Improved headphone apparatus

Abstract: A headphone apparatus includes a speaker unit (23) accommodated in an accommodating member of an open-air type, a microphone (28) disposed at a front side of the speaker unit, a filter (5) for lowering a level of a high frequency component of a signal picked up by the microphone, and a negative feedback loop for feeding back an output of the filter (5) to the speaker unit (23) to thereby lower the level of a low frequency component of circumference noise output from the speaker unit. This headphone apparatus further includes an equalizer (2) having a frequency characteristic substantially in opposite to that of the filter, wherein an input audio signal is added to the negative feedback loop through the equalizer (2) and then output from the speaker unit (23).

Description: The present invention generally relates to headphone apparatus and, more particularly, is directed to a headphone apparatus for reducing the noise from the outside. In recent years, a headphone apparatus has been developed which has a function of electrically shielding the noise from the outside. In such a headphone apparatus, a microphone is provided at the rear side of each of miniature speaker units held over the right and left ears, for example, and an audio signal picked up by the microphone is inverted in its phase and fed back to the input side of the corresponding speaker unit to thereby reproduce the audio signal by the speaker unit. According to the thus constituted headphone apparatus, the audio signal thus fed back in opposite phase and reproduced by the speaker unit serves so as to cancel sound transmitted to the ears from the outside, so that a person is prevented from hearing noise outside (circumference noise). In the thus constituted headphone apparatus for shielding the circumference noise, however, since the microphone for picking up the signal to be fed back is provided at the rear side of the speaker unit, the microphone may pick up noise other than sound transmitted to the ear, for example, sound of wind caused by movement of an object such as a hand near the ear. In this case, a phase of the feedback signal does not become completely in opposite to that of the sound transmitted to the ear from the outside due to the above-mentioned noise picked up by the microphone, so that undesirable sound is reproduced from the speaker unit and transmitted to the ear disadvantageously. In order to obviate this problem, there has been developed a closed type headphone apparatus called a pressure type headphone apparatus in which a microphone for picking up the feedback signal is provided at the front side of the speaker unit. In the thus constituted closed type headphone apparatus, a space between the ear and the speaker unit is shielded from the outside by means of an ear pad with a good sound insulation efficiency, and the microphone for picking up the feedback signal is disposed within the shielded space. Therefore, since the microphone does not pick up the undesirable external noise, only the circumference noise transmitted to the ear from the outside is fed back to the speaker unit and so the external circumference noise can be shielded efficiently. Such a system is described in EP-A-0 208 389 which is in accordance with the pre-characterizing portion of claim 1. However, when the thus constituted closed type headphone apparatus is configured as a headphone apparatus for shielding the external circumference noise, there is then the problem that the headphone apparatus can not be used for a long period of time. That is, since the closed type headphone apparatus is used in a state that the space between the ear and the speaker unit is shielded from the outside by means of the ear pad, the ear pad is urged or pressed to the ear side with a relatively large force. As a result, the feeling of the attachment of the headphone apparatus is not good and so it is difficult to continuously use the headphone apparatus for a long period of time. Further, when the closed type headphone apparatus is constructed as the headphone apparatus for shielding the external circumference noise to thereby completely shield the circumference noise, the speech spoken by a person around the headphone apparatus can not be listened at all, which can be dangerous. If the headphone apparatus for shielding the circumference noise is used in an airplane and the pilot cannot listen to an engine sound during the flight, the use of the closed type headphone apparatus is not preferable since it is difficult to continuously use the closed type headphone apparatus for a long period of tine such as a flight of several hours due to the unfavorable feeling thereof. Further, since sound such as an alarm sound broadcasted in the airplane is shielded by the use of the headphone apparatus for shielding the circumference noise, upon occurrence of an energency, a measure or proceeding against the energency may be delayed due to the usage of the headphone apparatus, which is an important problem in safety. Therefore, it is an object of the present invention to provide an improved headphone apparatus for reducing the circumference noise in which the aforementioned shortcomings and disadvantages encountered with the prior art can be eliminated. More specifically, it is an object of the present invention to provide a headphone apparatus for reducing circumference noise which can not only provide feeling of attachment sufficient for a person to use for a long period of time but transmit external sound necessary at a minimum to the ears of a person using the headphone apparatus. According to the present invention there is provided a headphone apparatus comprising: a speaker unit accommodated in an accommodating member; a microphone disposed at a front side of said speaker unit for picking-up