Electroacoustic transducer

Abstract

[Problem] A technical problem of the present disclosure is to suppress the occurrence of howling in advance, and to enable reproduced sound to be heard as natural sound. [Solution] The present disclosure is any one of electroacoustic transducers including headphones and earphones worn on the head, and comprises: a microphone 2; a speaker unit 3 that acoustically reproduces sound collected by the microphone 2; a signal generation unit 11 for converting the sound collected by the microphone into a signal having predetermined characteristics; an amplitude detector 15 that detects an amplitude of the sound collected by the microphone and a change in the amplitude; and an adder 16 that generates a drive signal for driving the speaker unit. The amplitude detector 15 has a detection function of detecting a characteristic change in a surrounding environment and a signal processing system by detecting that an amplitude in a high-frequency band exceeding an audible band of the sound has exceeded a predetermined amplitude.

Description

Electroacoustic transducer

[0001] The present disclosure relates to an electroacoustic transducer having a detection function for detecting changes in the surrounding environment and characteristics of a signal processing system.

[0002] Conventionally, an electroacoustic transducer having an audio processing system that outputs the audio collected by a microphone from a speaker unit has been used. As this type of electroacoustic transducer, headphones and earphones that are used by mounting a speaker unit on the head or auricle are widely used.

[0003] Electroacoustic transducers including these headphones and earphones are equipped with a noise cancellation mechanism (ANC) that actively reduces the noise in the surrounding environment and enables high-quality sound listening by performing predetermined signal processing on the audio collected by the microphone and outputting the audio signal subjected to this signal processing from the speaker unit. In an electroacoustic transducer, for example, headphones, the sound wave output from the speaker unit is transmitted to the inside and outside of the housing that supports the speaker unit. A part of the sound wave output from the speaker unit is collected by the microphone and forms a closed loop that is output again from the speaker unit and fed back. When such a closed loop of sound waves is formed, a state of being greatly amplified at some frequencies may be repeated, inducing howling.

[0004] Headphones equipped with ANC can be provided with means for detecting the presence or absence of howling and adjusting the gain and phase of the audio signal when the occurrence of howling is detected to suppress the occurrence of howling. The means for suppressing the occurrence of howling includes signal level detection means for detecting the signal level of the audio signal in the entire band collected by the microphone and output from the speaker unit. This howling suppression means extracts signals in a specific band having a predetermined bandwidth that is considered likely to generate howling from the signal level of the audio signal detected by the signal level detection means.

[0005] The howling suppression means sets a threshold for detecting whether or not howling occurs based on the signal level of the full-band signal detected by the signal level detection means. This howling suppression means includes an extraction means for extracting signals of a predetermined bandwidth for each of one or more predetermined center frequencies. The howling suppression means includes a howling detection means that determines whether or not the waveform of the signal level of a specific band of the predetermined bandwidth extracted by the extraction means is a periodic waveform having an amplitude exceeding the threshold set by the signal level detection means, and detects whether or not howling is occurring. When the howling detection means detects the occurrence of howling, the howling suppression technology uses a howling occurrence adjustment means to adjust one or both of the gain and phase of the audio signal forming the closed loop to suppress the occurrence of howling.

[0006] Japanese Patent Publication No. 2010-016429

[0007] As described above, headphones equipped with ANC (Active Noise Cancellation) extract signals from a predetermined audible frequency range that are considered highly likely to cause feedback from the full-band audio signal collected by the microphone and output from the speaker unit. When it is detected that the extracted audible frequency range signal exceeds a predetermined threshold, a limiter operation is performed to actively reduce the gain of the signal in that frequency range, thereby suppressing the occurrence of feedback.

[0008] Conventional limiter methods for suppressing feedback involve repeatedly increasing the gain at a specific frequency before feedback occurs, and then decreasing the gain to suppress the feedback. As a result, unnatural fluctuations in the amplitude of the sound occur in the audible range, which can be perceived as unpleasant sound reproduction by headphone users.

[0009] Furthermore, in headphones employing a feedforward (FF) ANC system, howling can be induced if foreign objects such as fingers come into close proximity to the FF microphone, which collects noise generated in the external environment. For example, howling can be induced when sound waves output from the speaker unit are reflected by foreign objects such as fingers that come into close proximity to the FF microphone and then collected again by the FF microphone, forming a closed loop.

[0010] Furthermore, in headphones employing a feedback-type (FB-type) ANC, when the user puts the headphones on their head, or changes the position of the headphones on their head, a portion of the sound waves output from the speaker unit repeatedly reflects between the FB microphone and a part of the head that is close to it, forming a closed loop of sound waves and potentially inducing howling.

[0011] The technical problem addressed in this disclosure is to provide a novel electroacoustic converter that solves the problems of conventionally proposed technologies for suppressing howling.

[0012] Furthermore, the technical problem addressed by this disclosure is to provide an electroacoustic converter that enables the sound collected by a sound collection means and reproduced from a speaker unit to be heard as natural sound, or to be heard with enhanced sound.

[0013] Furthermore, the technical problem addressed by this disclosure is to provide an electroacoustic transducer that prevents the occurrence of howling in the audible frequency range and suppresses the generation of unpleasant sounds caused by howling.

[0014] Furthermore, the technical problem addressed in this disclosure is to provide an electroacoustic converter that detects changes in the characteristics of speech caused by changes in the user's surrounding environment or user operations, and enables the speech reproduced from the speaker unit to be heard as natural speech.

[0015] Furthermore, the technical problem addressed by this disclosure is to provide an electroacoustic transducer that can suppress howling from being perceived as an unpleasant sound without increasing the number of parts or the complexity of the mechanism.

[0016] One disclosure proposed to solve the above-mentioned technical problems comprises a sound collection means, a speaker unit for acoustically reproducing the sound collected by the sound collection means, a signal generation means for converting the sound collected by the sound collection means into a signal having predetermined characteristics, an amplitude detection means for detecting the amplitude of the sound collected by the sound collection means and changes therein, and a drive signal generation means for generating a drive signal to drive the speaker unit. The amplitude detection means has a detection function that detects changes in the characteristics of the surrounding environment and the signal processing system by detecting when the amplitude of the high-frequency band of the sound collected by the sound collection means exceeds a predetermined amplitude.

[0017] In this disclosure, the speaker unit may be mounted within a housing that is attached to the head.

[0018] In this disclosure, the signal generation means includes noise cancellation signal generation means that generates a noise cancellation signal for reducing environmental noise using sound collected by the sound collection means.

[0019] The signal generation means comprising this disclosure generates signals that cause the user to perceive the collected sound naturally or in an enhanced manner.

[0020] The amplitude detection means includes a variable amplification means, and upon detection of amplitude, the amplitude of the signal generated by the signal generation means is reduced and input to the drive signal generation means.

[0021] Furthermore, the amplitude detection means detects changes in the user's usage state and operations by detecting changes in the characteristics of the surrounding environment and signal processing system in conjunction with the detection of the amplitude detection function.

[0022] The drive signal generation means then combines the playback audio signal supplied from the playback sound source with the signal generated by the signal generation means.

[0023] The sound collection means is installed in the housing and faces outward from the housing, detecting sound incident from outside the housing, and the signal generation means generates the noise cancellation signal in a feedforward manner.

[0024] The present disclosure includes further sound collection means. The further sound collection means is installed in the front chamber of the housing facing the front side of the speaker unit and detects sound waves radiated from the speaker unit and noise components incident into the front chamber from outside the housing. The present disclosure also includes further signal generation means that generates a noise cancellation signal in a feedback manner to reduce the noise components collected by the further sound collection means. The noise cancellation signal generated by the further signal generation means is input to a drive signal generation means.

[0025] Furthermore, in this disclosure, the sound collection means is installed in the front chamber of the housing facing the front side of the speaker unit, and detects sound waves radiated from the speaker unit and noise components incident into the front chamber from outside the housing, and the signal generation means generates a noise cancellation signal in a feedback manner.

[0026] This disclosure includes a signal generation means that converts sound collected by a sound collection means installed in the front chamber of the housing facing the front side of the speaker unit into predetermined characteristics, and further includes a sound collection means that detects sound incident from outside the housing, and a further signal generation means that generates a noise cancellation signal in a feedforward manner to reduce noise components collected by the further sound collection means. The noise cancellation signal generated by the further signal generation means is input to a drive signal generation means.

