Most low frequency sources radiate energy in an omni-directional manner. This often leads to unsatisfying results regarding the reproduction of low frequencies in small listening rooms. The influence of different radiation characteristics is investigated concerning the reproduction of low frequencies in a sparsely modal environment. In this paper the room transfer function characteristic of a monopole, a dipole, and a cardioid are compared. The different room mode excitation mechanisms are explained using comparative measurements taken in a reverberation chamber. Furthermore the effect of a single reflective boundary on the low frequency response is simulated. The cardioid turns out to be the more preferable low frequency source for the three types investigated.
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