ACOUSTIC SIGNAL ATTENUATOR

Abstract: Apparatus for detecting energisation of a first acoustic signal source, such as a doorbell, telephone, or other generator of alerting signals, and operable to attenuate acoustic signals which may be generated from a further source, such as a radio, television, gramophone, tape recorder or the like, having means (15, 24, 84) for detecting the energisation of the selected source, and a switching circuit (29, 30; 88, 90; 54, 53) which, in dependence on signals from the sensor (15, 24, 84) triggers a control signal in a control circuit (32, 35, 43, 46, 47; 91, 91A, 91B) to cause attenuation of acoustic signals from other sources which may interfere with the audibility of signals from the selected source.

Description: Acoustic Signal Attenuator The present invention relates generally to apparatus for effecting attenuation of acoustic signals in selected circumstances, and in particular to a device for assign¬ ing priority to acoustic signals emanating from one source over acoustic signals generated by another. There are many circumstances occurring in recent times when more than one acoustic source radiates sound into the same environment for the same intended audience and it is often the case that one set of acoustic signals is masked or obscu ed by the other despite the fact that they would, if the audience had the choice, take priority. For example, when broadcast receiving equipment is being operated in a room it is frequently so loud that the doorbell or telephone, which may be situated in another room, cannot be heard. The same applies to sound repro¬ ducing equipment generally, where the acoustic signals emanating from the sound reproducing equipment are "wanted" signals in normal circumstances , but effectively become background noise by the occurrence of an event such as the telephone or doorbell being energised. A similar situation occurs within a motor vehicle where the car radio or cassette player may be operated for recreational purposes in normal circumstances. However, in vehicles equipped with citizen's band radio (herein¬ after referred to as CB radio) , or a commercial radio telephone such as are employed for taxi cabs , or with the telecommunications receivers shortly to be intro¬ duced with the development of cellular radio, the originally wanted acoustic signals from the car radio or cassette player become unwanted background noise when an alerting signal is generated by any of these communications sytems. Unfortunately, if the background noise is too loud, the alerting signals from the communications systems may be inaudible or, even if heard, may be substantially obscured by the sound of the radio or cassette player. Likewise, unless action is taken to turn down the volume of the radio or cassette player the attempt at communication through such tele¬ communications systems is significantly and detrimentally affected. The latter circumstance is, of course, merely a nuisance rather than being of serious effect, and it is open to the user to modulate the volume of the various pieces of equipment to achieve an appropriate balance for the immediate purposes. The initial difficulty, however, is more serious in that attempts to communicate with an individual may fail due to the inaudibility of the alerting signals over the background noise already present in the vehicle and being generated by other acoustic signal generating equipment, and there is no action which the user can take to overcome this problem. The present invention seeks, therefore, to provide apparatus capable of monitoring the occurrence of an event such as the sounding of a warning or alerting signal, either by detecting the acoustic signals or the electrical energis¬ ation of the equipment and operating to effect attenuation of the background acoustic signals to allow the event signal to be heard more clearly. According to one aspect of the present invention, there¬ fore, there is provided apparatus sensitive to the energisation of a selected acoustic source and operable to attenuate acoustic signals emanating from one or a plurality of other sources in response thereto, -whereby to allow acoustic signals from the said selected acoustic source to be heard over a background noise generated by the other source or sources. As mentioned above the monitoring of the selected source may be achieved in one of a number of ways. An acoustic- signal sensor may be placed close to the selected source in order to pick up signals emanating therefrom, the positioning of the sensor being such that it is more sensitive to signals from the selected source than the background noise. Alternatively, an electrical sensor may be connected in circuit with the selected source so that, regardless of the local or environmental acoustic situation the effective attenuation of the or any now- unwanted signal sources can be achieved by positive identification of a priority signal from the selected source. According to another aspect of the present invention apparatus for use in an environment into which it is intended to radiate acoustic signals from two or more sources in circumstances where both sources may be simultaneously energised is provided in which, so as to be able to assign priority to signals from one of the sources over the other, such coincidence of energisa¬ tion is detected and energisation of the said other source is modified whereby to allow the signals from the said one source to be heard over those of the said other source. Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram illustrating a basic circuit unit for sensing energisation of an electri- cally operated acoustic signal source; Figure 2 is a circuit diagram of an accessory unit, connectable to the basic unit of Figure 1 , for detect¬ ing energisation of a telephone; Figure 3 is a circuit diagram illustrating a relay unit connectable in circuit with loudspeakers to be attenuated by the circuit of Figure 1 or of Figure 1 combined with Figure 2; Figure 4 is a circuit diagram illustrating a relay unit for connection in series with a mains operated electri¬ cal appliance; and Figure 5 is a circuit diagram of a system adapted for use with a cellular radio telephone. Referring first to Figure 1 the unit has two inputs , a first input 11 for connection to a microphone and a pair of terminals 12 , 13 for connection across a loudspeaker. The microphone terminal 11 is connected via a capaci¬ tor 14 to the base of a transistor 15 the collector of which is connected via a resistor 16 to a positive supply line 17 and the emitter of which is connected directly to the return line 18. A biasing resistor 19 is connected across the collector/base junction of the transistor 1 5 and a resistor 20 is connected from the collector of the transistor 15 to an intermediate line 21 which is connected , via a resistor 22 to the terminal 12. The intermediate line 21 is connected via a capacitor 23 to the base of a transistor 24 which, like the trans¬ istor 15, is connected with its collector/emitter junction between the positive supply line 17 and the return line 18 with the interposition of a resistor 25 between the collector and the supply line and with a resistor 26 connected across the collector/base unction. The collector of the transistor 24 is coupled via a capacitor 27 to voltage doubling diodes 10 and 28, the latter of which is connected to the base of a switch¬ ing transistor 29 the emitter of which is connected to the base of a transistor 30 and the collector of which is connected both to the collector of the trans¬ istor 30, to the supply line 17 via a diode 31 and to a coil 32 of a relay the contacts 35 of which are connected between the supply line 17 and two termin¬ als 36 and 37. The base of the transistor 29 is connected to the return line 18 through parallel connected resistor 33 and capacitor 34. The relay contacts 35 are normally open contacts and the funct¬ ion of the terminal 36 and the terminal 37 will be described in greater detail below. The emitter of the transistor 30 is connected to a terminal 38 and to a terminal 39 via the return line 18. Three other connection terminals 40, 41; 42 are provided for connection to the telephone sensing unit illustrated in Figure 2 and which will be described in greater detail below. The circuit illustrated in Figure 1 is intended to be employed as a sensing unit with a relay circuit as illustrated in Figure 3 connected in series with the loudspeakers of a radio, gramophone, television receiver or other sound reproduction equipment. The relay unit illustrated in Figure 3, comprises a relay coil 43 having terminals 44, 45 which are connected, in use, across terminals 37, 38 respectively of the circuit illustrated in Figure 1. The relay coil 43 has associated two sets of normally closed relay con- tacts 46, 47 each of which has a variable resistor 48, 49 respectively connected in parallel across it. The unit has terminals A, B and A« , B» for connection in series with one of the supply lines to respective loudspeakers. Further terminals D, E and D 1 , E* are provided for convenience allowing the two-line cables to be cut and the individual relay units to be inser¬ ted physically into the lines. In normal operation when the sound reproduction equipment of which the loudspeakers form part is in use the relay contacts 46 and 47 are normally closed allowing operation to take place in a normal fashion. For the purpose of this description it is assumed that the loudspeakers in question are the loudspeakers of a motor vehicle entertainment unit such as a car radio or cassette player and that the vehicle is also equipped with citizens band radio having a loudspeaker for communi- cation with the driver, and which will be connected across the terminals 12, 13 of the circuit illustrated in Figure 1. If, alternatively, the loudspeakers to which the unit illustrated in Figure 3 were connected comprise the loudspeakers of a domestic audio system, the unit illustrated in Figure 1 may be connected, for example, to detect the signal from a doorbell, in which case the microphone terminal 11 would be connected to a microphone positioned closely adjacent the doorbell to pick up signals generated thereby. Dealing, first, with the example of a motor vehicle system; upon occurrence of a signal from the citizens band radio at the same tx e as sound is emanating from the entertainment system, a signal appears across the terminals 12, 13. This signal is coupled via the capacitor 23 to the base of the transistor 24 which acts as an amplifier. The amplified signal is coupled via the capacitor 27 to voltage doubling diodes 10, 28 which act to rectify the signal , which is then smoothed by capacitor 34 before being passed to the base of transistor 29. Transistor 29 is held normally off by the resistor 33 , and is connected as part of a Darlington pair with transistor 30 so as to provide high input impedance for operation of the relay 32. This causes the relay contact 35 to close applying the supply voltage to the terminal 36 and to the terminal 37 * This causes current to flow in the relay coil 43 of the remote unit illustrated in Figure 3 and the relay contacts 46 and 47 consequently open bringing the variable resistors 48 and 49 into series with the loudspeaker or loudspeakers thereby muting these. The acoustic signals from the speaker connec- ted across the terminals 12, 13 can therefore be heard over the signals from the muted speakers without the user taking any action. Immediately the sound from the CB speaker terminates the capacitor 34 starts to discharge and the length of time it takes to discharge determines the delay time before the transistor 29 is again turned on so that the transistor 30 is turned off to cut off the relay 32 and hence the . relay 43 allowing the speakers connected across the contacts 46 and 47 to resume normal operation. The operation of the circuit in response to a signal on the terminal 11 from a microphone positioned, for example, as indicated above to detect energisation of a doorbell or telephone bell is similar, the normally conducting transistor 24 being turned off by a signal applied to its base through the capaci¬ tor 23 from the collector of the transistor 15 which is normally conducting and which is turned off by the arrival of a signal on the terminal 11 thereby causing the voltage at the junction between the resistors 16 and 20 to rise. The circuit illustrated in Figure 2 includes three terminals 50, 51, 52 intended for connection to the terminals 40, 41, 42 respectively of the circuit of Figure 1. The terminal 51 is connected to the coll- ector of a