[0027] The electroacoustic transducer according to this disclosure, which is equipped with a sound-collecting means in the front chamber of the housing, has ear pads surrounding the front chamber.

[0028] Furthermore, this disclosure includes a sound collection means installed facing the outside of a housing equipped with a speaker unit and detecting sound incident from outside the housing; a signal generation means for converting the sound collected by the sound collection means into a signal having predetermined characteristics; and a further amplitude detection means for detecting the amplitude of the sound collected by the sound collection means and changes thereto. Furthermore, this disclosure includes a further sound collection means installed in a front chamber facing the front side of the speaker unit of the housing and detecting sound waves radiated from the speaker unit and noise components incident into the front chamber from outside the housing; a further signal generation means for converting the sound collected by the further sound collection means into a signal having predetermined characteristics; and a further amplitude detection means for detecting the amplitude of the sound collected by the further sound collection means and changes thereto. In this disclosure, the signal generation means includes a noise cancellation signal generation means that generates a noise cancellation signal for reducing environmental noise using the sound collected by the sound collection means. This noise cancellation signal generation means generates the noise cancellation signal in a feedforward (FF) manner. The amplitude detection means has a detection function that detects changes in the characteristics of the surrounding environment and the signal processing system by detecting when the amplitude of the high-frequency band exceeding the audible range of the sound collected by the sound collection means exceeds a predetermined amplitude.

[0029] Further signal generation means include noise cancellation signal generation means that generate a noise cancellation signal to reduce environmental noise using sound collected by further sound collection means. This noise cancellation signal generation means generates the noise cancellation signal using a feedback (FB) method. Further amplitude detection means has a detection function that detects changes in the characteristics of the surrounding environment and the signal processing system by detecting when the amplitude of the high-frequency band exceeding the audible band of the sound collected by the sound collection means exceeds a predetermined amplitude.

[0030] Further signal generation means, like the signal generation means, generate signals that cause the user to perceive the collected sound naturally or in an enhanced way.

[0031] The further amplitude detection means, like the amplitude detection means, includes a variable amplitude means, and upon detection of a detection function provided by the further amplitude detection means, reduces the amplitude of the signal generated by the signal generation means and inputs it to the drive signal generation means.

[0032] The further amplitude detection means, similar to the amplitude detection means, detects changes in the user's usage state and operations by detecting changes in the surrounding environment and the characteristics of the signal processing system in conjunction with the detection of the detection function.

[0033] The drive signal generation means then combines the playback audio signal supplied from the playback sound source, the signal generated by the signal generation means, and the signal generated by a further signal generation means.

[0034] Further technical challenges and more specific technical means relating to this disclosure will be further clarified by the embodiments shown below with reference to the drawings.

[0035] This disclosure enables the natural listening or enhanced listening of sound collected by a sound collection means and reproduced by a speaker unit.

[0036] Furthermore, this disclosure can prevent the occurrence of feedback in the audible range and suppress the generation of unpleasant sounds caused by feedback.

[0037] Furthermore, this disclosure detects changes in the characteristics of the voice caused by changes in the user's surrounding environment or user operations, making the voice reproduced from the speaker unit sound natural.

[0038] Furthermore, this disclosure makes it possible to detect the cause of howling and suppress howling without complicating the mechanism.

[0039] This is a schematic diagram showing a first embodiment in which the present disclosure is applied to headphones. This is a Bode plot showing the amplitude and phase characteristics of an amplitude-variable signal in which the amplitude of 30 kHz, which is outside the audible range, is amplified to a constant level. This is an amplitude control flowchart showing a procedure for detecting the amplitude of an audio signal and controlling its amplitude. This is a spectral diagram showing a state in which the amplitude of 30 kHz included in the audio signal is reduced to below a threshold. This is a schematic diagram showing a second embodiment in which the present disclosure is applied to headphones. This is a schematic diagram showing a third embodiment in which the present disclosure is applied to headphones.

[0040] Hereinafter, several embodiments to which this disclosure applies will be described with reference to the drawings.

[0041] (First Embodiment) A first embodiment of the present disclosure applied to headphones worn on the head will be described. The headphones according to the first embodiment include a pair of headphone units that cover the left and right ears. The pair of headphone units are connected by a headband. Since the pair of headphone units have the same configuration for both the left and right sides, one headphone unit will be used as an example for the description.

[0042] One headphone unit 1 constituting the headphones of this embodiment includes, as shown in Figure 1, a first microphone 2 which constitutes a sound collection means and a speaker unit 3 to which the audio signal collected by the first microphone 2 is input. The speaker unit 3 reproduces and outputs the audio signal input by the first microphone 2 as sound.

[0043] In this embodiment, the speaker unit 3 is mounted inside a housing 4 that covers the auricle and is worn on the head. At this time, the speaker unit 3 is mounted inside the housing 4 with the front side facing the housing 4 facing the front side of the housing 4. In addition, although not shown in detail, the speaker unit 3 is mounted inside the housing 4 with a frame 3a supporting the diaphragm supported by a baffle plate 5 provided on the front side of the housing 4.

[0044] An ear pad 6 is attached to the front side of the housing 4 facing the diaphragm of the speaker unit 3. The ear pad 6 is attached to the front side of the baffle plate 5 so as to surround the diaphragm of the speaker unit 3.

[0045] The headset unit 1 according to the present embodiment is worn by pressing the ear pad 6 against the user's head. The ear pad 6 forms an acoustic closed space between the housing 4 and the user's head H when the headset unit 1 is worn on the head. This closed space is the front air chamber 7 of the headset unit 1. The front air chamber 7 is an acoustic space in which sound waves from the speaker unit 3 are radiated.

[0046] In the headset unit 1 of the present embodiment, the first microphone 2 is supported and installed on the housing 4. The first microphone 2 constitutes a sound collection means for collecting sound of voice transmitted from the outside of the headset unit 1. And the first microphone 2 is installed by facing the sound collection surface outward of the housing 4 and being located on the rear air chamber 8 side of the housing 4 where the back side of the speaker unit 3 faces so as to be able to collect external environmental sound transmitted from the outside of the headset unit 1. In the present embodiment, the external environmental sound collected by the first microphone 2 includes the sound of voice radiated from the speaker unit 3. The first microphone 2 outputs the collected external environmental sound as a voice signal.

[0047] The first microphone 2 incorporates a microphone amplifier and an A / D converter (not shown). The voice signal collected and output by the first microphone 2 is input to the microphone amplifier and amplified to a voltage level suitable for subsequent stage signal processing. The voice signal amplified by the microphone amplifier is input to the A / D converter connected to the next stage and converted into a digital signal.

[0048] The headset unit 1 according to the present embodiment includes a signal generation unit 11 to which a voice signal collected by the first microphone 2 and A / D converted is input. This signal generation unit 11 constitutes a signal generation means for performing predetermined signal processing on the voice signal output from the A / D converter and converting it into a signal having predetermined characteristics and outputting it.

[0049] As shown in Figure 1, the signal generation unit 11 includes a first noise cancellation signal generation circuit 12 and an ultrasonic amplifier 13. In this embodiment, the first noise cancellation signal generation circuit 12 generates a noise cancellation signal using a feedforward method (hereinafter referred to as the FF method). The first noise cancellation signal generation circuit 12 employing the FF method analyzes the noise contained in the sound collected by the first microphone 2, predicts the change in noise until it reaches the listener's playback sound listening point, and based on this prediction result, applies appropriate filtering processing to the noise to generate a noise cancellation signal that is out of phase with the noise. The first noise cancellation signal generation circuit 12 then superimposes the noise cancellation signal on the audio signal collected by the first microphone 2 and outputs an audio signal that reduces noise components contained in at least the audible range.

[0050] The ultrasonic amplifier 13 generates an amplitude-variable signal with adjusted amplitude-phase characteristics so that howling is likely to occur at frequencies above 20 kHz that are outside the audible range. In this embodiment, as shown in Figure 2, the ultrasonic amplifier 13 generates an amplitude-variable signal in which the amplitude at 30 kHz, which is outside the audible range, is amplified to a constant level. The amplitude-amplified signal, in which the amplitude at 30 kHz is amplified sharply, has its phase changed as shown in Figure 2.

