A typical bass loudspeaker driver has an inertial air load which is about 30% of its actual cone mass. This air load mass is often poorly understood, but it is significant in defining the resonance frequency, and the purpose of this paper is to understand the concept, clarify important aspects, and present some corroborative measurements. The immediate surroundings of the diaphragm determine the low-frequency air load, and measurements on a test driver with different mounting arrangements are made and assessed, including measurements in vacuum. A loudspeaker box presents its own complications. Simulations are used to show how the air load depends on baffle size. In general the air load may not be accurately represented by the usual approximations that apply to a piston in an infinite baffle or to a freely oscillating disk, but they do give a rough estimate.
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