GB2150731A

GB2150731A - Air powered sound source

Info

Publication number: GB2150731A
Application number: GB08332139A
Authority: GB
Inventors: Mgr Inz Wladyslaw Wygnanski
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-12-01
Filing date: 1983-12-01
Publication date: 1985-07-03
Also published as: GB2150731B; GB8332139D0

Abstract

An air powered sound source comprises a plurality of chambers maintained at an air pressure different to the environmental air pressure, each chamber having a respective valve controlled output orifice and the valves being selectively operated to open and close the orifices in order to control the expulsion or suction of air through the orifices. The valves are selectively operated by a control unit 14 which receives a digital control signal 16. <IMAGE>

Description

SPECIFICATION Air powered digital sound source Field of the Invention This invention relates to an air powered sound source which can be used to produce an analogue audible sound from a digital controlling signal.

Summary of the Invention According to the invention, there is provided an air powered sound source comprising a plurality of chambers, means for supplying these chambers with compressed or rarefield air, an output orifice from each chamber, valves for opening and closing the orifices and a control unit for controlling movement of the valves.

The compressed or rarefied air supplied to the chambers may be at the same pressure for each chamber or may be at different pressures for the different chambers. The sizes of the orifices also can be the same for each chamber or different for the different chambers.

By selective opening of the valves in accordance with an input signal to the control unit, varying amounts of air at varying pressures will be expelled from (or sucked into) the chambers leading to the production of an audible sound. At the point of creation of the sound, operation is digital in that a particular orifice is either opened or closed.

Since each valve controls the expulsion or suction of a different but specifically predetermined amount of air from or into a pressure chamber within a period defined by a sampling rate (which is typically 0.03 ms, period) a specific pressure pulse is obtained in the surrounding fluid (air), for each such opening.

The combination of such pulses generated by simultaneous opening of some or all of the valves produces by summation an effective output pressure pulse having an amplitude equal to the sum of the specific pulses which have individually been generated at that particular moment.

Consequently, different combinations of the synchronously opened valves will generate different amplitudes of effective output pressure pulse. The opening of the valves is determined by a digital control signal which may be derived from an analogue audio signal for example or may be an originally derived digital signal.

A series of effective pressure pulses will be integrated in the surrounding fluid/air to become an audible acoustic wave which radiates from the transducer.

An advantage of the fact that operation is digital at the point of creation of sound, is that power can be increased without increasing distortion, since one is merely amplifying a fixed digital signal.

The invention will now be further described, by way of example with reference to the accompanying drawing which is a schematic diagram of a sound source in accordance with the invention.

The unit shown in the drawing has a number of pressure chambers P, P, P. . . P arranged in a common housing 1 0. Each chamber has an inlet 1 2 for compressed or rarefied air, and an outlet orifice 0, O, 0. .0. Valves V1, V2, V3 . . Vn are associated with each orifice and the valves are operated by a control unit 1 4. A digital signal 1 6 is fed to the control unit, and the valves which are normally closed are opened and closed in dependence on the signal 1 6.

The operation of the control unit 14 will be basically digital, in that a command can be produced to open a combination of the valves at regular, frequent time intervals. A suitable frequency for these commands may be of the order of 30 KHz.

Opening of one or more valves will result in expulsion or suction of air from or in to the associated chamber or chambers to produce an audible sound.

A compressed air source (or vacuum pump) will be connected up to the inputs 12 to the chambers. Most conveniently, this source will provide for an equal pressure to exist in each of the chambers, but it may also be possible to provide for different pressures in different chambers. This unit can be used to produce very loud audible signals, with little distortion.

The moving parts at the sound creating interface are the valves which just move between an open and a closed position. This is in contrast to a conventional loudspeaker, where analogue movement of the loudspeaker cone occurs at the sound creation interface, and this mechanical movement can give rise to distortion and inefficiency.

The invention allows a digital signal to be decoded and converted into an audio signal directly by relying on the integration of the air pulses released to form a combined audible signal at a distance from the radiator.

1. An air powered sound source which comprises a plurality of chambers, means for supply of air to each chamber at a pressure differing from the environmental air pressure, an output orifice from each chamber, valves for opening and closing the said orifices and a control unit for controlling the operations of the valves.

