This class provides for: (a) wired one-way electrical transmission or processing systems for audio signals, (b) Stereophonic systems, which are not elsewhere classified, (c) instrument or process for converting an electrical audio information signal to or from humanly audible form.
(1) Note. A "system" is an assemblage of two or more elements having diverse functions.
(2) Note. An "audio" signal is an electrical signal which represents spoken or other sounds which vary with time, and may be in analog or digital form.
(3) Note. Combinations of a loudspeaker or microphone with another audio signal processing device (e.g., amplifier, filter, etc.) or other circuit (e.g., bias circuit) are classified herein even if the loudspeaker or microphone is included by name only.
(4) Note. Nominal recitation of "audio" is not sufficient to afford classification herein of an invention which would be otherwise classified elsewhere.

LINES WITH OTHER CLASSES AND WITHIN THIS CLASS
A transducer for conversion of speech or similar sound (e.g., music) to or from a corresponding electrical signal, and the combination of such a transducer with acoustical structure is classified herein (see Subclass References to the Current Class, below). Note that transducer structure combined with circuitry, other than a lead or connector, is classified with the system, either in this class (381), or in an external class for processing an audio signal.
Excluded from this class are two-way wired electrical audio signal transmission systems which are classified elsewhere. Transmissions of pulse signals which do not represent audio signals is classified elsewhere. Multiplex Communication Systems (except stereophonic multiplex systems) are classified elsewhere. Modulated Carrier Wave Communication Systems and devices are classified elsewhere. Combinations of subject matter of this class with structure of a more comprehensive combination (e.g., Television Set) are classified with the combination. (See References to Other Classes, below.)

SEE OR SEARCH THIS CLASS, SUBCLASS:
150 for a transducer for conversion of speech or similar sound (e.g., music) to or from a corresponding electrical signal, and the combination of such a transducer with acoustical structure.

REFERENCES TO OTHER CLASSES

SEE OR SEARCH CLASS:
27, Undertaking, subclass 31 for systems adapted for communication with entombed persons.
73, Measuring and Testing, 584 for measuring sound waves, especially subclass 585 for audiometers (ear or hearing testing), and subclasses 646+ for measuring sound intensity.
84, Music, 600 for electronic musical instruments.
178, Telegraphy, for transmissions of pulse signals which do not represent audio signals. (Lines With Other Classes and Within This Class)
181, Acoustics, appropriate subclasses for mechanical audio systems.
330, Amplifiers, for amplifiers not having specific input signals or specific loads.
340, Communications: Electrical, appropriate subclasses for electrical communications in general.
367, Communications, Electrical: Acoustic Wave Systems and Devices, subclass 132 for underwater speech transmission by an acoustic wave; subclasses 140+ for an acoustic transducer not related to speech signal conversion.
369, Dynamic Information Storage or Retrieval, appropriate subclasses for storing and retrieving sound signals.
370, Multiplex Communications, appropriate subclasses for multiplex communications and for multiplex communication systems (except stereophonic multiplex systems). (Lines With Other Classes and Within This Class)
375, Pulse or Digital Communications, for transmissions of pulse signals which do not represent audio signals. (Lines With Other Classes and Within This Class)
379, Telephonic Communications, for two-way wired electrical audio signal transmission systems. (Lines With Other Classes and Within This Class)
455, Telecommunications, appropriate subclasses for modulated carrier wave speech communications, and for modulated carrier wave communication systems and devices. (Lines With Other Classes and Within This Class,
505, Superconductor Technology: Apparatus, Material, Process, 150 for high temperature (T[subscrpt]c[end subscrpt] 30 K) superconducting devices, and particularly subclasses 202+ for electric communication system containing transmitter or receiver of pulse, digital, or electromagnetic radio, television, or radar wave form.
600, Surgery, subclass 559 for audiometers (ear or testing by auditory stimulus).
623, Prosthesis (i.e., Artificial Body Members), Parts Thereof, or Aids and Accessories Therefor, subclass 9 for mechanical artificial larynxes.
704, Data Processing: Speech Signal Processing, Linguistics,
Language Translation, and Audio Compression/Decompression, 200 for speech signal processing using a computer.

BINAURAL AND STEREOPHONIC:
This subclass is indented under the class definition. Subject matter where there are two or more independent sound signals which are to be separately reproduced so as to create a sense of depth.
(1) Note. "Sound signals" are electric signals representing sounds.
(2) Note. Stereophonic or pseudo stereo- phonic systems are classified here, not in Class 370.

SEE OR SEARCH CLASS:
360, Dynamic Magnetic Information Storage or Retrieval, for magnetically recording or reproducing stored stereophonic information.
369, Dynamic Information Storage or Retrieval, 85 for recording or reproducing stored stereophonic information.
370, Multiplex Communications, appropriate subclasses for multiplex in general.

Broadcast or multiplex stereo:
This subclass is indented under subclass 1. Subject matter for the broadcasting or transmission of two or more independent sound signals which are to be reproduced so as to create a sense of depth.

SEE OR SEARCH CLASS:
360, Dynamic Magnetic Information Storage or Retrieval, for magnetically recording or reproducing stored stereophonic information.
369, Dynamic Information Storage or Retrieval, 85 for recording or reproducing stored stereophonic information.
370, Multiplex Communications, appropriate subclasses for multiplex in general.
455, Telecommunications, appropriate subclasses for broadcast, nonstereo radio communications.

FM final modulation:
This subclass is indented under subclass 2. Subject matter where stereophonic signals are broadcast by means of a radio carrier wave which is only frequency modulated.
(1) Note. There may also be an amplitude modulated subcarrier.

SEE OR SEARCH CLASS:
455, Telecommunications, 42, 93, 110+, and 205+ for frequency modulated carrier wave communications in general.

AM subcarrier:
This subclass is indented under subclass 3. Subject matter where a carrier wave is frequency modulated by a subcarrier which has been amplitude modulated by a signal.

Four discrete channels:
This subclass is indented under subclass 4. Subject matter where the independent sound signals are four in number.

SEE OR SEARCH THIS CLASS, SUBCLASS:
19 for quadrisonic sound systems in general.

Having transmitter:
This subclass is indented under subclass 5. Subject matter including means for generating and modulating a carrier wave by a stereophonic signal and usually including the coupling of the modulated carrier wave to the transmission medium.

SEE OR SEARCH CLASS:
455, Telecommunications, subclasses 39-129 for radio transmitters in general.

Switch-type detector or modulator:
This subclass is indented under subclass 4. Subject matter having a detector or modulator which extracts information from or adds information to an input waveform only at instants determined by a selector pulse.

Two diodes:
This subclass is indented under subclass 7. Subject matter in which the detector or demodulator is limited to containing, two diodes.

Four or more diodes:
This subclass is indented under subclass 7. Subject matter in which the detector or demodulator contains at least four diodes.

Channel separation control:
This subclass is indented under subclass 4. Subject matter where there is control over the electrical or acoustical difference between the independent sound signals.

Automatic switchover between mono and stereo modes:
This subclass is indented under subclass 4. Subject matter where a receiver is changed from a monaural receiver to a stereophonic receiver in response to the presence of a stereophonic signal at its input.

Stereo indicators (e.g., stereo presence):
This subclass is indented under subclass 4. Subject matter having an indicator which gives an indication in response to the presence of a stereophonic signal.

Antinoise:
This subclass is indented under subclass 4. Subject matter having provision for the reduction or elimination of an unwanted signal.

SEE OR SEARCH CLASS:
455, Telecommunications, 50.1, 63+, 222+, 283+, and 296+ for noise elimination in radio communications in general.

