Dynaudio AIR 15, Справочное руководство

Страница: 111 / 129

Appendix: Acoustics
Dynaudio Professional AIR reference manual – 2014-09-28 108
Sabine’s formula
Wallace Clement Sabine (1868-1919) 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
will have longer reverberation. More absorption leads
to shorter reverberation. This can be expressed in Sa-
bine’s formula:
T = 0.161 * V / A
where:
►
T: Reverberation time in seconds
►
V: Volume in m
3
►
A: Absorption in m
2
Sabine
►
0.161: A constant (to adapt the calculation to the
actual units)
One square meter (1 m
2
) Sabine is comparable to an
open window with an area of one square meter. The
sound that hits this hypothetical window will disappear
and never return. In other words: One square meter Sa-
bine 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 behav-
ior of the materials in the room. The low frequencies
are the hardest to control. This is why the reverberation
time against frequency in practice may look like this:
Fig. 60: Reverberation time measured in a control
room. From 250 Hz and above, the curve is nicely
placed around 0.3 seconds. But for lower frequencies,
the reverb time rises to 0.75 seconds, which is too
much.