vrijdag 18 mei 2012
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 Calculate Room Modes




  This calculator is an easy way to calculate Room Modes or Standing Waves in an enclosed rectangular space.
You need to look out for Modes that are close together and below about 300 Hz.

Enter the dimension of your space and the speed of sound (distance per second) and click "calculate".

Sound at sea level = 342 meters per second, or 1122 feet per second.


These mathematical models will not replace accurate measurements. 		 


Choose:  meter feet
Speed of Sound m/s   ft/s
Length of Room m   ft
Width of Room m   ft
Height of Room m   ft
Estimated reverberation time T60 ms


Calculations


Floor area A = m2   ft2
Volume V = m3   ft3
Surface area S = m2   ft2
Edge length Le = m ft
Schroeder frequency fs = Hz
Monopole reverb distance Rm = m ft
Avg wall absorption a = %


Axial Modes

Involve Two Parallel Surfaces - opposite walls, or the floor and ceiling. These are the strongest modes.
Length Width Height
Mode Frequency Mode Frequency Mode Frequency
1 0 0 0 1 0 0 0 1
2 0 0 0 2 0 0 0 2
3 0 0 0 3 0 0 0 3
4 0 0 0 4 0 0 0 4
5 0 0 0 5 0 0 0 5
6 0 0 0 6 0 0 0 6
7 0 0 0 7 0 0 0 7
8 0 0 0 8 0 0 0 8
9 0 0 0 9 0 0 0 9



Tangential Modes

Involve Two sets of Parallel Surfaces - all four walls, or two walls the ceiling and the floor. These are about half as strong as the Axial modes.
Length & Width Length & Height Width & Height
Mode Frequency Mode Frequency Mode Frequency
1 1 0 1 0 1 0 1 1
1 2 0 1 0 2 0 1 2
1 3 0 1 0 3 0 1 3
1 4 0 1 0 4 0 1 4
2 1 0 2 0 1 0 2 1
2 2 0 2 0 2 0 2 2
2 3 0 2 0 3 0 2 3
2 4 0 2 0 4 0 2 4
3 1 0 3 0 1 0 3 1
3 2 0 3 0 2 0 3 2
3 3 0 3 0 3 0 3 3
3 4 0 3 0 4 0 3 4
4 1 0 4 0 1 0 4 1
4 2 0 4 0 2 0 4 2
4 3 0 4 0 3 0 4 3
4 4 0 4 0 4 0 4 4



Oblique Modes

Involve all six surfaces - four walls, the ceiling and the floor. These are about one quarter as strong as the Axial modes, and half as strong as the tangential modes.
Mode Frequency Mode Frequency Mode Frequency Mode Frequency
1 1 1 1 1 2 1 2 1 2 1 1
2 2 2 2 2 1 2 1 2 1 2 2



Since the wavelengths at these frequencies fit exactly into the room, you'll find much higher sound levels at the room boundaries (and particularly in the corners, where two or more sets of modes coincide), plus a series of low and high levels (minima and maxima) spaced between the boundaries.

If you're lucky, or have built the room with acoustics in mind, the three sets of Axial modes will be smoothly spaced from the lowest room-mode frequency to several hundred Hertz, beyond which their numerous peaks and troughs can be effectively treated using acoustic tiles. If not, some frequencies from the different mode series will coincide, causing even larger peaks and troughs in your frequency response.

The very worst case is a cubic room, since all three mode series will be identical, but thankfully there are published lists of preferred ratios for room dimensions that ensure relatively smoothly spaced modes.





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