Noise cancellation apparatus

An active noise reduction apparatus for reducing ambient noise in the vicinity of an eardrum, comprising:

• a housing for receiving an input audio signal;
• an output transducer located in the housing;
• an input transducer for detecting and reducing ambient noise, the input transducer not located in substantially the same plane as the output transducer;
• signal processing means to reduce the ambient noise detected by the input transducer;
• an acoustic means including an acoustic waveguide for transmitting the input audio signal to the eardrum without disturbance of the ambient noise and
• having low pass filter characteristics with a zero phase shift over a desired bandwidth to isolate the output transducer from the input transducer for channeling the input audio signal representing substantial speech between the output transducer and the eardrum, wherein a quiet zone is created to isolate sound transmitted from the input transducer.

An active noise reduction apparatus comprising:

• a housing having an earphone;
• microphone means mounted in the earphone facing towards an ear of a user for detecting unwanted ambient noise;
• means to convert the noise to electric signals;
• phase shifting and attenuation means connected to the microphone to provide an inverted anti-noise signal;
• an output transducer substantially out of plane with the microphone means for transmitting the audio signal to the user's ear;
• means for preventing mechanical vibration induced low frequency disturbances from being transmitted to the output transducer;
• an acoustic waveguide isolating the microphone means from the output transducer for creating a quiet zone in close proximity to the output transducer and thereby excluding the unwanted ambient noise from reaching the user's ear.

An active noise reduction apparatus for use in a headset with a boom microphone to reduce ambient noise from reaching a user's ear without disturbing a desired audio signal outputted to the listening ear comprising an earphone located within the headset;

• a pick-up microphone for detecting noise signals within the earphone facing towards the ear;
• means for converting the noise signals into electric signals;
• electro-acoustic means for applying the electric signals to the earphone to produce acoustic signals 180.degree. degrees out of phase with the ambient noise;
• an output transducer means mounted in the earphone having an acoustical filter having low pass filter characteristics with a zero shift phase over a desired bandwidth for coupling speech to the user's ear and isolating vibration induced low frequency disturbances from reaching the user's ear.

A noise reduction system for use with an active noise cancellation apparatus comprising:

• a pick-up microphone located in the headset for detecting noise signals to convert to electrical signals;
• a speaker located in the headset having a acoustic means with low pass filter characteristics with a zero phase shift over a desired bandwidth;
• an audio transmission signal;
• means for electrically rejecting vibrations of the electrical signal;
• a variable gain/control means for inverting the noise signal to produce an anti noise-signal;
• the acoustic means for filtering out mechanical vibration induced low frequency disturbances from reaching the speaker;
• acoustic summing means to combine the anti-noise signal
• and the noise signal to produce a quiet zone in the acoustic means;
• means for transmitting the audio signal to the speaker;
• and means for maintaining phase agreement between the noise signal and the anti-noise signal of the speaker.

An active noise reduction apparatus for reducing ambient noise in the vicinity of an eardrum, comprising:

• a housing for receiving an input audio signal;
• an output transducer located in the housing;
• an input transducer located in the housing for detecting ambient noise located in the housing;
• a signal processing means to process noise detected by the input transducer;
• an acoustic means for channeling the input audio signal representing substantial speech between the output transducer and the eardrum;
• and an acoustic waveguide means for transmitting the input audio signal without disturbance of the noise to the eardrum creating a quiet zone to isolate sound transmitted from the input transducer.

A method for calibrating an active noise reduction apparatus including a housing comprising a speaker to produce an acoustic anti-noise signal in the housing, a microphone to detect an external noise signal, and an amplitude adjustment means to calibrate the acoustic anti-noise signal to create a quiet zone in the housing for operation with an independent electrical assembly, wherein the apparatus is calibrated separately from the electrical assembly, the method comprising the steps of:

• inputting the external noise signal received by the microphone to produce an anti-noise signal;
• transmitting to the speaker the anti-noise signal having an equal gain and opposite phase response to the external noise signal detected by the microphone;
• and
• balancing the gain and phase response of the anti-noise signal by the amplitude adjustment means located in the noise reduction apparatus to match the gain and phase response of the external noise signal to yield a theoretical zero in the quiet zone.