OTO-LARYNGEAL COMMUNICATION SYSTEM

Abstract: Voice transmitting system comprising: a microphone having a high impedance, means to hold the microphone in or adjacent an outer ear of a person so as substantially to enclose air between the microphone and the tympanic membrane of the ear, and a circuit for transmitting a signal produced or modulated by the microphone in response to sound waves, if any, which are transmitted via the persons oto-laryngeal system to the tympanic membrane and propagated in the enclosed air.

Description: "OTO-LARYNGEAL COMMUNICATION SYSTEM" TECHNICAL FIELD OF THE INVENTION This invention relates to a communications system and more particularly to a system for voice transmission. BACKGROUND ART Voice transmitting systems employ a microphone, that is to say a transducer whereby sound waves are caused to generate or modulate an electrical signal. The microphone is connected to the input side of a circuit which transmits the >electrical signal by wire or wireless means to a receiver. A telephone is an example of a voice transmitter in which the voice of a person speaking is detected by a microphone, the microphone signal is amplified and then delivered to a receiver comprising the earphone of a listener. Commonly used radio transceivers provide a voice transmitting system on which the voice of a person speaking is detected by a microphone adapted to modulate the, frequency or amplitude of a radio signal which may be detected by a receiver. There are various circumstances in which the use of a microphone in existant voice transmitting systems is disadvantageous. In a noisy environment the electrical signal is modulated by environmental noise as well as by the voice leading to poor communication between a person speaking and the receiver. A person wearing a respirator or other mask is unable to communicate by microphone unless the microphone is incorporated within the mask adding substantially to the cost of the mask and often making the mask bulkier than need be since the microphone must be spaced from the mouth. In many circumstances a person wishes to be mobile, to have both hands free, and to use a radio transceiver without the need to hold a microphone before his mouth. Sometimes, as during surveillence, it is desirable that voice communication be possible without the presence of a microphone being readily apparent. Although emphasis has been placed on voice transmission, it is clearly desirable that the person speaking also be able to receive and hear voice communications transmitted to him. When a person speaks sound is conveyed via his oto-laryngeal system to his ear. It has been proposed to employ an earphone for the dual purpose of producing sound waves in the ear of a wearer and as a microphone to detect sounds conveyed via the oto-laryngeal system of the wearer. The earphone transducers hitherto employed have a low impedance typically of 400-600 ohms O ?I ' ' at 1kHz. Such earphone transducers, while having the advantage of being able to be worn beneath a mask and of permitting hands free operation have not proved satisfactory, especially when used in noisy environments DISCLOSURE OF THE INVENTION According to one aspect the present invention consists in a voice transmitting system comprising: a microphone having a high impedance as herein defined; earplug means adapted to hold the microphone in or adjacent an outer ear of a person so as substantially to enclose air between the microphone and the tympanic membrane of the ear, and a circuit for transmitting a signal produced or modulated by the microphone in response to sound waves, if any, which are transmitted via the persons oto-laryngeal system to the tympanic membrane and propogated in the enclosed air. By "high impedance" is meant that the microphone has an impedance equivalent to at least 1000 ohms, and preferably greater than 2000 ohms at 1kHz. For preference the microphone is worn by means of an earplug individually cast for the ear of the wearer in the manner of a hearing aid earplug and is a transducer which is also operable as an earphone. It was previously believed that increasing the sensitivity of a microphone plugged to the oto-laryngeal ^TΪΪE O PI system would merely aggrevate problems of extraneous noise. The present invention is based on the surprising discovery that when air is enclosed between the tympanic membrane and a sufficiently high impedance microphone, the effect of external noise and vibration is greatly - reduced, and in preferred embodiments, is halved. Apparently when a low impedance (400-800 ohms) transducer is employed as a microphone a high proportion of the detected audio energy is transmitted via bone structure and is thus subjected to noise vibrations from the general environment. It has been found that when a high impedance microphone is employed in accordance with the present invention, a high proportion of the detected audio energy is substantially transmitted from the tympanic membrane by means of the air column in the auditory canal and is much less influenced by vibrations in the bone which originate externally. DESCRIPTION OF PREFERRED EMBODIMENT By way of example only the invention will now be. described with reference to the accompanying circuit schematic diagram (FIG. 1) . The circuit is an interface circuit for use with a two way radio transceiver (not shown) having connectors for external speaker and microphone. The interface circuit of Fig. 1 comprises a high impedance transducer T, a two stage amplifier and an electronic switch and is powered by a 1.5 V battery. C- In use terminal Al is connected to the audio output of the radio transceiver. When ganged switch SIB is in the "NC" position as shown in Fig. 1 an audio signal from the transceiver connected at the "audio-in" terminal Al is routed to transducer T via capacitor C8 and resistor Rll. Capacitor C8 provides DC blocking and resistor R7 provides overload protection for transducer T which is a type AP2000 earpiece supplied by Crystal Aid Pty. Ltd., Australia, having an impedance of around 2000 ohms at 1kHz and developed for use as a hearing aid. When ganged switch SW1A/SW1B is in the "NO" position, that is to say in the "transmit" mode, power is applied to electronic switch Ql and the two amplifier stages Q2 and Q3 via switch S1A. Transistor Ql is turned on causing the PTT ("PUSH TO TALK") line connected via terminal A3 to the associated transceiver to go low. With switch SIB in the "NO" position the audio signal from transducer T is-applied at the- ase of the first amplifier stage Q2. Transistor Q3 provides further amplification and impedance matching. The audio signal is then attenuated to the required level by variable resistance RV1 and fed to the associated transceiver via terminal A2 "audio out". As mentioned above "Earpiece"- T comprises a high impedance coil having a DC resistance of about 2000 ohms and preferably higher and has a magnet moveable relative to the coil by a diaphram affixed either to the magnet or the coil. The "earpiece" is thus able to function either as a microphone to modulate a signal in response to movement of the diaphram or as an earphone when fed with a modulated signal. For preference the "earpiece" is of a size similar to a hearing aid earpiece and is held in the ear of a wearer by a custom made hollow casting such as is often used to seal a hearing aid earphone to an ear. However . the earpiece may be otherwise adapted by shape to fit in or adjacent the ear so as to enclose air between the transducer and tympanic membrane. Switch SW1 serves to disconnect the audio reception line from the transceiver to the transducer when the transducer is used for voice transmission. Because the apparatus operates from a 1.5 battery it is non-sparking and useable in hazardous environments. Fl is a ferrite bead providing shielding. Ql, Q2 and Q3 are each type BC 549 transistors. - The circuit - parameters shown in Fig. 1 and indeed the circuit itself may be varied in ways which will be apparent to those skilled in the art from the teaching hereof. For preference the interface circuit is adapted to be worn on the belt. As will be apparent to those skilled in the art, ear protectors if desired, may be worn over the earpiece to further reduce extraneous noise. In other embodiments the microphone is built into ear protectors. Q ' -

