Scan & Paint | TPA

Last year Microflown Technologies introduced Scan & Paint as a fast and affordable sound source localisation tool to the market. The solution immediately had its impact and was adopted very fast. The Scan & Paint method is very simple; the surface is scanned with one PU probe while a camera is positioned toward the surface to film the scanning. After the video and audio are recorded and synchronized the data is post-processed. For each frame of the video a position of the probe is extracted. The auto-tracking function in the software enables to automatically recognize the probe by the colour. At each measurement point the particle velocity, sound intensity and sound pressure are calculated from the relative time block of the audio data. A high resolution sound colour map in a very short measurement and processing time is produced as result.

A high velocity at the surface however does not necessary mean a high pressure contribution in a certain position furhter from the surface. In a complex environment such as an vehicle interior of a car the surface velocity can only give an indication about the source ranking of different surfaces. Traditionally transfer path analysis requires a multichannel frontend system with multiple sensors. An advanced version of the traditional Scan & Paint, called Scan & Paint TPA, is being developed as solution for airborne TPA. This system introduces a fast method and requires only a low number of channels. The Scan & Paint TPA not only maps the surfaces source strengths but transfer functions and phase references are introduced. This opens the option to have the phase information between different positions and the contributions to a defined position with only 3 channels and two sensors solution.

The pressure (referred to certain position) can be calculated in two measurement steps by Scan & Paint TPA:

  • Velocity distribution over the surface
  • FRF Transfer functions using reciprocal measurements with sweep method

Step 1: Similar to the standard Scan & Paint the source strength in operational conditions is measured by scanning the surface with a PU probe. The difference with the TPA version is that now a reference microphone is added at a defined position to have the phase correlation different surface velocities.

Step 2: The transfer function is measured in a reciprocal way. This means a monopole sound source is positioned at the listener position and the sound pressure is measured over the surface with the same method as Scan & Paint (sweep method) to have the transfer function to each position as were the source strength has been measured. The cross-spectrum between particle velocity at the surface and the pressure at the reference position is calculated and contains the relative phase information between the panel vibration and pressure at the reference position.

The airborne TPA is performed to evaluate and rank the contributions from different sound sources. The measurement versus synthesis ( SPL vs Sum of contributions ) validation is included in the Scan & Paint TPA.

For more information please read the report under this link: Internal Report


  • Only a low amount of channel and sensors are required
  • Short setup, measurement and processing time
  • High resolution results of:
    • Source strengths
    • Contributions