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Noise source identi cation techniques : simple to advanced applications
Selection of an array design
Once the engineer has decided upon an NSI technique,
there is still the question of selecting the best array design.
If NSI needs to be performed inside a vehicle cabin, then
it could be advantageous to use a double layered array
for SONAH in order to minimize the effects of the reverbe-
rant field or a spherical array for Beamforming. In engine
test cells and other nearly free field situations, a planar
array would be adequate; if such an array is designed to
be used with both SONAH and Beamforming, it is usually
termed a Combo array. Outdoor measurements, such as
measurements on wind turbines and trains, are prone
to interference from extraneous sources. In such cases
a foldable array in the form of a funnel, can be used to
reduce the influence of sound arriving from the rear of
the array. For some outdoor measurements such as large
wind turbines and fly-over beamforming, the necessary
array is so large that it has to be mounted on the ground.
Each microphone should be situated on a hard reflective
surface (e.g. the runway tarmac or large hard plate) to
avoid the effects of ground impedance as a function of
the angle of incidence of the sound. For measurements
on small objects such as hearing aids and dental drills,
the array could consist of no more than two micropho-
nes: a stationary reference microphone and a probe
microphone moved from position to position in a very
fine mesh by means of a robot.
Conclusion
The list of techniques available for the NVH engineer to
perform noise source identification is continually expan-
ding. This article reviewed and compared the most
common techniques together with guidelines as to how
and when they can be employed. For the engineer to opti-
mally exploit the techniques the implementation should
be simple; superfluous parameters should be hidden from
view and engineering expertise should be embodied in
the solution so that the engineer can concentrate on the
task in hand: noise source identification.
Fig. 11 : Left: Conformal sound intensity map on a hearing aid at
2 400 Hz. Right: refined beamforming sound intensity map
on wind turbine at 4 000 Hz
Gauche : Carte d’intensité sonore conforme sur
une aide acoustique à 2 400 Hz. Droite : Carte
d’intensite sonore d’une éolienne à partir d’une
méthode fine de faisceaux à 4 000 Hz
References
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