In order to discuss the sound radiation from a direct‐radiator loudspeaker in the high‐frequency region, an elastically supported circular plate in an infinite baffle is used. The normal modes of this plate is consistently treated from the free boundary to the simply supported boundary, which are the limiting cases of the elastically supported boundary, by defining a dimensionless parameter representing the ratio of the edge stiffness to the bending stiffness of the plate. It is found that the frequency response curve is determined by the resonance between the plate and the acoustic fluid for heavy loading, and between the plate and the mechanical impedance of the voicecoil for light loading, both with different shapes of response curves around the resonance frequencies.