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MVA 02 rev 5 - December 2017
3.8.7
General information on noise emission data
Level of acoustic power
– LwA
This is the average value of acoustic power expressed in dBA (value weighted according to scale A) emitted
into the environment by a fan with ducting on both the intake and exit sides.
The value refers to channelled air with a density of 1.226 kg/m
3
, at the maximum permitted rotation speed of
the impeller and with operation at the optimum point on the curve.
It is assumed that the fan is positioned in a free space, or in an area of dimensions such as to not cause
significant reflection, and resting on a flat and rigid surface.
The possible contribution to the overall noise level of the noise caused by the motor, the transmission
system and any accessories that may be present is not considered.
In addition, the value of background noise of the installation environment is not considered to be significant.
Level of acoustic pressure
– LpA
This is the average of the average temporal values of acoustic pressure emitted into the environment by a
fan with ducting on both the intake and exit sides.
Pressure values are recorded on the measurement surface surrounding the fan (parallelepiped
measurement surface).
Sound pressure measurements are obtained experimentally with 8 microphones located on the reference
surface at a height equivalent to the fan rotation axis (see Fig. 3-13).
The pressure value is expressed in dBA (value weighted according to scale A).
The value refers to channelled air with a density of 1.226 kg/m
3
, at the maximum permitted rotation speed of
the impeller and with operation at the optimum point on the performance curve.
The measured values refer to a measurement distance of one metre.
It is assumed that the fan is positioned in a free space, or in an area of dimensions such as to not cause
significant reflection, and resting on a flat and rigid surface.
The possible contribution to the overall noise level of the noise caused by the motor, the transmission
system and any accessories that may be present is not considered.
In addition, the value of background noise of the installation environment is not considered to be significant.
The point at which maximum acoustic pressure is found normally corresponds to the exit duct (external to the
ducting), and its value is 3
–4% higher than the average value.
