Noise reduction is becoming increasingly important. Disturbing noise should be kept low or avoided at all for passengers inside the vehicles and also for residents when vehicles pass by or airplanes fly over. The Acoustic Camera helps the sound designer to implement the necessary corrective measures. Last but not least, national and international standards and specifications demand the sometimes drastical reduction of noise emissions. In order to know where suitable actions should be taken, it is necessary to determine as early as possible where loud sound sources occur. The Acoustic Camera localizes these sources, both in the time domain and in the frequency domain. In a train or airplane cabin, for example, a spherical microphone array including the measurement and analysis software NoiseImage are used to calculate a 3-dimensional acoustic image that reliably and impressively depicts weak points.
When driving by, even a long freight train is recorded and put together to one single picture which is color-coded with the acoustic data. This pass-by picture shows at a glance which areas of the train are noisy.
The PassBy 2D software module creates a panoramic image with the feature point method. That means: Looking for feature points in individual frames and stitching them together. From the moving distances of the feature points and the frame rate of the camera velocity information of the measured object is also created.
The calculation of an acoustic map works like a TDBF (time domain beamforming) algorithm with variable runtimes. Every point of the measured object is followed a given amount of time while it is in the proximity of the microphone array.
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The main sound source of rail traffic is the rolling noise of the wheel-rail contact. This can be localized with the help of the Acoustic Camera, as can aeroacoustic noise on the control car and drive noise. The core of the evaluations is the pass-by algorithm of the NoiseImage software, which enables the display of an acoustic map of the complete train.
Travelling in a business aircraft should be as pleasant as possible for the passenger. A company responsible for the interior design of the aircraft discovered an annoying noise during a quiet flight in its new top-class business aircraft. To ensure a high standard of quality, the noise level during the flight should be kept as low as possible. The Acoustic Camera was used to identify the main sources of noise. Acoustic insulation could then be installed during the next maintenance cycle.
