Abstract: A system and method for achieving extended low-frequency response and increased low-frequency sound pressure output capability in a loudspeaker system is provided. The system and method comprise mounting a low-frequency driver in a ported box, tuning the ported box to a sufficiently low frequency so as to result in a frequency response that can be modeled substantially as a second-order response, and equalizing the response of said driver-box combination with a second-order biquadratic filter function to achieve the desired frequency response characteristic.

Abstract: A multi-wavelength optical receiver including multiple photodetectors receiving different ones of a multi-wavelength signal. For each wavelength-dedicated photodetector, a separate electronic receiver circuitry is provided including a current-to-voltage converting input transistor and an emitter-follower output transistor arranged as an operational amplifier with a feedback resistor.

Abstract: A family of window comparator circuits are arranged to monitor differential input signals and indicate when the difference between the signals is between two limits. Each of the window comparator circuits includes an input circuit having at least one current source. The input circuit is responsive to a differential input signal for conducting two dependently variable currents through an output circuit. At least one voltage dropping element is connected to each current source in the input circuit for establishing the limits of the window comparator. The output circuit responds to changes in the ratio between the two currents conducted therethrough for indicating that the differential input signal is between the two limits.

Abstract: A narrow-band tone decoder has a controllable oscillator, connected in a fast-capture phase-locked loop, for generating a signal having a frequency determined by a control signal produced within the loop. A synchronous detector, which responds to an input signal of the tone decoder and to a signal from the controllable oscillator, produces a signal having a magnitude dependent upon the magnitudes of the input signal and of the signal from the controllable oscillator. A window comparator monitors the control signal within the loop for deciding when the generated signal is within a predetermined frequency range.