noise from the exterior; means for subtracting the output signal of the microphone from an input audio signal for said speaker unit in order to reduce noise from the exterior. characterised in that said accommodating member is of the open-air type; and in that a filter is provided for selectively lowering the level of the high frequency component of the output signal of said microphone whereby the level of a low frequency component of the exterior noise is reduced by the output signal of said speaker unit. The apparatus may further comprise an equalizer having a frequency property substantially opposite to that of said filter, and wherein the input audio signal is passed through said equalizer, then has subtracted from it the output signal of the microphone, the result being passed through said filter and then output from said speaker unit. Alternatively, the output of the microphone may be filtered before being subtracted from the input signal. The headphone apparatus preferably further includes a through circuit for supplying the input audio signal directly to the speaker unit when a voltage of a power supply for driving a driving circuit of the speaker unit decreases below a predetermined value. With the invention since the headphone apparatus is of the open-air type and the noise reduction signal has its high frequency components lowered by the filter, not only good feeling of attachment of the headphone apparatus is obtained and a person can use the headphone apparatus for a long period of time without being tired but sound of a relatively high frequency component such as speech is not cancelled by the noise reduction signal. As a consequence, a person using the headphone apparatus can listen to required sounds. The use of the equalizer having the substantially opposite frequency characteristic to that of the filter gives a substantially flat frequency characteristic, so not only sound such as music or the like is reproduced satisfactorily but circumference noise other than sound of relatively high frequency band such as speech is cancelled by the noise reduction signal, so that a person can satisfactorily listen to the input audio signal such as music without being disturbed by circumference noise. The use of the through circuit for directly supplying the input audio signal to the speaker unit when a voltage of the power supply for driving the driving circuit of the speaker unit decreases below the predetermined value allows ordinary use of the apparatus even when the cancelling operation is not possible due to the decrease in power supply voltage. The invention will be further described by way of example in the following detailed description of an illustrative embodiment thereof when read in conjunction with the accompanying drawings, in which like reference numerals are used to identify the same or similar parts in the several views, and in which:- FIG. 1 shows in block form an arrangement for cancelling circumference noise mounted in a headphone apparatus according to an embodiment of the present invention; FIG. 2 is a schematic diagram generally illustrating a headphone apparatus according to the embodiment; FIG. 3 is a schematic perspective view illustrating the headphone apparatus according to the embodiment; FIG. 4 shows a schematic sectional view of the headphone apparatus according to the embodiment taken along a line IV-IV of FIG. 3; and FIGS. 5A to 5D are schematic diagrams illustrating frequency characteristics at various portions of the circuit arrangement of FIG. 1, respectively. A headphone apparatus according to an embodiment will now be described with reference to FIG. 1 to FIGS. 5A through 5D, in which case, the present invention is applied to a headphone apparatus used within a vehicle such as an airplane or the like. FIG. 2 generally shows an arrangement of the headphone apparatus of the embodiment of the present invention. Referring to FIG. 2, the headphone apparatus 10 is constituted by attaching right and left speaker devices 20R and 20L to a headband 11. Each of the speaker devices 20R and 20L is arranged to constitute a so-called open-air type headphone. Signal lines 12L and 12R are respectively led out from the speaker devices 20L and 20R and connected to a battery case 40, so that electric power for driving the speaker devices is supplied from a battery contained in the battery case 40 to the speaker devices 20L and 20R. The battery case 40 is provided with a power supply switch 41 and a pilot lamp 42. A plug 44 is attached to a top of a signal line 43 led out from the battery case 40. The plug 44 is connected to a stereo audio signal output jack mounted at each passenger seat. An audio signal output from the stereo audio signal output terminal is supplied to the left and right speaker devices 20L and 20R through the signal line 43 and the signal lines 12L and 12R, respectively, to thereby reproduce the audio signal from speaker units contained in the speaker devices 20L and 20R. Each of the signal lines 12L and 12R contains an audio signal transmission line and a power supply line. Each of the speaker devices 20L and 20R is constituted as shown in FIGS. 3 and 4. Referring to FIG. 4, a pair of cases 21 and 22 formed by synthetic resin are bonded to form a housing. A miniature speaker unit 23 is disposed almost at the center portion of the housing. A diaphragm 24 attached to the speaker unit 23 is driven or vibrated by a magnetic circuit (not shown) such as a voice coil or the like to thereby generate a sound wave. The sound wave thus generated is transmitted to a front side of the speaker device through through-holes 26 bored through a protector 25 provided at the front side of the diaphragm. As shown in FIG. 3, a highly sealed or airtight elastic material 27 of ring-like configuration is attached at the periphery portion