Reverberation time Reverberation time

Reverberation time

Reverberation time

Reverberation time (1) Reverberation time (1)

Let’s consider a room containing an active sound source, and let’s abruptly interrupt the emission of sound energy. We define as reverberation time RT (s) of an environment, the time necessary for the sound energy density to decrease to a millionth (60 dB) of the value it had before the source was switched off.

Sound energy density

Steady-state sound energy density Relative sound pressure level (dB)

Reverberation time (2)

Reverberation time (2)

Reverberation time (2) Reverberation time (2)

Lp (dB)

Time (s) 45 dB

ISO 3382 - 2011

-5 dB

-25 dB

T₂₀

T20 -5 / -25 (x 3)

T30 -5 / -35 (x 2)

T10 (unused) -5 / -15 (x 6) EDT (early decay time) 0 / -10

Sabine

Sabine ’ ’ s Formula (3) s Formula (3)

If the environment is perfectly reverberant the value of the reverberation time is the same in all points and is

• (s)

where V is the volume of the environment. This relation is known as “Sabine’s formula”.

By measuring the reverberation time, it is possible to determine:

•

A=  S equivalent area of acoustic absorption RT = 0.16 × V

( 

× S

)

i

å

Sabine’s Formula

60 20

60

16 . 0 16

. 0

T A V

S T V

T

i i

= ×

× 

= ×

= å ^

60

cr 60 T

V 100

Q T

V 16 . 0 16

d Q ×



= ×

× ×



= ×

Substituting in the critical distance formula: