Noise reducing receiver device

Abstract: The present invention is concerned with a receiver device for converting electrical signal from a headphone (4), a telephone receiver or the like into acoustic signals and outputting these acoustic signals. More particularly, it relates to a noise reducing receive device in which acoustic signals in the vicinity of an electro-acoustic transducer element (4) are converted by a microphone (6) into electrical signals and negatively fed back to an amplifier circuit (13) which is adapted for amplifying input electrical signals and supplying the amplified signals to the electro-acoustic transducer element (4). With the present noise reducing receiver device, the input electrical signals are amplified by the amplifier circuit (13) and converted by the electro-acoustic transducer element (4) into acoustic signals, which are output as output acoustic signals. A microphone (6) is arranged in the vicinity of the electro-acoustic transducer element and adapted for converting the output acoustic signals and external noises into electrical signals, which are negatively fed back to the amplifier circuit (13) via feedback circuit (7). The output acoustic signals may be heard at the desired noise reduction level by having the transfer function H of the electro-acoustic transducer element (4), the transfer function A of the amplifier circuit (13), the transfer function M of the microphone (6) and the transfer function β of the feedback circuit (7) presettable within the range of |AHMβ|» 1.

Description: SPECIFICATION This invention relates to a so-called active type noise reducing receiver device for converting electrical signals into acoustic signals and outputting these acoustic signals. More particularly, it relates to a noise reducing receiver device in which acoustic signals in the vicinity of an electro-acoustic transducer element are converted by a microphone into electrical signals and negatively fed back for noise reduction to an amplifier circuit which is adapted for amplifying input electrical signals and supplying the amplified signals to the electro-acoustic transducer element. Prior Art As a headphone device or a receiver attached to the listener's ear, a passive type device making use only of an electro-acoustic transducer element is used extensively. However, with such passive type headphone device, not only its acoustic output, but also the noise from the surrounding is input to the listener's ear. For this reason, a so-called active type noise-reducing headphone device has recently been proposed, as disclosed for example in US Patents 4455675 and 4494074, according to which the noise in the vicinity of the headphone unit is reduced by a negative feedback loop, by means of which output acoustic signals in the vicinity of the headphone unit adapted to output acoustic signals converted from electrical signals are converted into electrical signals and fed back with an antiphase relation to the input electrical signals. Referring to Fig. 1, in which the basic construction of the above mentioned active type noise reducing headphone device is illustrated, a microphone unit 6 is provided in the vicinity of a headphone unit 4 attached to a listener's ear 20, and a signal synthesizer 2 is provided at an input side of an amplifier 3 which is adapted for amplifying an input electrical signal S applied from a signal source 10 to a signal input terminal 1 before supplying the signal to the headphone unit 4. The acoustic signals in the vicinity of the headphone unit 4 are converted by the microphone unit 6 into electrical signals which are supplied via feedback circuit 7 to the signal synthesizer 2 where the input electrical signal S and feedback signals output from the feedback circuit 7 are summed together before being supplied to the amplifier 3 by way of performing a negative feedback around the amplifier 3. As in the above described active type noise reducing headphone device, the noise level in the acoustic signal input to the listener's ear 20 may be reduced by summing acoustic output signals by the headphone unit 4 and noise signals from the surrounding in the vicinity of the acoustic meatus of the listener's ear 20 to produce an acoustic signal, converting the acoustic signal by the microphone unit 6 into an electrical signal and negatively feeding back the electrical signal via feedback circuit 7 to the input side of the amplifier 3. With the conventional passive type headphone device, its frequency characteristics are monistically determined by the size or the weight of the diaphragm of the headphone unit, impedance characteristics of the voice coil or the acoustic circuit around the diaphragm of the headphone unit. The frequency characteristics can only be corrected by gradually changing various factors influencing the frequency characteristics for adjustment to desired characteristics. Moreover, distortions proper to the magnetic circuits or due to mechanical nonlinearities, such as edges, occur frequently and, above all, distortions at the low range resonant frequency of not more than f₀ occur predominantly. It is noted that, with the active type noise reducing headphone device, having the function of reducing the external noise, too large a noise reduction level may result in a listener listening to music broadcasting with the reduced external noise failing to hear another person talking to him or failing to hear an emergency broadcasting. On the other hand, two low a noise reduction level proves to be uneffective in factories or at the construction sites with high noise level. The conventional active type noise reducing headphone device suffers from a drawback