc.
That is a bit lost in translation thing for me.
Certain words and definitions are still stuck in my head with my native language, which can be translated in different ways to English, depending on context.
Also some of the jargon and terminology of acousticians sometimes seem to be every so slightly different than loudspeaker people, weirdly enough.....
Strangely i've had the inverse experience about acousticians and modelling software.
Please put name on the one(s) who did it by 'intuition' since 90's : except for the first iteration of Hidley's room ( before he made a break end 70's before coming back during 80's with Zero Environement concept) most of the one i've been in had simulation availlable from initial request of place owner.
Maybe it was the case for some guy ( J. Sayer?) which had worldwide recognition for the outcome of their rooms but 70's and 80's are way back now... as the field become more and more technical ( can be questioned though) people require technical proof too.
I mean it's a conservative field we agree on this, but people ok to spend a fortune for room treatments requires some kind of 'proof of concept' ( even if they don't understand the said proof...) before leting cash flow.
This have been my experience and the case for the name given in the other thread you refer to.
Of course if you talk about 'the average studio' ( a concept i have issue with as it can cover a wide range of things) you are into the wild for numerous reason: lack of knowledge, lack of budget, needs of the place and customers,...
About the modeling software, well please give names too. The one i've seen were not based on rule of thumb ( Comsol, Ease, Odeon,...) and quite right in their outcome vs reality.
Anyway i've got same issue with translation, it seems some jargon is not always translated in same terms ( been astounded to have to explain 'polarised rooms' which is comon in my native language to talk about LEDE and derivative rooms).
@krivium
I am mostly talking from the perspective of acoustic consultancy companies who do all kinds of acoustics.
The vast majority is offices as well as theaters, sometimes studios if they show up
(which isn't often, studios are the most simple of all those things).
I am not gonna name any companies for obvious reasons I think.
But they are THE biggest companies over here, doing massive projects.
For existing buildings and rooms I have rarely seen modeling software.
They always go in and actually measure on location, following current regulations.
Give advise accordingly.
Otherwise I have seen quite often just scaled down models being used when things get very complex.
The software they used was all proprietary, made and maintained by themselves.
And yeah translating jargon is a pain, haha
(especially when it was being taught in your native language at school and university)
I am mostly talking from the perspective of acoustic consultancy companies who do all kinds of acoustics.
The vast majority is offices as well as theaters, sometimes studios if they show up
(which isn't often, studios are the most simple of all those things).
I am not gonna name any companies for obvious reasons I think.
But they are THE biggest companies over here, doing massive projects.
For existing buildings and rooms I have rarely seen modeling software.
They always go in and actually measure on location, following current regulations.
Give advise accordingly.
Otherwise I have seen quite often just scaled down models being used when things get very complex.
The software they used was all proprietary, made and maintained by themselves.
And yeah translating jargon is a pain, haha
(especially when it was being taught in your native language at school and university)
So there are different experiences. MIne is mostly friends who design auditorium and performing arts, and they use a lot of modeling. Heck, we were doing car interior modeling back in the 80's. And my notions about LFs in small rooms comes directly from the modeling that I did for my PhD (back in the 70's). Some people use it and some don't.
Far field and near field are concepts applied to transducers where the far field is where the sound falls at 6 dB per DD. They are independent from the space that the transducer is in.
Direct field and reverb field define the field where the sound drops 6 dB per DD, so it's similar to the near field from the transducer, but not the same. The reverb field is that part of the sound field where the reverb level > direct field.
Further, these are all steady state concepts. Transients, especially perception, can be very different.
Far field and near field are concepts applied to transducers where the far field is where the sound falls at 6 dB per DD. They are independent from the space that the transducer is in.
Direct field and reverb field define the field where the sound drops 6 dB per DD, so it's similar to the near field from the transducer, but not the same. The reverb field is that part of the sound field where the reverb level > direct field.
Further, these are all steady state concepts. Transients, especially perception, can be very different.
It is. But to room acoustics often applies what is true for speaker engineering. You can’t afford extensive and costly modeling when numbers are low. A thousand identical rooms? Sure. One room? Heck no.
Now I’m lost in translation, or did you refer to the boundary near field changes into far field?
My comment wasn't clear, so I'll restate:
A transducer has two fields, the near field and the far field. In the near field the sound is collumated and does not fall with distance. It is greater at HFs and gets shorter at LFs. In the far field the SPL falls with distance. All this is independent of the room because this is a free field concept.
In a room we have a direct field and a reverb field. In the direct field the SPL falls with distance, but the reverb field does not. The distance at which the direct field equals the reverb field is called the critical distance. If the room absorption is frequency independent (almost never the case) then these field are also independent of frequency.
I hope this is clearer.
Yes. The classic acoustic, and mathematical definition of near and far field. Which is as best I understand primarily about the distance at which a speaker begins to obey inverse square law attenuation .
This link pertains more to large scale live sound boxes, but i like it because i think the principles hold true regardless of speaker size.
https://www.prosoundtraining.com/2010/06/28/far-field-criteria-for-loudspeaker-balloon-data/
What's really interesting to me, is how it shows it takes more distance to get into the far-field with VHF than anything else.
Is it incorrect to think of rooms have three fields....direct, indirect, and then reverb if room is large?
Because it seems to me if a room isn't large enough to support real reverb, there still is a distance in it that reflected sound equals direct sound.
Probably the majority of all domestic rooms???
Clear to me. As Earl Geddes meant to say (IIRC), all this philosophy about sound fields in listening rooms is not that useful as they are defined as steady state fields. These iterations of what is going on with music reproduction aren’t precise enough. Just like the (R)T60 or 30 like I wrote. Those values only roughly give indications of the sound field behavior whereas other aspects are of far more importance, especially in small rooms. So forget about them.
So basically, there is a connection to large room acoustics, and high DI loudspeakers in small rooms, in that they both have reduced levels of the VER in comparison to low DI in small room. The larger room pushes timings back, removing that energy from the "VE" region, and the High DI in small room, reduces VER levels by focusing more the sound towards the listener instead of the walls.
This is what I have been trying to say the whole time, ie.... High DI makes a small room sound larger.
How? Timing is the most telling of size, and damping does nothing for timing. Are you thinking of reverb times, and shorter duration? The largest spaces have like outside, have highest damping, don't they?
I guess its all a matter of perspective
Which is what I think that I said.
Rooms could be thought of that way. I suppose I think of them that way. The direct and reverb fields we have already discussed. Yes, I would agree that there would be an indirect field particularly in small rooms, this would be when the reflections are spaced out and strong enough so as to be significant, ie. early and distinct. As the room gets larger this region gets smaller to the point of an auditorium where there would not be any indirect field (or there should not be, which has been a noted flaw in many designs.) The reflections would arrive in too short a time spacing and at random angles which would make it already a decorrelated signal (reverb is scientifically called a decorrelation filter.)
To me, this "indirect field" is the most important, its when these VER (Very Early Reflections) are not well controlled that we have problems with imaging. One can also add spaciousness by exciting this region with low DI designs, but that will give up imaging.