Dimitri M. Donskoy
Davidson Lab., Stevens Inst. of Technol., Castle Point on the Hudson, Hoboken, NJ 07030
A new design of a low-frequency sound source has been developed and tested. The oscillation of a rigid body and an arrangement for converting a dipole oscillation of the rigid body to a monopole pulsation are used in this radiator. The oscillation of the rigid body provides large displacement of a radiating surface without deformation of the material. Monopole pulsation of the entire source provides much higher acoustic radiation than dipole oscillation of a small (as compared with sound wavelength) body. The vibromotive force is generated by oscillation of a mass inside the rigid body. To prove the concept, a small version of the source has been built. It has a diameter of 0.32 m, a frequency of 35--150 Hz, and an acoustic power output of 25 W on a 80-Hz frequency. The full scale source will be capable of radiating different kinds of signals (cw, FM, or pulse) in the frequency range of tens to hundreds of Hz with a source level over 200 dB re: 1 (mu)Pa and efficiency of approximately 70%. A high source level in the low-frequency range can be achieved due to the lack of limitation in the displacement of the radiating surface. The source has a potential for high reliability and relatively low cost due to very simple construction, the use of highly reliable and inexpensive mass-manufactured units (like electric motors), and very small material deformation.