Sabines Formula - Dynaudio pmn User Manual

Air_US_rev_111.qxd 16-12-2004

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:
V:
A:
0.161:
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ACOUSTICS
Reverberation time in seconds
Volume in m3
Absorption in m2 Sabine
Is a constant (to make the calculation
right with the actual units)
0 ,8 0
0 ,7 0
0 ,6 0
0 ,5 0
0 ,4 0
0 ,3 0
0 ,2 0
0 ,1 0
0 ,0 0
6 3 1 2 5
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.
- BACKGROUND INFO
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:
X-s tu d io , re v e rb e ra tio n tim e in c o n tro l ro o m
2 5 0 5 0 0 1 0 0 0
Fre que nc y [Hz]
2 0 0 0 4 0 0 0 8 0 0 0
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