What is by far the most obvious element in the hardware of an acoustic camera?
The answer will most likely be the microphone array, but why is that?
First of all, the microphone-array is relatively large. The reason is the 2 centimeter spacing between the 64 microphones.
Integrating 8 x 8 microphones with 2 cm spacing results in a 16 x 16 cm array-size.
Then comes the most basic question, why an array of microphones?
The quality and resolution of a single microphone is sufficient to reflect a spectrum of all recorded frequencies, but it contains no directional information.
In the application of an acoustic camera we need more than one microphone.
Microphone array for beamforming
In a microphone array setup, a sound wave will reach all the individual microphones with a slightly different, measurable interval.
From these intervals, the software can calculate the direction of the sound.
The array setup enables determination of the sound direction.
Pattern of the microphones
The array consists of a number of microphones. It is a design choice how to organize the microphone layout.
A square setup with a fixed 2 centimetre horizontal and vertical spacing is a very useful one.
It delivers an interesting resolution, flexibility in handling and a acceptable range of analysis types, but most importantly, it allows you to do high resolution near-field acoustic holography measurements.
There is one potential side-effect to a rectangular arrangement: it may lead to ghost-sources, known as aliasing.
If the chance on a wrong interpretation is present, aliasing can be prevented by choosing a different microphone pattern preset. The Sorama Portal software allows the user to choose from multiple microphone pattern presets. For instance, the sunflower microphone pattern is best suited for far field analysis. With the randomness of the microphone selection, less microphones are needed to calculated a proper far field analysis.
Microphone array for Near Field Holography
The behavior of the sound waves in the Near field and Far field zones
Next to Far field, acoustic research can also apply to Near field measurements. These two types of measurement are completely different, still both techniques have one thing in common, the microphone array is the same. In Near field measurement the microphone array is placed near the surface of interest. In order to have a reliable data-capturing without disturbing the waves, our microphone array is as open as possible. We call this Near field Acoustic Holography, patented by Sorama.