## ACCEPTABLE ROOM RATIOS

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

### ACCEPTABLE ROOM RATIOS

I made an overview, but entered it in the FAQ section, so it doesn't get lost in the mass.

http://forum.studiotips.com/viewtopic.php?p=5570

Please LEAVE this info were it is. And I DO mean that.
If you want to help others just link to the topic.

Any comments or ideas are welcome. :)

Best regards
Eric
Eric.Desart
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Looks great Eric.

Morse & Bolt state that tangential modes require twice the power to produce the same sound pressure as a similar axial one, while oblique modes require four times
as much. It is therefore necessary to divide the sound pressure so calculated by sqrt(2) for each non-zero nx, ny, or nz over one.

I thought that the ratio of axial/tangential and axial/oblique was dependant upon the aborbtion for that frequency of the wall. For example at 2khz if the walls are concrete and paint then the ratio is much smaller than that (e.g. 1.1 instead of 4.0), and if the walls are 4" of fiberglass then the ratio is much larger than that (e.g. 20 instead of 4). Hmm. maybe it's just the number of bounces that counts, since the absorbtion is going to be hitting the axial as well.

Another source I've been using lately for room proportions is that graph in the room ratios tab of "Control Room Calculator V2.6 OfficeXP.xls" by Prof Trevor Cox. The best spot on there is 1 : 2.23 : 3.05

Any chance you could:
a) normalize the ratios so they all start with 1 instead of 2.7 : 5.3 : 7
b) sort the ratios by the second dimension

You've got Louden's favourite room size. What's yours?
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Joined: Sun Feb 08, 2004 4:37 am

Bob

Bob wrote:I thought that the ratio of axial/tangential and axial/oblique was dependant upon the aborbtion for that frequency of the wall.

Of course that's true. But that's true for the whole Room Mode Calculation.
Any Room Mode Calculator assumes a highly reflective room.

Once you start treating the room, the interference patterns will change completely. Not only the ratios between the different types of modes.
In fact a room mode calculator is a relative limited tool to prevent that you start with wrong ratios asking for build-in problems. Nothing more.
A room mode calculator is NO simulation software.

Bob wrote:Another source I've been using lately for room proportions is that graph in the room ratios tab of "Control Room Calculator V2.6 OfficeXP.xls" by Prof Trevor Cox. The best spot on there is 1 : 2.23 : 3.05

If you have a link, I can study it and integrate it in the post, with all credentials and references.

Bob wrote:Any chance you could:
a) normalize the ratios so they all start with 1 instead of 2.7 : 5.3 : 7
b) sort the ratios by the second dimension

On EVERY picture the Room ratio is mentioned as you want it.
The way I did it is to preserve the approach of the original source.
E.g. the one you mention above is mentioned in the official recommendation as I did, since they do not present it as a ratio but really as a room size expressed in meters (metric).
So now you have it double: The official publication AND the ratio on the picture.

I can sort them as you like, if that's the general opinion.
For me it doesn't matter that much. The way I did it was to keep the original Authors together as they published it.
And I did it more historically.
And the ones I can't assign to anything I put last.
E.g. Louden really ranks his ratios. I don't like scrambling that.
And I don't like to scramble the individual ratios, loosing relationship with the Authors.

So I first want other's opinion too, because you can look at it from all different sides.

I like the Louden and Sepmeyer ones. But in fact I don't mind that much. I put it in (non-commercial) simulation software.

If you or anybody else can find or know the original sources of the ratios I don't know, I should gladly hear about it.
If anybody has other interesting data to add, I will complete it respecting all sources.

Warm regards
Eric
Eric.Desart
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Bob,

I will add at the bottom a few lists were they are sorted in different ways and I will number them + use the 1: x:x method.
You can see that every picture has an ID number.

Maybe today, otherwise tomorrow.

Eric
Eric.Desart
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Location: Antwerp, Belgium

Bob wrote:
Another source I've been using lately for room proportions is that graph in the room ratios tab of "Control Room Calculator V2.6 OfficeXP.xls" by Prof Trevor Cox. The best spot on there is 1 : 2.23 : 3.05

If you have a link, I can study it and integrate it in the post, with all credentials and references.

