Welcome, Guest. Please Login or Register
Decware Audio Forums
07/24/14 at 09:30:05


Pages: 1
Send Topic Print
Auditorium Proportions? (Read 201 times)
Brian
Seasoned Member
****




Posts: 282
Auditorium Proportions?
05/21/14 at 18:52:55
 
We have the proportions Steve gave us from the "Masters Handbook on Acoustics". Where did the book author get these numbers? Are they a calculation, or were they discovered in listening or measuring experiments with sample rooms?

Three sets of proportions are given, are these three out of several, or are these three the only proportions which sound well?  

What are the tolerances? If a length is off by one inch, is the failing audible? Is error a quantum leap sort of thing, or does the sound of wrong measurement degrade gradually as the length of the room is progressively made worse? Are width and length and height all equally sensitive to error of proportion?

If side walls are given a rippled surface to act as treble diffusers, is the width measurement taken trough to trough or crest to crest? Or perhaps half way between?
Back to top
 
 
  IP Logged
Lonely Raven
Seasoned Member
****


Jack of all Trades,
Master of None

Posts: 1153
Re: Auditorium Proportions?
Reply #1 - 05/22/14 at 16:31:53
 
Brian, those are awesome questions and show that you're really thinking this out (which we need more of). You're questions are really at the level of an acoustics technician, which I think is above where most, if not all of us here fall.

I've studied (casually) for years, so I could probably fudge my way through your questions, and I have some of my own opinions I've come up with through my own (only slightly scientific) testing.

Your best bet to get some answers at that level would be to check with the guys at GearSlutz.com They have an acoustics section that a couple of real acoustics techs hang out.


Which proportions exactly are you talking about in your first question? Are you talking about room proportions?

Here is the theory of room proportions and why they work.

If I recall correctly (it's been a while since I've read Steve's papers) Steve uses Fibonacci's Golden Ratio to try and get a room that *doesn't* have as many damaging nodes. Every room will have sound damaging nodes, but having a room of specific dimensions you can then avoid known problem dimensions. For example, a typical room has an 8' ceiling. You wouldn't therefor want any of your other dimensions to be a multiple of 8 because that would cause bad nodes. You probably wouldn't want the rest of the room to be even numbers as well because those even numbers would cause smaller nodes. So using Fibonacci's golden ratio, or building a room on prime numbers, you're less likely to have bad nodes due to even or common wavelengths.

I hope I'm explaining that well, I'm probably not.

If you've seen recording studios and concert halls that have non-parallel walls, that's the easy way of avoiding those common nodes. If you had a room with 8' ceilings, 16' wide and 24' long, you would have all sorts of hot spots and dead spots at those multiples. For example, you'd probably have a hot spot and/or dead spot at 2', 4', 8', 12', 16', 20' because those dimensions are all multiples of the room size. And that's just in one direction! You'd still have those same hot/dead spots left to right, and up and down! So your room would be a minefield of uneven sound.

Now, if you're room was (using prime numbers) 13' ceiling, 17' wide, and 31' feet long, you would have fewer frequencies that would be effected by the room dimensions. 13 is only divisible by itself, so you don't have hot/dead spots at multiples. Plus the other room dimensions aren't multiples of 13, nor do they have a common denominator. All that equals a room with less wave interaction, and more even sound.

There is no such thing as a room without these nodes, unless it's an anechoic chamber, or you're outdoors without any room reflections at all.

So the dimensions aren't exactly "good sounding", but less damaging.

Damn, I probably should have just started with that last line. LOL
Back to top
 
« Last Edit: 05/22/14 at 16:36:18 by Lonely Raven »  
WWW Lonely Raven   IP Logged
Lonely Raven
Seasoned Member
****


Jack of all Trades,
Master of None

Posts: 1153
Re: Auditorium Proportions?
Reply #2 - 05/22/14 at 16:43:09
 

To try and answer your other questions, you should really consult some software that helps you figure out what the problem nodes are going to be for your given dimensions. Some even have graphical displays that will *show* where those hot/dead spots are going to be. If I recall from my studies, most of that mess starts below 500hz. So having some minor treble diffusion on the walls, or being 1"off isn't going to change a whole lot when your trouble frequency wave is (500hz at 70F) ~ 2.25' The only thing a small change of 1" in room dimensions is going to do is change that 500hz trouble spot to 505hz (for example).

If you're starting with a room from scratch (again, check out the GearSlutz folks, they've been down this path before, and there are some really smart guys there) - I would either use the Fibonacci sequence, Steve's Ratios, or prime numbers. Again, the goal is to have fewer trouble frequencies. An inch here and there isn't going to break things. But keep in mind, you will always have nodes to deal with. That's where diffusion/absorption, and especially speaker and listener positioning comes in.
Back to top
 
 
WWW Lonely Raven   IP Logged
Brian
Seasoned Member
****




Posts: 282
Re: Auditorium Proportions?
Reply #3 - 05/23/14 at 02:26:16
 
Quote:
"Which proportions exactly are you talking about in your first question? Are you talking about room proportions?"

I meant these:
Optimal Dimensions for Listening Rooms:

         Design Option    Design Option       Design Option
                   A                      B                          C

Room width =  
          1.14 x Height     1.28 x Height            1.60 x Height

Room length =  
       1.39 x Height       1.54 x Height           2.33 x Height

Length/Width =  
              1.22                       1.20                           1.46


I yesterday bought a couple of Alton Everest's books: "The Master Handbook of Acoustics 3rd Edition", and "Acoustic Techniques for Home and Studio 2nd Edition".  They ought to arrive in a few weeks.  Perhaps I can get a better understanding from these.  

Your explanation that the dimensions are wave length dependent so that being off by only 1 inch is not going to effect low frequencies, makes sense.  I was told once that it is the highs which create the sound stage, so perhaps the dimensions need to be fairly close after all.  
Back to top
 
 
  IP Logged
Brian
Seasoned Member
****




Posts: 282
Re: Auditorium Proportions?
Reply #4 - 06/06/14 at 21:32:21
 
I got my Alton Everest books.
Those room proportions are from an acoustician named L. W. Sepmayer. Values from three other acousticians are also listed. Altogether, all their values fall into a domain described by R. H. Bolt.  Both Everest and Bolt believe the numbers are approximate.

The other proportions listed are: (with a 10 ft ceiling)
M. M. Louden - 14 x 19, 13 x 19, 15 x 21
J. E. Volkman - 15 x 25
C. P. Boner - 12.6 x 15.9

Mr Louden published a list of 125 room dimension ratios arranged in descending order of quality. These were his three best.  

Interestingly, five of these rooms plot on a straight line. They are: (listed from most nearly square to most elongated) Sepmayer's 11.4 x 13.9, Boner, Louden's 14 x 19, Louden's 15 x 21, and Sepmayer's 16 x 23.33

Boner's number is evidently a calculation, being: Height one, Width the cube root of 2, Length the cube root of 4.

Volkman's number also seems not to derive from listening tests; at least not directly, for it is the rather arbitrary proportion 2:3:5.  


All these room ratios are for low frequency sound quality, and seem to have nothing to do with treble.

If I learn more about these proportions from further reading, I will try to remember to post it here.  

- Brian
Back to top
 
 
  IP Logged
Pages: 1
Send Topic Print