[0051] In the first microphone 2, when an audio signal in phase with an amplitude-variable signal including a frequency of 30 kHz, which is amplified by the ultrasonic amplifier 13, is collected and input to the ultrasonic amplifier 13, the amplitude is superimposed at a frequency of 30 kHz and further amplified. If this amplitude amplification exceeds a threshold set by the processing characteristics of the signal processing system that controls the audio output gain of the headphones according to this embodiment, it can cause resonance and lead to howling.

[0052] In other words, the signal generation unit 11 generates a first noise cancellation signal using the first noise cancellation signal generation circuit 12, and the ultrasonic amplifier 13 generates an amplitude-variable signal that includes components that cause resonance and generate howling at frequencies outside the audible range.

[0053] The headphone unit 1 according to this embodiment is connected to a signal generation unit 11 and includes a variable amplifier 14 and an amplitude detector 15 for detecting the amplitude of the audio signal output from the variable amplifier 14.

[0054] The variable amplifier 14 receives an audio signal in which the first noise cancellation signal generated by the first noise cancellation signal generation circuit 12 of the signal generation unit 11 and the amplitude variable signal whose amplitude and phase at a frequency of 30 kHz have been adjusted by the ultrasonic amplifier 13 are superimposed. As shown in the flowchart of Figure 3, the variable amplifier 14 adjusts the amplitude of the audio signal by setting the gain to a predetermined value so that the noise cancellation signal output from the speaker unit 3 has an appropriate sound pressure (S1).

[0055] The audio signal, whose amplitude has been adjusted by the variable amplifier 14, is input to the amplitude detector 15. The amplitude detector 15 detects the amplitude of the audio signal input from the variable amplifier 14. As shown in the amplitude control flowchart in Figure 3, the amplitude detector 15 detects whether the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold value (S2).

[0056] When the amplitude detector 15 detects that the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold, it determines that the audio signal contains a component that causes resonance and howling, and applies a delay process to the audio signal for a certain period of time, as shown in Figure 3 (S3). The amplitude detector 15 again detects whether the 30 kHz amplitude of the audio signal exceeds a predetermined threshold (S4). If it is detected again that the audio signal contains a component with an amplitude of 30 kHz exceeding the threshold, the audio signal is fed back to the variable amplifier 14, as shown in Figure 3. The variable amplifier 14 reduces the 30 kHz amplitude included in the fed-back audio signal so that it is below the threshold, as shown in Figure 4 (S5). This amplitude reduction is performed including the audible range included in the audio signal, as shown in Figure 4. The audio signal whose amplitude has been reduced to below the threshold by the variable amplifier 14 is subjected to a delay process for a certain period of time (S6). After that, the audio signal is input to the amplitude detector 15 again, and the amplitude is detected. When it is detected that the 30 kHz amplitude contained in the audio signal has been reduced to below a predetermined threshold, the audio signal is output from the amplitude detector 15.

[0057] The audio signal output from the amplitude detector 15 has its amplitude at 30 kHz reduced to below a predetermined threshold, and a first noise cancellation signal is superimposed on it before it is input to the adder 16. The audio signal input to the adder 16 is output as a drive signal to drive the speaker unit 3, thereby driving the speaker unit 3.

[0058] Furthermore, in this embodiment, the headphone unit 1 has a second microphone 17 installed in a front chamber 7, which is formed by ear pads 6 attached to the front side of the baffle plate 5 so as to surround the diaphragm of the speaker unit 3.

[0059] In this embodiment, the second microphone 17 constitutes a noise cancellation mechanism that reduces noise using the FB method. This second microphone 17 collects noise and reproduced sound. The noise collected by the second microphone 17 includes noise components from the external environment transmitted through the housing 4 and baffle plate 5, and noise components from the external environment transmitted through the ear pad 6 as a vibration transmission member, or transmitted through the gap between the ear pad 6 and the listener's head. The reproduced sound is the reproduced sound radiated from the speaker unit 3.

[0060] The second microphone 17 is connected to a second noise cancellation signal generation circuit 18, which generates a second noise cancellation signal. The second cancellation signal generation circuit 18 receives a noise signal generated from noise components incident from the external environment collected by the second microphone 17, and a playback audio signal generated from the playback sound radiated from the speaker unit 3.

[0061] The second noise cancellation signal generation circuit 18 is composed of a digital filter circuit and generates a second noise cancellation signal using the FB method. This second noise cancellation signal generation circuit 18 generates the second noise cancellation signal by successively inverting the phase of the noise signal input from the second microphone 17. The second noise cancellation signal is input to the adder 16.

[0062] The adder 16 combines the audio signal, which is collected by the first microphone 2 and has a first noise cancellation signal superimposed on it while its amplitude is detected and adjusted, with the second noise cancellation signal to generate and output a drive signal that vibrates the diaphragm of the speaker unit 3. The drive signal output from the adder 16 is input to the voice coil that constitutes the drive unit of the speaker unit 3, causing the diaphragm to vibrate. As the diaphragm vibrates, the reproduced sound is radiated.

[0063] The speaker unit 3 collects sound with the first microphone 2, superimposes the first noise cancellation signal, and reproduces an audio signal in which the amplitude at 30 kHz is reduced to below a predetermined threshold. This achieves sound reproduction that suppresses resonance and howling at 30 kHz, which is outside the audible range. Furthermore, the drive signal includes an acoustic reproduction component from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 22.

[0064] Then, the sound reproduction component from the first noise cancellation signal generated by the first noise cancellation signal generation circuit 12, and the sound reproduction component from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 18, which are contained in the sound reproduced and emitted by the speaker unit 3, are radiated into the front chamber 7 of the headphone unit 1.

[0065] The reproduced sound from the first noise cancellation signal is acoustically combined with noise components transmitted from the external environment that enter the front chamber 7 of the headphone unit 1. This process reduces the noise components transmitted from the external environment at the noise cancellation point Pc formed on the front chamber 7 side.

[0066] Furthermore, the reproduced sound from the second noise cancellation signal is acoustically synthesized with noise components transmitted from the external environment that enters the front chamber 7 of the headphone unit 1 and noise components transmitted through the ear pads 6. As a result, each noise component is reduced at the noise cancellation point Pc formed on the front chamber 7 side.

[0067] The headphones according to this embodiment reduce noise components directly incident on the headphone unit 1 from the external environment using an FF-type noise cancellation mechanism, and further reduce noise components incident on the front chamber 7 using the ear pads 6 as a transmission member using an FB-type noise cancellation mechanism. As a result, various noise components incident on the headphone unit 1 are reduced, enabling the listening of even higher quality reproduced sound.

[0068] Incidentally, in headphones in which the first microphone 2 collects external ambient sounds and the resulting sound is reproduced by the speaker unit 3, the sound reproduced by the speaker unit 3 is collected by the first microphone 2 via the inside or outside of the housing 4. When using this type of headphones, sound reflectors such as building walls or parts of the body such as fingers may come into close proximity to the first microphone 2. In this case, the sound radiated from the speaker unit 2 is reflected by the sound reflector and collected by the first microphone 2, and this closed loop is repeated, which may cause a portion of the sound signal to be modulated to a frequency outside the audible range and amplified.

[0069] As described above, in the headphone unit 1 according to this embodiment, an audio signal amplified at a frequency of 30 kHz outside the audible range, collected by the first microphone 2, is superimposed on an amplitude-variable signal whose amplitude and phase at a frequency of 30 kHz have been adjusted by the ultrasonic amplifier 13. In this headphone unit 1, when the amplitude detector 15 detects that the amplitude of the amplitude-variable signal on which the audio signal amplified at a frequency of 30 kHz is superimposed exceeds a threshold, there is a risk of resonance and howling. Therefore, the variable amplifier 14 adjusts the amplitude of the collected audio signal so that the amplitude at 30 kHz is below the threshold, thereby suppressing the occurrence of howling due to resonance.

[0070] Furthermore, the frequency modulation and amplification that occurs when the sound emitted from the speaker unit 2 is reflected by an acoustic reflector and collected by the first microphone 2 in a closed loop occurs during the headphone wearing process or while listening to sound. In this embodiment, the occurrence of howling that occurs before the headphones are properly worn is suppressed in advance, and when the headphones are worn in the proper listening position, sound is reproduced with the appropriate amplitude, thereby suppressing howling and reducing the generation of unpleasant sounds, resulting in high-quality sound listening.

