Line microphones have long been popular for use as narrow directional microphones. Their structure is comprised of a leaky acoustic tube with many slits to suppress off-axis sensitivity, together with a directional capsule attached to this tube. Although many microphones of this type are currently on the market, there seems to be no quantitative model to explain their behavior, which is very important in terms of effectively designing the directivity. We thus modeled a leaky acoustic tube using a distributed equivalent circuit and combined it with the directional capsule's equivalent circuit model. Analysis showed that the model agreed well with the measurement results, particularly at the directional characteristics, while the conventional model adopting acoustic tube by delay-and-sum modeling did not.
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