2. A sound source according to claim 1, wherein the air supply means is operative equally to pressurise each chamber.

3. A sound source according to claim 1 or claim 2, wherein the air supply means is operative to pressurise each chamber above the environmental pressure.

4. A sound source according to any of claims 1 to 3, wherein the control means is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Air powered digital sound source Field of the Invention This invention relates to an air powered sound source which can be used to produce an analogue audible sound from a digital controlling signal. Summary of the Invention According to the invention, there is provided an air powered sound source comprising a plurality of chambers, means for supplying these chambers with compressed or rarefield air, an output orifice from each chamber, valves for opening and closing the orifices and a control unit for controlling movement of the valves. The compressed or rarefied air supplied to the chambers may be at the same pressure for each chamber or may be at different pressures for the different chambers. The sizes of the orifices also can be the same for each chamber or different for the different chambers. By selective opening of the valves in accordance with an input signal to the control unit, varying amounts of air at varying pressures will be expelled from (or sucked into) the chambers leading to the production of an audible sound. At the point of creation of the sound, operation is digital in that a particular orifice is either opened or closed. Since each valve controls the expulsion or suction of a different but specifically predetermined amount of air from or into a pressure chamber within a period defined by a sampling rate (which is typically 0.03 ms, period) a specific pressure pulse is obtained in the surrounding fluid (air), for each such opening. The combination of such pulses generated by simultaneous opening of some or all of the valves produces by summation an effective output pressure pulse having an amplitude equal to the sum of the specific pulses which have individually been generated at that particular moment. Consequently, different combinations of the synchronously opened valves will generate different amplitudes of effective output pressure pulse. The opening of the valves is determined by a digital control signal which may be derived from an analogue audio signal for example or may be an originally derived digital signal. A series of effective pressure pulses will be integrated in the surrounding fluid/air to become an audible acoustic wave which radiates from the transducer. An advantage of the fact that operation is digital at the point of creation of sound, is that power can be increased without increasing distortion, since one is merely amplifying a fixed digital signal. The invention will now be further described, by way of example with reference to the accompanying drawing which is a schematic diagram of a sound source in accordance with the invention. The unit shown in the drawing has a number of pressure chambers P, P, P. . . P arranged in a common housing 1 0. Each chamber has an inlet 1 2 for compressed or rarefied air, and an outlet orifice 0, O, 0. .0. Valves V1, V2, V3 . . Vn are associated with each orifice and the valves are operated by a control unit 1 4. A digital signal 1 6 is fed to the control unit, and the valves which are normally closed are opened and closed in dependence on the signal 1 6. The operation of the control unit 14 will be basically digital, in that a command can be produced to open a combination of the valves at regular, frequent time intervals. A suitable frequency for these commands may be of the order of 30 KHz. Opening of one or more valves will result in expulsion or suction of air from or in to the associated chamber or chambers to produce an audible sound. A compressed air source (or vacuum pump) will be connected up to the inputs 12 to the chambers. Most conveniently, this source will provide for an equal pressure to exist in each of the chambers, but it may also be possible to provide for different pressures in different chambers. This unit can be used to produce very loud audible signals, with little distortion. The moving parts at the sound creating interface are the valves which just move between an open and a closed position. This is in contrast to a conventional loudspeaker, where analogue movement of the loudspeaker cone occurs at the sound creation interface, and this mechanical movement can give rise to distortion and inefficiency. The invention allows a digital signal to be decoded and converted into an audio signal directly by relying on the integration of the air pulses released to form a combined audible signal at a distance from the radiator. CLAIMS

4. A sound source according to any of claims 1 to 3, wherein the control means is operative selectively to operate the valves responsively to an input signal.

5. A sound source according to any one of claims 1 to 4, wherein each valve is controlled at a sampling rate of approximate period 0.03 ms.

6. An air powered sound source substantially as hereinbefore described with reference to the accompanying drawing.

7. A method of sound generation according to which a plurality of chambers are each supplied with air at a pressure differing from the environmental air pressure and expulsion or suction of air pressure pulses from or to the chambers through outlet orifices is controlled by valves which open and close the orifice selectively.

8. A method of sound generation substantially as hereinbefore described.