Explanations and Notes

To see a really bad room, try (10 foot by 10 foot by 10 foot).
To see a less bad room, try (10 foot by 10 foot by 9 foot).

History: Although I can't say that Jeff D. Szymanski was the inspiration for this webpage, I can certainly say he was the impetus for it.
Specifically, in this post Room modes, calculated versus measured Jeff compared a bunch of Mode Calculators, most of which run in Microsoft Excel, and suggested that a new one be written in MsDos. Well, I thought that was the wrong environment. Frankly I spend so much time on the internet, the correct place I thought was to put it into a website, preferably all in html without any webserver computations.

The weighting is my attempt to mix the rules of Gilford, Bonello, and Eric Desart, which are:

Gilford wrote:
There will be room modes...in all parts of the audible spectrum, but whether or not they will be appreciable as colorations depends on the following factors:
(1) the bandwidth of the mode
(2) the degree of excitation of the mode
(3) its separation from neighboring strongly excited modes
(4) the positions of the sound source and microphone with respect to standing-wave systems
(5) the frequency content of the source.
For the case of a typical small studio...calculation shows that no frequency is likely to become prominent unless it (has) a high early intensity and a long decay. This condition* is satisfied only by the axial modes, which are therefore the only ones likely to become individually significant. An exception to this rule is that a few tangential or oblique modes of low frequency may possibly be audible, owing to their high initial intensities or wide spacings.
A simple calculation...enables a list of all the axial modes for all three dimensions to be written down in order of frequency. It will be unnecessary to continue the list beyond, say, 350 Hz because...the axial modes in a well-designed talks studio will not be prominent above that frequency. The list must next be examined to find modes, or groups of modes with almost the same frequency, which are separated from their nearest neighbors on either side by intervals appreciably larger than their bandwidths. In practice the minimum separation for audibility appears to be about 20 Hz.
Modes or groups separated from their neighbors by greater intervals than this should be noted, and...attempts should be made to alter the groupings by changes in the proposed room dimensions.


References

  1. Recording.org thread: Room modes, calculated versus measured
  2. Studiotips thread: Room Mode calculator - HTML only version, with comments by Eric Desart and testing by Dan Nelson and others
  3. Studiotips FAQ: ROOM RATIOS
  4. Recording.org thread: Jeff D. Szymanski's (aka lovecow aka savant) interpretation of Gilford
  5. ITU control room recommended RT60
  6. Terry Montlick's Room Modes Calculator version of BBC Walker
  7. The frequencies for the piano were rounded from this website, as well as from Master Handbook of Acoustics 4th pg 105 figure 5-11
  8. Book: Master Handbook of Acoustics 4th by F. Alton Everest, ISBN: 0071360972
  9. Book: How to Build A Small Budget Recording Studio From Scratch With 12 Tested Designs by Mike Shea and F. Alton Everest, ISBN: 0071387005
  10. Subjective assessment of audio quality the means and methods within the EBU, by W. Hoeg, L. Christensen, R. Walker (BBC)
  11. HAA's Acoustical Analysis Report by Dr. Will Smith
  12. bonello
  13. gillford
  14. walker