that, since it has fixed characteristics, it cannot be used at the occasionally desirable noise reduction level. The above mentioned conventional active type noise reducing headphone device has also a drawback that, when mechanical vibrations, such as impact vibrations applied to the housing of the headphone device or frictional vibrations of connection cords, are transmitted to the microphone unit, these vibrational noises are converted by the microphone unit into electrical signals, so that external noises cannot be reduced in a regular manner. In other words, the microphone unit, which is adapted for converting the sound pressure into electrical signals, is also responsive to mechanical vibrations to convert vibrational noises caused by mechanical vibrations into output electrical signals. It is an object of the present invention to provide an active type noise reducing receiver device which may be used at an occasionally desirable noise reduction level. It is another object of the present invention to provide a noise reducing receiver device in which the noise reducing level may be changed without affecting the signal level of the acoustic signal output from the electro-acoustic transducer element. It is further object of the present invention to provide a noise reducing receiver device in which frequency characteristics as well as the noise reduction level may be changed to occasionally desirable values. It is a further object of the present invention to provide a noise reducing receiver device in which the external noise may perpetually be reduced in a regular manner without being influenced by vibrational noises caused by mechanical vibrations. According to the present invention, there is provided a noise reducing receiver device having an electro-acoustic transducer element for converting input electrical signals into acoustic output signals, comprising an amplifier circuit for amplifying input electrical signals supplied to said electro-acoustic transducer elements a microphone unit arranged at a position to which output acoustic signals of said electro-acoustic transducer element are input, said microphone unit being adapted for converting said output acoustic signals into electrical signals, and a feedback circuit for negatively feeding back electrical signals obtained by said microphone unit to an input terminal of said amplifier circuit , characterised in that the product of the transfer functions H, A, M and β of said electro-acoustic transducer element , the amplifier circuit , the microphone unit and the feedback circuit , respectively, is variably settable by the user within the range of |AHMβ|>>1. Fig. 1 is a diagrammatic view showing the basic construction of an active type noise reducing receiver to which the present invention is applied. Figs. 2 to 4 are equivalent block diagrams showing an active reducing receiver to which the present invention is applied. Fig. 5 is a perspective view showing a specific example of a microphone device shown in Fig. 4. Fig. 6 is a connection diagram of the microphone device shown in Fig. 5. By referring to the drawings, certain preferred embodiments of the present invention will be explained in detail. In an embodiment shown in the equivalent block diagram of Fig. 2, the present invention is applied to the above described active type noise reducing headphone device shown in Fig. 1, in which a synthesized output signal from a signal synthesizer 2 is supplied to a headphone unit 4 via a variable gain amplifier 13 having a variable presettable gain A. The acoustic output signal by the headphone unit 4 is summed to a noise signal N from the environment at an equivalent signal adder 15 in an acoustic space in the vicinity of the headphone unit 4. The synthesized output from the signal adder 15 is supplied via a feedback circuit 7 to the signal synthesizer or adder 2 as the acoustic signal in the vicinity of the headphone unit 4 after conversion into electrical signals by the microphone unit 6. With the above described headphone device, the transfer function, that is the gain A, of the aforementioned variable gain amplifier 13, may be preset within the range of AHMβ >> 1, where H, M, β and A denote transfer functions, expressed in the frequency domain, of the headphone unit 4, microphone unit 6, feedback circuit 7 and the variable gain amplifier 13, respectively. With the above described headphone device, the acoustic signal having a sound pressure level P P = AH 1 + AHMβ S + 1 1 + AHMβ · N is produced at a signal output terminal 19, placed at an entrance to the acoustic meatus of the listener's ear, to which the headphone device is attached, as a synthesized output synthesized by the signal adder 15. In the above formula, S denotes the signal level of an input electrical signal supplied to the signal input terminal 1 and N the signal level of an external noise signal applied to a signal input terminal 18. With the above acoustic signal of the sound pressure level P, obtained at signal output terminal 19, the signal level S of the input electrical signal remains constant, with 1/Mβ being at a constant level, while the signal level N of the external noise is reduced to 1/AHMβ . Thus the noise reduction level or the noise signal level N is a function of the gain A of the variable gain amplifier circuit 13 which is variably set within the range of |AHMβ| > 1. That is, with the headphone device of the present illustrative embodiment, an acoustic signal may be produced at signal output terminal 19, in which, by variably setting the gain A of the variable gain amplifier circuit 13 within the range of |AHMβ| >> 1, the signal level S of the input electrical signal