Noise cancellation apparatus

An open-loop active noise reduction apparatus for reducing ambient noise in the vicinity of a 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;
• an open-loop 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 open-loop 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 acoustical 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 open-loop 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 ear comprising an earphone located within the headset;

• a pick-up microphone for detecting noise signals within the earphone facing towards the ear;
• open-loop 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. 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 phase shift 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.

An open loop 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 an 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 open loop active noise reduction apparatus for reducing ambient noise in the vicinity of the 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 open loop signal processing means to process noise detected by the input transducer;
• an acoustic means having low pass filter characteristics with a zero phase shift over the 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;
• 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.

An active noise cancellation and noise reduction system for use in a headset for transmitting audio signals from microphones and for receiving external audio from a surrounding environment comprising:

• a first microphone means having a first switch means having a noise canceling mode and a talk thru mode and a second microphone means;
• a microphone amplifier means connected to the microphones by a second switch means having a noise canceling mode and a talk thru mode;
• an audio microphone transmission means for connecting the amplifier means when the first switch means and the second switch means are operating in the noise canceling mode, wherein the microphone transmission means is bypassed when the first switch means and the second switch means are in the talk-thru mode;
• a transmission gate for transmitting the audio signal from both microphone means to a buffer amplifier when the first switch means and second switch means are in the noise canceling mode, wherein the transmission gate is disabled when the second switch means is in the talk thru mode;
• the buffer amplifier means for transmitting the audio signal received from the transmission gate to an audio system and to a scaling amplifier when the first switch means and second switch means are operating in the noise canceling mode;
• the buffer amplifier means for directly outputting the audio signals received by the microphone amplifier means when the first switch means and second switch means are operating in the talk thru mode;
• the scaling amplifier having a third switch means having a noise canceling mode and a talk-thru mode, provides a sidetone signal to an earcup of a speaker transmitted from both microphone means and from the external audio when all the switch means are operating in the noise canceling mode;
• the scaling amplifier having a gain control, wherein the gain control is increased when all the switch means are operating in the talk thru mode to increase the sidetone signal to a speaker;
• an active noise reduction system receives and outputs the sidetone signal to the speaker in the headset.

A method for independently 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, an acoustical waveguide having zero phase shift over a desired bandwidth to isolate and direct the acoustic anti-noise signal from the microphone, 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:

• producing the external noise signal having a gain and phase response detected by the microphone in the housing;
• inputting the external noise signal received by the microphone through acoustic-electro processing means in the electrical assembly to produce an electrical anti-noise signal,
• transmitting to the speaker the electrical 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 electrical 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.