[0071] Furthermore, in this embodiment, the amplitude of the audio signal at a frequency of 30 kHz, which is outside the audible range, is detected and the amplitude is adjusted to suppress the occurrence of howling. This prevents the headphone user from hearing unpleasant sounds during the amplitude adjustment process.

[0072] Thus, the headphone unit 1 according to this embodiment is equipped with a detection function that detects an amplitude of 30 kHz, which is outside the audible range, reaching a predetermined threshold. This allows the headphone unit 1 to detect changes in the surrounding environment of the headphones used by the user and to detect changes in the characteristics of the audio signal generated by the signal generation unit 11.

[0073] (Second Embodiment) Next, a second embodiment of the present invention applied to headphones worn on the head will be described. The headphones according to the second embodiment also include a pair of headphone units that cover the left and right ears, similar to the first embodiment. The pair of headphone units are connected by a headband. Since the pair of headphone units have the same configuration for both the left and right sides, one headphone unit will be used as an example for the description.

[0074] One headphone unit 21 constituting the headphones according to this embodiment includes, as shown in Figure 5, a first microphone 22 that constitutes a sound collection means and a speaker unit 23 to which the audio signal collected by the first microphone 22 is input. The speaker unit 23 reproduces the audio signal input by the first microphone 22 as sound and outputs it.

[0075] In this embodiment, the speaker unit 23 is mounted inside a housing 24 that covers the auricle and is worn on the head. At this time, the speaker unit 23 is mounted inside the housing 24 with the front side facing the diaphragm facing the front side of the housing 24. In addition, although not shown in detail, the speaker unit 23 is mounted inside the housing 4 with a frame 23a supporting the diaphragm supported by a baffle plate 25 provided on the front side of the housing 24.

[0076] An ear pad 26 is attached to the front side of the housing 24, which faces the diaphragm of the speaker unit 23. The ear pad 26 is attached to the front side of the baffle plate 25 so as to surround the diaphragm of the speaker unit 23.

[0077] The headphone unit 21 according to this embodiment is attached by pressing the ear pads 26 against the side of the user's head. When the headphone unit 21 is attached to the head, the ear pads 26 form an acoustically closed space between the housing 24 and the side of the user's head H. This closed space is the front chamber 27 of the headphone unit 21. This front chamber 27 is an acoustic space into which sound waves from the speaker unit 23 are radiated.

[0078] In the headphone unit 21 of this embodiment, the first microphone 22 is supported and installed on the housing 24. The first microphone 22 constitutes a sound collection means for collecting sound transmitted from outside the headphone unit 1. The first microphone 22 is installed with its sound collection surface facing outward from the housing 24 and positioned on the rear air chamber 28 side of the housing 24, facing the rear side of the speaker unit 23, so that it can collect external ambient sounds transmitted from outside the headphone unit 21. In this embodiment, the external ambient sounds collected by the first microphone 22 include the sound emitted by the speaker unit 23. The first microphone 22 outputs the collected external ambient sounds as an audio signal.

[0079] The first microphone 22 is connected to a microphone amplifier and an A / D converter, although these are not shown in the diagram. The audio signal picked up and output by the first microphone 22 is input to the microphone amplifier and amplified to a voltage level suitable for signal processing in the subsequent stage. The audio signal amplified by the microphone amplifier is input to the A / D converter connected to the next stage and converted into a digital signal.

[0080] The headphone unit 21 according to this embodiment includes a first noise cancellation signal generation circuit 32 to which an audio signal collected by a first microphone 22 and converted by A / D is input. The first noise cancellation signal generation circuit 32 generates a noise cancellation signal using a feedforward (FF) method. The first noise cancellation signal generation circuit 32 employing the FF method analyzes the noise contained in the audio collected by the first microphone 32, predicts the change in noise until it reaches the listener's playback sound listening point, and based on this prediction result applies appropriate filtering processing to the noise to generate a noise cancellation signal that is out of phase with respect to the noise. The first noise cancellation signal generation circuit 32 then superimposes the noise cancellation signal on the audio signal collected by the first microphone 22 and outputs an audio signal that reduces noise components contained in at least the audible range.

[0081] The noise cancellation signal generated by the first noise cancellation signal generation circuit 32 is superimposed on the audio signal collected by the first microphone 22 and input to the adder 36, which generates a drive signal to drive the speaker unit 23.

[0082] Furthermore, the headphone unit 21 according to this embodiment is equipped with a second microphone 37. The second microphone 37 is installed in a front chamber 27, which is formed by being surrounded by ear pads 26 equipped on the front side of the baffle plate 25 so as to surround the diaphragm of the speaker unit 23. In this embodiment, the installation position of the second microphone 37 is the music listening position of the listener wearing the headphones, and is an acoustic synthesis position where noise and the reproduced sound with noise reduction audio signals are combined. This acoustic synthesis position is the noise cancellation point Pc.

[0083] The second microphone 37 incorporates a microphone amplifier and an A / D converter (not shown in the diagram). The audio signal picked up and output by the second microphone 37 is input to the microphone amplifier and amplified to a voltage level suitable for signal processing in the subsequent stage. The audio signal amplified by the microphone amplifier is input to the A / D converter connected to the next stage and converted into a digital signal.

[0084] The headphone unit 21 according to this embodiment includes a signal generation unit 41 to which an audio signal collected by a second microphone 37 and converted by A / D conversion is input. The signal generation unit 41 constitutes a signal generation means that applies predetermined signal processing to the audio signal output from the A / D converter, converts it into a signal having predetermined characteristics, and outputs it.

[0085] As shown in Figure 5, the signal generation unit 41 includes a second noise cancellation signal generation circuit 42 and an ultrasonic amplifier 43. In this embodiment, the second noise cancellation signal generation circuit 42 generates a noise cancellation signal using a feedforward (FB) method. The second noise cancellation signal generation circuit 42 employing the FB method generates a second noise cancellation signal by successively inverting the phase of the noise signal collected and output by the second microphone 37.

[0086] The second noise cancellation signal generated by the second noise cancellation signal generation circuit 42 is radiated as sound from the speaker unit 23 and, at the noise cancellation point Pc configured in the front chamber 27, is superimposed with the sound radiated from the speaker unit 23, reducing noise components that are at least in the audible range.

[0087] The ultrasonic amplifier 43 generates an amplitude-variable signal with adjusted amplitude-phase characteristics so that howling is likely to occur at frequencies above 20 kHz that are outside the audible range. In this embodiment, as in the first embodiment described above, the ultrasonic amplifier 43 generates an amplitude-variable signal in which the amplitude at 30 kHz, which is outside the audible range, is amplified to a constant level, as shown in Figure 2. The amplitude-amplified signal, in which the amplitude at 30 kHz is amplified sharply, has its phase changed as shown in Figure 2.

[0088] In the second microphone 37, when an audio signal in phase with an amplitude-variable signal including a frequency of 30 kHz, which is amplified by the ultrasonic amplifier 43, is collected and input to the ultrasonic amplifier 43, the amplitude is superimposed at a frequency of 30 kHz and further amplified. If this amplitude amplification exceeds a threshold set by the processing characteristics of the signal processing system that controls the audio output gain of the headphones according to this embodiment, it can cause resonance and lead to howling.

[0089] In other words, the signal generation unit 41 generates a second noise cancellation signal using the second noise cancellation signal generation circuit 42, and the ultrasonic amplifier 43 generates an amplitude-variable signal that includes components that cause resonance and generate howling at frequencies outside the audible range.

[0090] The headphone unit 21 according to this embodiment is connected to a signal generation unit 41 and includes a variable amplifier 44 and an amplitude detector 45 for detecting the amplitude of the audio signal output from the variable amplifier 44.

[0091] The variable amplifier 44 receives an audio signal in which a second noise cancellation signal generated by the second noise cancellation signal generation circuit 42 of the signal generation unit 41 and an amplitude-variable signal whose amplitude and phase have been adjusted by the ultrasonic amplifier 43 at a frequency of 30 kHz are superimposed. As shown in the flowchart of Figure 3, the variable amplifier 44 adjusts the amplitude of the audio signal, whose gain is set to a specified value, so that the sound output from the speaker unit 3 has an appropriate sound pressure (S1).