Having transmitter:
This subclass is indented under subclass 4. Subject matter including means for generating and modulating a carrier wave by a stereophonic signal and usually including the coupling of the modulated carrier wave to the transmission medium.

SEE OR SEARCH CLASS:
455, Telecommunications, subclasses 39-129 for radio transmitters in general.

AM or both AM and angle final modulation:
This subclass is indented under subclass 2. Subject matter having a carrier wave which is amplitude modulated and which may also be angle modulated.

Having transmitter:
This subclass is indented under subclass 15. Subject matter including means for generating and modulating a carrier wave
by a stereophonic signal and usually including the coupling of the modulated carrier wave to the transmission medium.

SEE OR SEARCH CLASS:
455, Telecommunications, subclasses 39-129 for radio transmitter in general.

Pseudo stereophonic:
This subclass is indented under subclass 1. Subject matter having a device or arrangement which transforms single channel audio signals into a plurality of channels of audio information to create a sense of depth.

SEE OR SEARCH THIS CLASS, SUBCLASS:
63 for reverberators, which are often used to create a stereophonic effect.

Pseudo quadrasonic:
This subclass is indented under subclass 17. Subject matter where the plurality of channels are four in number.

Quadrasonic:
This subclass is indented under subclass 1. Subject matter in which four independent sound signals are to be reproduced.

Matrix:
This subclass is indented under subclass 19. Subject matter where the four independent sound signals are either (1) combined or coded to give one or more complex signals or (2) one or more complex signals are combined or decoded to recover the four independent sound signals.

4-2-4:
This subclass is indented under subclass 20. Subject matter where four quadrasonic signals are multiplexed into two more complex signals, then expanded back into four signals.

Variable decoder:
This subclass is indented under subclass 21. Subject matter where the two more complex signals are combined in variable ratios in order to recover the four independent sound signals.

With encoder:
This subclass is indented under subclass 21. Subject matter where the four independent sound signals are combined or coded to give two complex signals.

Hearing aid:
This subclass is indented under subclass 1. Subject matter having a small ambient sound reproducing system wherein two or mote output transducers transmit independent sound signals directly into the ear or skull for use by a hearing impaired individual to increase the sound level received by the ear (i.e., listening assistance.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68 and the search notes therein for hearing aids, in general.

Stereo sound pickup device (microphone):
This subclass is indented under subclass 1. Subject matter including a single transducer system for converting sound waves into two or more independent sound signals.

Center channel:
This subclass is indented under subclass 1. Subject matter where a third sound signal is derived from combination of two independent sound signals.

Amplifier:
This subclass is indented under subclass 1. Subject matter including a device to increase the amplitude of the independent sound signals.

SEE OR SEARCH CLASS:
330, Amplifiers, appropriate subclasses for an amplifier not having a specific source of input signals or a specific load.

HELIUM SPEECH:
This subclass is indented under the class definition. Subject matter where an output speech signal is of differing apparent predominant frequency but of the same duration as the input speech signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
29 for bandwidth compression or expansion of a speech signal.

AUDIO TRANSDUCER PROTECTION CIRCUITRY:
This subclass is indented under the class definition. Subject matter where there is an audio transducer and circuitry to protect the transducer from damage due to abnormal operating conditions.

SEE OR SEARCH THIS CLASS, SUBCLASS:
111 for systems having specific audio transducers.

SEE OR SEARCH CLASS:
361, Electricity: Electrical Systems and Devices, 1 for circuitry to protect other systems and devices in general from damage due to abnormal operating conditions.

MONITORING OF SOUND:
This subclass is indented under the class definition. Subject matter having a qualitative (yes-no) indication dependent upon a parameter of sound waves, e.g., loudness, quality, etc.

SEE OR SEARCH THIS CLASS, SUBCLASS:
58 for monitoring the operation of audio devices.
77 for systems having a microphone at a location remote from a listening location (i.e., one-way intercoms).

SEE OR SEARCH CLASS:
73, Measuring and Testing, 570 for measuring and testing sound waves where a quantative (numerical) indication is given, especially 645+ for measuring an acoustic parameter.
367, Communications, Electrical: Acoustic Wave Systems and Devices, 135 for acoustic wave receiver circuitry.

Amplification control responsive to ambient sound:
This subclass is indented under subclass 56. Subject matter where the ambient sound level, at a place where sound is being reproduced, is evaluated and the result used to control the volume of the reproduced sound.

MONITORING/MEASURING OF AUDIO DEVICES:
This subclass is indented under the class definition. Subject matter having an indicator, measuring device, or eavesdropping means.

SEE OR SEARCH THIS CLASS, SUBCLASS:
56 for monitoring of sound waves.

SEE OR SEARCH CLASS:
340, Communications: Electrical, 500 for condition responsive alarms.
714, Error Detection/Correction and Fault Detection/Recovery, 712 for testing transmission facilities.

Loudspeaker operation:
This subclass is indented under subclass 58. Subject matter where an operating parameter of a sound reproducing transducer is measured or indicated.

Testing of hearing aids:
This subclass is indented under subclass 58. Subject matter in which at least part of a hearing aid is tested.
(1) Note. A hearing aid is a small audio reproducing system for the hard of hearing.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68 for hearing aids.

SEE OR SEARCH CLASS:
73, Measuring and Testing, 570 for measuring vibration including sound waves.
324, Electricity: Measuring and Testing, for electrical testing or measuring in general.
370, Multiplex Communications, 241 for multiplex testing.
455, Telecommunications, 67.1 for modulated carrier system testing: subclasses 115+ for transmitter testing; and subclasses 226.1+ for receiver testing.

SOUND EFFECTS:
This subclass is indented under the class definition. Subject matter where the audio signal is selectively
distorted.

SEE OR SEARCH CLASS:
369, Dynamic Information Storage or Retrieval, 174 for signal modification in a recording system.

Tremolo or vibrato effects:
This subclass is indented under subclass 61. Subject matter having means to produce a rapid variation in amplitude or pitch of a signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
63 for means to introduce echoes into a signal.

SEE OR SEARCH CLASS:
84, Music, subclass 1.25 for producing vibrato in an electronic musical instrument.
181, Acoustics, subclass 143 for a moving sound producer or deflector which can produce tremolo effects.

Reverberators:
This subclass is indented under subclass 61. Subject matter having a device for producing echoes in the audio signal.

SEE OR SEARCH CLASS:
84, Music, subclass 1.24 for reverberation production in electronic musical instruments, and digest 26 for musical reverberation.
181, Acoustics, 123 for echo system.
333, Wave Transmission Lines and Networks, subclasses 138-164 for delay lines.
360, Dynamic Magnetic Information Storage or Retrieval, subclass 7 for recording for momentary delay to produce echoes.
369, Dynamic Information Storage or Retrieval, subclass 60.01 for using a recording system to delay a signal.

Mechanical (e.g., reverberation chamber):
This subclass is indented under subclass 63. Subject matter where the echoes are produced by other than electrical means.

Helical spring:
This subclass is indented under subclass 64. Subject matter where the echoes are produced by reflecting a compressional sound wave along a helical spring.

DEREVEBERATORS:
This subclass is indented under the class definition. Subject matter for removing echoes from a sound signal.

STETHOSCOPES, ELECTRICAL:
This subclass is indented under the class definition. Subject matter forming an instrument used to convey sounds to the ear of a user.
(1) Note. If the instrument is particularly adapted for use on or in a living body, classification is in Class 128, Surgery, but if the instrument can be used generally (e.g., to detect leaks or the internal sounds of machinery) classification is here.

SEE OR SEARCH CLASS:
181, Acoustics, subclass 131 for mechanical stethoscopes.
600, Surgery, subclass 528 for specific structure, adapted to be placed on or in a living body, for detecting sounds emanating from the heart.

