Description Of Sound Measurements - Man L23/30DF Project Manual

MAN Diesel & Turbo
1609510-3.5
Page 1 (1)
L28/32S, L23/30DF, L28/32S-DF, L27/38S, L23/30S, L21/31S, L16/24S, L28/32DF,
General
Purpose
This should be seen as an easily comprehensible
sound analysis of MAN GenSets. These measure-
ments can be used in the project phase as a basis
for decisions concerning damping and isolation in
buildings, engine rooms and around exhaust sys-
tems.
Measuring equipment
All measurements have been made with Precision
Sound Level Meters according to standard IEC
Publication 651or 804, type 1 – with 1/1 or 1/3
octave filters according to standard IEC Publication
225. Used sound calibrators are according to
standard IEC Publication 942, class 1.
Definitions
Sound Pressure Level: L
where P is the RMS value of sound pressure in pas-
cals, and P is 20 μPa for measurement in air.
0
Sound Power Level: L
where P is the RMS value of sound power in watts,
and P is 1 pW.
0
Measuring conditions
All measurements are carried out in one of MAN
Diesel & Turbo's test bed facilities.
During measurements, the exhaust gas is led out-
side the test bed through a silencer. The GenSet is
placed on a resilient bed with generator and engine
on a common base frame.
Sound Power is normally determined from Sound
Pressure measurements.
New measurement of exhaust sound is carried out
at the test bed, unsilenced, directly after turbo-
charger, with a probe microphone inside the
exhaust pipe.
Previously used method for measuring exhaust
sound are DS/ISO 2923 and DIN 45635, here is
measured on unsilenced exhaust sound, one meter
from the opening of the exhaust pipe, see fig.1.
2016.02.22

Description of sound measurements

V28/32H, V28/32S, L16/24, L21/31, L23/30H, L27/38, L28/32H
= 20 x log P/P [dB ]
P 0
= 10 x log P/P [dB]
W 0
Sound measuring "on-site"
The Sound Power Level can be directly applied to
on-site conditions. It does not, however, necessarily
result in the same Sound Pressure Level as meas-
ured on test bed.
Normally the Sound Pressure Level on-site is 3-5
dB higher than the given surface Sound Pressure
Level (L ) measured at test bed. However, it
pf
depends strongly on the acoustical properties of the
actual engine room.
Standards
Determination of Sound Power from Sound Pres-
sure measurements will normally be carried out
according to:
ISO 3744 (Measuring method, instruments, back-
ground noise, no of microphone positions etc) and
ISO 3746 (Accuracy due to criterion for suitability of
test environment, K2>2 dB).
Figure 1: .
D 10 25 0