transistor 53 the emitter of which is connected to the terminal 52 and the base of which is connected via a resistor 54 to terminal 50 and to the collector of the transistor 55 the emitter of which is connected to the emitter of the transistor 53 and and to the terminal 52, and the base of which is connected via resistor 75 and capacitor 76 to a diode bridge circuit comprising two diodes 56, 57 connected back to back and two diodes 58 , 59 connect¬ ed in opposition across the input terminals 60, 61 of the circuit intended for connection to the telephone lines. A third terminal 62 is connected via a resistor 63 to the return line terminal 52. Normally the transistor 55 is biased off and holds the transistor 53 off, but switching occurs upon the arrival of a signal on the telephone lines which would energise the telephone bell, causing the transistor 53 to conduct and there¬ by complete a path through the relay coil 32 closing the normally open relay contacts 35 in the manner described above. Operation of the remaining part of the circuit is identical with that described hereinabove. Figure 4 illustrates a simple relay circuit which can be connected in series with a conventional mains lead, for example, at the plug and socket connection or at the appliance and incorporates terminals 70, 71 across a relay coil 72 for connection to the terminals 36 and 39 respectively. The relay includes normally closed contacts 73 which are opened to isolate the appliance from the mains when the relay contacts 35 are closed to apply the supply voltage on the line 70 to the relay coil 72. The energis¬ ation of a doorbell or the telephone bell can thus be used to switch off a noisy appliance, such as a vacuum cleaner, lawn mower or any other electric- ally driven item the noise of which may be sufficien¬ tly great to prevent the user from hearing the door¬ bell. Again, once the initiating signal has ceased the connection is reestablished after a delay time determined by the capacitor 34 in the circuit illustrated in Figure 1. Turning now to Figure 5, there is shown a circuit for sensing when a cellular radio telephone in a motor vehicle is in operation. This circuit has a supply terminal 101 for connection to a positive voltage supply and a negative terminal 103 for connection to the negative side of the supply circuit. It is conventional for motor vehicle electrical circuits to utilise the vehicle body or chassis as one of the supply routes and which of the terminals 101 , 103 is connected to the body vehicle or "earth" will depend on the polarity of the vehicle 1 s electrical circuit commonly the negative supply line is "earthed" to the vehicle body but this is not always the case. The circuit has a third terminal 102 connected to the terminal 101 via a resistor 81. The positive supply to the cellular car telephone (radio telephone) is made via the terminal 102 so that the telephone is connected across terminals 102 and 103. The terminal 102 leads via a resistor 83 to the base of a PNP transistor 84 the emitter of which is connected to the positive supply line via a resistor 82, and earthed by a capacitor 93, and the collector of which is connected to the negative supply line 103 via a resistor 85 and to the base of a transistor 88 via a resistor 86. The base of the transistor 88 is also connected to the negative supply line via a variable resistor 87. The transistor 88 is connected, with a further trans¬ istor 90 as a darlington pair, the collector of the transistor 90 being connected to the positive supply line via a relay coil 91 and the emitter being connected to the negative supply line. The relay coil 91 is shunted by a diode 92 for the purpose of preventing back EMF through the coil 91 from damaging the transistor 90. Bias to the transistor 88 is supplied via a resistor 89 and the aforementioned resistor 82. The relay 91 operates two sets of normally closed contacts 91/A and 91/B, the former being connected across two resistors 94, 95 (the latter being a variable resistor) between two terminals 104 and 96, and the contacts 91/B being connected across two resistors 116, 117 between two terminals 98 and 100. Two pairs of directly connected terminals 105, 97 and 99, 112 are- also provided for purposes which will be described hereinbelow. When a cellular .radio telephone is in operation it draws an operating current which is significantly higher than the low, quiescent current passing when it is not in operation. Thus, in the quiescent state the transistor 90 of the darlington pair is off and the relay coil 91 has no current passing through it so that the relay contact 91/A and 9 /B are closed. The terminals 104, 105 and 98, 99 are provided for connection to the speaker outputs of a motor vehicle stereo system, whilst the terminals 96, 97 and 100, 112 are provided for connection to the two loudspea¬ kers of the system. In fitting the relay contacts it is necessary only to cut the wires leading from the stereo system to the loudspeakers and to insert the contacts via the terminals 104, 105, 96, 97 for one speaker and 98, 99 100, 112 for the other speaker. When the radio telephone starts to operate the current drawn causes a voltage drop across the resistor 81 which is passed, via the resistor 83 to the base of the transistor 84 which acts as an amplifier and passes the signal to the darlington pair 88, 90 switching on the transistor 90 and causing current to flow through the relay coil 91. Upon this occurrence the contacts 91/A and 91/B open thereby introducing the resistors 94, 95 and 116, 117 into the loudspeaker circuits thereby effectively attenuating the sound generated thereby without modifying the output from the stereo system itself. The variable resistor 87 connected to the base of the transistor 88 of the darlington pair allows bias variations to be introduced to set up the system to accommodate different signals generated by the different amount of current drawn by different radio telephones so that the same circuit can be used for all radio telephones with a simple adjustment being necessary upon installation. The resistor 82 and capacitor 93 prevent electrical interference within the motor vehicle from accidently tripping the relay 91 and, as mentioned above, the diode 9 prevents back EMF generated by the relay from damaging the transistor 90.

