MY HOME GUIDE 2 WIRE SOUND SYSTEM
31
GENERAL RULES FOR INSTALLATION
1
st
example
The first example refers to a shop showroom with the following features:
H = 3.5m thus d = 5m
L1 = 10m
2
L2 = 20m
2
shop showroom = 60dBA + 10dB = 70dBA
From the data one obtains:
N = 3
d = 5
locating 3 loudspeakers one obtains D = 12
Attenuation (D = 12m) = -14dB
Loudspeaker sensitivity = 88dB
Sound level required = 74dBA (perfect sound coverage)
2
nd
example
The second example refers to a electronics industrial site with the following
features:
H = 4.5m thus d = 7m
L1 = 20m
2
L2 = 40m
2
electronics industry = 70dBA + 10dB = 80dBA
From the data one obtains:
N = 10
d = 7
locating 10 loudspeakers one obtains D = 6
Attenuation (D = 6m) = -10dB
Loudspeaker sensitivity = 88dB
Sound level required = 78dBA (insufficient sound coverage)
As the sound level calculated is insufficient, just put two loudspeakers
close together at each playing point (giving an equivalent loudspeaker with
sensitivity +6dB greater than that of the single loudspeaker) and the sound
coverage is found to be sufficient.
EXAMPLE OF THE SOUND LEVEL CALCULATION
Some examples for identifying the sound level are given below.
If when calculating the sound level the value obtained is greater by a small
margin (2 – 4dB) we have sufficient sound coverage for the room. If it is
smaller the possibilities are as follows:
1. put two loudspeakers close together at each playing point (this gives an
equivalent loudspeaker with sensitivity +6dB greater than that of the
single loudspeaker);
2. put four loudspeakers close together at each playing point (this gives an
equivalent loudspeaker with sensitivity +12dB greater than that of the
single loudspeaker).
Attenuation
D (m) Attenuation (dB)
1 0
2 -4
4 -8
8 -12
16 -16
Checking the sound level
LSA + 10dB > S + A
Legend:
LSA = room sound level (see “sound coverage level” table)
10dB = margin to be added
S = sensitivity of the loudspeakers (dB)
A= attenuation as a function of the distance between the loudspeaker and
the listener (see “attenuation” table)
Calculating the attenuation and checking the sound level
Another feature to be considered to cover a room correctly is the sound level.
In fact the sound level of a loudspeaker decreases as the distance between
loudspeaker and listener increases. When calculating the attenuation leave
a margin of 10dB with respect to the values indicated above (e.g. electronic
industry 80dB + 10dB).
If distance D is known the attenuation can be obtained:
D
Note: When there are metal iodide lamps or sodium vapour lamps at high
and low pressure (loads A) lay the wiring respecting the following rules:
1. to supply Loads A use power cables with minimum insulation 300/500V;
2. provide a dedicated power line for amplifiers F502;
3. keep “power line Loads A” and “BUS line or power line F502” separate
by at least 1 m;
4. wire the loudspeakers with twisted cables (e.g. Item 336904);
5. keep the wiring to the loudspeakers as short as possible positioning the
F502 amplifiers near the loudspeakers.
Failure to respect the above rules may affect correct operation of the devices.
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