room mode calculator
- Formula used f = C / 2.0 * sqrt((nx/lx)^2 + (ny/ly)^2 + (nz/lz)^2);
- The 3 modes:
- axial = standing waves between two surfaces, ex: (1,0,0)
- tangential = standing waves between 4 surfaces, ex: (0,1,1)
- oblique = standing waves between all 6 surfaces, ex: (1,2,3)
- My experience has shown that the 1st and 2nd axial modes between the
front and back wall are usually the most significant.
- Moving the listening postion will effect the magnitude (dB) of these
- When the frequencies start doubling or bunching up, (1,0,0) = 40Hz and
(0,1,0) = 40Hz, this is bad and the magnitude of the hump will be greater.
I've seen +12dB humps caused by some diabolical room modes.
Square rooms are bad. Perfect cubical rooms are even worse.
When trying to find the perfect room dimensions it is recommended to aviod
frequency clumping and have the room mode frequencies spread out evenly.
- The THX people used to say that the ideal room was 16' x 24' x 8'.
These dimensions give a three clumping at 70Hz! This not as bad as a square
room, but I wouldn't call these dimensions ideal.
- Theory is great, but it is always best to back this up with some
good old experimental data such as pink noise and an RTA.
- Fixing excessive room modes with EQ works, but it is trading a frequency
response problem into a time domain one. With the EQ solution, the direct
sound is affected, and transients also suffer. Many experts claim
absorbative room treatments and bass traps are the proper solution.
- WIP (work in progress): plot bunching of modes and do a simulated
magnitude vs frequency graph.
- Check out Alton Everests "Master Handbook of Acoustics" for some
excellent coverage on the topic of room modes. Also I'd recommend reading
some of Floyd E. Toole's papers.
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