Claims: CLAIMS 1. Apparatus sensitive to the energisation of a selected one of a plurality of acoustic sources and operable in response to the detection of energisation.of the said one source to cause attenuation of acoustic signals from the other source or all the other sources comprising the said plurality thereof, whereby to allcw acoustic signals from the said one source to be heard over those generated b the other source or -sources. 2. Apparatus as claimed in Claim 1 comprising a detector circuit having means sensitive to the energisation of the said one source and trigger means responsive to the output of the detector to produce a control signal for controlling operation of attenuator means when the detector circuit senses energisa¬ tion of the said one source. 3. Apparatus as claimed in Claim 2, in which the said control signal is generated by the said trigger means only whilst the said one source is energised, and the control signal is removed upon cessation of energisation of the said one source whereby to allow attenuation of the said other sources to be terminated. 4. Apparatus as claimed in Claim 2 or Claim 3, in which the attenuator means comprise one or more relays having relay contacts connectable in circuit with the said other sources and a relay coil connectable to receive the said control signal. 5. Apparatus as claimed in Claim 4, adapted for attenua¬ ting acoustic signals generated by loudspeakers, in which the attenuator means includes resistorsconnectable in series with the said loudspeakers and shunted by the said relay contacts whereby to allow normal operation of the loudspeakers when the relay is not energised, and to attenuate the loudspeakers when the relay is energised. 6. Apparatus as claimed in any preceding Claim, in which the detector means includes a microphone sensitive to acoustic signals generated by the said one source. 7. Apparatus as claimed in any preceding Claim, in which the detector means includes means sensitive to an electrical current energising the said one source whereby to effect switch¬ ing of the trigger means when an energising current is flowing in the said one source. 8. Apparatus as claimed in Claim 6 and Claim 7, in which the detector circuit is provided with a first set of terminals for connection to the said one source for detecting electrical energisation thereof, and second terminals for connection to a microphone for detecting acoustic signals . generated by the said one source. 9. Apparatus as claimed in Claim 6, Claim 7 or Claim 8, in which the detector means is further provided with terminals for connecticn to a subsidiary circuit adapted for connection to a telephone line for sensing energisation of the telephone and effecting triggering of the said trigger means when the telephone is energised. 10. Apparatus as claimed in any of Claims 1 to 5, in which attenuation of the said other source or other sources is effected by switching off a power supply to the said other source or sources upon detection of energisation of the said one source. 11. Apparatus as claimed in any preceding Claim, adapted for detecting energisation of a radio telephone and for attenuating signals from a vehicle radio or cassette player, in which the trigger means coπprises a switching transistor circuit and the detector means coπprises an amplifying transistor the base/collector junction of which is connected across the telephone supply. 12. Apparatus as claimed in Claim 11, in which the switching transistor circuit includes two transistors connected as a Darlington pair with the collector/emitter junction of one transistor in series with the relay coil of the attenuator means. 13. Apparatus as claimed in any preceding Claim, having a plurality of terminals for selectively connecting two alternative types of source, comprising a microphone terminal,, terminals for connection to a telephone circuit, and terminals for connection across a loudspeaker to detect electrical energisation thereof. 14. Apparatus sensitive to the energisation of a selected one of a plurality of acoustic sources, substantially as hereinbefore described with reference to, and as shown in, the accoπpairying drawings.

Inventors: LAMBE JOHN CHARLES, WARRACK ANDREW, LAMBE, JOHN, CHARLES, WARRACK, ANDREW
Applicants: LAMBE JOHN CHARLES, WARRACK ANDREW, LAMBE, JOHN, CHARLES, WARRACK, ANDREW
Application year: 1985
Main classification: H03G3
IPC codes: G08B3, H03G3, H04M1