Handbook for Sound Engineers

1662 Chapter 48

(48-69)

where,

V is the room volume,
S is the surface area,
a is the total absorption coefficient,
X is the space length,
Y is the space width,

Z is the space height.

Signal Delay. Signal delay is the time required for a
signal, traveling at the speed of sound, to travel from the
source to a specified point in space

(48-70)

where,
SD is the signal delay in milliseconds,
c is the speed of sound.

48.6 ISO Numbers

“Preferred Numbers were developed in France by
Charles Renard in 1879 because of a need for a rational
basis for grading cotton rope. The sizing system that
resulted from his work was based upon a geometric
series of mass per unit length such that every fifth step
of the series increased the size of rope by a factor of
ten.” (From the American National Standards for
Preferred Numbers). This same system of preferred
numbers is used today in acoustics. The one-twelfth,
one-sixth, one-third, one-half, two-thirds, and one
octave preferred center frequency numbers are not the
exact n series number. The exact n series number is
found by the equation

(48-71)

where,
n is the ordinal numbers in the series.

For instance, the third n number for a 40 series
would be

The preferred ISO number is 1.18. Table 48-4 is a

table of preferred International Standards Organization

(ISO) numbers.

RT 60 0.049**V

S^2

-----------------------^2 XY

• ln 1 – aXY

-------------------------------

2 XZ

• ln 1 – aXZ

-------------------------------^2 YZ

• ln 1 – aYZ

-------------------------------

+

+

=

** 0.161 for SI units

SD Distance

c

---------------------=

n Series number 10

1

n--- 10

1

n---

©¹

̈ ̧

§·

10

1

n---

©¹

̈ ̧

§·

= }

10

1

40 ----- - 10

1

40 ----- -

©¹

̈ ̧

§·

10

1

40 ----- -

©¹

̈ ̧

§·

= 1.1885022

Table 48-4. Internationally Preferred ISO Numbers

(^1) e oct. (^1) e oct. (^1) e oct. (^1) e oct. (^2) e oct. (^1) e oct.
40 ser. 20 ser. 10 ser. 61 e
ser.
5
ser.
31 e
ser.
Exact value
1.00 1.00 1.00 1.00 1.00 1.00 1.000000000
1.06 1.059253725
1.12 1.12 1.122018454
1.18 1.188502227
1.25 1.25 1.25 1.258925411
1.32 1.333521431
1.40 1.40 1.412537543
1.50 1.496235654
1.60 1.60 1.60 1.60 1.584893190
1.70 1.678804015
1.80 1.80 1.778279406
1.90 1.883649085
2.00 2.00 2.00 2.00 2.00 1.995262310
2.12 2.113489034
2.24 2.24 2.238721132
2.36 2.371373698
2.50 2.50 2.50 2.50 2.511886423
2.65 2.660725050
2.80 2.80 2.80 2.818382920
3.00 2.985382606
3.15 3.15 3.15 3.162277646
3.35 3.349654376
3.55 3.55 3.548133875
3.75 3.758374024
4.00 4.00 4.00 4.00 4.00 4.00 3.981071685
4.25 4.216965012
4.50 4.50 4.466835897
4.75 4.731512563
5.00 5.00 5.00 5.011872307
5.30 5.308844410
5.60 5.60 5.60 5.623413217
6.00 5.956621397
6.30 6.30 6.30 6.30 6.309573403
6.70 6.683439130
7.10 7.10 7.079457794
7.50 7.498942039
8.00 8.00 8.00 8.00 8.00 7.943282288
8.50 8.413951352