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Old 6th December 2012, 01:24 AM   #51
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http://www.umcs.maine.edu/~markov/GoldenRatio.pdf

this is a better copy: http://www.cdlmadrid.org/cdl/htdocs/.../markowsky.pdf
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 6th December 2012, 03:25 AM   #52
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mathematically what numbers do you want for the dimensions? What should the numbers satisfy?
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Old 6th December 2012, 05:05 AM   #53
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Originally Posted by speaker dave View Post
As such, looking at the longest dimension, we should strive to have the 2nd and third modes equally spaced between the long dimension first mode and its second harmonic. The only approach that guarantees that is the cube root of 2 approach. It places the three dimension's fundamental modes 1/3 Octave apart in the first Octave.
Not sure I agree with you, Dave. Even spacing will get you some cancellation, but you will end up with an augmented sequence and those chord tones often sound dissonant.

I'd rather go with Jean-Michel's 1:1.5:2, which apparently causes a lot more cancellation, and produces a dyadic "power chord" which is less likely to generate unpleasant overtones in whatever resonances remain undamped.

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And I still don't think it matters if the cabinet is well damped!
Well, no, but I'm thinking of all those people who won't listen to you about damping.
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Old 6th December 2012, 08:09 AM   #54
Jmmlc is offline Jmmlc  France
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Hello David,

The ratio on the graph are just the ratio between the combined L, W and H in Rayleigh's formula :

http://www.bobgolds.com/Tangental/Ev...deEquation.GIF

Taking a given dimension as 1 allows to apply the formula whatever the size of the resonator, so the formula applies for parallelipipedic enclosures as well as parallelepipedic auditoriums (only the values frequencies are differents but not their progression).

Comparisons with Louden's real measurements and classification of the best shapes of auditorium is excellent.

Best regards from Paris, France

Jean-Michel Le Cléac'h



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But it looks like that approach compares the first dimension to the second and the second to the third, but not the first to the third. As an example 1:1.5:2 would have lots of overlapping modes from the 1 and 2 dimensions.

Isn't the cube root of 2 approach guaranteed to be the most uniform distribution?

(Not that I still think any of this matters when damping is applied.)

David

Last edited by Jmmlc; 6th December 2012 at 08:11 AM.
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Old 6th December 2012, 11:17 AM   #55
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Originally Posted by Jmmlc View Post
Hello David,

The ratio on the graph are just the ratio between the combined L, W and H in Rayleigh's formula .......

Jean-Michel Le Cléac'h
Yes, I understand the origins of the formula, but you are comparing dimension 1 to dimension 2, then dimension 2 to dimension 3, while ignoring the 1 to 3 comparison. Optimizing those two while ignoring the third has taken you down a wrong path.

Clearly for the case of 1:1.5:2, the 2 to 1 dimensions will have every one of the short dimensions resonances coincident wth half of the long dimension's resonances. Not exactly the solution for optimum spacing.

I've worked in the field of architectural acoustics. Unlike small room acoustics, nobody talks of room dimension ratios. Dimensions are relatively long and standing waves hence are dense and not a consideration. (i'd be happy to read a contrary reference if you can find one.)

Room length and width are determined by audience considerations ( seat count, sight lines, legal requirements for exit rows, distance to stage) and then the ceiling is raised until he RT is to target.

David
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Old 6th December 2012, 11:52 AM   #56
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Originally Posted by Keriwena View Post
Not sure I agree with you, Dave. Even spacing will get you some cancellation, but you will end up with an augmented sequence and those chord tones often sound dissonant.

I'd rather go with Jean-Michel's 1:1.5:2, which apparently causes a lot more cancellation, and produces a dyadic "power chord" which is less likely to generate unpleasant overtones in whatever resonances remain undamped.
You have made a huge jump to saying we perceive chords in resonances. I'd ask you to substantiate that. Even in rooms were the resonances are relatively undamped and high Q nobody suggests that chordal qualites are perceived.

Getting a little absurd...

David
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Old 6th December 2012, 12:37 PM   #57
Jmmlc is offline Jmmlc  France
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Hello Dave,

Sorry to have to say that but your question is a silly question,

You have to think more about the problem... (think 1 degree of freedom... so it is obvious ration between dimension 1 and 3 is perfectly defined knowing the ratio D1/D2 and D2/D3...).

From the point of view of resoannt frequencies, it doesn't matter if the room is elongated along x, y ou z...

Best regards from Paris

Jean-Michel Le Cléac'h



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Originally Posted by speaker dave View Post
Yes, I understand the origins of the formula, but you are comparing dimension 1 to dimension 2, then dimension 2 to dimension 3, while ignoring the 1 to 3 comparison. Optimizing those two while ignoring the third has taken you down a wrong path.

Clearly for the case of 1:1.5:2, the 2 to 1 dimensions will have every one of the short dimensions resonances coincident wth half of the long dimension's resonances. Not exactly the solution for optimum spacing.

I've worked in the field of architectural acoustics. Unlike small room acoustics, nobody talks of room dimension ratios. Dimensions are relatively long and standing waves hence are dense and not a consideration. (i'd be happy to read a contrary reference if you can find one.)

Room length and width are determined by audience considerations ( seat count, sight lines, legal requirements for exit rows, distance to stage) and then the ceiling is raised until he RT is to target.

David
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Old 6th December 2012, 12:48 PM   #58
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Originally Posted by Jmmlc View Post

You have to think more about the problem... (think 1 degree of freedom... so it is obvious ration between dimension 1 and 3 is perfectly defined knowing the ratio D1/D2 and D2/D3...).

Best regards from Paris

Jean-Michel Le Cléac'h
Of course. But a dimension ratio of 2 to 1 is clearly the worst possible choice if well spaced harmonics are desired.

You do understand that, right?
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Old 6th December 2012, 01:43 PM   #59
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Originally Posted by speaker dave View Post
You have made a huge jump to saying we perceive chords in resonances. I'd ask you to substantiate that. Even in rooms were the resonances are relatively undamped and high Q nobody suggests that chordal qualites are perceived.

Getting a little absurd...
Probably absurd, yeh, I'm working with musicians!

I can build two pine guitar cabinets of different dimensions that resonate noticeably, and one will be preferred to the other. They'll say it sounds "sweeter".

It's known that some concert halls sound better than others, no? And they're not dead. I don't think it's just the RT60, I think content matters, as well.

Granted, I'm talking euphonics on a hifi forum, and that's always thin ice.
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Old 6th December 2012, 03:57 PM   #60
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It's known that some concert halls sound better than others, no? And they're not dead. I don't think it's just the RT60, I think content matters, as well.
O yeah, lots of factors beyond RT60 are considered important. Most have to do with signal difference between the ears, strength of direct signal, RT balance from low to high, early reflection patterns, etc. But nobody looks at standing waves due to hall dimensions because the dimensions tend to be big and the modes start very low.

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Granted, I'm talking euphonics on a hifi forum, and that's always thin ice.
But it is nice to think about music every once in a while, and consonance and dissonance related to intervals is worth knowing about.

David
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