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Old 10th October 2012, 08:53 AM   #31
Jmmlc is offline Jmmlc  France
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Hello,

Using Rayleigh formula , I simulated thousands of orthogonal parallelepipeds. I derived a graph summarizing the results.

Here it is.

The shapes (ratio length/heigh and ratio width / height) that lead to the best distributions (less audible resonances) are located on the red curve.

(Useful both to design enclosures or auditoriums)

The best dimensions of auditoriums given by Louden in his papers fall all of them on or nearby the red curve.

Ref :
Louden M.M., « Dimensions ratios of rectangular rooms with good
distribution of Eigentones » ; Acustica, 1971 ; Vol. 24 ; pp. 101-104


Best regards from Paris
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File Type: gif Rayleigh_min.gif (89.3 KB, 149 views)
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Old 10th October 2012, 01:21 PM   #32
Remlab is offline Remlab  United States
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Thanks! Very interesting that the "curve" is not perfectly linear and changes based on the size of the room. F. Alton Everest also covers this subject in detail(With graphs) in his book. In fact, it could probably be inferred from this "curve" that something as small as a loudspeaker cabinet would require very different ratios than an actual room..
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Old 10th October 2012, 01:32 PM   #33
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I find it interesting that 1 x 1.5 x 2 is on the red line.

I'm intrigued with the idea that Western ears would find dissonant harmonic relationships pleasing.
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Old 10th October 2012, 01:40 PM   #34
Jmmlc is offline Jmmlc  France
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Hello Remlab,

Well, the graph is independant on the absolute dimensions.
(BTW : the criterion mapped here we want to minimize is the max interval of frequency between one resonance to the next and it is expressed on the graph in Hz x height )

Only the frequency of the resonances are changing but their relation, one to the next don't. So we can say it is quite universal and can be used either for a large auditorium eitner for a smalll enclosure.


Best regards from Paris, France

Jean-Michel Le Cléac'h
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Old 10th October 2012, 03:37 PM   #35
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Jean-Michel,

A very useful study. Thanx for posting.

Any chance you have a higher resolution graphic? (or even one in vector format?)

dave
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Old 10th October 2012, 03:47 PM   #36
badman is offline badman  United States
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Quote:
Originally Posted by planet10 View Post
The inside of a sphere has one very strong standing wave since all distances across the inside are the same. The outside is very nice.

dave
Doesn't really matter if the sphere is small enough that the magnet occupies the center, though. Plus since stuffing in the middle of a sphere would be at max velocity (where it's most effective) the inside of a sphere isn't necessarily a biggie. I'd want to be careful if the walls could "see" each other though.
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Old 10th October 2012, 03:49 PM   #37
Jmmlc is offline Jmmlc  France
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Quote:
Originally Posted by planet10 View Post
Jean-Michel,

A very useful study. Thanx for posting.

Any chance you have a higher resolution graphic? (or even one in vector format?)

dave

hello Dave,

That one (see attached file) has a better resolution but the grid line and numbers doesn't have the color I wanted them to have.

Best regards from Paris, France

Jean-Michel Le Cléac'h
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File Type: gif rayleigh_.gif (42.5 KB, 108 views)

Last edited by Jmmlc; 10th October 2012 at 04:11 PM.
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Old 10th October 2012, 04:02 PM   #38
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Thanx.

dave
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Old 10th October 2012, 08:55 PM   #39
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Keriwena View Post
I find it interesting that 1 x 1.5 x 2 is on the red line.
Hi,

That can't be good, as its very bad regarding coincidences of
room mode harmonics, e.g. 1(1st) = 2(2nd), 1(n) =2(2n),
1.5(3rd) = 1(2nd) = 2(4th), etc.

I can't see how a good criteria would suggest the above.

rgds, sreten.
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Old 10th October 2012, 10:05 PM   #40
Remlab is offline Remlab  United States
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Quote:
Originally Posted by sreten View Post
Hi,

That can't be good, as its very bad regarding coincidences of
room mode harmonics, e.g. 1(1st) = 2(2nd), 1(n) =2(2n),
1.5(3rd) = 1(2nd) = 2(4th), etc.

I can't see how a good criteria would suggest the above.

rgds, sreten.
Plug it into a room mode calculator and observe. Not pretty..
http://www.bobgolds.com/Mode/RoomModes.htm
The Bonello curve at the bottom of the page looks good though. Hmm..
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Last edited by Remlab; 10th October 2012 at 10:15 PM.
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