Measurements | Acoustic Comfort: Exterior Noise

Acoustic Comfort: Exterior Noise

The noise measurements of the external acoustic fields are usually performed to detect the noise sources on the vehicle surface.
The 2 microphone arrays (see fig.1), placed respectively on the ceiling and on the side wall of the test section, localize the noise sources of the upper and lateral parts of the vehicle. The signals acquired by the microphones are processed with the “Beamforming” algorithm that is able to estimate the Sound Pressure Level (SPL) of a noise source localized in a specific area of the space.

 



Planar Beamforming

The term Planar Beamfoming (PBF) refers to an investigation of the noise sources on a plane parallel to the array and close to the vehicle.
Some examples of time-averaged and time-resolved results of the PBF are plotted in figureas under the text





3D Beamforming

3D Beamforming (3D BF) is able to investigate the noise sources directly on the vehicle’s surface. In this way, the Sound Pressure Level (SPL) accuracy and the localization of the noise sources increase.

The survey of the 3D Geometry of the vehicle is preformed by an optical scanning system fully integrated in the Wind Tunnel.

The results plotted in figure under highlight the better accuracy of the 3D BF compare with the PBF. In fig. 5 is plotted an example of noise map achieved with the 3D BF.

 





The 3D BF algorithm and the optical scanning system have been designed and developed by the Pininfarina Wind Tunnel. For more details see reference [1].

ARRAY SPECIFICATIONS

  • Microphones Num. : 66 Top Array and 78 Side Array
  • Array Diameter D: 3 m
  • Freq. range f : 0.2 ÷10 (kHz)
  • Array Resolution R : α·(z /D) ·λ
  • α : Array Coefficient (~1.22)
  • z : Distance between the measurement plane and the Array
  • λ : Wave length