Quote:

Originally Posted by

**naethoven** Wes,

Thank you so much for taking time to respond to my post. I kind of see what you are saying, but could you break it down it detail for me? As far as the ratios being equal to pitch intervals, and why certain intervals are more desireable? You don't want the dimensions to harmonize with each other/ ie: have coincident modes or harmonics, right?

As for the 1:1.33:1.64 ratio, I plugged it into the bobgolds.com modecalc and I was amazed at the results. It seemed to have good distribution down to around 60Hz, it passed all the R. Walker BBC tests, the Bonello test looked great, and it was 2028cuft vol. I couldn't imagine it being much better! I see what you're saying about the coinciding harmonics, but why did they not show up on the modecalc as problems, and how could they be that big of an issue when all the tests look so good?

I really appreciate your time!

Nathan Webb

Nathan,

Well think about it - if each dimension of the room is like a drum, with a resonant frequency, and each of those dimensions is identical (ratio of 1 : 1 : 1), then the room resonates in one key only, the worst case scenario. If the ratios are closely related mathematically (e.g. ratio of 1 : 2, 2 : 3, or 3 : 4) then a similar thing happens, only a couple of "next door' keys are resonating. These are the so-called "Perfect" intervals, 1 : 2, 2 : 3, and 3 : 4 (octave, P5th, and P4th).

The other, non-perfect musical intervals are actually quite good for room ratios, and you see them listed throughout the modal literature, although I guess that disguised as numerical ratios their musical significance as intervals may often go unnoticed. For instance, the ratio 1 : 1.6 is really a minor 6th (just intonation). The ratio 1 : 1.4 is a diminished 5th. The ratio 1 : 1.26 is a Major 3rd. The ratio 1 :1.9 is a Major 7th. The ratio 1 : 2.1 is a minor 9th. And so on...

You get the picture. The well known "good" ratios are almost without exception right on, or very near, the Major, minor, augmented, and diminished intervals. And inversely, the Perfect intervals are "bad" for room ratios. The one notable exception that proves the rule is Louden's recommendation of 1 : 1.5. I can't explain that one. I don't know what Louden was thinking that day. I stand by my contention that 1 : 1.5 is bad, very very bad. The only ratios worse than the P5th are the octave and the unison.

For a more detailed description of modal resonance from a musical perspective, you can read this paper from a lecture I gave a while back:

Wes Lachot Design || Studio Design and Acoustic Consulting
I thinks it's important for folks to understand the musical implications of the various modal ratios, rather than expecting a modal calculator do the thinking and give an "answer". As to your specific question, I would point out that even though the spread may have looked good, there is a coincidence between the 3rd harmonic of the width dimension and the 4th harmonic of the height dimension. Maybe the modal calculator doesn't give negative points for this. But you ears will. Only by understanding ratios on a musical level will you be able to best interpret the modal calculator's results.

--Wes