Abstract: The present invention is an audio frequency power amplifier input circuit having improved vacuum tube circuit topology. The improved circuit includes a direct current feedback circuit within the input circuitry which stabilizes the operating point of a phase inverter. The feedback circuit maintains optimum operation of the circuit despite variations in tube characteristics or supply voltages. Another aspect of the improved circuit comprises a low impedance phase inverter which improves the drive capability of the phase inverter to push-pull power output vacuum-tube grids.

Abstract: A loudspeaker system includes at least two loudspeaker drivers, together with an electrical crossover network having filter circuits with at least two separate mutually exclusive frequency passbands. The filter circuits comprising the crossover network each possess brick-wall amplitude responses, i.e., passbands with very high band-edge amplitude vs. frequency response slops, on the order of 100 dB/octave in the better embodiments. The high passband band-edge slopes, which are realized by the inclusion of transmission zeros in the separate crossover filter transfer functions, takes together with further appropriate crossover filter transfer function synthesis causes the separate loudspeaker drivers comprising the loudspeaker system to function independently of one another in their contribution to total system acoustic output.

Abstract: An audio speaker system is disclosed providing improved fidelity of performance from overdamped woofer drivers in small sealed enclosures. At least two woofer drivers are employed, and are driven electrically in such a manner that the phase difference in the electrical signals to the two drivers, or sets of drivers if more than two are employed, will be near zero at the lowest bass frequency and will increase to a value up to 180 degrees at the highest bass frequency which is generally taken as the woofer-midrange crossover frequency. This aforementioned phase difference in the electrical signal inputs to two sets of woofers common to one sealed enclosure improves over prior art by providing increased low-bass acoustic output, less acoustic wave interference between the woofers and the midrange drivers, and a smoother input impedance characteristic in the bass frequency region.