Doc.No.: 03118-000-IS
Page 7 of 12
2.1.2 Loudspeaker selection / SPL
The calculation of sound pressure level (SPL) is also dependant of distance from the loudspeaker:
The calculation is according to the formula:
SPL =A+(10*LOG10(B))-(20*LOG10(C))
where:
Sound Pressure Level figure at a specific point [dBA]
Loudspeaker specific data - SPL figure at 1W / 1m (according to loudspeaker data sheet)
dBA]
Loudspeaker specific data – Output power ((tapping according to loudspeaker data sheet)
[W]
Distance from the loudspeaker to the measurement point [m]
An example:
The mounted loudspeaker is a DNH HP15T, (108 dBA at 1W/1m. The distance to the loudspeaker is
10m and the tapping of the loudspeaker is 4W.
The SPL in that point is calculated to:
SPL =108(dBA) + (10*LOG10(4(W))) - (20*LOG10(10(m))) = 94dBA
Note:
Under no circumstances SPL figures in available spaces are allowed to exceed 120 dBA.
2.1.3 Amount of loudspeakers
To determine the required amount, type and tapping of loudspeakers in a MPA 1600 system it is
necessary to make an installation SPL requirement chart over the site/vessel. Within this chart noise
figures must be known or estimated. This, along with the environment requirement will make a basis
for the loudspeaker selection.
When this is prepared, an SPL calculation can be performed to find the requirement of loudspeaker
denseness. The above SPL formula must be used.
The type and amount of loudspeakers can be established. This will also include information about
tapping and output power.
It is also vital to take duplication into consideration. Whenever the MPA 1600 system handles General
Alarm or the vessel is intended for passenger transportation the system shall be fully duplicated (A &
B system) using separately located central equipment with physically separated cables and loudspeaker
segregation. All spaces shall be covered from both duplication loops.
2.1.4 Cable arrangement
In an MPA 1600 system that handles General Alarm (PA/GA) or the vessel is intended for passenger
transportation each loudspeaker distribution cable shall be organised as a closed loop starting and
ending at the central equipment point. This increases redundancy regarding cable problems and can
make system work without disturbances during cable failure.
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