Originally Posted by naethoven
Thanks Wes. I know you say the mode calc doesn't show all, but that Bonello on 1.28:1.66 was the smoothest curve I've seen. Is it really that smooth or am I seeing a weakness of the mode calc?
Also, here again, I'm debating greater volume vs better ratio...I could have 1900+/- cuft if I didn't care about the ratios, but having a good ratio, good intervals, and a good graph puts me at around 1600 cuft...thoughts?
P.S. Why does 1:1.25:1.75 look so bad on the calc? Fails a Walter, bad Bonello. I thought it should be good because all three relationships are good, aren't they? Isn't 1.25:1.75 a diminished 5th? With all three being good, I don't understand why the calc isn't perfect.
I can't tell you anything about the weighting that goes into the various mode calculators. I know some of them give too much weight to tangential and oblique modes. My contention has always been that if the axial modes are well spaced, the others will fill in the gaps and will be evenly spaced as well, by virture of the fact that they are proportionally related to the axial modes.
The ratios you mention, 1 : 1.25 : 1.75 are not as evenly spaced as 1 : 1.26 : 1.59, particularly at the bottom. Having a major 3rd between the first two resonances is 33% better than having a diminished 5th (in the lowest octave, and this advantage is compounded as you go up the harmonic series). And that first octave really matters - the bottom end is very critical - these modes are all about bass, after all. But the former ratios will perform better than ratios which span more than an octave, for instance. It's a simple matter of more dense spacing, which is the name of the modal game, as long as the spacing is even.
If a mode calc (or any other computer program) gives me an answer that I know to be inconsistent with my own empirical knowledge and experience, I discount its weight. What my ears and experience tell me is that the musical approach is the one that works, so it's the one I use.
As to your question about cubic volume vs. better modal spacing, for me the real question for a control room lies in the available depth, along the axis of the throw of the speakers. The reason for this is twofold:
First, the distance of the listener from the back wall affects the frequency of the back wall null, which is the most deadly of the boundary interference nulls. I try to get as close to 20 ft. as possible for the depth dimension, which allows puts the listener to sit somewhere around 12 ft. from the back wall if things are set up properly. This puts the 1/4 wavelength null at 23 Hz, which is too low to do any real damage. If the listener were only 8 ft. from the back wall, that null would be at 35 Hz, which could be audibly problematic.
Second, the depth dimension is often the longest dimension, and as such will determine the natural cut-off frequency of the room. A 20 ft. depth will take you down to 30 Hz, which is a good practical cutoff for a working class studio. You'll hear stuff below 30, but the dropoff slope will be steep. I'd rather have that slope start at 30 Hz than at 40 Hz, which would be the case in a 16 ft. deep control room, for instance.
So all of these things (and a good many more) should be taken into consideration, not just whether a particular ratio set wins over another in a vacuum.
Volume in and of itself is like anything else, meaning more is better all things being equal, but rarely are all things really equal.