Coaxial loudspeaker drivers are known to produce intermodulation distortion. In a simplified model, the woofer is treated as a baffled planar piston and the tweeter is treated as an acoustic monopole located in front. An integral solution to the second-order wave equation shows that the boundary effects dominate air nonlinearities. Several numerical investigations of the model were compared with experiments. Intermodulation products decrease as the tweeter is moved off axis.
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