The Acoustic Camera as an Effective Tool for the NVH Analysis of Vehicles

Vehicle Interior Measurement

A car vendor in Berlin needed help with NVH analysis. When customers brought in their recently purchased cars because of a disturbing squeak and rattle noise while driving, their engineers were not able to locate the source of noise. During a measurement session various methods were evaluated in order to pinpoint noise sources inside of the cars. As the subjective opinions about the origin of certain noise sources differed, the Acoustic Camera came into operation in order to reliably locate the unknown squeak and rattle sources.

Measurements

Measurement object

VW Tiguan, VW EOS and VW Golf

Measurement set up

For the measurement, the Microphone Array and the Data Recorder were positioned inside the cabin of each car. The mobile power supply was set up in the trunk of the car. All measurements were conducted while driving on the road to capture real-life conditions. Afterwards, CAD models of the vehicles were integrated into the channel data and each cabin was analyzed three-dimensionally with the Software NoiseImage.

System Characteristics

Microphone array Sphere48 AC Pro

  • 48 microphones
  • 35 cm diameter
  • Acoustic mapping range: 12 dB -130 dB
  • Recommended mapping frequencies: 291 Hz - 20 kHz
  • Dynamic range: 9 dB - 14 dB, up to 50 dB with Advanced Algorithms
  • Typical measurement distance: > 0.3 m

Data Recorder mcdRec

  • Sampling rate: 192 kHz (32 bit)
  • Channels: up to 168 time-synchronized, analog channels (7 cards with 24 channels each)
  • Interface: 1 Gbit Ethernet PC interface streaming capabilities
  • Max. recording time (with 192 kHz): 87 s
  • Diverse measurement cards available

Software NoiseImage

  • Acoustic Photo 2D
  • Acoustic Photo 3D
  • Record Interface
  • Spectral Analysis
  • Advanced Algorithms
  • Project Manager

Power Supply

  • Mobile power supply/battery pack

Results

VW Tiguan

The Acoustic hotspots were located at the roof of the car (Fig. 1). Crack appeared regularly at maximum sound pressure level of 39.9 dB(A). Also a second source was localized under the seat (Fig. 2). In the Spectrogram you can see the frequency range of the source marked from 1.7 to 5.7 kHz at a maximum level of 33.1 dB(A).

VW EOS

A squeal in C-pillar of the electric roof was located emitting noise at 1.8 to 9.8 kHz. The channel data and the spectrogram with marked frequency band and associated Acoustic Photo 3D show several sources on the roof top.

VW Golf

Unusual squeaking noise located above the driver seat with a peak level of 68.1 dB(A). Acoustic hotspot is shown on the CAD model of the car.