ARTIFICIAL LARYNX, ELECTRICAL:
This subclass is indented under the class definition. Subject matter for replacing or supplementing the larynx and involving electrical actuation.

SEE OR SEARCH CLASS:
84, Music, subclass 375 for imitation trumpets, jew's harps, and reed horns of variable pitch.
116, Signals and Indicators, 137 for horns, whistles and compressional wave generators.
128, Surgery, 207.14 for tubes to be inserted into the trachea or larynx.
181, Acoustics, pertinent subclasses for sound amplifying and transmitting means and methods.
446, Amusement Devices: Toys, 297 for a toy having means to emit sound imitating a voice.
472, Amusement Devices, particularly subclass 64 for an illusion caused by sound imitation or effect.
623, Prosthesis (i.e., Artificial Body Members), Parts Thereof, or Aids and Accessories Therefor, 24 for electrically actuated artificial body members other than a larynx and subclass 9 for nonelectrical artificial larynxes.
704, Data Processing: Speech Signal Processing, Linguistics, Language Translation, and Audio Compression/Decompression, 258 for speech signal synthesis and subclass 271 for speech signal processing applied to a handicap aid.

ACOUSTICAL NOISE OR SOUND CANCELLATION:
This subclass is indented under the class definition. Subject matter, not elsewhere classifiable, comprising a noise cancellation system where audible noise is at least partially eliminated by generating and acoustically emitting an out-of-phase replica of an offending sound.

SEE OR SEARCH THIS CLASS, SUBCLASS:
73.1 for sound or noise masking.
94.1 for suppression of the effects of unwanted signals on desired signals.

SEE OR SEARCH CLASS:
415, Rotary Kinetic Fluid Motors or Pumps, subclass 119 for
noise elimination in fans, turbines, jet engines, etc.

Adaptive filter topology:
This subclass is indented under subclass 71.8. Subject matter having the functional interconnections between two or more transfer function models which make up an overall circuit or computational arrangement designed to generate a counterwave.

SEE OR SEARCH THIS CLASS, SUBCLASS:
71.13 for the generation of the out-of-phase replica using analog circuitry or non-adaptive filter.

SEE OR SEARCH CLASS:
708, Electrical Computers: Arithmetic Processing and Calculating, 322 for adaptive digital filter structures, per se.

Algorithm or formula (e.g., LMS, Filtered-X, etc.):
This subclass is indented under subclass 71.8. Subject matter having a specific computational sequence or a mathematical formula used in computation of a counterwave.

Analog or nonadaptive:
This subclass is indented under subclass 71.8. Subject matter in which the out-of-phase replica is generated using either analog circuitry or an electrical circuit having a fixed transfer function.

SEE OR SEARCH THIS CLASS, SUBCLASS:
71.11 for the generation of a counterwave using adaptive filter topology.

Tonal noise or particular frequency or band:
This subclass is indented under subclass 71.8. Subject matter in which the noise cancellation system is particularly designed to either eliminate noise having a high degree of underlying periodicity or process noise at a particular frequency or within a limited or particular frequency band.

Acoustic, nonairborne vibration sensing or counterwave emission:
This subclass is indented under subclass 71.1. Subject matter which senses vibration from or which imparts a cancelling wave directly to a solid or liquid medium or structure.
(1) Note. In order to be properly classifiable here, the primary object should be attenuation of acoustic sounds. In most cases, this will mean that a sensor such as a microphone will be needed to detect sound propagated through air, such as the residual sound after the counterwave source's output has been acoustically summed with the original noise.

SEE OR SEARCH CLASS:
52, Static Structures (e.g., Buildings), subclass 167.1 + for means compensating for an earth-transmitted force, i.e., earthquake.
267, Spring Devices, 136 for resilient shock or vibration absorbers. See especially subclasses 140.14 and 140.15 for subject matter including electronic or magnetic control, or subclass 140.11 for subject matter having an energy absorbing feature.

From appliance:
This subclass is indented under subclass 71.1. Subject matter wherein the noise cancellation system cancels noise emanating from a device such as an air conditioner, refrigerator, vacuum cleaner, etc.

Within cabin or compartment of vehicle:
This subclass is indented under subclass 71.1. Subject matter wherein the noise cancellation system cancels noise within a humanly occupied space of an aircraft, automobile,
etc.

SEE OR SEARCH THIS CLASS, SUBCLASS:
86 for electrical audio systems combined with vehicles.

Within duct:
This subclass is indented under subclass 71.1. Subject matter wherein the noise cancellation system cancels noise propagating in a tube, canal, pipe, or similar conduit, including automobile inlet and exhaust pipes.

Adjacent ear:
This subclass is indented under subclass 71.1. Subject matter wherein the noise cancellation system is associated with a structure in a manner designed to cancel noise in the immediate vicinity of a person's ears.
(1) Note. Structures included in this subclass are headrests, hearing protectors, etc. Hearing protectors based on active noise cancellation are classified herein.

SEE OR SEARCH THIS CLASS, SUBCLASS:
72 for hearing protector without noise cancellation.

Particular transducer or enclosure structure:
This subclass is indented under subclass 71.1. Subject matter specifying details of an electro-acoustic energy converter or housing for use in an active noise cancellation system.

SEE OR SEARCH THIS CLASS, SUBCLASS:
88 for enclosure or housing.
150 for electro-acoustic audio transducer.

Counterwave generation control path:
This subclass is indented under subclass 71.1. Subject matter having either a feedback or feedforward circuit or a sequence of computations to generate the out-of-phase replica of the offending noise.

Non-acoustically derived reference signal:
This subclass is indented under subclass 71.8. Subject matter in which a transducer used to obtain a signal for processing detects a form of energy other than sound vibration.
(1) Note. Examples are spark timing, crankshaft position, manifold pressure of an engine, etc.

HEARING PROTECTORS, ELECTRICAL:
This subclass is indented under the class definition. Subject matter which provides a barrier to the transmission of at least some sounds to the ear.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68 for hearing aids, electrical.

SOUND OR NOISE MASKING:
This subclass is indented under the class definition. Subject matter which utilizes sound to reduce the distractive influences of unwanted sound or other audible noise.
(1) Note. The unwanted sound may include intelligence bearing sound (e.g., conversation).

SEE OR SEARCH CLASS:
128, Surgery, subclass 1 for pain reducing or relaxation inducing sound.
380, Cryptography, subclasses 252-254 for an electrical audio signal masked for concealment by another signal.

HEADPHONE CIRCUITS:
This subclass is indented under the class definition. Subject matter having means to perform a desired electrical or electronic function in conjunction with a device held against the ear having a diaphragm which vibrates according to current variations.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68 for electrical hearing aids.

MEGAPHONES:
This subclass is indented under the class definition. Subject matter for amplifying the human voice and which is capable of being carried.

SEE OR SEARCH THIS CLASS, SUBCLASS:
74 for headphone circuits.

SEE OR SEARCH CLASS:
181, Acoustics, 177 for sound intensifying horns.

LECTERNS:
This subclass is indented under the class definition. Subject matter having an enclosure in the form of a reading desk.
(1) Note. Excluded from here are lecterns which have no electric audio signal processing circuitry.

SEE OR SEARCH CLASS:
312, Supports: Cabinet Structure, appropriate subclasses for lecterns, per se.
362, Illumination, appropriate subclasses of light sources for use with lecterns.

ONE-WAY AUDIO SIGNAL PROGRAM DISTRIBUTION:
This subclass is indented under the class definition. Subject matter for delivering the output of an audio signal source to a remote location, or to a plurality of electric-signal-to-sound transducers.