[0092] The audio signal, whose amplitude has been adjusted by the variable amplifier 44, is input to the amplitude detector 45. The amplitude detector 45 detects the amplitude of the audio signal input from the variable amplifier 44. As shown in the amplitude control flowchart of Figure 3 above, the amplitude detector 45 detects whether the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold value (S2).

[0093] When the amplitude detector 45 detects that the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold, it determines that the audio signal contains a component that causes resonance and howling, and applies a delay process to the audio signal for a certain period of time, as shown in Figure 3 (S3). The amplitude detector 45 again detects whether the 30 kHz amplitude of the audio signal exceeds a predetermined threshold (S4). If it is detected again that the audio signal contains a component with an amplitude of 30 kHz exceeding the threshold, the audio signal is fed back to the variable amplifier 44, as shown in Figure 3. The variable amplifier 44 reduces the 30 kHz amplitude included in the fed-back audio signal so that it is below the threshold, as shown in Figure 4 (S5). This amplitude reduction is performed including the audible range included in the audio signal, as shown in Figure 4. The audio signal whose amplitude has been reduced to below the threshold by the variable amplifier 44 is subjected to a delay process for a certain period of time (S6). After that, the audio signal is input to the amplitude detector 45 again, and the amplitude is detected. When it is detected that the 30 kHz amplitude contained in the audio signal has been reduced to below a predetermined threshold, the audio signal is output from the amplitude detector 45.

[0094] The audio signal output from the amplitude detector 45 has its amplitude at 30 kHz reduced to below a predetermined threshold, and a second noise cancellation signal is superimposed on it before it is input to the adder 36. In this embodiment, the adder 36 is further input to the playback audio signal output from the playback sound source 46.

[0095] The adder 36 combines the audio signal, which is collected by the first microphone 22 and has a first noise cancellation signal superimposed on it, with the audio signal, which has a second noise cancellation signal superimposed on it and whose amplitude has been detected and adjusted, and the reproduced audio signal, and outputs it as a drive signal that vibrates the diaphragm of the speaker unit 23.

[0096] The drive signal output from the adder 36 is input to the voice coil that constitutes the drive unit of the speaker unit 23, causing the diaphragm to vibrate and radiate sound from the diaphragm.

[0097] The speaker unit 23 superimposes an FB-type noise cancellation signal generated from the audio signal collected by the second microphone 37, and reproduces an audio signal in which the amplitude at 30 kHz has been reduced to below a predetermined threshold. This achieves sound reproduction that suppresses resonance at 30 kHz, which is outside the audible range, and prevents howling. Since the noise cancellation signal is superimposed on the audio signal collected by the first microphone 22, noise components transmitted from the external environment when using headphones are reduced. Furthermore, the drive signal includes sound reproduction components from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 42.

[0098] Then, the sound reproduction component from the first noise cancellation signal generated by the first noise cancellation signal generation circuit 32, which is contained in the sound reproduced and emitted by the speaker unit 23, and the sound reproduction component from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 42, are radiated into the front chamber 7 of the headphone unit 1.

[0099] The reproduced sound from the first noise cancellation signal is acoustically combined with noise components transmitted from the external environment that enter the front chamber 27 of the headphone unit 21, and the noise components transmitted from the external environment are reduced at the noise cancellation point Pc formed on the front chamber 27 side.

[0100] Furthermore, the reproduced sound from the second noise cancellation signal is acoustically synthesized with noise components transmitted from the external environment that enters the front chamber 27 of the headphone unit 21 and noise components transmitted via the ear pads 26, and these noise components are reduced at the noise cancellation point Pc formed on the front chamber 27 side.

[0101] The headphones according to this embodiment reduce noise components that are directly incident on the headphone unit 21 from the external environment using an FF-type noise cancellation mechanism, and further reduce noise components that are incident on the front air chamber 27 using the ear pads 26 as a transmission member using an FB-type noise cancellation mechanism. As a result, various noise components incident on the headphone unit 1 are reduced, enabling the listening of even higher quality reproduced sound.

[0102] The speaker unit 23 collects sound from the second microphone 37, and a noise cancellation signal is superimposed on it. Furthermore, an audio signal is reproduced in which the amplitude at 30 kHz is reduced to below a predetermined threshold. This achieves sound reproduction that suppresses resonance at 30 kHz, which is outside the audible range, and prevents howling. Since the noise cancellation signal is superimposed on the audio signal collected by the second microphone 37, the aforementioned noise components collected by the second microphone 37 are reduced. In addition, the drive signal includes an audio reproduction component from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 42.

[0103] The headphones according to this embodiment reduce noise components that are directly incident on the headphone unit 21 from the external environment, and further reduce noise components that are incident on the front chamber 27 by using the ear pads 26 as a transmission member. As a result, various noise components incident on the headphones are reduced, enabling the listening of even higher quality reproduced sound.

[0104] Incidentally, the sound picked up by the second microphone 37 includes noise components from the external environment transmitted through the housing 24 and the baffle plate 25, and noise components from the external environment transmitted through the ear pad 26 as a vibration transmission member, or through the gap between the ear pad 26 and the listener's head.

[0105] In the headphone unit 21 worn on the head according to this embodiment, when adjusting the wearing position, foreign objects such as fingers may come into close proximity to the second microphone 37. At this time, the sound emitted from the speaker unit 23 is reflected by the sound reflector and collected by the second microphone 37, and as this closed loop is repeated, a part of the sound signal may be modulated to a frequency outside the audible range and amplified.

[0106] In this embodiment, as described above, when the amplitude detector 45 detects that the amplitude of the audio signal exceeds a threshold at a frequency of 30 kHz, which is outside the audible range of the audio signal, there is a risk of resonance and howling. Therefore, the variable amplifier 44 adjusts the amplitude across the entire frequency band of the audio signal so that the amplitude at 30 kHz is below the threshold, thereby suppressing howling due to resonance.

[0107] Furthermore, frequency modulation and amplification, which occur when the sound emitted from the speaker unit 23 is reflected by an acoustic reflector and collected by the second microphone 37 in a closed loop, occur during the headphone wearing process or while listening to sound. In this embodiment, the occurrence of howling that occurs before the headphones are properly worn is suppressed in advance, and when the headphones are worn in the proper listening position, sound is reproduced with the appropriate amplitude, thereby suppressing howling and reducing the generation of unpleasant sounds, resulting in high-quality sound listening.

[0108] Furthermore, in this embodiment, the amplitude of the audio signal at a frequency of 30 kHz, which is outside the audible range, is detected and the amplitude is adjusted to suppress the occurrence of howling. This also prevents the headphone user from hearing unpleasant sounds during the amplitude adjustment process.

[0109] (Third Embodiment) Next, a third embodiment of the present invention applied to headphones worn on the head will be described. The headphones according to the third embodiment also include a pair of headphone units that cover the left and right ears, similar to the first and second embodiments. The pair of headphone units are connected by a headband. Since the pair of headphone units have the same configuration for both the left and right sides, one headphone unit will be used as an example for the description.

[0110] One headphone unit 51 constituting the headphones according to this embodiment includes, as shown in Figure 6, a first microphone 52 which constitutes a sound collection means and a speaker unit 53 to which the audio signal collected by the first microphone 52 is input. The speaker unit 53 reproduces and outputs the audio signal input by the first microphone 52 as sound.

[0111] In this embodiment, the speaker unit 53 is mounted inside a housing 54 that covers the auricle and is worn on the head. At this time, the speaker unit 53 is mounted inside the housing 54 with the front side facing the housing 54 facing the front side of the housing 54. In addition, although not shown in detail, the speaker unit 53 has a frame 53a that supports the diaphragm, which is supported by a baffle plate 55 provided on the front side of the housing 54.

[0112] An ear pad 56 is attached to the front side of the housing 54, which faces the diaphragm of the speaker unit 53. The ear pad 56 is attached to the front side of the baffle plate 55 so as to surround the diaphragm of the speaker unit 53.

[0113] The headphone unit 51 according to this embodiment is attached to the user's side of the head by pressing the ear pad 56 against it, similar to the embodiment described above. When the headphone unit 51 is attached to the head, the ear pad 56 forms an acoustically closed space between the housing 54 and the user's side of the head H. This closed space is the front chamber 57 of the headphone unit 51. This front chamber 57 is an acoustic space into which sound waves from the speaker unit 53 are radiated.