of the front face of the protector 25. The elastic material 27 has a function of adjusting frequency characteristics of the headphone device. A miniature microphone 28 is disposed in a notch 27a provided at a lower portion of the elastic material 27. An omni- or non-directional microphone is used as the microphone 28, for example. A cushion 29a and an ear pad 29b are attached to the front side of each of the speaker devices 20L and 20R so as to cover the microphone 28 and the elastic material 27. Each of the cushion 29a and the ear pad 29b is made of elastic material with air permeability and having relatively low density such as sponge or the like so as not to prevent the transmission of sound wave generated from the speaker unit 23. Owing to the cushion 29a, not only howling or acoustic feedback is prevented but feeling of the headphone device when held over the ear can be improved. Since the cushion 29a and the ear pad 29b each having good air permeability are provided so as to cover the front side of each of the speaker devices 20L and 20R, the headphone apparatus 10 is constituted as an open-air type (that is, velocity type) headphone apparatus in which a space between the ear and the speaker unit 23 is not sealed. A circuit board 31, on which a circuit arrangement for cancelling the circumference noise is mounted, is mounted at the rear side of the speaker unit 23 by screws 30. A circuit arrangement of the headphone apparatus mounted on the circuit board 31 will be described with reference to FIG. 1. Referring to FIG. 1, an audio signal of a right or left channel transmitted from an external audio device through the signal line 12R or 12L is supplied to an audio signal input terminal 1. The audio signal applied to the input terminal 1 is supplied to an adder 3 through an equalizer 2. The equalizer 2 is arranged so as to boost a frequency component of about 1 kHz or more of an input signal as shown in FIG. 5A so that its frequency characteristic is substantially in opposite to that of a filter 5 which will be described later on. An audio signal picked up by the microphone 28 is also supplied to the adder 3 in which a sum of the audio signal from the microphone 28 and the output of the equalizer 2 are added to each other. In this case, a polarity of the audio signal from the microphone 28 is made in opposite to that of the audio signal from the equalizer 2 upon addition. Then, the added signal from the adder 3 is applied to the filter 5 through an input amplifier 4. The filter 5 is arranged so as to lower a level of a frequency component of about 1 kHz or more of an input signal as shown in FIG. 5B so that its frequency characteristic is substantially in opposite to that of the equalizer 2. An output of the filter 5 is supplied to the speaker unit 23 through an output amplifier 6, so that the diaphragm 24 of the speaker unit 23 is vibrated in accordance with the audio signal from the output amplifier 6 to thereby output a sound. The circuits such as the input amplifier 4, the output amplifier 6 or the like requiring a power supply to be operated are supplied with electric power through the signal lines 12R and 12L from the battery case 40. The audio signal applied to the input terminal 1 is also supplied to the speaker unit 23 through a through circuit 7. The through circuit 7 is constituted by resistors R1, R2 and R3 connected in series in which the audio signal from the input terminal 1 is applied to the resistor R1 side and an audio signal output from the resistor R3 side is applied to the speaker unit 23. A connection point between the resistors R1 and R2 is grounded through a switch SW1 and a connection point between the resistors R2 and R3 is grounded through a switch SW2. The switches SW1 and SW2 are controlled in accordance with a voltage of the power supply supplied from the battery case 40 through the signal line 12L or 12R. That is, each of the speaker devices 20L and 20R has a detection circuit (not shown) for detecting the voltage of the power supply (battery) supplied from the battery case 40. Each of the switches SW1 and SW2 is placed in an opened or disconnected state when the detection circuit detects that the voltage of the power supply decreases to a level difficult to operate the respective circuits. Each of the switches SW1 and SW2 is constituted by a semiconductor switch and constituted so as to be maintained in the disconnected state when a voltage sufficient for operating the switches is not obtained. Since the through circuit 7 is constituted as mentioned above, when each of the switches SW1 and SW2 is in a closed or connected state, the through circuit 7 operates so as to electrically disconnect the path between the input terminal 1 and the speaker unit 23, so that the audio signal applied to the input terminal 1 is supplied to the speaker unit 23 through a path from the equalizer 2 to the output amplifier 6. In contrast, when each of the switches SW1 and SW2 is in the disconnected state, the speaker unit 23 is directly connected to the input terminal 1 through the resistors R1, R2 and R3. In this embodiment, the circuit arrangement of FIG. 1 is incorporated in each of the right and left speaker devices 20R and 20L, so that two sets of the circuit arrangement of FIG. 1 are provided, one for the right and one for the left speaker device of one headphone apparatus. Operation of the headphone apparatus according to the embodiment will be described. First, operation will be described in a case where the headphone apparatus is supplied with a voltage sufficient for operating it from the power supply (battery) of the battery case 40, that is, a case where a voltage of the power supply for driving the driving circuit of the speaker unit is not below a predetermined value. In this case, the audio signal from the input terminal 1 