SEE OR SEARCH CLASS:
340, Communications: Electrical, 825.26 for stock quotation systems.
348, Television, 6 for wired television broadcasting and distribution system.
370, Multiplex Communications, 486 for multiplex program distribution systems.
455, Telecommunications, 3.1 for radio program distribution systems.

Drive-in:
This subclass is indented under subclass 77. Subject matter for providing one-way communication between a central location and one or more stations accessible to occupants of automobiles.

SEE OR SEARCH THIS CLASS, SUBCLASS:
87 for audio systems having nonelectrical features such as mountings, housings etc.

Near field:
This subclass is indented under subclass 77. Subject matter which is a near field or limited range system (i.e., field strength 1/d where d = distance from the transmitter to the receiver) where signal transfer from transmitter to receiver is inductive or capacitive rather wired.

SEE OR SEARCH CLASS:
455, Telecommunications, subclass 41 for near field modulated carrier wave systems.

Multiple channel:
This subclass is indented under subclass 77. Subject matter having more than one audio signal path.

With switching:
This subclass is indented under subclass 80. Subject matter where there is the making, breaking or changing connections between audio signal paths.

Public address system:
This subclass is indented under subclass 77. Subject matter having an input transducer to convert sound into an electrical signal and an output transducer converting the electrical signal into sound so that the sound can be heard over a large area.

SEE OR SEARCH THIS CLASS, SUBCLASS:
75 for megaphones.

SEE OR SEARCH CLASS:
369, Dynamic Information Storage or Retrieval, 1 for public address systems combined with recording reproducers.

Feedback suppression:
This subclass is indented under subclass 82. Subject matter having provision for preventing audio coupling from loudspeaker to microphone.

SEE OR SEARCH THIS CLASS, SUBCLASS:
93 for feedback suppression in audio systems in general.

Spare amplifier substitution:
This subclass is indented under subclass 82. Subject matter having provision for substituting one amplifier for another.

Speaker or channel switching:
This subclass is indented under subclass 82. Subject matter having provision for changing audio signal paths or audio reproducers.

VEHICLE:
This subclass is indented under the class definition. Subject matter with a vehicle.
(1) Note. Classified here are electrical audio systems combined with vehicles, other communication devices with vehicles are classified in Class 340, Communications: Electrical, subclasses 425.5+.

SEE OR SEARCH CLASS:
340, Communications: Electrical, 425.5, note especially subclasses 460 and 474 for vehicle with horn, siren, or other electrical communication means not elsewhere provided for.
455, Telecommunications, 345 for a vehicle mounted radio receiver.

HAVING NON-ELECTRICAL FEATURE (E.G., MOUNTING):
This subclass is indented under the class definition. Subject matter including a mechanical adjunct or device such as a mounting means or a specific container for electrical components.

SEE OR SEARCH THIS CLASS, SUBCLASS:
386 for a mounting or support feature of a housed loudspeaker.

Loudspeakers driven in given phase relationship:
This subclass is indented under subclass 87. Subject matter where there are a plurality of loudspeakers in the specific container which are driven such as that their output sound has a particular phase relationship.

Having microphone:
This subclass is indented under subclass 87. Subject matter where the specific container holds a microphone.
(1) Note. There are both claimed electrical features in this subclass as well as nonelectrical features.

SEE OR SEARCH THIS CLASS, SUBCLASS:
111 for circuitry combined with a specific type of microphone.
122 for a microphone combined with an element having a diverse function, e.g., an amplifier.
355 for a housed microphone.
369 for a microphone capsule, per se.
375 for a microphone in particular support structure, wherein there is no claimed electrical feature of the transducer.

DIRECTIVE CIRCUITS FOR MICROPHONES:
This subclass is indented under the class definition. Subject matter including a circuit for imparting directional pickup characteristics to microphones.

SEE OR SEARCH THIS CLASS, SUBCLASS:
155 for a directional microphone, per se.

FEEDBACK SUPPRESSION:
This subclass is indented under the class definition. Subject matter for prevention or reduction of an output
signal from being returned to an input.

SEE OR SEARCH THIS CLASS, SUBCLASS:
83 for feedback suppression in a public address system.
95 for a microphone system having feedback.
96 for a loudspeaker system having feedback.

NOISE OR DISTORTION SUPPRESSION:
This subclass is indented under the class definition. Subject matter with provisions for reducing the effects of an unwanted signal on a desired signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
13 for antinoise means in broadcast or multiplex stereo systems.
71.1 for acoustical noise or sound cancellation.
73.1 for audio masking.

SEE OR SEARCH CLASS:
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, 551 for unwanted signal suppression.
708, Electrical Computers: Arithmetic Processing and Calculating, 300 for digital selection or rejection of signal components and subclass 819 for filtering electrical signals by analog computation.

Spectral adjustment:
This subclass is indented under subclass 94.1. Subject matter in which the unwanted signal is either at least partially removed by processing a selected frequency or frequency band, such as by subtracting the contents of a particular frequency band from the input signal, or is overcome by preemphasis of a particular frequency or band to enhance the signal to noise ratio.

SEE OR SEARCH THIS CLASS, SUBCLASS:
83 for feedback elimination in a public address system (this is frequently done by spectral subtraction using notch
filters, for example).
93 for feedback elimination in an audio system under the class definition.
94.7 for noise suppression using a signal channel and noise channel.
98 for control of frequency characteristics in an audio signal in general, such as for equalization.
106 for compression/expansion ("compansion") systems, which achieve enhanced signal to noise ratio through compression. Preemphasis is often found with compression.

In multiple frequency bands:
This subclass is indented under subclass 94.2. Subject matter in which processing takes place in more than one spectral region, i.e., more than one frequency or frequency band is processed.

Interpolation:
This subclass is indented under subclass 94.1. Subject matter in which a segment of a desired signal which contains noise is replaced with an estimate of what it would or should have been in the absence of noise, the estimate being based on the desired signal's values before or after, or before and after, the noise occurred.

SEE OR SEARCH CLASS:
702, Data Processing: Measuring, Calibrating, or Testing, 189 for measured signal processing including weighting, averaging, and matrix operation.
708, Electrical Computers: Arithmetic Processing and Calculating, subclass 290 for interpolation, per se.

Soft switching, muting, or noise gating:
This subclass is indented under subclass 94.1. Subject matter designed to prevent a momentary, sudden fluctuation of voltage or current (a "pop") in a circuit as a result of a
sudden change of an operating parameter in the circuit, such as the application of power; or to attenuate or cutoff on a broad-band basis the audio output of a circuit when the audio signal does not contain intelligence; or to switch off the signal input to a system when the signal or noise level on the input is above a certain threshold (a condition which usually indicates that only noise is present).

SEE OR SEARCH THIS CLASS, SUBCLASS:
94.8 for peak limiting or pulsive noise compensation.

SEE OR SEARCH CLASS:
455, Telecommunications, 194.1 for muting and subclasses 218+ for squelch.

Hum or ground loop:
This subclass is indented under subclass 94.1. Subject matter designed to eliminate frequency components generated as a result of AC power supply contamination, or compensate for noise transmission caused by currents flowing through an electrical conductor which connects two different circuit points, each of which is nominally at ground potential.

SEE OR SEARCH CLASS:
330, Amplifiers, subclass 149 for hum or noise or distortion bucking introduced into signal channel.
455, Telecommunications, 298 for noise or interference elimination in the receiver power supply.

Using signal channel and noise channel:
This subclass is indented under subclass 94.1. Subject matter having separate inputs, each respectively containing primarily the desired and undesired signals, and which derives at least one "clean" output having the desired signal by utilizing both inputs, such as by subtracting one input from the other.

