GB2150789A - Loudspeaker - Google Patents

Abstract

A transducer for transducing an electrical audio signal into audible sound, comprising a voice coil (12), a loudspeaker cone (10), a plate (14) co- operating with the cone to define an air chamber (18) therein, an aperture (20) in the plate, a valve (22) for opening and closing said aperture, and means for operating the valve at a high frequency substantially in excess of audio frequencies, whereby when the cone is driven by the electrical audio signal, vibrations of the cone result in expulsion of air through the aperture in the closure plate. <IMAGE>

Description

SPECIFICATION Sound pressure active transformer Field of the Invention This invention relates to a transducer for converting an electrical transmitted analogue audio signal into audible sound.

Background to the Invention Conventional transducers in the form of loudspeakers have a cone which is displaced to move a column of air extending forward from the loudspeaker, and thus to generate audible sound. It is known that conventional loudspeakers are very inefficient, in that a large proportion of the power from the input signal is wasted as heat in the speech coil.

Summary of the Invention According to the present invention, there is provided a transducer having a movable diaphragm means for moving the diaphragm cone in response to an input audio signal, an end plate forming with the cone an enclosed pressure chamber, an aperture in the end plate, a valve for opening and closing the aperture, and means for repetitively opening the said valve at a controlled rate.

The valve is set to open and close the aperture in the end plate at a high frequency, typically of the order of 25kHz.

As the diaphragm moves, the level in the chamber alters. Each time the valve opens, air is exhausted from the chamber at a pressure determined by the movement of the diaphragm.

The impulsively exhausted air can reach high acceleration and finally high output velocity. The output velocity is determined by the movement of the diaphragm but much higher than velocity of the diaphragm movement itself. The valve operating with high frequency excels a series of air pulses the amplitude of which are strictly dependent on the diaphragm excursion. The series of air pulses become integrated in surrounding fluid such as air and become audible acoustic wave.

Since the diaphragm only has to compress a relatively small volume of air, its efficiency can be higher than that of a conventional loudspeaker and improved radiation effectiveness is obtained particularly in low frequency ranges where conventional loudspeakers, because of low acceleration, generate very low output pressures.

The valve is typically a second loudspeaker adopted to operate at very high frequencies.

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

The drawing shows a transducer in the form of a conventional loudspeaker with a cone 10 and a voice coil 12 which is able to vibrate the cone. An end plate 14 covers the end face of the loudspeaker and is attached thereto around the periphery 16 of the cone. The end plate 14 and the cone 10 define between them a chamber 18. The end plate 14 has a central opening 20, and a valve 22 controlled by a control unit 24 is mounted so as to be able to open and close the opening as the valve member moves backwards and forwards.

An analogue input power signal is fed to the speech cone through a line 26, and a control signal is fed to the valve controlling unit 24 through a line 28.

In operation, the input through line 26 energises the coil 12 which vibrates the cone 10 backwards and forwards. This produces a varying pressure within the chamber 18. Whilst the cone is moving and the pressure is varying, the valve 22 is operating to open and close the opening 20 regularly. Each time the valve opens, air at a pressure characteristic of the instantaneous pressure in the chamber is expelled from the chamber 18.

For reproduction of a sound it is of course necessary that the valve 22 be opened and shut at a frequency which is much higher than the frequency of the sound to be reproduced. Typically a frequency of 25 kHz is used as the switching/gating frequency.

The advantage of the invention is that the loudspeaker cone is now used merely to cause increase and decrease in the air pressure in the chamber and this varying air pressure is delivered via the valve 22 (itself another loudspeaker type device albeit operating at above audio frequencies) as a series of impulses which when integrated reproduce the original sound.

The loudspeaker 10 is preferably contained within a sealed enclosure 24 so as to prevent back radiation from the diaphragm to reduce phase cancellation effects.

1. A transducer having a movable diaphragm means for moving a diaphragm cone in response to an input audio signal, an apertured plate cooperating with the cone to form an enclosed pressure chamber, a valve for opening and closing the aperture in the plate, and means for repetitively opening the said valve at a controlled rate.

2. A transducer as claimed in claim 1, wherein the last mentioned means is adapted to operate the valve at a frequency of the order of 25 kHz.

3. A transducer as claimed in claim 1 or claim 2, wherein the said plate is an end plate attached to the cone at the outside periphery thereof.

4. A transducer as claimed in any of claims 1 to 3, wherein the said diaphragm means and cone are housed in an enclosure sealing to the outer periphery of the cone.

5. A transducer as claimed in any of claims 1 to 4, wherein the said valve is a loudspeaker device adapted to operate above audio frequencies.

