Juha Backman, "Low-frequency polar pattern control for improved in-room response", presented at the AES 115th Convention, New York, 2003 October 10-13, preprint 5867:
"As a summary of the results presented above for the room-speaker interaction it can be stated that cardioid source has more immunity against changes in source placement or room absorption in sparsely modal range. Below the lowest mode the cardioid speaker does not have any advantage over the monopole source, but both exhibit higher output and less source position dependence than the dipole speaker. These results indicate that creating a loudspeaker that has unidirectional polar pattern in the sparsely modal region and omnidirectional below the lowest mode represents a good compromise between low-frequency output capability and avoiding room coloration effects."
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