SEE OR SEARCH THIS CLASS, SUBCLASS:
94.2 for noise suppression using spectral adjustment.

Peak limiting or pulsive noise compensation:
This subclass is indented under subclass 94.1. Subject matter designed to restrict the amplitude of relatively short duration, high amplitude excursions of a desired signal to prevent distortion in a subsequent stage such as a modulator or amplifier, or compensate for the effects of sporadic or short duration undesired signals ("pulses").

SEE OR SEARCH THIS CLASS, SUBCLASS:
94.5 for soft switching, muting, or noise gating.

SEE OR SEARCH CLASS:
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, 310 for limiting, clipping, or clamping lessens or eliminates an intermittent spuriously generated component from a signal.
455, Telecommunications, 223 for noise blanking.

Feedforward circuitry for transducer compensation:
This subclass is indented under subclass 94.1. Subject matter having circuitry designed to compensate for distortion which is generated by a transducer itself (such as a loudspeaker or microphone), without using feedback.

SEE OR SEARCH THIS CLASS, SUBCLASS:
95 for microphones with feedback.
96 for systems which compensate for loudspeaker distortion using feedback.

MICROPHONE FEEDBACK:
This subclass is indented under the class definition. Subject matter having a microphone and a circuit and also having provision for returning a fraction of an output signal of the circuit to an input of the circuit.

SEE OR SEARCH THIS CLASS, SUBCLASS:
93 for feedback suppression in audio systems.
96 for a loudspeaker circuit with feedback.
168 for a microphone, per se.

LOUDSPEAKER FEEDBACK:
This subclass is indented under the class definition. The mechanical or electromechanical coupling of a portion of a sound wave output of a system to a preceding part or input circuit of the system.

SEE OR SEARCH THIS CLASS, SUBCLASS:
93 for feedback suppression in audio systems.
95 for microphones with feedback.
150 for a loudspeaker, per se.

INCLUDING PHASE CONTROL:
This subclass is indented under the class definition. Subject matter with means to vary or maintain the phrase of an electrical signal relative to either another signal or a standard.

INCLUDING FREQUENCY CONTROL:
This subclass is indented under the class definition. Subject matter with means to vary or maintain the frequency response of the system.

SEE OR SEARCH THIS CLASS, SUBCLASS:
62 for vibrato effects.

SEE OR SEARCH CLASS:
333, Wave Transmission Lines and Networks, subclasses 165-212 for filters, per se.
455, Telecommunications, 255, 266 and 268 for frequency response control in radio receivers.

Having crossover filter:
This subclass is indented under subclass 98. Subject matter that separates a signal into two or more separate frequency bands.

SEE OR SEARCH CLASS:
333, Wave Transmission Lines and Networks, 132 for crossover networks, per se.
369, Dynamic Information Storage or Retrieval, subclass 175 for record players with frequency dependent signal separation.

With active device:
This subclass is indented under subclass 99. Subject matter having an electrical or electronic element capable of controlling voltages or currents to produce gain or switching action in a circuit (e.g., transistor, vacuum tube, or saturable reactor).

Automatic tone control:
This subclass is indented under subclass 98. Subject matter having a control used to alter automatically the frequency response of the system so that a listener can be provided the most pleasing sound.

SEE OR SEARCH CLASS:
333, Wave Transmission Lines and Networks, subclass 28, and 167-212 for tone control, per se.
455, Telecommunications, subclass 267 for tone control in a radio receiver.

With amplitude control:
This subclass is indented under subclass 101. Subject matter including automatic tone control combined with means for
adjusting or setting the signal level or for obtaining a substantially constant amplitude output signal for a range of variations of the amplitude of an input signal.

SEE OR SEARCH CLASS:
455, Telecommunications, subclass 233.1 for combined volume and tone control in a radio receiver.

Having automatic equalizer circuit:
This subclass is indented under subclass 98. Subject matter designed to compensate for an undesired amplitude-frequency and/or phrase-frequency characteristic of the system.

SEE OR SEARCH CLASS:
333, Wave Transmission Lines and Networks, subclass 28 for equalizers, per se.
369, Dynamic Information Storage or Retrieval, subclass 133 for recording with equalization.

INCLUDING AMPLITUDE OR VOLUME CONTROL:
This subclass is indented under the class definition. Subject matter including means for adjusting or setting the signal level or for obtaining a substantially constant amplitude output signal for a range of variations of the amplitude of an input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
102 for amplitude control combined with automatic tone control.

SEE OR SEARCH CLASS:
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, 306 for miscellaneous amplitude control circuits.
330, Amplifiers, 129, 254 and 278+ for amplitude control for amplifiers.
338, Electrical Resistors, 13 and 68+ for variable resistors.
455, Telecommunications, 232.1 for amplitude control in a
radio receiver.

Remote:
This subclass is indented under subclass 104. Subject matter where the amplitude or volume is controlled by at least one or more devices from a remote point.

SEE OR SEARCH CLASS:
340, Communications: Electrical, 825 for remote control in general.
369, Dynamic Information Storage or Retrieval, 24 for remote control of a recording or reproducing device.
455, Telecommunications, subclass 355 for remote amplitude or volume control in a radio receiver.

With amplitude compression/expansion:
This subclass is indented under subclass 104. Subject matter having electrical audio signal system combined with provision for decreasing the amplitude range of an applied audio signal or for restoring the full amplitude range of an amplitude compressed audio signal.

SEE OR SEARCH CLASS:
333, Wave Transmission Lines and Networks, subclass 14 for amplitude compression/expansion, per se.
370, Multiplex Communications, subclass 202 for amplitude compression or expansion in a multiplex system.
455, Telecommunications, subclass 72 for amplitude compression/expansion in a radio system.
704, Data Processing: Speech Signal Processing, Linguistics, Language Translation, and Audio Compression/Decompression, 500 for audio signal bandwidth compression or expansion and subclasses 503+ for audio signal time compression or expansion.

Automatic:
This subclass is indented under subclass 104. Subject matter having means to control the signal level adjusting means automatically as a function of some characteristic of an input signal.

SEE OR SEARCH THIS CLASS, SUBCLASS:
22 for automatic gain control for decoding quadrasonic signals.

Including feedback:
This subclass is indented under subclass 107. Subject matter further having provision for returning a fraction of an output signal back to an input.

SEE OR SEARCH THIS CLASS, SUBCLASS:
83 for feedback suppression in a public address system.
93 for feedback suppression in a audio systems in general.
95 for microphone circuits with feedback.
96 for loudspeaker circuits with feedback.

With manual volume control:
This subclass is indented under subclass 104. Subject matter wherein volume is controlled in accordance with the position of a device which is adjusted by hand.

VOICE CONTROLLED:
This subclass is indented under the class definition. Subject matter which is controlled in some manner in response to a voice signal.

SEE OR SEARCH CLASS:
367, Communications, Electrical: Acoustic Wave Systems and Devices, subclass 198 for speech responsive selective control in general.

CIRCUITRY COMBINED WITH SPECIFIC TYPE MICROPHONE OR LOUDSPEAKER:
This subclass is indented under the class definition. Subject matter combined with a specific audio-to-electrical signal or electrical-to-audio transducer.
(1) Note. Classified herein are microphone or loudspeakers combined with a diverse type of circuit (e.g., amplifier) or circuit element (e.g., resistor) other than a lead or connector.

SEE OR SEARCH THIS CLASS, SUBCLASS:
122 for audio signal systems having a generic microphone.
150 for a specific type of microphone or loudspeaker.

With carbon microphone:
This subclass is indented under subclass 111. Subject matter where the transducer is a carbon microphone.

