Abstract: A circuit arrangement is disclosed for converting digital signals into analog signals and analog signals into digital signals. The circuit arrangement is used as a conference set for use by individual subscribers on a multiplex line. Digital signals of all subscribers are consecutively converted into analog signals and an analog summation signal is formed therefrom. This summation signal is again converted back into a digital signal and can be multiply transmitted as such. Alternatively, a number n of circuit arrangements are provided for a maximum number n of subscribers. Each of the circuit arrangements converts digital signals of n-1 conference subscribers (excluding an allocated subscriber) into analog signals and forms an analog summation signal therefrom. This analog summation signal is converted back into a digital signal which is transmitted in a time slot allocated to the allocated conference subscriber to which the circuit arrangement is allocated.

Abstract: An essential user bypass circuit for use in switch units of a telephone switching system. Telephone subscribers at each switch unit are able to communicate with each other and with subscribers at other switch units via associated subscriber apparatus and trunk group lines interconnecting the switch units. All call processing operations, including the formation of "from-to" address signals for connecting subscribers with each other and with trunk group lines, are normally controlled by a processor unit (containing dual processors) at each switch unit.

Abstract: An earphone comprises a housing including a partition plate with an opening containing a diaphragm. An annular cushion is secured to the periphery of the partition and engages around the wearer's ear to form a coupling space between the diaphragm and the ear. A back covering is connected to the partition defining a soundproof cavity between the partition and the back covering. A partial wall is spaced from the partition on a side opposite the diaphragm to define a first high restoring force cavity. A duct is connected from the restoring force cavity to the outside, and it encloses an air mass which acts as an acoustic mass.

Abstract: The headphone includes a cup-shaped case forming the coupling space and this cup-shaped case, in use, engages the user's head and encloses the user's ear. At least one electroacoustic transducer is included in the cup-shaped case, and the case either is designed as an acoustic frictional resistance or as a supporting structure of such a resistance. The headphone is equipped with acoustic and/or electrical systems compensating the drop at the low frequencies, and there are no reflecting surfaces located close to the external ear of the user. The low frequencies drop may be compensated by passive or blind diaphragms, or the diaphragm of the electroacoustic transducer may be coupled to an air mass. A headset, including two headphones, may be designed for quadraphonic reproduction.

Abstract: An automatic disconnect circuit is described for disconnecting a remote telephone in resonse to a hang-up click generated when the remote telephone goes on-hook. To distinguish a remote hang-up click from a local hang-up click, voice signals, and the like, all signals on the line are passed through a discriminator for attenuating high frequencies. Signals passing through the discriminator are sensed both as to their amplitude and their duration. Any such signal whose amplitude is too small results in no disconnect. Similarly, any such signal whose duration is atypical of a remote hang-up click results in no disconnect. Only a signal whose amplitude and duration are within predetermined limits, typical of a remote hang-up, causes the remote telephone to be disconnected.

Abstract: A stereo speaker system removably mountable on the back of a seat includes two speaker assembly enclosures pivotally mounted on a spacer bar to maintain the speakers at a desired separation and orientation and a strap for securing the enclosures and spacer bar to the back of the seat. Each enclosure includes a chamber substantially occupied by a speaker assembly and a duct portion for directing the sound.

Abstract: An audiometric headset having a transducer mounting and sound insulation system which closely couples the transducer to the ear. The headset is comprised of a pair of domes having a soft foam liner and soft sponge sound-absorbent material surrounding a floating sound transducer mounted in an open side of the case. The sound transducer is mounted in a socket of a circular resilient hub supported on a resilient flange by a pair of resilient strips providing a semi-circular opening between the interior of the case and the exterior of the earpiece. The resilient flange provides a channel for mounting on a rim around the periphery of the opening in the dome or case. An ear cushion snap-locked into a channel surrounding the socket supporting the transducer closely couples the transducer to the ear. A resilient earmuff is mounted around the rim of the case opening and is filled with a sound-filtering soft material whereby the muff seals around the ear to eliminate external ambient noise.

Abstract: A network in a four-wire communication system for verifying the source of a call seeking access to restricted telephone channels through a toll switch prior to granting such access comprises handshake circuits on the operator and subscriber sides, respectively, of the toll switch in both pairs of transmission lines, the operator input to the toll switch being on a dedicated trunk. The handshake circuits comprise two D.C. verification signal sources, the first being connectable to the transmission line pair (T lines) on the subscriber side of the toll switch, and the second being connectable to the receive line pair (TR lines) on the operator side of the toll switch. The first D.C. verification signal is applied to the T lines on completion of the dialing and is detected, in accordance with this invention, on the operator side of the toll switch by a first detector connected to the T lines in the dedicated trunk. The output of this detector causes the second D.C.

Abstract: A switching network with k=p+q inputs and as many outputs comprises one or more symmetrical time-division matrices, k being eight or a multiple of eight in the embodiments specifically disclosed. A larger number p of incoming subscriber links and a smaller number q of exchange outputs are respectively connected to p outgoing subscriber links and q exchange inputs. Digitized voice samples arriving over each incoming link in successive time slots of a recurrent frame, allocated to respective subscribers, are stored in each matrix and are selectively distributed to the reduced number of time slots sent to the exchange under the control of switching instructions from the exchange; conversely, signal samples received from the exchange in successive time slots are distributed to selected time slots of outgoing links. Signal paths can also be established between network inputs and outputs connected to incoming and outgoing links, thereby enabling direct communication between subscribers served by the network.

