Weaker beamforming response for sources further from origin?

[Ryan Christopher Schmelzle]

Hello,

I'm currently trying to perform time-domain delay-and-sum beamforming using a grid of microphones with a source/sources placed above the mics. However, I'm running into an issue where the signal gets weaker as the source is placed futher from ~(0, 0). 

A couple examples of the response to a single source placed at different locations are shown below (where blue dots indicate mics in the grid, red indicates a source).

When placing two identical sources in the same scene at different locations (at the same height above the microphone array plane), I get the following beamformer response:

Does anyone have any suggestions as to where I may be going wrong? Or advice for resolving this? 

Code for the approach is below:

https://pastebin.com/ddnZj8GM

Thanks!!

[Ryan Christopher Schmelzle]

Apologies, it looks like the screenshots didn't come through; the top three are a single source at three different locations

And the following are two identical sources at different locations (both on the rectgrid plane above the mic array)

[Acoular-users]

Hi,

in Acoular, what you call 'response' is actually the MS sound pressure at the origin (0,0,0). Therefore you results make sense, because this will be smaller the further away the sources are.

It is implemented this way assuming that the center of gravity of the array is also at the origin. For the frequency domain beamformers it is also possible to set another reference point e.g. 1m from the source (which only makes sense if you somehow know that you have an omnidirectional source). This is, however, presently not implemented for time domain beamformers in Acoular.

If you want to know more about why the steering works like this, see https://downloads.hindawi.com/archive/2012/292695.pdf

Hope this helps.