SEE OR SEARCH THIS CLASS, SUBCLASS:
180 for a carbon microphone, per se.

With electrostatic microphone:
This subclass is indented under subclass 111. Subject matter where the transducer is an electrostatic microphone.

SEE OR SEARCH THIS CLASS, SUBCLASS:
173 for an electrostatic microphone, per se.

With piezoelectric microphone:
This subclass is indented under subclass 111. Subject matter where the transducer is a piezoelectric microphone.

SEE OR SEARCH THIS CLASS, SUBCLASS:
173 for a piezoelectric microphone, per se.

SEE OR SEARCH CLASS:
310, Electrical Generator or Motor Structure, 311 for piezoelectric transducers.
367, Communications, Electrical: Acoustic Wave Systems and Devices, 157 for underwater type piezoelectric transducers.

With magnetic microphone:
This subclass is indented under subclass 111. Subject matter where the transducer is a magnetic microphone.

SEE OR SEARCH THIS CLASS, SUBCLASS:
176 for a magnetic microphones, per se.

With electrostatic loudspeaker:
This subclass is indented under subclass 111. Subject matter where the transducer is an electrostatic loudspeaker.

SEE OR SEARCH THIS CLASS, SUBCLASS:
191 for an electrostatic loudspeakers, per se.

With magnetic loudspeaker:
This subclass is indented under subclass 111. Subject matter where the transducer is a magnetic loudspeaker.

SEE OR SEARCH THIS CLASS, SUBCLASS:
192 for a magnetic loudspeaker, per se.

WITH MUSICAL INSTRUMENT:
This subclass is indented under the class definition. Subject matter for amplifying or reproducing the sounds of musical instruments.
(1) Note. The subject matter classified herein merely receives, amplifies and/or reproduces signals representing musical sounds while the subject matter classified in Class 84 generates musical sounds.

SEE OR SEARCH CLASS:
84, Music, 1 for musical instruments, especially subclasses 1.01+ for electronic musical instruments.

WITH MIXER:
This subclass is indented under the class definition. Subject matter including a circuit having two or more inputs and a common output which combines separate input signals linearly in desired proportions to produce an output signal.

WITH AMPLIFIER:
This subclass is indented under the class definition. Subject matter including a device for producing an output of greater amplitude than is applied at an input.

SEE OR SEARCH CLASS:
330, Amplifiers, appropriate subclasses for amplifiers not having specific input signals or specific loads.
379, Telephonic Communications, subclass 395 for amplifiers combined with telephone systems.

Feedback:
This subclass is indented under subclass 120. Subject matter where a fraction of an output signal is returned to an input.

SEE OR SEARCH THIS CLASS, SUBCLASS:
71.1 for acoustical sound cancellation.
83 for public address systems with feedback suppression.
93 for feedback suppression for audio systems in general.
95 for microphone circuits with feedback.
96 for loudspeaker circuits with feedback.
108 for automatic amplitude control having feedback.

HAVING MICROPHONE:
This subclass is indented under the class definition. Subject matter including a generic microphone combined with an element having diverse function (e.g., a microphone and an amplifier).
(1) Note. Subject matter under the class definition having a specific microphone combined with a diverse element is found in subclasses 111+.
(2) Note. Microphones are also found in the subject matter of subclasses 26, 55-58, 64+, 67-69, 75-85, 91, and 95.

SEE OR SEARCH THIS CLASS, SUBCLASS:
168 for a microphone, per se.

SWITCHING:
This subclass is indented under the class definition. Subject matter where there is the making, breaking or changing connections in an electrical circuit.

SEE OR SEARCH THIS CLASS, SUBCLASS:
7 for switch type stereo modulators or detectors.
11 for switching between mono and stereo modes.
55 for audio transducer protection circuitry.
81 for switching in multiple channel program distribution.
85 for speaker or channel switching in a public address system.
110 for voice controlled switching of audio systems.

SEE OR SEARCH CLASS:
200, Electricity: Circuit Makers and Breakers, for switches, per se.
307, Electrical Transmission or Interconnection Systems, 112 for electrical transmission or interconnection switching systems.
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, 365 for miscellaneous gating circuits including channel selection.
335, Electricity: Magnetically Operated Switches, Magnets, and Electromagnets for magnetic switches.
340, Communications: Electrical, subclass 825.01 for spare channel switching.
361, Electricity: Electrical Systems and Devices, 139 for relay or solenoid circuits.
370, Multiplex Communications, 357 for multiplex switching circuit.
379, Telephonic Communications, 242 for switching in telephone systems, and subclass 325 for telephone switches, per se.
455, Telecommunications, 78 for transmitter-receiver switching.
714, Error Detection/Correction and Fault Detection/Recovery, 3 for replacing a faulty apparatus with a spare.

MISCELLANEOUS:
This subclass is indented under the class definition. Subject matter not hereinabove classified.

ELECTRO-ACOUSTIC AUDIO TRANSDUCER:
This subclass is indented under the class definition. Subject matter having a structure or process for converting an information signal between audible sound vibrations and a corresponding time-varying electrical quantity.
(1) Note. Included herein are instruments such as microphones, speakers earphones, and housings or supports
peculiar thereto. However, combinations with circuitry, other than leads, terminals, or connectors, are not classified herein, but are classified in the preceding subclasses of this class (381).
(2) Note. The audible sound vibrations are generally speech or music.

SEE OR SEARCH CLASS:
181, Acoustics, appropriate subclasses for an attachment to a casing of an audio transducer.
310, Electrical Generator or Motor Structure, 300 for a piezoelectric transducer not limited to audio utility.
367, Communications, Electrical: Acoustic Wave System and Devices, 140 for a nonaudio acoustical transducer.

Body contact wave transfer (e.g., bone-conduction earphone, larynx microphone):
This subclass is indented under subclass 150. Subject matter wherein sound vibrations are obtained from or imparted to a portion of a human body in direct contact with a vibrating component of an electroacoustical transducer.

SEE OR SEARCH THIS CLASS, SUBCLASS:
68.3 for similar subject matter used in a hearing aid.

Driven diverse static structure (e.g., wall, sounding board):
This subclass is indented under subclass 150. Subject matter combined with a stationary structural element having a function independent of electricity-to-sound conversion and being driven to radiate sound waves by an audio transducer mounted thereon.
(1) Note. Devices which vibrate walls to emit intelligible sound are classified herein.

Reflecting element:
This subclass is indented under subclass 153. Subject matter having an element which reflects the sound waves.

With mechanical amplifier arrangement:
This subclass is indented under subclass 150. Subject matter having a vibrating solid element intermediate a conversion between mechanically increases the amplitude of the vibrations of the solid.

Detail of mechanical vibration coupling to transducer (e.g., tuned vibrating element):
This subclass is indented under subclass 150. Subject matter including a detail of a mechanical element which transfers sound vibrations to or from the audio transducer.

Having bi-directional transducer:
This subclass is indented under subclass 150. Subject matter having a single device which converts sound waves to electrical variations and electrical variations to sound waves.
(1) Note. For classification herein, conversion in both directions must be specifically included.

SEE OR SEARCH CLASS:
379, Telephonic Communications, subclass 420 for a loudspeaking type telephone set with a single bi-directional transducer; subclass 433 for a handset having a single bi-directional transducer.

Thermal response to, or generation of, sound vibration:
This subclass is indented under subclass 150. Subject matter where sound waves either modify or are emitted by a temperature effect on an element material, or area of the device.

By modifying fluid flow:
This subclass is indented under subclass 150. Subject matter having a source of gas flow which flow interacts with an electrical circuit to either (a) vary the current therein in accordance with incident sound waves, or (b) produce sound waves corresponding to an applied audio information signal in the electric circuit.

