Patent ID: 7477751

Claim:
An apparatus for transducing an acoustic signal produced by a source, the signal having a frequency within a range from a low to a high, and corresponding wavelength within a range from a long to a short, the apparatus comprising: a. an array of at least two pressure sensors spaced apart along a sensor axis and located at an array location; b. a loudspeaker that is configured to output sound waves in response to an input, at a loudspeaker location that is on the sensor axis; c. a first signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to an estimate of a pressure derivative approximately along the sensor axis, at the array location; d. a second signal processor, having an input that is coupled to an output of the first signal processor, and having an output that is coupled to the loudspeaker input, which second signal processor is configured to generate an output signal that is proportional to the estimate of derivative signal; e. a third signal processor, coupled to an output from the array of pressure sensors, configured to generate a signal that corresponds to a weighted source pressure sum; f. a comparator, coupled to an output of the third signal processor that generates the weighted pressure sum signal, configured to generate a pressure sum error signal that corresponds to whether the pressure sum signal is less than a threshold signal ε; and g. a fourth signal processor, coupled to an output of the comparator, configured to generate a coefficient signal based on the pressure sum error signal, which coefficient signal is input to the second signal processor which is further configured to generate an output signal that is proportional to the estimate of derivative signal, with a proportionality that is based on the coefficient signal.