[0114] In the headphone unit 51 of this embodiment, the first microphone 52 is supported and installed on the housing 54. The first microphone 52 constitutes a sound collection means for collecting sound transmitted from outside the headphone unit 51. The first microphone 52 is installed with its sound collection surface facing outward from the housing 54 and positioned on the rear air chamber 58 side of the housing 54, facing the rear side of the speaker unit 53, so that it can collect external ambient sounds transmitted from outside the headphone unit 51. In this embodiment, the external ambient sounds collected by the first microphone 52 include the sound emitted by the speaker unit 53. The first microphone 52 then outputs the collected external ambient sounds as an audio signal.

[0115] The first microphone 52 is connected to a microphone amplifier and an A / D converter (not shown). The audio signal picked up and output by the first microphone 52 is input to the microphone amplifier and amplified to a voltage level suitable for signal processing in the subsequent stage. The audio signal amplified by the microphone amplifier is input to the A / D converter connected to the next stage and converted into a digital signal.

[0116] Furthermore, the headphone unit 51 according to this embodiment, similar to the first embodiment, includes a signal generation unit 61 to which an audio signal collected by the first microphone 52 and converted by A / D conversion is input. The signal generation unit 61 constitutes a signal generation means that applies predetermined signal processing to the audio signal output from the A / D converter, converts it into a signal having predetermined characteristics, and outputs it.

[0117] As shown in Figure 5, the signal generation unit 61 includes a first noise cancellation signal generation circuit 62 and an ultrasonic amplifier 63. In this embodiment, the first noise cancellation signal generation circuit 62 generates a noise cancellation signal using the FF method. The first noise cancellation signal generation circuit 62, employing the FF method, analyzes the noise contained in the sound collected by the first microphone 52, predicts the change in noise until it reaches the listener's playback sound listening point, and based on this prediction result, applies appropriate filtering processing to the noise to generate a noise cancellation signal that is out of phase with the noise. The first noise cancellation signal generation circuit 62 then superimposes the noise cancellation signal onto the audio signal collected by the first microphone 52 and outputs an audio signal that reduces noise components contained in at least the audible range.

[0118] The ultrasonic amplifier 63 generates an amplitude-variable signal with adjusted amplitude-phase characteristics so that howling is likely to occur at frequencies outside the audible range of 20 kHz or higher. In this embodiment, as shown in Figure 2, the ultrasonic amplifier 63 generates an ultrasonic amplified signal in which the amplitude at 30 kHz, which is outside the audible range, is amplified to a certain level. The amplitude amplified signal, in which the amplitude at 30 kHz is amplified sharply, has its phase changed as shown in Figure 2.

[0119] In the first microphone 2, when an audio signal in phase with an amplitude-amplified signal containing a frequency of 30 kHz, which is amplified by the ultrasonic amplifier 63, is collected and input to the ultrasonic amplifier 63, the amplitude is superimposed at a frequency of 30 kHz and further amplified. If this amplitude amplification exceeds a threshold set by the processing characteristics of the signal processing system that controls the audio output gain of the headphones according to this embodiment, it can cause resonance and lead to howling.

[0120] In other words, the signal generation unit 61 generates a first noise cancellation signal using the first noise cancellation signal generation circuit 62, and the ultrasonic amplifier 63 generates an amplitude-variable signal that includes components that cause resonance and generate howling at frequencies outside the audible range.

[0121] The headphone unit 51 according to this embodiment, similar to the first embodiment, is connected to the signal generation unit 61 and includes a variable amplifier 64 and an amplitude detector 65 for detecting the amplitude of the audio signal output from the variable amplifier 64.

[0122] The variable amplifier 64 receives an audio signal in which the first noise cancellation signal generated by the first noise cancellation signal generation circuit 62 of the signal generation unit 61 is superimposed with an amplitude-variable signal whose amplitude and phase have been adjusted by the ultrasonic amplifier 63 to a frequency of 30 kHz. As shown in the flowchart of Figure 3, the variable amplifier 64 sets the amplitude of the audio signal with a gain set to a specified value so that the noise cancellation signal output from the speaker unit 53 has an appropriate sound pressure (S1).

[0123] The audio signal, whose amplitude has been adjusted by the variable amplifier 63, is input to the amplitude detector 65. The amplitude detector 65 detects the amplitude of the audio signal input from the variable amplifier 64. As shown in the amplitude control flowchart in Figure 3, the amplitude detector 65 detects whether the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold value (S2).

[0124] When the amplitude detector 65 detects that the 30 kHz amplitude of the input audio signal exceeds the threshold, it determines that the audio signal contains a component that causes resonance and howling, and applies a delay process to the audio signal for a certain period of time, as shown in Figure 3 (S3). The amplitude detector 45 again detects whether the 30 kHz amplitude of the audio signal exceeds a predetermined threshold (S4). If it is detected again that the audio signal contains a component with an amplitude of 30 kHz exceeding the threshold, the audio signal is fed back to the variable amplifier 64, as shown in Figure 3. The variable amplifier 64 reduces the 30 kHz amplitude included in the fed-back audio signal so that it is below the threshold, as shown in Figure 4 (S5). This amplitude reduction is performed including the audible range included in the audio signal, as shown in Figure 4. The audio signal whose amplitude has been reduced to below the threshold by the variable amplifier 64 is subjected to a delay process for a certain period of time (S6). After that, the audio signal is input to the amplitude detector 65 again, and the amplitude is detected. When it is detected that the 30 kHz amplitude contained in the audio signal has been reduced to below a predetermined threshold, the audio signal is output from the amplitude detector 65.

[0125] Then, the audio signal, on which the first noise cancellation signal is superimposed and whose amplitude at 30 kHz has been reduced to below a predetermined threshold, is input to the adder 66. This adder 66 generates a drive signal to drive the speaker unit 53.

[0126] Furthermore, in this embodiment, the headphone unit 51 has a second microphone 69 installed in a front chamber 57, which is formed by an ear pad 56 attached to the front side of a baffle plate 55 so as to surround the diaphragm of the speaker unit 53. In this embodiment, the second microphone 69 is located at the music listening position of the listener wearing the headphones, at the sound synthesis position where noise and the reproduced sound with noise reduction audio signals are combined, and is installed at the noise cancellation point Pc.

[0127] The second microphone 69, although not shown, incorporates a microphone amplifier and an A / D converter. The audio signal picked up and output by the second microphone 69 is input to the microphone amplifier and amplified to a voltage level suitable for signal processing in the subsequent stage. The audio signal amplified by the microphone amplifier is input to the A / D converter connected to the next stage and converted into a digital signal.

[0128] Furthermore, the headphone unit 51 according to this embodiment includes a signal generation unit 71 to which an audio signal collected by a second microphone 69 and converted by A / D conversion is input. The signal generation unit 71 constitutes a signal generation means that applies predetermined signal processing to the audio signal output from the A / D converter, converts it into a signal having predetermined characteristics, and outputs it.

[0129] As shown in Figure 6, the signal generation unit 71 includes a second noise cancellation signal generation circuit 72 and an ultrasonic amplifier 73. In this embodiment, the second noise cancellation signal generation circuit 72 generates a noise cancellation signal using the FB method. The second noise cancellation signal generation circuit 72, employing the FB method, generates a second noise cancellation signal by successively inverting the phase of the noise signal collected and output by the second microphone 69.

[0130] The second noise cancellation signal generated by the second noise cancellation signal generation circuit 72 is radiated as sound from the speaker unit 53 and superimposed on the sound radiated from the speaker unit 53 at the noise cancellation point Pc configured in the front chamber 57, reducing noise components that are at least in the audible range.

[0131] Furthermore, the ultrasonic amplifier 73 generates an amplitude-variable signal with adjusted amplitude-phase characteristics so that howling is likely to occur at frequencies outside the audible range of 20 kHz or higher. In this embodiment, as in the first and second embodiments described above, the ultrasonic amplifier 73 generates an amplitude-variable signal with an amplitude of 30 kHz, which is outside the audible range, amplified to a constant level, as shown in Figure 2. The amplitude-amplified signal, with its 30 kHz amplitude amplified sharply, has its phase changed as shown in Figure 2.