It's the one by ChrisW at http://www.rmmpnet.org/members/ChrisW/ControlRoom.html (that is, the spreadsheet is ChrisW's, but the graph is acredited to Prof Trevor Cox.)
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Joined: Sun Feb 08, 2004 4:37 am

Bob wrote:
Any chance you could:
a) normalize the ratios so they all start with 1 instead of 2.7 : 5.3 : 7
b) sort the ratios by the second dimension

On EVERY picture the Room ratio is mentioned as you want it.

Ah. I'm looking at
J. E. Volkmann: 1942 (later discussed by H. Bolt) - 2:3:5
Polycylindrical Diffusers in Room Acoustical Design.
Journal Acoustic Society America Volume 13 , 1942, pp 234-243.

and I can see in your spreadsheet, 2nd line, in tiny print, is the ratio 1:1.5:2.5
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Joined: Sun Feb 08, 2004 4:37 am

Bob,

Thanks.
If you find something that looks wrong I'll check it.
If needed will adjust everything tomorrow.

But anyhow thanks for helping.

Best regards
Eric
Eric.Desart
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Bob,

You can easily use that to find a suitable ratio.
http://forum.studiotips.com/viewtopic.php?p=5570

Is that OK, or do you still want this other sort order lists at the bottom.

I'm going to do the rest later (this becomes rather time consuming).
I will further extend the topic when I feel like it.

Best regards
Eric
Eric.Desart
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Location: Antwerp, Belgium

Hi Eric:

Graph vs Sorting:
It's a little different than the way I usually wrap my mind around it - I was thinking more in terms of whenever I spot another ratio to be able to quickly check this page to see if it's already there. Normalized and sorted data would do that.
Nevertheless to that end I think the solution you've come up with is both useable and provides additional spatial information. The only thing I'd be worried about is that if you add an additional ratio you'll have to redraw that graph.
It's good enough. Thanks.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

Posts: 4360
Joined: Sun Feb 08, 2004 4:37 am

He-He,

This graph is made by a complete automated Excel program.
The number of possibilities is rather large.
I just have to enter parameters and measures or ratios.
Still times goes fast when bringing things together in such a post.

Only I never can find the time and energy to finish it, to put it on my site, as a free download.

That's standard: 10% time for the functionality and 90% to make is usable for (and protect it against) others.

Do you now still want those sorted lists or not???

Regards
Eric
Eric.Desart
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Location: Antwerp, Belgium

It's good enough. Thanks.
Bob

Posts: 4360
Joined: Sun Feb 08, 2004 4:37 am

Eric:

This is twice this week that you have hekped open my eyes to see things that I have known , but not how to look at them properly.

Thanks

Bob:

Your input and analysis of the data and its presentation is excellent. It also remnds me that there are many ways to look at something.

Thanks
avare

Posts: 965
Joined: Thu Mar 04, 2004 10:22 pm

Nice article, being able to have images in the post is a great improvement over the old yahoo group. I will most likely force it down the list so the faq order follows the table of contents after we decide where is should be in the contents order.

Dan
Dan Nelson

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Joined: Sat Jan 31, 2004 2:52 am

Eric:

Somewhere in the past month you mused that room proportions are best at certain volumes. That if one keeps the proportions the same, but changes the volume, strange things happen. This quote is about much different sizes, but I'd presume that some of the physics is transferable, especially in the last three sentences. For example, if a room of 10x15x20 were built using 10cm stone blocks with 3cm x 1cm hollows between the blocks, and then another room of 15x22x30 (same proportions, 1.5 times larger in all dimensions) were built using the same 10cm stone blocks, the effects wouldn't scale linearly.

