GB2093317A - Electronic sound distribution system - Google Patents

Abstract

An electronic sound distribution system comprises a sound generating or reproducing appliance, one or more sound diffusers (21) incorporating a loudspeaker (28) and a central unit (1) Fig. 1 not shown interposed between the appliance and the diffusers, the central unit being operable to switch on and off the appliance in response to switching on and off of a diffuser and to supply audio and power signals to the diffusers, each diffuser having means (25) for separating the audio signal from the electrical supply signal received from the central unit, means (26) for regulating the power and tone of the audio signal and means (27) for amplifying the audio signal to the level required by the loudspeaker. The appliance is switched on by operation of a relay (16) in response to detection (13) of supply current when a diffuser is switched on. Further circuitry (6) ensures the output of the central unit automatically accommodates the change in load as more diffusers are switched on. <IMAGE>

Description

SPECIFICATION Electronic sound distribution system This invention relates to electronic sound distribution systems.

The object of the present invention is to improve and simplify the assembly and operation of the aforementioned systems, particularly for use as background music installations and in halls of entertainment, commercial establishments, etc.

Indeed, existing systems have various drawbacks which differ from one system to another, and which can be broadly summarised as follows: 1. Difficulty in establishing the design of an installation especially when the power amplifiers are centralised because it is necessary to resort to complicated calculations in order to match the impedances of the lines which run to the audio diffusers so that these latter correctly load the power amplifier and therefore, so that the power is adequately distributed among the various diffusers, especially when these latter are of different power ratings, without in any circumstances overloading the central amplifier.

This problem is complicated even more when it is desired separately to regulate the volume of sound from the various diffusers, since it is necessary to use very bulky wound potentiometers in which a fair amount of power is dissipated, since they upset the impedances of the installation and produce considerable noise when operated, their effective life being very short since a lot of faults occur. Similarly, this system offers poor quality sound by reason of the use of line transformers and due to the losses which occur therein whether, because the impedances are low, high currents circulate and losses occur due to the cross-sections of the conductors, or alternatively, the impedances are high, then by reason of the capacity between the line conductors, the disadvantage then is the high levels of voltage which they carry.

2. Difficulty of installation: this is evident in the previously described system and in the case of systems offering decentralised amplification, such systems normally being installed using numerous conductors so that installation is complicated and there is the danger of a mistake in connection with the inevitability of damage to the equipment, especially if the installation is supplied with an electrical supply conductor together with other conductors, in which case if there is a mistake in installation destruction of the equipment is inevitable.

The invention is concerned with overcoming the disadvantages and difficulties mentioned hereinabove.

The main feature of the system, in addition to the provision of decentralised amplification, resides in the fact that low frequency audio signals are transmitted by the same line, the supply to the amplifiers of low voltage direct current, and the signal for remote control of the equipment when any diffuser is operated, requiring only two conductor wires. From all this, it will be deduced that there is greater security because the equipment operates on low voltage, for example 24 volts direct current, representing no danger to persons, so that equipment may even be installed in bathrooms.

Being based on decentralised amplification, the result is a better quality of audio response because the signal transmitted is at a very low impedance and yet with considerable modulation voltage, for example 3 volts effective, and these two factors together provide considerable immunity to extraneous noise and disturbing external signals, in addition, thanks to the fact that the diffusers incorporate their own amplifier so the impedance which they offer to the line is high and therefore, the currents in them are very low, for which reason there are no losses of transmitted signal.

Likewise, on account of these characteristics there is no problem with the matching of impedances and a greater effective life is achieved since control of the low frequency signals is carried out at very low levels.

The system permits remote control of central musical equipment from any of the diffusers so that when any of the music diffusers is put into operation, it will act on the central unit in such a way that this latter connects the music equipment with the associated unit and will remain connected so long as there is any diffuser in operation. When they have all been switched off the music equipment associated with the central unit will also be disconnected.

An element of the system has been designed which operates as the central unit for the system and which is of the multiple function type because it undertakes to: 1) supply low voltage direct current to the diffusers; 2) to modulate in relation to the supply voltage of the diffusers the low frequency signal which they are required to amplify; 3) to carry out remote control of the music equipment connected to it when it detects that there is a diffuser operating; 4) furthermore to adapt the signal which reaches it from the musical equipment to the modulation level established in the series so that it is possible to connect to it almost any monaural or stereophonic unit, from an input level of for instance 100 mV up to the output of a power amplifier which might for example attain levels close to 100 W; 5) to comprise in addition a circuit which indicates the level of modulation at the output, facilitating adjustments of sensitivity at the central unit; 6) likewise to incorporate a remote control activity beacon, a switch for putting this into effect from the same central unit and another indicator which shows that the central unit is connected to the electricity supply mains.

