ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

4pEA6. The improvement of low-frequency driver performance using an amplifier with negative output resistance.

Thomas D. Kite

Elmer L. Hixson

Dept. of Elec. and Comput. Eng., Univ. of Texas at Austin, Austin, TX 78712

A low-frequency dynamic driver (woofer) was modeled on pspice, an electric circuit simulator. The far-field pressure response of the driver was computed as the dc resistance of the voice coil, R[sub e], was varied. In the limit of zero R[sub e], the on-axis response for a constant voltage input was shown to rise at 6 dB/octave. The input to the driver was therefore equalized with an integrator to produce a flat pressure response with frequency. A beneficial side effect of reducing R[sub e] was the improvement of the transient response of the driver, since it became possible to critically damp the system. The system was found to be stable for values of R[sub e] greater than zero. The simulated results were tested in an anechoic chamber using a power amplifier with variable negative output resistance. The far-field pressure response of the driver was found to be substantially flat over a broad range of frequencies around the natural resonance of the driver, and transient response was improved, as predicted by the circuit simulation.