6. A transducer substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of transducing an electrical signal of audio frequency into a sound wave, according to which a loudspeaker cone is closed by an apertured plate to define an air chamber therein, the cone is driven by the electrical signal of audio frequency

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sound pressure active transformer Field of the Invention This invention relates to a transducer for converting an electrical transmitted analogue audio signal into audible sound. Background to the Invention Conventional transducers in the form of loudspeakers have a cone which is displaced to move a column of air extending forward from the loudspeaker, and thus to generate audible sound. It is known that conventional loudspeakers are very inefficient, in that a large proportion of the power from the input signal is wasted as heat in the speech coil. Summary of the Invention According to the present invention, there is provided a transducer having a movable diaphragm means for moving the diaphragm cone in response to an input audio signal, an end plate forming with the cone an enclosed pressure chamber, an aperture in the end plate, a valve for opening and closing the aperture, and means for repetitively opening the said valve at a controlled rate. The valve is set to open and close the aperture in the end plate at a high frequency, typically of the order of 25kHz. As the diaphragm moves, the level in the chamber alters. Each time the valve opens, air is exhausted from the chamber at a pressure determined by the movement of the diaphragm. The impulsively exhausted air can reach high acceleration and finally high output velocity. The output velocity is determined by the movement of the diaphragm but much higher than velocity of the diaphragm movement itself. The valve operating with high frequency excels a series of air pulses the amplitude of which are strictly dependent on the diaphragm excursion. The series of air pulses become integrated in surrounding fluid such as air and become audible acoustic wave. Since the diaphragm only has to compress a relatively small volume of air, its efficiency can be higher than that of a conventional loudspeaker and improved radiation effectiveness is obtained particularly in low frequency ranges where conventional loudspeakers, because of low acceleration, generate very low output pressures. The valve is typically a second loudspeaker adopted to operate at very high frequencies. The invention will now be further described, by way of example, with reference to the accompanying drawing which is a schematic side view of a transducer in accordance with the invention. The drawing shows a transducer in the form of a conventional loudspeaker with a cone 10 and a voice coil 12 which is able to vibrate the cone. An end plate 14 covers the end face of the loudspeaker and is attached thereto around the periphery 16 of the cone. The end plate 14 and the cone 10 define between them a chamber 18. The end plate 14 has a central opening 20, and a valve 22 controlled by a control unit 24 is mounted so as to be able to open and close the opening as the valve member moves backwards and forwards. An analogue input power signal is fed to the speech cone through a line 26, and a control signal is fed to the valve controlling unit 24 through a line 28. In operation, the input through line 26 energises the coil 12 which vibrates the cone 10 backwards and forwards. This produces a varying pressure within the chamber 18. Whilst the cone is moving and the pressure is varying, the valve 22 is operating to open and close the opening 20 regularly. Each time the valve opens, air at a pressure characteristic of the instantaneous pressure in the chamber is expelled from the chamber 18. For reproduction of a sound it is of course necessary that the valve 22 be opened and shut at a frequency which is much higher than the frequency of the sound to be reproduced. Typically a frequency of 25 kHz is used as the switching/gating frequency. The advantage of the invention is that the loudspeaker cone is now used merely to cause increase and decrease in the air pressure in the chamber and this varying air pressure is delivered via the valve 22 (itself another loudspeaker type device albeit operating at above audio frequencies) as a series of impulses which when integrated reproduce the original sound. The loudspeaker 10 is preferably contained within a sealed enclosure 24 so as to prevent back radiation from the diaphragm to reduce phase cancellation effects. CLAIMS

1. A transducer having a movable diaphragm means for moving a diaphragm cone in response to an input audio signal, an apertured plate cooperating with the cone to form an enclosed pressure chamber, a valve for opening and closing the aperture in the plate, and means for repetitively opening the said valve at a controlled rate.

2. A transducer as claimed in claim 1, wherein the last mentioned means is adapted to operate the valve at a frequency of the order of 25 kHz.

3. A transducer as claimed in claim 1 or claim 2, wherein the said plate is an end plate attached to the cone at the outside periphery thereof.

4. A transducer as claimed in any of claims 1 to 3, wherein the said diaphragm means and cone are housed in an enclosure sealing to the outer periphery of the cone.

5. A transducer as claimed in any of claims 1 to 4, wherein the said valve is a loudspeaker device adapted to operate above audio frequencies.

6. A transducer substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of transducing an electrical signal of audio frequency into a sound wave, according to which a loudspeaker cone is closed by an apertured plate to define an air chamber therein, the cone is driven by the electrical signal of audio frequency and the aperture in the closure plate is repetitively opened and closed by a valve at a frequency substantially in excess of audio frequencies, thereby to cause the cone to expel a series of air pulses of amplitude dependent on the magnitude of the excursion of the cone.

8. A method of transducing an electrical audio signal substantially as hereinbefore described.