Microphone Array Techniques

Microphone Array Technics are capable to measure

* Transient and static sound field measurement
* Measurement of vibration of structures and air columns by backpropagation of sound field variables
* Description of radiation of instrument in space using backpropagated sound field
* Source detection
* Surface description
* Binaural calculation of diffusion of musical instruments
* Determination of psychoacoustic parameters of musical instrument sound field radiation

The aims of the measurements are:

* Detection of decisive parameters for musical instrument sounds
* Psychoacoustic relation between sound and tone quality depending upon musical instrument radiation behaviour
* Suggestions of simplified models for instrument and music performance in terms of
* loudspeakers
* room acoustis
* instrument building

The Acoustic Camera used at our Institute is developed here. It consists of a 128 channel device with simultaneous and synchronized digital data transfer rate of 48 kHz samplerate. The array has 128 microphones ordered in a matrix array. Additional configurations of arrays will be built.

The software is built at the Institute, too. The algorithms used are

* Nearfield Acoustic Holography (NAH) and Statistical Optimized Nearfield Acoustic Holography (SONAH)
* Beam forming
* Helmholtz-Least-Square method (HELS)
* Multipole-Radiators
* Minimum Energy method (used here)

Additional methods are developed suiting the special needs for musical instrument research.

* Methods for time-dependent transient measurement with solutions for each sample time point
* Methods taking the high number of microphones into consideration to formulate a high precision special solution

Measurements

Sufi duff frame drum

The following image shows the measurements of a Sufi frame drum in
comparison to a Finite Element solution.

Octopole of a Sufi Duff Frame-Drum: left: measured, middle: FEM solution, right: picture of drum. From: Bader, R.: Reconstruction of radiating sound fields using minimim energy method. J. Acoust. Soc. Am. 127(1), 300-308, 2010
Octopole of a Sufi Duff Frame-Drum: left: measured, middle: FEM solution, right: picture of drum.
From: Bader, R.: Reconstruction of radiating sound fields using minimim energy method. J. Acoust. Soc. Am. 127(1), 300-308, 2010

 

Numerous other musical instruments were measured, including:

* Classical guitars
* violins
* Trumpets
* Saxophones and clarinet
* Human voice
* Flutes
* Guitar amplifiers
* Studio monitors