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ACOUSTICS - BACKGROUND INFO
Sabines formula
Sabine is the father of modern acoustics. He found that
reverberation time is described by a relationship between
the room size and the amount of absorption in the room.
Larger rooms - longer reverberation. More absorption -
shorter reverberation.
T = 0.161 * V / A
where
T: Reverberation time in seconds
V: Volume in m3
A: Absorption in m2 Sabine
0.161: Is a constant (to make the calculation
right with the actual units)
X-studio, reverberation time in control room
0,00
0,10
0,20
0,30
0,40
0,50
0,60
0,70
0,80
63 125 250 500 1000 2000 4000 8000
Frequency [Hz]
Reverb time [s]
One square meter (1 m2) Sabine is comparable to
an open window with an area of one square meter:
The sound that hits the window will disappear and
never return. One square meter Sabine is one
square meter with full absorption.
The basic formula sounds simple, but the problem is that
the materials in the room will absorb differently at different
frequencies. The absorption may range from nothing (fully
reflective) to total absorption.
A proper reverb time should be constant with frequency,
but this is not always the case because of the behavior of
the materials in the room. The low frequencies are the
most difficult to control.
This is why the reverberation time against frequency in
practice may look like this:
Reverberation time measured in a control room. From 250 Hz and above the curve is nicely placed
around .3 sec. But belov the reverb time rises to .75 sec. which is too much.