Furthermore, the greater virtue of this system is its simplicity of installation because it is necessary only to install one parallel wire which can easily be concealed when installation is carried out on the surface, connection to the diffusers being very simple, normally by mere pressure, and in addition the entire system is completely protected; at the diffusers there is no danger of reversing the polarity because simply in the event of the line not being correctly connected the units will not operate and then when the wires of the line are reversed, correct functioning will be possible. The central unit is protected against short-circuits in the line and against excesses of temperature in the case of a prolonged overioad of the central unit because this becomes automatically disconnected, its capacity to function being restored only once the problem has been remedied.In the same way, the amplifiers of the diffusers are completely protected against excesses of temperature, short-circuits at their output and overloading.

For a greater understanding of the invention the accompanying drawings illustrate one embodiment of the invention by way of example.

In the drawings: Fig. 1 is a block diagram of the central unit; and Fig. 2 is a block diagram of a sound diffuser.

As will be ascertained from careful observation of the aforesaid drawings, the system comprises a central module 1, Fig. 1, to which it is possible to connect various audio sources such as a tape recorder, radio, amplifier, etc., through inputs 2 to a circuit 3 which functions as a variable attenuator and channel summator in the case of stereophony, so that the equipment connected to the central unit, the sound level of which may be variable within a wide range, is adapted to a constant level.

From the circuit 3, the audio signal passes through a circuit 4 which protects the input, avoiding any possibility of overload, especially when the variable attenuator 3 is at maximum sensitivity, so that it is possible to avoid damage to the electronic components of an amplifier 5 which is on the downstream side of the circuit 4 and which is operable to correct and amplify the signal to the appropriate level, and in addition to lower the transmission impedance in order subsequently to carry it to the key part 6 of the system which is the circuit designed to superimpose the audio signal on the supply voltage to the sound diffusers.In the circuit 6 which is based on a typical circuit with a stabilised source of supply and is shown subdivided into various modules for better understanding, the low frequency signal emanating from the amplifier 5 enters a differential amplifier 7, the function of which is to compare the signal with a reference voltage which may vary and which is supplied by a circuit 10.

Variation of this reference voltage will bring about a variation in the direct current output voltage so that by means of the circuit 10 it is possible to adjust this voltage to the desired value, for example 24 volts. Furthermore, as this circuit takes its voltage from the output, it will tend to stabilise the mean value of this voltage so that it will automatically compensate for the increase in power consumption when more diffusers are connected.

The output voltage from the differential amplifier 7 controls a power circuit 8 which is in series with the supply line so that, assuming that the voltage supplied by the circuit 7 is constant, the output voltage will also be constant but as the voltage supplied by the circuit 7 is variable, firstly on account of the mean variation of the output voltage, which will compensate for fluctuations in consumption at the output and secondly by reason of the low frequency signal delivered to the circuit 7, and further assuming that this signal in turn reflects at its output, which means that at the outlet of the power circuit 8 there will, in addition, be a voltage of a stable mean value, a superimposed low frequency signal with a very low output impedance, which is the object of the invention.Furthermore, there is provided a protective circuit 9 which limits the output current with respect to an established value so that in the event of a short circuit in the line, no damage can occur in the power circuit 8. Similarly, the protective circuit 9 has the task of measuring the temperature in the power circuit, limiting the current emanating therefrom in relation to the temperature, and even shutting it down if it reaches a dangerous level.

Located at the outlet from the protective circuit 9 is a circuit 11 which, by means of a visual indication from, for example, LED's, indicatiny instruments, gauges, etc., serves to provide information concerning the level of modulation present in the output line 1 2 so that it is possible to influence the variable inlet attenuator 3 to bring it to the standard level within the system. Just before the output line 12 there is a fuse which provides additional protection.

Others in the circuits incorporated in the central unit provide for remote control of the equipment in the following manner: a circuit 1 3 serves to detect when a limit is connected to the output, by noting the amount of current consumed from a source of supply 15, and sending a control signal to a circuit 14 which operates a relay 1 6 to connect the electricity supply mains to terminals 1 7. This connection is indicated by the operation of a warning light 18. The relay 1 6 can also be operated to apply to the terminals 1 7 without any diffuser having been switched on, by manual operation of a switch 19, indicated by illumination of a warning light 20. This is a useful means of operating the equipment connected to the central unit without employing the remote control.

The supply source 1 5 to transform the electricity main supply, namely 120 to 240 V alternating current, into low voltage direct current for supply to the diffusers and also to feed all the electronic circuits in the central unit and incorporates protective fuses' mains indicator light, etc.

From the central module 1, the sound is distributed to sound diffusers 21, Fig. 2, via the twin-cable line 1 2 which, as already stated, also carries the supply and remote control connectors.

