The freefield resonant frequency and the deflection under given static pressure of a thin, circular, clamped‐edge diaphragm may be calculated theoretically by well‐known equations. Also, experimental means exist for a determination of these quantities. No satisfactory theoretical or experimental method has appeared, however, by which it is possible to obtain, for a complicated physical system, the diaphragm deflection as a function of the frequency of an applied sinusoidal pressure, over a frequency range that includes the natural diaphragm resonance. An experimental method is described by which a piezoelectric driver is employed to generate a sinusoidal pressure of variable frequency in a confined gas, to which one side of a test diaphragm may be exposed. Equations are derived describing the gas‐coupling medium and the piezoelectric driver. By use of these equations, it is possible to predict the characteristics of the apparatus. A study is made of the dynamic response of a series of thin, circular, clamped‐edge diaphragms. Since the diaphragm geometry is simple, the resonant frequency may be calculated theoretically. A shock‐excitation technique is also employed to determine the resonant frequency. Comparison is then made between the latter two methods and the result given by the apparatus. The static‐pressure dependence of the resonant amplitude and resonant frequency of the diaphragms is studied and discussed. The magnitude of the dynamic‐pressure amplitude is determined, employing a calibrated commercial pressure gauge below its own resonance. Modifications of the apparatus are reported that extend the dynamic‐pressure amplitude and the useful frequency range, and the possibility of utilizing the apparatus for dynamic calibration of pressure gauges is noted.