remains constant, and only the noise level is reduced as a function of the gain A of the variable gain amplifier circuit 13. In an embodiment shown by an equivalent block diagram shown in Fig. 3, the present invention is applied to the active type noise reducing headphone device, described in connection with Fig. 1, according to which electrical signals converted from acoustic signals in the vicinity of the headphone unit 4 by the microphone unit 6 are supplied via a feedback circuit 17 having a variable presettable transfer function β to a signal synthesizer 2 provided at an input side of an amplifier 3 which is adapted for amplifying input electrical signals supplied to a headphone unit 4. The acoustic output signal by the headphone unit 4 is added to by a noise signal N from the environment at an equivalent signal adder 15 in an acoustic space in the vicinity of the headphone unit 4. The synthesized output from the signal adder 15 is supplied via a feedback circuit 17 to the signal adder 2 as the acoustic signal in the vicinity of the headphone 15 unit 4 as the acoustic signal in the vicinity of the headphone unit 4, after conversion into electrical signals by the microphone unit 6. As the feedback circuit 17 in the above headphone device, such a circuit in which phase or frequency characteristics may be variably preset is employed. The transfer function β of the feedback circuit 17 in the headphone device may be variably preset within the range of |AHMβ|>>1, where A, H and M denote transfer functions, expressed in the frequency domain, of the amplifier 3, headphone unit 4 and the microphone unit 6, respectively. With the above described headphone device, an acoustic signal having the sound pressure level P, expressed by the formula (1), may similarly be produced at a signal output terminal 19 placed at the entrance to the acoustic meatus of the listener's ear wearing this headphone device. With the acoustic signal of the sound pressure level P, obtained at signal output terminal 19, conversion characteristics equal to 1/Mβ are afforded to the input electrical signal S, as a function of the transfer function of the feedback circuit 17, which is variably set within the range of |AHMβ| >> 1 to compensate for frequency characteristics or distortions, while the signal level N of the external noise is reduced to 1/AHMβ . That is, with the headphone device of the present illustrative embodiment, an acoustic signal may be produced at signal output terminal 19, in which, by variably setting the transfer function β of the feedback circuit 17 so as to be within the range of |AHMβ| >> 1 as a function of the state of the external noises, conversion characteristics equal to 1/Mβ are afforded to the input electrical signals to compensate for frequency characteristics or distortions, while the signal level is reduced. In an embodiment shown by an equivalent circuit diagram of Fig. 4, the present invention is applied to the above described active noise-reducing headphone device shown in Fig. 1. In lieu of the microphone device 6 adapted to convert acoustic signals in the vicinity of the microphone device 4 into electrical signals, a microphone device 16 including a pair of microphone units 16A, 16B having their diaphragms 16a, 16b opposing to each other with a short distance from each other, is employed. The electrical signals produced at the microphone units 16A, 16B are summed together at a signal adder 16C so as to be output via feedback circuit 7 to a signal adder 2 provided at the input side of an amplifier 3 which is adapted to amplify input electrical signals supplied to the headphone unit 4. The acoustic output signal by the headphone unit 4 is added to by a noise signal N from the environment at an equivalent signal adder 15 in an acoustic space in the vicinity of the headphone unit 4. The synthesized output from the signal adder 15 is supplied via a feedback circuit 7 to the signal adder 2 as the acoustic signal in the vicinity of the headphone unit 4 as the acoustic signal in the vicinity of the headphone unit 4 after conversion into electrical signals by the microphone device 16. Referring to Fig. 5, in which a specific embodiment of the microphone device 16 is illustrated, the microphone device 16 is constituted by, for example, a pair of non-directional capacitor microphone units 16A, 16B having their characteristics matched to each other and interconnected by a highly stiff connecting element 23, with the diaphragms 16a, 16b lying closely adjacent and facing to each other. The connecting element 23 has a plurality of through-holes 24 for transmitting acoustic signals to the diaphragms 16a, 16b of the microphone units 16A, 16B. As shown in Fig. 6, the microphone device 16 is provided with output terminals 20A, 20B to which the positive and the negative signal output terminals of the microphone units 16A, 16B are connected, respectively, as shown. With the above described microphone device 16, the diaphragms 16a, 16b of the microphone units 16A, 16B are thrust and deformed as a function of the sound pressure P of acoustic signals transmitted by way of the through-holes 24 formed in the connecting element 23 to produce corresponding electrical signals which are summed and synthesized in phase to each other so as to be output at output terminals 20A, 20B. Since the microphone units 16A, 16B of the microphone device 16 are interconnected by the connecting element 23, noise vibration components, such as impact vibrations applied to the microphone housing or frictional vibrations applied to connection cords, are converted by the microphone units 16A, 16B into anti-phase electrical signals, which are summed