Apparently there are three main categories: near-field acoustic holography, acoustic beamforming, and inverse methods. Are there specific criterias on how to select one from another?
Hi Armando, the reason to choose a method is up to the application. Here are some comments you may find useful:
- No need of real-time processing: the problem can be solved with inverse methods (e.g. IBEM) as well as near-field holography (NAH) and beamforming. Even though inverse methods usually have a heavier computational cost, they yield very good results in terms of accuracy of the reconstruction. However, for real-time I would avoid inverse methods and take another path.
- The resolution of inverse methods usually depends on the amount of elements used to solve the inverse problem. Whereas the resolution in classical NAH usually depends of measurement constraints and the regularization technique used to solve the (ill-posed) inverse problem.
- On the other hand, classical forms of NAH can be very accurate for low- and mid-frequencies, but may not behave as good as beamforming for high frequencies. You should also check p-u measurement techniques (e.g. Microflown sensor).
- Most of the near-field techniques present a strong dependence of the source geometry (i.e. separable geometries) and the assumption of a free half-space (i.e. anechoic 'behind' the measurements). To solve arbitrary source geometries, the equivalent-source method (ESM) could be most accurate. For enclosed spaces, inverse methods can shake hands with room acoustics; however, at the expense of a heavy computational cost.
Good luck,
//E
You may want to categorize the sources you're after.
any of the methods usually come with pro and cons depending on the field of use >
- nearfield methods like NAH are good for low frequency sources but still have a long list of prcatical troubles (hot engine test > you dont want to ruin your 1000$ sensore) then you end in the far field using beamforming methods
- far field methods like beamforming are usually good when you handle sources with freuqencies from say 300Hz up to 20kHz (i did measure and map above and below but that is a matter of interpretation) measurement distances from 30-40cm up to kilometers are possible depending on your environment
if you more interested in beamforming - there is a great collection of papers on bebec.eu > some of those papers are around here already
if you have more questions feel free to contact me and i can direct you to some more experts
cheers from berlin !
G
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