The pressure radiated by a column of in-phase monopole sources may be expressed as:
Create a model (spreadsheet / MATLAB etc) for a 6 element column, where d=0.2m. Figure gives an example solution, where f=1kHz. You may choose an arbitrary source strength, but r must be large compared to source dimensions.
Figure: Column source directivity where N=6, d=0.2, f=1kHz