Norsonic nor118, Инструкция по эксплуатации

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70 Chapter 13
Measuring the sound power
71 Norsonic Nor118
User Guide
The environmental correction factor K
2
accounts for the influence of undesired sound reflections from room boundaries and/or
reflecting objects near the source under test. The magnitude of this environmental correction factor depends principally on the
ratio of the sound absorption area A of the test room to the area S of the measurement surface. The magnitude does not depend
strongly on the location of the source in the test room.
Calculating the A: The value of the mean acoustic absorption coefficient
α
is estimated by using the above table or by means
of reverberation time measurements. The value of A is then given, in m
2
by A = α × S
V
in which S
V
is the total area of the surface
of the test room (walls, ceiling and floor) in m
2
Hemisphere: S = 2 π r
2
Calculating the S:
When measuring in accordance with the ISO 3746, the environmental correction factor K
2
is obtained from this graph by enter-
ing the abscissa with the appropriate value of A/S
α
Description of Room
0.05 Nearly empty room, smooth hard walls made con-
crete, brick, plaster or tile
0.1 Partly empty room, room with smooth walls
0.15 Room with furniture, rectangular machinery or in-
dustrial room
0.2 Irregularly shaped room with furniture, irregularly
shaped machinery or industrial room
0.25 Room with upholstered furniture, machinery or
industrial room with small amount of acoustical
material
0.35 Room with acoustical material om both ceilings
and walls
0.5 Room with large amounts of acoustical material on
ceiling and wall
Parallelepiped: S = 4(ab + bc + ca)
l
1
, l
2
, l
3
are the
dimensions of the
rectangular refer-
ence parallelepiped
a =
l
1 + d
2
b =
l
2
+ d
2
c =
l
3
+ d
2
10
9
8
7
6
5
4
3
2
1
0
0.5 1 5 10 50 100 300
A/S
dB
K
2
= 10log
10
[1+ 4 ]
A/S