Acoustic Plane Wave Generation by a Short, Actively Terminated Waveguide

A compact device is needed to generate planar acoustic waves over a symmetrically dimensioned volume of approximately one cubic meter in the frequency range 60 Hz to 5 kHz. This normally requires an anechoic chamber or other environment that results in acceptably low acoustic reflection or scattering back into the volume of interest. ORINCON proposes an approach that confines sections of planar acoustic waves within a section of a waveguide enclosing the test volume. The plane waves will be created by a specially developed plane wave source at one end. The plane wave source will be carefully designed to minimize evanescent waves and excitation of modes other than the plane wave mode in the wave guide above its cutoff frequency. The far end of the enclosure will be terminated by an acoustically active sound control transducer or array to suppress reflection or diffraction of sound back into the enclosure and to suppress evanescent waves created by the acoustic impedance mismatch between the wave guide and the room at low frequencies. Anticipated Benefits/Potential Applications - This device will be useful for calibration and measurement of directional response patterns of microphones over a broad frequency range. It may also be applicable to testing techniques for active cancellation of acoustic scattering from small objects, or from small-scale models of larger objects.