is prevented from passing through the through circuit 7 since both the switches SW1 and SW2 are closed. The audio signal from the input terminal 1 is added to the audio signal picked up by the microphone 28 at the adder 3, and the added audio signal from the adder 3 is output from the speaker unit 23. Since the microphone 28 is disposed at a front side of the speaker unit 23, the circumference noise transmitted to ears of a person using the headphone apparatus 10 is cancelled by a signal output from the speaker unit 23 having opposite phase to that of the circumference noise. Therefore, the circumference noise is not transmitted to the ears of the person using the headphone apparatus 10. In this regard, since the signal fed back from the microphone 28 to the speaker unit 23 is passed through the filter 5 for lowering a level of the higher frequency component of about 1 kHz or more, the fed-back signal has only a relatively lower frequency component lower than 1 kHz, so that the circumference noise of only a frequency component lower than 1 kHz is cancelled by the output signal from the speaker unit 23. Thus, circumference sound of a relatively high frequency such as speech, alarm sound or the like can be heared by a person even if the person uses the headphone apparatus 10. For example, even if the person uses the headphone apparatus 10, since the person can immediately judge a circumference state, the safety of the person can be ensured. Further, rasping circumference noise of a relatively low frequency such as engine sound of an airplane can be effectively removed by the circuit arrangement of the embodiment. The audio signal applied to the input terminal 1 is boosted in its high frequency component by the equalizer 2 and then lowered in its high frequency component by the filter 5 having the frequency characteristic substantially in opposite to that of the equalizer 2, so that the entire frequency characteristic of the circuit arrangement from the equalizer 2 to the speaker unit 23 of FIG. 1 is substantially flat. That is, when the frequency characteristics of the equalizer 2, the filter 5 and the speaker unit 23 are set as shown in FIGS. 5A, 5B and 5C, respectively, the entire frequency characteristic of the circuit arrangement of FIG. 1 will be substantially flat over an entire audio reproduction frequency band as shown by a curve a in FIG. 5D. In contrast, only the signal fed back from the microphone 28 to the speaker unit 23 is lowered in its high frequency component of almost 1 kHz or more as shown by a dotted line b in FIG. 5D. Accordingly, since an audio signal such as music or the like applied to the input terminal 1 is reproduced in a state where the circumference noise of a lower frequency component is eliminated, a person can listen an audio signal such as music or the like with the influence of circumference noise being eliminated even if the person uses the headphone apparatus in a vehicle with a large noise level such as an airplane. Consequently, the person can satisfactorily listen an audio signal such as music and so forth even if a sound volume of a reproduced signal is made relatively small. Thus, bad influence to the auditory sense can be minimized even if the person uses the headphone apparatus for a long period of time with a large sound volume. Since the headphone apparatus 10 according to the embodiment is constituted as an open-air type, a pressure (side pressure) applied around the ears of a person using the headphone apparatus 10 is relatively small, so that feeling of attachment of the headphone apparatus 10 is good and a person using the headphone apparatus 10 will not be tired even if it is attached for a long period of time. In this case, since the peripheral portion of the microphone 28 for obtaining the signal to be fed back is covered by the highly sealed or airtight elastic material 27, the signal to be fed back can be picked up by the microphone 28 with good efficiency. As a result, the headphone apparatus of the embodiment can attain the efficiency substantially same as a headphone apparatus for shielding circumference noise which is constituted by a closed type headphone apparatus. The highly sealed or airtight elastic material 27 may be made of a hard material such as synthetic resin or the like, but in this case feeling of the attachment of the headphone apparatus will be degraded slightly. When a voltage supplied to the headphone apparatus 10 becomes an insufficient value for operating the apparatus due to the consumption of the power supply (battery) in the battery case 40, that is, when a voltage of the power supply for driving the driving circuit of the speaker unit decreases below the predetermined value, the switches SW1 and SW2 are opened. As a consequence, the circumference noise is not eliminated, but the audio signal applied to the input terminal 1 is supplied to the speaker unit 23 through the through circuit 7, so that the audio signal can be reproduced in the same manner as in an ordinary headphone apparatus. Accordingly, even if the power supply is consumed, the audio signal applied to the input terminal 1 through the plug 44 (FIG. 2) from the external audio device can be output from the speaker unit 23, and so a person can surely listen sound such as an announcement or the like in a vehicle, for example. While, in the above-described embodiment, the signal to be fed back from the microphone 28 is added to the audio signal from the input terminal 1 at the preceding stage of the filter 5, the present invention may be modified in a manner that only the signal to be fed back from the microphone 28 is input to the filter 5 and the audio signal from the input terminal 1 is added to the output signal of the filter 5 at the rear stage thereof. In this case, however, the frequency characteristic of the