[0132] Then, in the second microphone 69, when an audio signal in phase with the amplitude-variable signal including a frequency of 30 kHz, which is amplified by the ultrasonic amplifier 73, is collected and input to the ultrasonic amplifier 73, the amplitude is superimposed at a frequency of 30 kHz and further amplified. If this amplitude amplification exceeds a threshold set by the processing characteristics of the signal processing system that controls the audio output gain of the headphones according to this embodiment, it will cause resonance and become a factor in generating howling.

[0133] In other words, the signal generation unit 71 generates a second noise cancellation signal using the second noise cancellation signal generation circuit 72, and the ultrasonic amplifier 73 generates an amplitude-variable signal that includes components that cause resonance and generate howling at frequencies outside the audible range.

[0134] As shown in Figure 6, the headphone unit 51 according to this embodiment is connected to the signal generation unit 71 and includes a variable amplifier 74 and an amplitude detector 75 for detecting the amplitude of the audio signal output from the variable amplifier 74.

[0135] The variable amplifier 74 receives an audio signal in which the second noise cancellation signal generated by the second noise cancellation signal generation circuit 72 of the signal generation unit 71 is superimposed with an amplitude-variable signal whose amplitude and phase have been adjusted by the ultrasonic amplifier 73 to a frequency of 30 kHz. As shown in the flowchart in Figure 3, the variable amplifier 74 sets the gain to a specified value and the amplitude of the audio signal so that the noise cancellation signal output from the speaker unit 53 has an appropriate sound pressure (S1).

[0136] The audio signal, whose amplitude has been adjusted by the variable amplifier 73, is input to the amplitude detector 75. The amplitude detector 75 detects the amplitude of the audio signal input from the variable amplifier 73. As shown in the amplitude control flowchart of Figure 3 above, the amplitude detector 75 detects whether the 30 kHz amplitude of the input audio signal exceeds a predetermined threshold value (S2).

[0137] When the amplitude detector 75 detects that the 30 kHz amplitude of the input audio signal exceeds the threshold, it determines that the audio signal contains a component that causes resonance and howling, and applies a delay process to the audio signal for a certain period of time, as shown in Figure 3 (S3). The amplitude detector 75 again detects whether the 30 kHz amplitude of the audio signal exceeds a predetermined threshold (S4). If it is detected again that the audio signal contains a component with an amplitude of 30 kHz that exceeds the aforementioned threshold, the audio signal is fed back to the variable amplifier 74, as shown in Figure 3. The variable amplifier 74 reduces the 30 kHz amplitude included in the fed-back audio signal so that it is below the threshold, as shown in Figure 4 (S5). This amplitude reduction is performed including the audible range included in the audio signal, as shown in Figure 4. The audio signal whose amplitude has been reduced to below the threshold by the variable amplifier 74 is subjected to a delay process for a certain period of time (S6). After that, the audio signal is input to the amplitude detector 75 again, and the amplitude is detected. When it is detected that the 30 kHz amplitude contained in the audio signal has been reduced to below a predetermined threshold, the audio signal is output from the amplitude detector 75.

[0138] Then, the audio signal to which the second noise cancellation signal is superimposed and whose amplitude at 30 kHz has been reduced to below a predetermined threshold is input to the adder 66. In this embodiment, the adder 66 is further input to the playback audio signal output from the playback sound source 76.

[0139] The adder 66 combines the audio signal collected by the first microphone 52, on which a first noise cancellation signal is superimposed and whose amplitude is detected and adjusted, with the audio signal on which a second noise cancellation signal is superimposed and whose amplitude is detected and adjusted, and the reproduced audio signal, and outputs it as a drive signal that vibrates the diaphragm of the speaker unit 53.

[0140] The drive signal output from the adder 66 is input to the voice coil that constitutes the drive unit of the speaker unit 53, causing the diaphragm to vibrate and radiate sound from the diaphragm.

[0141] In the speaker unit 53, an FF-type noise cancellation signal generated from the audio signal collected by the first microphone 52 is superimposed, and an audio signal with an amplitude of 30 kHz reduced to below a predetermined threshold is reproduced. Furthermore, an FB-type noise cancellation signal generated from the audio signal collected by the second microphone 69 is superimposed, and an audio signal with an amplitude of 30 kHz reduced to below a predetermined threshold is reproduced, thereby achieving sound reproduction that suppresses resonance at 30 kHz, which is outside the audible range, and prevents howling. In addition, since the noise cancellation signal is superimposed on the audio signal collected by the first microphone 52, noise components transmitted from the external environment using headphones are reduced. Furthermore, the drive signal includes sound reproduction components from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 72.

[0142] The sound reproduced and emitted by the speaker unit 53, including the sound reproduction component due to the first noise cancellation signal generated by the first noise cancellation signal generation circuit 62, and the sound reproduction component due to the second noise cancellation signal generated by the second noise cancellation signal generation circuit 72, are radiated into the front chamber 57 of the headphone unit 51.

[0143] The reproduced sound from the first noise cancellation signal is acoustically combined with noise components transmitted from the external environment that enter the front chamber 57 of the headphone unit 51, and the noise components transmitted from the external environment are reduced at the noise cancellation point Pc formed on the front chamber 57 side.

[0144] The reproduced sound from the second noise cancellation signal is acoustically synthesized with noise components transmitted from the external environment that enters the front chamber 57 of the headphone unit 51 and noise components transmitted through the ear pads 26. At the noise cancellation point Pc formed on the front chamber 57 side, these noise components are reduced.

[0145] The headphones according to this embodiment reduce noise components that are directly incident on the headphone unit 51 from the external environment using an FF-type noise cancellation mechanism, and further reduce noise components that are incident on the front air chamber 57 using the ear pads 56 as a transmission member using an FB-type noise cancellation mechanism.

[0146] Incidentally, in this embodiment, the speaker unit 53 is configured such that sound is collected by the first microphone 52, a noise cancellation signal is superimposed on it, and an audio signal with an amplitude of 30 kHz reduced to below a predetermined threshold is reproduced. Furthermore, sound is collected by the second microphone 69, a noise cancellation signal is superimposed on it, and an audio signal with an amplitude of 30 kHz reduced to below a predetermined threshold is reproduced. This achieves sound reproduction that suppresses resonance at 30 kHz, which is outside the audible range, and prevents howling. Moreover, since a noise cancellation signal is superimposed on the audio signals collected by the first microphone 52 and the second microphone 57, the aforementioned noise components collected by the first microphone 52 and the second microphone 69 are reduced. Furthermore, the drive signal includes an audio reproduction component from the second noise cancellation signal generated by the second noise cancellation signal generation circuit 42.

[0147] Therefore, the headphones according to this embodiment reduce noise components that are directly incident on the headphone unit 51 from the external environment, and further reduce noise components that are incident on the front chamber 57 using the ear pads 56 as a transmission member. As a result, various noise components incident on the headphones are reduced, enabling the listening of even higher quality reproduced sound.

[0148] Incidentally, in the headphone unit 51 according to this embodiment, as described above, the audio signal amplified at a frequency of 30 kHz outside the audible range, collected by the first microphone 52, is superimposed on an amplitude-variable signal whose amplitude and phase at a frequency of 30 kHz have been adjusted by the ultrasonic amplifier 63. When the amplitude detector 65 detects that the amplitude exceeds a threshold, there is a risk of resonance and howling. Therefore, the variable amplifier 54 adjusts the amplitude of the collected audio signal so that the amplitude at 30 kHz is below the threshold, thereby suppressing the occurrence of howling due to resonance.

[0149] Furthermore, frequency modulation and amplification, which occur when the sound emitted from the speaker unit 53 is reflected by an acoustic reflector and collected by the first microphone 52 in a closed loop, occur during the headphone wearing process or while listening to sound. In this embodiment, the occurrence of howling that occurs before the headphones are properly worn is suppressed in advance, and when the headphones are worn in the proper listening position, sound is reproduced with an appropriate amplitude, thereby suppressing howling and reducing the generation of unpleasant sounds, resulting in high-quality sound listening.

[0150] Furthermore, in this embodiment, the amplitude of the audio signal at a frequency of 30 kHz, which is outside the audible range, is detected and the amplitude is adjusted to suppress the occurrence of howling. This prevents the headphone user from hearing unpleasant sounds during the amplitude adjustment process.