to and thereby cancel each other, so that only the electrical signals corresponding to the sound pressure P of the acoustic signal are produced at the output terminals 20A, 20B. Hence, with the above described headphone device, only the acoustic signals in the vicinity of the headphone unit 4 are converted by the microphone device 16 into corresponding electrical signals, which are supplied to the signal adder 2 by way of the feedback circuit 7. It is noted that, with the above described headphone device, the transfer functions A, H, M and β of the amplifier 3, headphone unit 4, microphone unit 16 and the feedback circuit 7 are set in a range which will satisfy the condition |AHMβ| >> 1 when expressed in the frequency domain. With the above described headphone device, the acoustic signal having the sound pressure level P as shown by the formula (1), that is the acoustic signal in which conversion characteristics corresponding to 1/Mβ are afforded to the input electrical signal S to compensate for frequency characteristics or distortions and in which the signal level N of the external noise is reduced to 1/AHMβ, is produced at signal output terminal 19 resting at an entrance to the acoustic meatus of the headphone wearer. With the above described embodiment, the acoustic signals in the vicinity of the headphone unit are converted into in phase electrical signals by a pair of microphone units having their diaphragms disposed closely adjacent and opposite to each other, while vibrational noises caused by mechanical noises are converted into anti-phase electrical signals, which are summed together and thereby cancelled, so that electrical signals corresponding only to acoustic signals in the vicinity of the headphone unit are produced. The sum of the anti-phase signals is supplied via feedback circuit to the amplifier which amplifies input electrical signals supplied to the headphone unit. Thus the external noises may perpetually be reduced in a regular manner without being affected by vibrational noises caused by mechanical vibrations. In the above described embodiments, the present invention is applied to the headphone device. However, when the present invention is applied to a telephone receiver, the signal level of an external noise in the vicinity of an ear piece provided with a speaker unit may also be reduced to 1/AHMβ , if the acoustic signals containing external noises in the vicinity of the ear piece are converted by the microphone unit into electrical signals, these electrical signals are negatively fed back via feedback circuit and the transfer functions of the amplifier circuit, speaker unit, microphone unit and the feedback circuit are set within the range of |AHMβ| >> 1. Thus a telephone receiver may be provided in which, even under an environment of high surrounding noise level, the external noise input to the user's ear 20 may be reduced to elevate the S/N ratio of the acoustic output of the speaker unit to enable the voice of the calling party to be heard clearly. For adjusting the volume of the acoustic signal or output produced at the signal output terminal 19, a sound volume adjustment unit may be provided at the sound source side, that is, upstream of the signal input terminal 1.

Claims: A noise reducing receiver device having an electro-acoustic transducer element (4) for converting input electrical signals into acoustic output signals, comprising an amplifier circuit (3) for amplifying input electrical signals supplied to said electro-acoustic transducer elements (4) a microphone unit (6) arranged at a position to which output acoustic signals of said electro-acoustic transducer element (4) are input, said microphone unit (6) being adapted for converting said output acoustic signals into electrical signals, and a feedback circuit (7) for negatively feeding back electrical signals obtained by said microphone unit (6) to an input terminal of said amplifier circuit (3), characterised in that the product of the transfer functions H, A, M and β of said electro-acoustic transducer element (4), the amplifier circuit (3), the microphone unit (6) and the feedback circuit (7), respectively, is variably settable by the user within the range of |AHMβ|>>1. The noise reducing receiver device according to claim 1 wherein said amplifier circuit (13) is a variable gain amplifier circuit and the gain A of said amplifier circuit (13) is variably settable within the range of |AHMβ|>>1. The noise reducing receiver device according to claim 1 wherein the transfer function of negative feedback of said feedback circuit (17) to the input terminal of said amplifier (3,13) circuit is variably settable and said transfer function β is variably settable within the range of |AHMβ|>>1. The noise reducing receiver device according to claim 1 wherein said electro-acoustic transducer element (4) is a headphone unit. The noise reducing receiver device according to claim 1 wherein said electro-acoustic transducer element (4) is a speaker unit provided in a handset of a telephone. A noise reducing receiver device according to any preceding claim wherein said microphone unit (16) consists of a pair of microphone units (16A,16B) having their diaphragms (16a,16b) disposed in proximity and in opposition to each other, said microphone units (16A,16B) being adapted for converting said output acoustic signals into electrical signals and said feedback circuit feeding back a sum signal of electrical signals obtained by said microphone units (16A,16B).

Inventors: KIMURA AKTRA, OHKUBO MASASHI, SASAKI TOORU, KIMURA, AKTRA, OHKUBO, MASASHI, SASAKI, TOORU
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: G10K11
IPC codes: G10K11