equalizer 2 is required to be changed slightly. Further, although, in the foregoing embodiment, the phase of the signal fed back is inverted upon the adding operation of the adder 3, the phase inversion operation may be performed by another circuit. Furthermore, although, in the foregoing embodiment, the filter 5 is arranged so as to lower a level of the frequency component of about 1 kHz or more of the input signal, the filter 5 may be arranged so as to lower a level of the frequency component of another frequency band, for example, 2 kHz or more. Further, while, in the aforementioned embodiment, the headphone apparatus 10 is supplied with electric power from the battery case 40 connected between the headphone apparatus 10 and the plug 44, a battery may be accommodated within the headphone apparatus or electric power may be supplied from the plug 44 side. In the latter case, another transmission lines for supplying electric power may be provided independently of the signal lines for the audio signal or electric power may be transmitted through the signal lines by superimposing it on the audio signal. Furthermore, the headphone apparatus may be miniaturized by incorporating the circuits such as the filter, the equalizer or the like in the battery case or the external audio device. Furthermore, while, in the aforementioned embodiment, the headphone apparatus is constituted so as to be used in a vehicle such as an airplane or the like, the headphone apparatus is not limited thereto and may be used in various states. As set out above, according to the invention, since the headphone apparatus is constituted as an open-air type and further the signal fed back to the speaker unit is lowered in its level of a high frequency component by the filter, not only good feeling of attachment of the headphone apparatus is obtained and a person can use the headphone apparatus for a long period of time without being tired but sound of a relatively high frequency component such as speach or the like is not cancelled by the feedback signal. As a consequence, a person using the headphone apparatus can listen sound required at a minimum to thereby ensure the safety of the person. Furthermore, according to the invention, the headphone apparatus is constituted as an open-air type, and the circuit arrangement of the headphone apparatus is configured in a manner that the filter is constituted to lower the input level of a high frequency component and the input audio signal is added, through the equalizer having the substantially opposite frequency characteristic to that of the filter, to the signal to be fed back and then output from the speaker unit. As a result, the input audio signal is output from the speaker unit with the frequency characteristic thereof being kept substantially flat, while circumference noise other than sound of relatively high frequency band such as speech or the like is cancelled by the feedback signal, so that a person can satisfactorily listen to the input audio signal such as music or the like without being disturbed by circumference noise. In this respect, the present invention provides the through circuit for directly supplying the input audio signal to the speaker unit when a voltage of the power supply for driving the driving circuit of the speaker unit decreases below a predetermined value. Therefore, when the cancelling operation of the circumference noise by the headphone apparatus does not operate due to the decrease of the output voltage of the power supply, the headphone apparatus according to the present invention can be used as an ordinary headphone apparatus for reproducing the input audio signal, so that the input audio signal can be continuously reproduced without being interrupted. Having described the preferred embodiment of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment and that various changes and modifications thereof could be effected by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims: A headphone apparatus (10) comprising: a speaker unit (23) accommodated in an accommodating member (11, 21, 22); a microphone (28) disposed at a front side of said speaker unit (23) for picking-up noise from the exterior; means (3) for subtracting the output signal of the microphone (28), from an input audio signal for said speaker unit (23) in order to reduce noise from the exterior; characterised in that said accommodating member (11, 21, 22) is of the open-air type; and in that a filter (5) is provided for selectively lowering the level of the high frequency component of the output signal of said microphone (28) whereby the level of a low frequency component of the exterior noise is reduced by the output signal of said speaker unit (23). A headphone apparatus (10) according to claim 1, further comprising: an equalizer (2) having a frequency property substantially opposite to that of said filter (5); and wherein the input audio signal is passed through said equalizer (2), then has subtracted from it the output signal of the microphone (28), the result being passed through said filter (5) and then output from said speaker unit (23). A headphone apparatus (10) according to claim 1, wherein the output of said microphone (28) is supplied to the filter (5) before being subtracted from the input audio signal. A headphone apparatus (10) according to any one of the preceding claims, further comprising a bypass circuit (7) for supplying the input audio signal directly to said speaker unit (23) when a voltage of a power supply for driving a driving circuit of said speaker unit (23) decreases below a predetermined value.

Inventors: ABE KENSAKU, KOBAYASHI NOBUO, NISHIMOTO HIROFUMI, SATO EIJI, ABE, KENSAKU, KOBAYASHI, NOBUO, NISHIMOTO, HIROFUMI, SATO, EIJI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: H04R3
IPC codes: G10K11, H04R1, H04R3