From "Recording Studio Design" by Phillip Newell, pg 254, section 10.2

Short of building full-size prototype rooms, the next best possibility would seem to be to build and test scale models. At concert hall level this is a proven method, at least as far as the major characteristics of the room are concerned. In a one-tenth scale model of a studio room, music can be played thorugh miniature loudspeakers in the model room, speeded up by ten times, and recorded via miniature microphones placed in the ears of a one-tenth scale head. The sounds can be recorded, and then slowed down by ten times, and the result heard on the headphones should be a reasonable representation of what the full-scale room should sound like. The above description of the technique is something of a simplification of the whole process, but the technique is useful and is used on some large-scale projects. One-fiftieth scale modelling is also used for larger halls, but because the frequencies must be scaled up by the same amount, air absorption losses are such that dry nitrogen is frequently used to fill the models, and in many cases, predictions are restricted to the low frequency range of the final, full-scale room. However, with rooms of studio size, the scale-modeling method would be expensive to put into operation. Furthermore, as the characteristics of acoustically small rooms are so dominated by surface features, which will not easily scale, the scale-modelling technique is likely to fail. Whilst frequencies, sizes and general modal responses can be scaled, the effects of absorbent treatments, the irregular surfaces of stonework, or the effects of floor resonances cannot be scaled. Mineral wool is almost impossible to scale, as are carpets or curtains. Scale models of small rooms can only be used to determine gross effects, and if effects are gross, they can normally be deduced from pure theory.
Bob

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Hello !

I think most of you probably know this link, anyway here it goes....

http://www.acoustics.salford.ac.uk/acou ... sizing.htm

It's Prof. Trevor Cox  publications about room ratios. Very interesting !  He's probably one of the best concerning room acoutics, particularly diffusers and also a very nice person himself.
andrebrito

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Location: London, uk

Thanks Bob and Andre

Andre we know this link and relared documents that's the reason some questions came up.
Bob, I goinf to check this more later.

I know scale models, was involved in several myself.
To study baffels and other materials the KULeuven even made a scaled reverb room to measure absorption of specialy produced mini baffels and other materials.  So one didn't scale only the rooms to be investigated but also the measurement facility.

But the problems are not about details as scaling diffusion from bricks and absorption material.

Standard room ratio calculations assume certain stylized boundary conditions. Real live influences of different boundary conditions and furniture are not taken into account, neither in the d'Antonio approach, nor in the others.

So for now I limited my thoughts and questionmarks to the basic approach of d'Antonio, telling that room ratios are only valid for specific volumes.  And strict mathematically, I can see only the fact that not everything is scaled as e.g. the listening height and position and source position as the reason for this.

Thanks for the info.

divinely-inspired
Eric.Desart
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Eric:

Bolt [1] investigated the average modal spacing to try and achieve evenly spaced modes, but using the average mode spacing is not ideal, and the standard deviation of the mode spacing is a better measure. Ratios of 2:3:5 and 1: 21/3:41/3 (1:1.26:1.59) were suggested, but Bolt also noted that there is a broad area over which the average modal spacing criterion is acceptable. (Note, this later ratio appears to be often rounded to the commonly quoted figures of 1:1.25:1.6).

Your page has as #14 (1 : 1.25 : 1.6)

The next page at the above URL, i.e. http://www.acoustics.salford.ac.uk/acou ... izing3.htm

The first one, the small one, room_ratios.xls, contains
50 m^3 room: 256 ratios
100 m^3 room: 268 ratios
200 m^3 room: 778 ratios

The second one, with the not as good ratio choices, contains
50 m^3 room: 10314 ratios
100 m^3 room: 10396 ratios
200 m^3 room: 18317 ratios
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Bob,

Many thanks.
I knew I had still to extend that topic in the FAQ.

For now, not to loose this, I will enter a link to this topic in the FAQ.

So that it can be found easier.
There must be another one to were AVARE started.
I will link that to (damned must find it.

Bob I really do appreciate your often systematic approach.

Warm regards

divinely-inspired
Eric.Desart
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Eric:

I knew I had still to extend that topic in the FAQ.

You have so many there it never occured to me that it needed expanding at all
Just yesterday I wrote it was "the most complete list I'd ever seen..."

EDIT: andrebrito - I see you mentioned that link above in this thread !!
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

Posts: 4360
Joined: Sun Feb 08, 2004 4:37 am

Eric:

Bob wrote:
Another source I've been using lately for room proportions is that graph in the room ratios tab of "Control Room Calculator V2.6 OfficeXP.xls" by Prof Trevor Cox. The best spot on there is 1 : 2.23 : 3.05

If you have a link, I can study it and integrate it in the post, with all credentials and references.

from http://www.acoustics.salford.ac.uk/acou ... izing3.htm
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Joined: Sun Feb 08, 2004 4:37 am