Abstract: A three-phase generator is used to directly drive an array of electroacoustic transducers without the usual high power amplifiers. Complex signals having general spectra are generated by driving the generator rotor field with an excitation comprised of in-phase and quadrature components. These components are appropriately transformed so that a readily available three-phase wound rotor machine can be used without modification. The three output phases of the generator are connected to a multi-tapped delta connected transformer. Appropriate tap connection for each transducer allows achieving the desired voltage and phase angle. Freedom in choosing taps simultaneously allows balancing of the generator load.

Abstract: Digital apparatus and a method are disclosed for determining the phase angle of a tone signal of known frequency by correlating a clipped version of the tone signal with a reference signal having a repetition rate equal to the tone frequency. Correlation is accomplished by multiplying the clipped tone signal with each of quadrature components of the reference signal and sampling the product signals to provide binary sample trains which are supplied to a pair of shift register accumulators which effectively frame a moving phase measurement window. Reversible counters and associated logic determine the magnitudes and signs of differences in numbers of samples of noncorresponding binary values in each of the accumulators, and provide counts representative of in-phase and quadrature components of the product of the tone signal and the reference signal. The counts are utilized in a digital processor to compute the phase angle of the tone signal relative to the reference signal.