[0151] Thus, the headphone unit 51 according to this embodiment is equipped with a detection function that detects an amplitude of 30 kHz, which is outside the audible range, reaching a predetermined threshold. This allows it to detect changes in the surrounding environment of the headphones used by the user and to detect changes in the characteristics of the audio signal generated by the signal generation unit 11.

[0152] In the headphone unit 51 worn on the head according to this embodiment, when adjusting the wearing position, foreign objects such as fingers may come into close proximity to the second microphone 69. At this time, the sound emitted from the speaker unit 53 is reflected by the sound reflector and collected by the second microphone 69, and as this closed loop is repeated, a part of the sound signal may be modulated to a frequency outside the audible range and amplified.

[0153] In this embodiment, as described above, when the amplitude detector 75 detects that the amplitude of the audio signal exceeds a threshold at a frequency of 30 kHz, which is outside the audible range of the audio signal, there is a risk of resonance and howling. Therefore, the variable amplifier 74 adjusts the amplitude across the entire frequency band of the audio signal so that the amplitude at 30 kHz is below the threshold, thereby suppressing howling due to resonance.

[0154] Furthermore, frequency modulation and amplification resulting from the repeated closed-loop process where sound emitted from the speaker unit 53 is reflected by an acoustic reflector and collected by the second microphone 69 occur during the headphone wearing process or while listening to sound. In this embodiment, the occurrence of howling that occurs before the headphones are properly worn is suppressed in advance, and when the headphones are worn in the proper listening position, sound is reproduced with the appropriate amplitude, thereby suppressing howling and reducing the generation of unpleasant sounds, resulting in high-quality sound listening.

[0155] Furthermore, in this embodiment, the amplitude of the 30 kHz frequency outside the audible range of the audio signal is detected, and the amplitude is adjusted to suppress the occurrence of howling. This also prevents the headphone user from hearing unpleasant sounds during the amplitude adjustment process. Thus, the headphone unit 51 according to this embodiment is equipped with a detection function that detects a predetermined threshold for the amplitude of the 30 kHz frequency outside the audible range, thereby detecting changes in the surrounding environment of the headphones used by the user and detecting changes in the characteristics of the audio signal generated by the signal generation units 61 and 71.

[0156] (Other Embodiments) The present invention can be applied to various electroacoustic converters equipped with a microphone as a sound-collecting means for collecting external ambient sounds, etc., and a speaker unit for acoustically reproducing the sound collected by the microphone, thereby obtaining the same advantages as when applied to the headphones described above.

[0157] 1 Headphone unit, 2 First microphone, 3 Speaker unit, 4 Housing, 5 Baffle plate, 6 Ear pad, 7 Front chamber, 11 Signal generation unit, 12 First noise cancellation signal generation circuit, 13 Ultrasonic amplifier, 14 Variable amplifier, 15 Amplitude detector, 16 Amplifier

Claims

1. An electroacoustic converter comprising: a sound collection means; a speaker unit for acoustically reproducing sound collected by the sound collection means; a signal generation means for converting the sound collected by the sound collection means into a signal having predetermined characteristics; an amplitude detection means for detecting the amplitude of the sound collected by the sound collection means and changes therein; and a drive signal generation means for generating a drive signal to drive the speaker unit, wherein the amplitude detection means has a detection function for detecting changes in the characteristics of the surrounding environment and the signal processing system by detecting when the amplitude of the high-frequency band exceeding the audible band of the sound collected by the sound collection means exceeds a predetermined amplitude.

2. The electroacoustic transducer according to claim 1, comprising a housing that is attached to the head, wherein the speaker unit is mounted within the housing.

3. The electroacoustic converter according to claim 1 or 2, characterized in that the signal generation means includes a noise cancellation signal generation means that generates a noise cancellation signal for reducing environmental noise using the sound collected by the sound collection means.

4. The electroacoustic converter according to claim 1 or 2, characterized in that the signal generating means generates a signal that causes the user to perceive the sound collected by the sound collecting means naturally or with emphasis.

5. The electroacoustic converter according to claim 1 or 2, wherein the amplitude detection means includes a variable amplification means, and upon detection of the detection function, the amplitude of the signal generated by the signal generation means is reduced and input to the drive signal generation means.

6. The electroacoustic converter according to claim 1 or 2, characterized in that the amplitude detection means detects changes in the user's usage state and operations by detecting changes in the characteristics of the surrounding environment and the signal processing system in conjunction with the detection of the detection function.

7. The electroacoustic converter according to claim 1 or 2, characterized in that the drive signal generation means synthesizes a playback audio signal supplied from a playback sound source with a signal generated by the signal generation means.

8. The electroacoustic transducer according to claim 1, comprising a housing that is attached to the head, the speaker unit being installed inside the housing, the sound collection means being installed inside the housing facing outwards and collecting sound transmitted from outside the housing, and the signal generation means including a noise cancellation signal generation means that generates a noise cancellation signal for reducing environmental noise using the sound collected by the sound collection means, the noise cancellation signal generation means generating the noise cancellation signal in a feedforward manner.

9. The electroacoustic converter according to claim 8, further comprising: a sound collection means installed in the front chamber of the housing facing the front side of the speaker unit, for detecting sound waves radiated from the speaker unit and noise components incident into the front chamber from outside the housing; and a signal generation means for generating a noise cancellation signal in a feedback manner to reduce the noise components collected by the further sound collection means, wherein the noise cancellation signal generated by the further signal generation means is input to the drive signal generation means.

10. The electroacoustic transducer according to claim 9, characterized in that ear pads are provided surrounding the front chamber of the housing, which is faced by the front side of the speaker unit.

11. The electroacoustic transducer according to claim 1, comprising a housing that is attached to the head, wherein the speaker unit is installed inside the housing, the sound collection means is installed in the front chamber of the housing facing the front side of the speaker unit and detects sound waves radiated from the speaker unit and noise components incident into the front chamber from outside the housing, the signal generation means includes a noise cancellation signal generation means that generates a noise cancellation signal for reducing environmental noise using the sound collected by the sound collection means, and the noise cancellation signal generation means generates the noise cancellation signal in a feedback manner.

12. The electroacoustic converter according to claim 11, further comprising: a further sound collection means installed facing the outside of the housing for detecting sound incident from the outside of the housing; a further signal generation means for generating a noise cancellation signal in a feedforward manner for reducing the noise component collected by the further sound collection means; and the noise cancellation signal generated by the further signal generation means being input to the drive signal generation means.

13. The electroacoustic transducer according to claim 11 or 12, characterized in that ear pads are provided surrounding the front chamber of the housing that faces the front side of the speaker unit.

14. An electroacoustic converter according to claim 8, comprising: a further sound collection means installed in the front chamber of the housing facing the front side of the speaker unit, for collecting sound radiated from the speaker unit and detecting noise components incident into the front chamber from outside the housing; a further signal generation means for converting the sound collected by the further sound collection means into a signal having predetermined characteristics; and a further amplitude detection means for detecting the amplitude of the sound collected by the further sound collection means and changes therein, wherein the further signal generation means includes a noise cancellation signal generation means for generating a noise cancellation signal to reduce environmental noise using the sound collected by the further sound collection means, the noise cancellation signal generation means generates the noise cancellation signal in a feedback manner, and the further amplitude detection means has a detection function for detecting changes in the characteristics of the surrounding environment and the signal processing system by detecting when the amplitude of the high-frequency band exceeding the audible band of the sound exceeds a predetermined amplitude.

15. The electroacoustic converter according to claim 14, wherein the further signal generating means generates a signal that causes the user to perceive the sound collected by the sound collecting means naturally or with emphasis.

16. The electroacoustic converter according to claim 14, wherein the further amplitude detection means includes a variable amplification means, and upon detection of the detection function, reduces the amplitude of the signal generated by the signal generation means and inputs it to the drive signal generation means.

17. The electroacoustic converter according to claim 14, characterized in that the further amplitude detection means detects changes in the user's usage state and operations by detecting changes in the characteristics of the surrounding environment and the signal processing system in conjunction with the detection of the detection function.

18. The electroacoustic converter according to claim 14, characterized in that the drive signal generation means synthesizes a playback audio signal supplied from a playback sound source, a signal generated by the signal generation means, and a signal generated by the further signal generation means.

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