SEE OR SEARCH THIS CLASS, SUBCLASS:
166 for similar subject matter having a fluid electrical conducting element absent fluid flow.

Having fluid as a conducting element:
This subclass is indented under subclass 150. Subject matter wherein an electrically conductive element of the transducer is a fluid.
(1) Note. The fluid conducting element may be either the portion converting the signal between electrical variations and sound waves, or an electrode connecting the circuit to another transducer.
(2) Note. The fluid may include an ionized path between electrodes.

SEE OR SEARCH THIS CLASS, SUBCLASS:
165 for a fluid flow modifying transducer.

Ionized gap, spark, or flame:
This subclass is indented under subclass 166. Subject matter which ionizes the air or other gas or causes sparks across a gap.
(1) Note. Included herein are also plasma, glow discharge, or flame.

Compound:
This subclass is indented under subclass 168. Subject matter having a plurality of independent microphone devices in a single casing.

Micromagnetic:
This subclass is indented under subclass 168. Subject matter in which the incident sound vibrates a diaphragm so as to vary both the resistance of a microphone contact and magnetic induction means which reinforce each other to produce a combined affect on an electric current.

Light modifying:
This subclass is indented under subclass 168. Subject matter for converting an incident sound wave to an audio signal by means of a light modifying element.

SEE OR SEARCH CLASS:
455, Telecommunications, 618 for a transmitter for light wave communication.

Piezoelectric or ferroelectric:
This subclass is indented under subclass 168. Subject matter having an element made of either (a) a material which produces a voltage when subjected to a mechanical stress or (b) a material having a spontaneous electrical polarization.

SEE OR SEARCH THIS CLASS, SUBCLASS:
190 and 191, for reproducer or generic transducer of the piezoelectric or ferroelectric type, respectively.

Capacitive:
This subclass is indented under subclass 168. Subject matter having an electrostatic capacitance element which varies in
accordance with sound waves incident thereon.

SEE OR SEARCH CLASS:
361, Electricity: Electrical Systems and Devices, 283.1 for pressure responsive electrostatic capacitors, per se.

Semiconductor junction microphone:
This subclass is indented under subclass 168. Subject matter having an element with conductivity intermediate that of a conductor and an insulator and having one region having predominantly electron conductivity (n-type) and another region having predominantly hole (p-type) conductivity forming a potential barrier layer therebetween.

SEE OR SEARCH CLASS:
257, Active Solid-State Devices (e.g., Transistors, Solid-State Diodes), 53, 108, 225+, and 414+ for nonelectrical input devices, including subclasses 415+ for pressure sensors.

Conductive diaphragm (e.g., reed, ribbon):
This subclass is indented under subclass 168. Subject matter having an electrically conductive element as a portion of the diaphragm.

Dynamic (e.g., magnetic):
This subclass is indented under subclass 168. Subject matter including a diaphragm to which a current conducting element is attached and which is positioned in a fixed magnetic field.

Vibrating electrical contact:
This subclass is indented under subclass 168. Subject matter in which two elements have an area of intermittent electrical contact caused by oscillatory motion of an element in
accordance with incident sound waves.

Resistive:
This subclass is indented under subclass 168. Subject matter having an element the resistance of which is varied by incident sound waves.

SEE OR SEARCH CLASS:
338, Electrical Resistors, appropriate subclasses for a condition responsive variable resistor.

Granular or carbon:
This subclass is indented under subclass 180. Subject matter having a sound responsive resistive element composed of either elemental carbon, or a mass of comminuted material.

Differential:
This subclass is indented under subclass 180. Subject matter having two sound responsive resistance elements one positioned on either side of a central diaphragm.

Plural or compound reproducers:
This subclass is indented under subclass 180. Subject matter having a plurality of sound producing transducer having two or more elements performing the same or similar functions.

Different types of diaphragms:
This subclass is indented under subclass 182. Subject matter having two or more flexible membranes which differ in size, shape or composition.

Having common voice coil:
This subclass is indented under subclass 182. Subject matter where two or more flexible membranes are driven by a common helix of conductive material carrying an electrical information signal.

Plural diaphragms:
This subclass is indented under subclass 182. Subject matter including a speaker having plural flexible membranes, for radiating sound waves.

Having protective or shielding feature:
This subclass is indented under subclass 150. Subject matter having structure for shielding a transducer from adverse environmental conditions or preventing undesired effects caused by an external magnetic field.
(1) Note. Adverse conditions include moisture and impact.

Electrostrictive, magnetostrictive, or piezoelectric:
This subclass is indented under subclass 150. Subject matter including an element which expands or contracts in accordance with an applied electric or magnetic field, or which produces a mechanical stress tending to produce deflection, expansion, or contraction when subjected to an applied electrical voltage.
(1) Note. The term deflection covers both twisting and bending.

SEE OR SEARCH THIS CLASS, SUBCLASS:
173 for a piezoelectric microphone.

Having electrostatic element (e.g., electret, vibrating plate):
This subclass is indented under subclass 150. Subject matter including either a capacitor with a vibratable plate, or an element which has a spontaneous electrical field, one of which is caused to vibrate by an audio signal or incident sound.

SEE OR SEARCH THIS CLASS, SUBCLASS:
174 for a capacitive microphone.

SEE OR SEARCH CLASS:
307, Electrical Transmission or Interconnection Systems, subclass 400 for electrets.
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits, and Systems, subclass 516 for miscellaneous vibration sensitive circuits.
361, Electricity: Electrical Systems and Devices, 283.1 for a pressure responsive capacitor, per se.

Stereo speaker arrangement:
This subclass is indented under subclass 1. Subject matter including transducers for reproducing the sound signals, and the spatial relationship of the transducers to their surroundings.

In furniture or clothing:
This subclass is indented under subclass 300. Subject matter in which the transducers are mounted on or within a pillow, headrest, couch, jacket, belt, etc.
(1) Note. A television set, computer monitor, etc. is considered to be an "image presentation means," and is not considered to be "furniture" for this class.

SEE OR SEARCH THIS CLASS, SUBCLASS:
306 for image projection means, i.e., a television set having stereo speakers.
333 for furniture, clothing, or image projection means
combined with a monaural loudspeaker.
364 for clothing combined with a microphone.
388 for furniture or clothing combined with mounting or support feature of housed loudspeaker.

In vehicle:
This subclass is indented under subclass 300. Subject matter in which the transducers are mounted on or within an automobile, aircraft, motorcycle, etc.

SEE OR SEARCH THIS CLASS, SUBCLASS:
365 for a housed microphone mounting or support in a vehicle.
389 for a mounting or support feature of a housed loudspeaker in a vehicle.

Optimization:
This subclass is indented under subclass 300. Subject matter in which steps are taken to enhance the stereo listening effect, such as by enlarging the area in which stereo audibility is satisfactory (i.e., the "sweet point").

Enclosure orientation:
This subclass is indented under subclass 303. Subject matter in which either a distance or relative angle between two or more transducer housings or baffles is adjusted or specified.

Enclosure adaptation:
This subclass is indented under subclass 303. Subject matter in which a modification is made within single housing or baffle, such as by providing a directible or directional capability.

With image presentation means:
This subclass is indented under subclass 300. Subject matter in which the transducers are arranged to emit sound in conjunction with a television screen, computer monitor, motion picture screen, etc.

