Acoustic measuring system for locating noise sources

1. A method for implementing a system for locating noise sources and measuring their intensity, the system comprising a plurality of microphones oriented in several directions and mounted in a support so that each one is flush with or disposed on a rigid surface, the microphones being connected to a signal processing device that processes the signals coming from the microphones to provide a noise source hologram, the noise source hologram being a distribution of the acoustic pressures or intensities at various points on a given surface, the method comprising:

positioning the support of the microphones in an enclosure, where three-dimensional coordinates of each microphone are known, to measure noise sources on a surface;

performing focusing operations sequentially at various focusing points of the surface, coordinates of which are known;

for each point and at each frequency, calculating a sound level from a pressure according to the formula:

P

⁡

(

x

,

y

,

z

)

=

∑

A

i

⁢

P

i

⁡

(

t

-

r

i

c

)

⁢

xHrtf

where:

P=calculation results at a point x, y, z of the hologram,

P i =pressure measured by a microphone i,

r i =distance between the microphone i and the calculation point,

A i =coefficient, and

Hrtf=transfer function of a rigid body, for a given microphone and a given focusing point (x, y, z), taking into account a nature, a shape, and a size of the support; and

establishing a hologram from the calculations results for the various focusing points.

2. The method according to claim 1 , further comprising:

distributing a number of microphones belonging to one or two supports into two groups before a measurement is made.

3. The method according to claim 2 , further comprising:

differential processing of the signals coming from the microphones in the two groups, for the two groups.

4. The method according to claim 3 , further comprising:

conducting a focusing operation for each group of microphones at each calculation point where it is desirable to know whether a noise source exists; and

then, for each calculation point, calculating a difference between focused signals of the two groups, the difference being zero when the calculation point corresponds to the location of the noise source.

5. The method according to claim 3 , further comprising:

conducting a focusing operation for a first group of microphones at first points located near the first group, to determine an existence of noise sources at the first points;

conducting a focusing operation for a second group of microphones at second points opposite to the first points; and

then, for each group of two points, calculating a difference between focused signals of the two groups, the difference being at a maximum when a calculation point corresponds to the location of a noise source.