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A voice transmitting system comprising: a microphone having a high impedance as herein defined; earplug means adapted to hold the microphone in or adjacent an outer ear of a person. so as substantially to enclose air between the microphone and the tympanic membrane of the ear; and a circuit for transmitting a signal produced or modulated by the microphone in response to sound waves, if any, which are transmitted via the persons oto-laryngeal system to the tympanic membrane and propogated in the enclosed air. 2. Apparatus according to claim 1 wherein the microphone has an impedance equivalent to at least 2000 ohms at 1kHz. 3. Apparatus according to claim 1 or claim 2 wherein the earplug includes an earpiece custom fitted to the • wearer. 4. Apparatus according to claim 3 further comprising a circuit whereby the microphone may be connected to drive a radio transceiver in a transmit mode or to receive a signal output by said transceiver in a receive mode. 5. Apparatus according to claim 4 comprising a two stage amplifier circuit and switch means which disconnect the transducer from signal reception during voice transmission. 6. Apparatus substantially as herein described with reference to the drawing.

Inventors: SPIKE ROBERT GRAEME, VANDER HEYDEN PAULUS PETRUS AD, SPIKE, ROBERT, GRAEME, VANDER HEYDEN, PAULUS, PETRUS, ADAMUS
Applicants: HEYDEN SPIKE CO, HEYDEN SPIKE CO. PTY. LIMITED
Application year: 1983
Main classification: H04R1
IPC codes: H04R1, H04R3