Abstract: A receiver for call signals, designed to actuate an electro-acoustic transducer such as a ringer in response to incoming alternating voltages of low amplitude and relatively high frequency (e.g. 400 to 450 Hz) or high amplitude and relatively low frequency (e.g. 20 t0 50 Hz), includes a detector for the high-frequency signal and an integrating threshold circuit for the low-frequency signal connected in parallel across a transmission line. The detector is preceded by a phase-locking circuit including a local oscillator of variable frequency adapted to latch on to the high-frequency signal. The presence of either type of call signal activates, through the detector or the threshold circuit, a binary pulse counter stepped by the squared output of the local oscillator to generate a low-frequency square wave subharmonically related to the oscillator frequency which periodically unblocks a gate circuit for the passage of the oscillator output to operate the transducer.

Abstract: A digital conference circuit provides greater stability in voice transmission by selectively inverting the signal in alternate conference channels, thereby providing cancellation of parasitic echo signals which tend to create oscillations or ringing. Selective gain control is also provided for conferences of different sizes and efficient use of conference lines is ensured by providing for selective combination of conference groups.

Abstract: This invention concerns a method of, and apparatus for, reducing the ambient noise level at a location in the vicinity of a source of recurring noise. In its preferred embodiments the invention involves generating a series of cancelling noise signals which are exactly synchronized with the bursts of recurring noise from the source and adapting the cancelling signals in the series on the basis of the success achieved in nulling the noise from the source at the location.

Abstract: A telephone multiline signaling system using a common signal pair of lines for transmitting coded electrical signals for selectively connecting one or more of a plurality of telephone lines to a telephone line or channel located at an operator's console. The operator can rapidly and automatically produce coded electrical signals by manipulating mechanical thumb wheel switches so as to instruct a service center to connect any one or more of a plurality of telephone lines to the console so as to enable the operator to listen and/or talk over a plurality of lines simultaneously. The system includes an on-site console having a plurality of mechanically operated thumb wheel switches provided thereon on which the desired lines to be connected thereto can be dialed in. Electrical coded signals are fed to a plurality of banks of line AND gates representing units, tens and hundreds, a group of channel gates and a command gate.

Abstract: A speaker supporting device used for radios or cassette tape recorders includes a cylindrical or annular elastic body for supporting a speaker on its inner peripheral surface, one open end of the elastic body is tightly secured to a baffle plate and other open end of the elastic body is tightly secured to the chassis of a casing.

Abstract: An improved protective helmet of the type including a two-way voice controlled communication system having electronic transmitting and receiving circuitry. When incoming signals are received by the voice communication system, a transducer vibrates a rigid portion of the helmet, causing the helmet to act as a diaphragm to produce intelligible audible sounds. The electronic circuitry of the voice communication system is mounted in a resilient carrier for protection against damage from impact and shock to the helmet. Alternatively, the electronic circuitry may be supported on and protected by the conventional cushion lining of a protective helmet.

Abstract: A hookswitch mechanism adapted to be operated responsive to movement of the cradle of a telephone instrument. The hookswitch mechanism has a plunger, axially operable to open and close contacts. The movable contacts are rectangular strips mounted on the movable plunger body. A housing encloses the plunger body and mounts the stationary contacts adjacent the ends of the contact strips. The mechanism is mounted on a bracket which also supports the cradle for pivotal movement thereby ensuring the relative positioning and alignment of cradle and hookswitch mechanism.

Abstract: An immediate ring-back control system for a time-division telephone exchange includes a time-division switching network of a time switch-space switch-time switch (T-S-T) system. An incoming time switch accommodates multi-channel interrupted ring-back tones (IRBT's) which are generated by a tone generator in a time-multiplexed manner, each of which has a different interruption phase. The interrupted ring-back tone having a phase starting from a tone-sending period is selected from the multi-channel interrupted ring-back tones (IRBT's) by an immediate ring-back control circuit provided in a time-division switch driving circuit (SDC) at the time of connection of the ring-back tone to a calling subscriber, and a channel number corresponding to the phase of the interrupted ring-back tone is stored in a control memory or a time slot memory associated with the time switch, so that the transmission of the interrupted ring-back tones to a calling subscriber can be started from a mark portion thereof.

Abstract: A system for limiting the instantaneous value of a noise transient, by means of an electronic circuit wherein the amplitude of the total input signal being monitored is compared with a threshold value which is varied continuously according to the peak carrier signal value, and the output signal is maintained below the threshold value.

Abstract: A post-mounted coin-operated public telephone apparatus employs one or more telephone units and coin operating and collecting equipment enclosed within rigid components of the pole structure for maximum security and protection against vandalism and to enable installation where conventional coin-operated telephones requiring separate enclosures cannot be utilized due to space limitations. The coin box is spaced from the telephone unit to minimize the likelihood of damage by attempted theft. The structure is adaptable for use by persons of different heights including standing adults as well as handicapped persons in wheelchairs or as a drive-up unit for use by persons in an automobile.

Abstract: A communication conferencing arrangement is disclosed which relies upon the use of a plus/minus (+/-) nonlocking button followed by the operation of a button associated with any other line appearing at the station. If the operated line button is associated with a currently active line that line will be removed from the conference. If, however, the operated button is associated with a nonactive line (held or idle) then that line will be added, in conference fashion, with the communication leads of the enabling station. Provision is made to allow any number of added connections up to a preset maximum number at any station.