Each diffuser 21, Fig. 2, comprises an electronic circuit which serves to separate the signals and amplify, regulate and correct the sound signal and one or more loudspeakers 28 for broadcasting the sound, which loudspeakers may be incorporated in the same cabinet as the remainder of the equipment or may be installed separately.

The signal arrives at the diffuser 21 from the line 12 and first enters a circuit 22 which provides protection against reversal of polarity in the line due to improper connection thereof. The signal then passes a make and break switch 23 which controls the operation of the diffuser, a warning light 24 being provided which lights up to indicate that the diffuser is operating and that remote control of the central unit is therefore in operation.

The signal is then fed to a separating circuit 25, operation of which is identical to but the reverse of the modulating circuit 6 of the central unit 1, in order to provide, on the one hand, a low frequency signal having no continuous component, which is the audio signal to be amplified, and, on the other, a stabilised supply voltage with no alternating component which is fed from the separating circuit 25 via a circuit 26, which regulates the volume and tone of the signal, to an amplifier 27 which amplifies the signal to the level required to drive a loudspeaker or speakers 28 which may or may not be in the same cabinet.

Claims (9)

1. An electronic sound distribution system comprising a central unit connected to a sound generating or reproducing appliance and operable to control the switching on and off of said appliance and to supply sound and electrical power to one or more sound diffusers each of which incorporates means for regulating the power and tone of the sound, means responsive to switching on and off of the diffuser for sending a remote control signal to the central unit, a separating circuit which separates the audio signal and the electricity supply signal from the central unit and an amplifier which amplifies the audio signal to the level of power required by a loudspeaker within or connected to said diffuser.

2. An electronic sound distribution system according to Claim 1, characterised in that the central unit has inputs connected to the audio generator, and an electronic circuit which adapts its output level to a standard value, said central unit serving to modulate the voltage supplied to the diffusers and also to supply power to the sound generating equipment in response to a diffuser being switched on.

3. An electronic sound distribution system according to the preceding claims, characterised in that the sound inputs of the central unit are connected to a variable attenuator circuit and channel summator in said central unit, the audio signal passing through an input protective circuit to an amplifier which corrects and amplifies the signal to a predetermined level so that it can be suitably transmitted to a circuit which superimposes the audio signal on the supply voltage for the diffusers and which comprises a differential amplifier in which the voltage is compared with a reference voltage emanating from a circuit fed from the aforesaid differential amplifier, the output voltage from said differential amplifier controlling a power circuit in series with the supply line in order to obtain voltage at a stable mean value and also a superimposed low frequency signal with a very low output impedance, the voltage and signal passing via a protective circuit to the output line connected to the diffusers, with or without the interposition of a circuit for displaying the level of modulation present in the output line.

4. An electronic sound distribution system according to any preceding claim, characterised in that the central unit contains a circuit for remotely controlling the sound generating equipment, said circuit comprising a current sensor for detecting the connection of a diffuser by measuring the consumption of current due to such connection and transmitting a signal to the remote control circuit to operate a relay to connect the electricity supply mains to said equipment which is capable of converting the alternating current voltage of the supply line into a very low voltage direct current for supplying the diffusers and other electronic elements.

5. An electronic sound distribution system according to any preceding claim, characterised in that the sound diffusers each incorporate an amplifier and a circuit for separating the audio signal from the electricity supply transmitted along the same line by the central unit.

6. An electronic sound distribution system according to any preceding claim, characterised in that the input voltage and audio signal fed into the diffuser passes through a circuit which protects it against reversal of polarity in the line and then through a make and break switch for switching on or shutting off the unit and provided with a warning light, the line subsequently passing through a separating circuit which separates the supply voltage for the aforesaid amplifier from the low frequency signal sent to the amplifier and subsequently to the loudspeaker.

7. An electronic sound distribution system according to any preceding claim, characterised in that the diffuser and the central unit each contain a demodulating or modulating circuit based on the general theory of stabilised supply sources, be they in series or in parallel or commutated, the purpose of which is to mix or separate the signals, varying the reference voltage in one case and maintaining it fixed in the other.

8. An electronic sound distribution system according to any preceding claim, characterised by the addition of a third wire and duplicated circuits in the diffuser and central unit, in order to transmit stereophony by the provision, in the diffuser, of a programmer clock, connected in parallel with the make and break switch, to programme the timed switch-on and shut-off thereof, and by the addition of simple circuits which act to control the switch-on of the diffuser and its volume, so that it is possible to use the system for the broadcasting of public address calls and information in addition to music.

9. An electronic sound distribution system, substantially as hereinbefore described with reference to or as shown in Figs. 1 and 2 of the accompanying drawings.