SEE OR SEARCH THIS CLASS, SUBCLASS:
333 for image presentation means combined with a loudspeaker
388 for image presentation means combined with a mounting or support feature of a housed loudspeaker

SEE OR SEARCH CLASS:
353, Optics: Image Projectors, 15 for sound accompaniment with an image projector
359, Optics: Systems and Elements, subclass 444 for a projection screen with a sound producer

Surround (i.e., front plus rear or side):
This subclass is indented under subclass 300. Subject matter in which, in addition to having at least one transducer arranged forward of a listening position, at least one transducer is arranged laterally or to the back of the listening position.

In single baffle:
This subclass is indented under subclass 300. Subject matter in which the two or more spatially related sounds are emitted from a only one transducer enclosure.

Stereo earphone:
This subclass is indented under subclass 300. Subject matter
in which the transducers are intended to be placed in or over the user's ears.

Virtual positioning:
This subclass is indented under subclass 309. Subject matter in which audio signals, prior to delivery to the earphone, are processed in order to give an illusion that the spatially related sounds are being emitted from physically distinct locations in the earphone user's environment.
(1) Note. The orientation of earphones with respect to the room changes as the user moves his or her head. Virtual positioning when specifically used with an earphone is often done for the purpose of making the sounds appear to come from an invariant physical location in the environment, irrespective of the orientation of the user's head. This is done to foster the illusion that the user is not in fact wearing headphones.

SEE OR SEARCH THIS CLASS, SUBCLASS:
17 for a device or arrangement which transforms single channel audio signals into a plurality of channels of audio information to create a sense of depth. Comprehended in subclass 17 is virtual positioning, typically used with loudspeakers.

Wireless or for use in diverse environment:
This subclass is indented under subclass 309. Subject matter in which a) audio signals are conveyed to the earphone without the use of conductors, such as by modulated RF or infrared carrier wave or b) the earphone is especially configured or adapted to be used in an unusual location, such as underwater or within a magnetic field such as Magnetic Resonance Imaging (MRI), etc.

SEE OR SEARCH CLASS:
359, Optics: Systems and Elements 109 for modulated wireless optical communications.
455, Telecommunications for modulated wireless communications, generally.

HEARING AIDS, ELECTRICAL:
This subclass is indented under the class definition. Subject matter having a small ambient sound reproducing system wherein an output transducer transmits directly into the ear or skull for use by the hard of hearing to increase the sound level received by the ear (i.e., listening assistance).

SEE OR SEARCH THIS CLASS, SUBCLASS:
23.1 for hearing aids in binaural and stereophonic circuits and systems.
60 for testing of hearing aids.
74 for headphone circuits.
75 for megaphones.
327 for hearing aids within the scope of this definition in combination with spectacle structure such as temples
370 for a headphone.

SEE OR SEARCH CLASS:
73, Measuring and Testing, subclass 585 for ear or hearing testing, and subclasses 645+ for measuring acoustic parameters.
128, Surgery, subclass 746, for testing by auditory stimulus (e.g., audiology)
181, Acoustics, 126 for mechanical hearing aids.
330, Amplifiers, particularly subclass 65 and 250+ for amplifiers involving structural details or elements, and transistor amplifiers.
351, Optics: Eye Examining, Vision Testing and Correcting, 41 for spectacles and eyeglasses, and subclasses 111+ for spectacle temples.
600, Surgery, subclass 25 for a surgically implanted vibratory hearing aid
623, Prosthesis (i.e., Artificial Body Members), Parts Thereof or Aids and Accessories Therefor, subclass 10 for artificial ears having electrical hearing aid as a subcombination.

Directional:
This subclass is indented under subclass 312. Subject matter where a response of an input transducer (i.e., microphone) to the ambient sound varies significantly with a location of a source relative to the transducer, the hearing aid, or the hearing aid user.

SEE OR SEARCH THIS CLASS, SUBCLASS:
356 for a directional microphone.

Programming interface circuitry:
This subclass is indented under subclass 312. Subject matter including circuitry within the hearing aid or external to the hearing aid for connection to the hearing aid in order to program it.

SEE OR SEARCH THIS CLASS, SUBCLASS:
323 for programming interface terminals in a hearing aid, without circuitry,

Remote control, wireless, or alarm:
This subclass is indented under subclass 312. Subject matter allowing for a) parameters of the hearing aid to be altered from a location different from the location of the hearing aid itself, b) processed sound from an amplifier to be conveyed to the ear without the use of conductors or an acoustic tube, or c) a warning sensor or device to make its warning known to a hearing aid user through the hearing aid.

SEE OR SEARCH CLASS:
340, Communications: Electrical, 635 for alarms responding to condition changes in electrical apparatus 825.69, for radio link remote control and 825.72 frequency responsive wireless remote control.

Frequency transposition:
This subclass is indented under subclass 312. Subject matter in which some portion of a received audio signal is shifted
in frequency prior to being delivered to the hearing aid's loudspeaker in order to enhance audibility.

SEE OR SEARCH THIS CLASS, SUBCLASS:
320 for spectral control in the hearing aid

Noise compensation circuit:
This subclass is indented under subclass 312. Subject matter including circuitry to ameliorate effects of undesired signals.

SEE OR SEARCH THIS CLASS, SUBCLASS:
94 for a device of this class including means for noise suppression.
322 for subject matter in which amelioration of noise is accomplished using purely mechanical or acoustic means.

SEE OR SEARCH CLASS:
327, Miscellaneous Active Electrical Nonlinear Devices, Circuits and Systems, 551 for unwanted signal suppression generally.

Feedback suppression:
This subclass is indented under subclass 317. Subject matter in which the particular kind of undesired signal is howling or screeching caused by a return to the hearing aid's input of a sufficient fraction of its output to cause oscillation.
(1) Note. Hearing aid feedback normally occurs via an acoustic path.

SEE OR SEARCH THIS CLASS, SUBCLASS:
83 for feedback suppression circuitry in a public address system.
93 for generic feedback circuitry under the class definition.

With vacuum tube amplifier:
This subclass is indented under subclass 312. Subject matter including means using one or more devices in which electron flow takes place in an evacuated envelope.

SEE OR SEARCH CLASS:
330, Amplifiers, subclass 64 for vacuum tube amplifiers generally.

Spectral control:
This subclass is indented under subclass 312. Subject matter including a circuit to control the amplitude of a received audio signal in at least two separate frequency bands, i.e., to selectively amplify or attenuate two or more different frequencies or frequency bands.
(1) Note. Included herein are tone control and filtering. Note that subject matter which emphasizes one frequency band relative to another inherently results in different treatment of two bands, and is properly classified here.

SEE OR SEARCH THIS CLASS, SUBCLASS:
316 for frequency transposition in hearing aids.

Wideband gain control:
This subclass is indented under subclass 312. Subject matter having a circuit to regulate the amplitude of the entire frequency range of a received audio signal (i.e., broad band amplitude regulation).
(1) Note. The amount of amplification may be adjusted either manually or in response to a sound parameter, as in automatic gain or volume control (AGC, AVC).

SEE OR SEARCH THIS CLASS, SUBCLASS:
104 for amplitude or volume control of an audio system.

SEE OR SEARCH CLASS:
330, Amplifiers, 278 for gain control means using a transistor.

Specified casing or housing:
This subclass is indented under subclass 312. Subject matter including a specific container for the hearing aid components.

Power supply or programming interface terminals:
This subclass is indented under subclass 322. Subject matter including a) an energy source such as a battery, solar cell, etc., or structural detail to accommodate an energy source, such as battery compartment detail, including contacts or b) contacts used for programming the hearing aid when hooked up to an interface.

SEE OR SEARCH THIS CLASS, SUBCLASS:
314 for programming interface circuitry.

SEE OR SEARCH CLASS:
323, Electricity: Power Supply or Regulation Systems, for power supply or regulation systems generally.