Automatic noise reduction device

Abstract

To address a problem in that with a conventional automatic noise reduction device, an emergency broadcast calling for emergency evacuation is difficult to correctly reach an operator at a work site where a loud noise occurs.SOLUTION: An automatic noise reduction device 10 of the present invention uses a first sound pressure level adjustment circuit part 31 and a second sound pressure level adjustment circuit part 32 to compress a sound pressure level of a first sound signal collected from a microphone part 22 in two stages to perform attenuation processing. By this control method, a sound such as an emergency broadcast overlapped on noise that occurs at a work site remains in a level which is audible for an operator and is emitted as an adjusted sound from an earphone part 23. As a result, the operator perceives an accident situation or the like at the work site in an early stage and evacuates, so that the safety of himself / herself and operators around him / her is achieved.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an automatic noise reduction device. [Background technology]

[0002] BACKGROUND ART For example, the structure described in Patent Document 1 is known as a conventional automatic noise reduction device.

[0003] Conventionally, soundproof earplugs have been used at noisy construction sites. Soundproof earplugs are cylindrically shaped pieces of soundproof material that are compressed and inserted into the ear canal. Because of this structure, these earplugs uniformly block external sounds, blocking not only noise but also speech.

[0004] Therefore, the automatic noise reduction device described in Patent Document 1 was developed to prevent deterioration of hearing function due to noise in noisy environments such as construction sites, and to make it easier to hear conversations that overlap with noise.

[0005] The automatic noise reduction device mainly comprises a microphone that generates a sound collection signal, a first filter circuit that removes low frequency components from the sound collection signal, a second filter circuit that removes high frequency components from the sound collection signal, a diode circuit that clamps audio signals of 100 dBspl or more, a variable attenuation circuit, earphones that emit the adjusted sound, and an automatic noise control circuit.

[0006] In an automatic noise reduction device, when a collected sound signal is continuously supplied at a signal level higher than normal conversation, the device determines that the input sound is noise. The first and second filter circuits of the automatic noise reduction device then remove high- and low-frequency components from the collected sound signal to generate a collected sound signal with mid-frequency components, and the diode circuit diode-clamps the collected sound signal at 100 dBspl or higher. The automatic noise reduction device then narrows the frequency band of the collected sound signal to a mid-frequency band centered on conversation, thereby preventing the conversation sound from being masked by noise. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 06-177683 Summary of the Invention [Problem to be solved by the invention]

[0008] When an accident or other trouble occurs at a construction site, it is necessary to notify workers working on site by using emergency broadcasts such as sirens and announcements, or by turning on lights, etc., and to evacuate the workers. In this case, sirens and emergency announcements are often made continuously at a higher sound pressure than normal conversation. In addition, even when making emergency announcements, the sound may be in a higher frequency range than normal conversation due to the speaker's nervousness, etc., in order to quickly convey evacuation instructions to workers.

[0009] As a result, conventional automatic noise reduction devices may determine that the continuously playing sirens, emergency broadcast announcements, etc. are noise, and remove high- and low-frequency components from the sound signal collected by a microphone, resulting in the siren, emergency broadcast announcements, etc. being attenuated along with the noise. Furthermore, there is a problem that workers may have difficulty hearing the emergency broadcast announcements, or may not be able to hear them at all, which could result in the emergency broadcast calling for emergency evacuation not being accurately conveyed to the workers, delaying their emergency evacuation and exacerbating the damage.

[0010] Furthermore, if the diode circuit also filters the mid-to-high frequency emergency broadcast audio signal whose low frequencies have been attenuated by the first filter circuit, some of the audio signal may be lost, making it possible for workers to not understand the content of the emergency broadcast announcement. In this case, the delay in the emergency evacuation of the workers mentioned above may lead to an increase in damage, which poses a major problem in terms of crisis prevention at construction sites, etc.

[0011] Furthermore, noise generated at construction sites and the like naturally exists not only in the high-frequency and low-frequency bands of the collected sound signal, but also in the mid-frequency band. As described above, conventional automatic noise reduction devices remove noise with high and low frequency components from the collected sound signal, but workers continue to hear high-sound-pressure noise along with conversation sounds present in the mid-frequency band. As a result, if conventional automatic noise reduction devices cannot adjust the volume of the sound pressure level, workers may develop hearing impairments, such as hearing loss, due to continued exposure to the high-sound-pressure noise.

[0012] In other words, in the conventional automatic noise reduction device described in Patent Document 1, the variable attenuation circuit is used as a circuit that adjusts the sound pressure level of the collected sound signal from which the above-mentioned certain noise band has been removed by the first and second filter circuits. In other words, in the conventional automatic noise reduction device, the sound pressure level is attenuated by one-stage control of the variable attenuation circuit, with the attenuation range being a maximum of 15 dB. Furthermore, it is described that the conventional automatic noise reduction device was invented with a limit sound pressure level of 100 dBspl. As a result, workers at construction sites and the like are exposed to noise of 85 dBspl on a daily basis, posing a problem of the risk of the workers developing hearing impairments such as hearing loss.

[0013] The present invention has been made in consideration of the above circumstances, and aims to provide an automatic noise reduction device that ensures the safety of workers by attenuating the sound pressure level of an external sound signal collected from a microphone unit in two stages and emitting an adjusted sound from an earphone unit that balances the noise and any voices that overlap with the noise. [Means for solving the problem]

[0014] The automatic noise reduction device of the present invention is an automatic noise reduction device used in factories or work sites where noise is generated, and is equipped with a microphone unit, a first sound pressure level adjustment circuit unit, a second sound pressure level adjustment circuit unit, and an earphone unit, and is characterized in that when the sound pressure level of a first audio signal collected and generated by the microphone unit is 85 dBspl or higher, the first sound pressure level adjustment circuit unit outputs a second audio signal in which the sound pressure level of the first audio signal has been automatically adjusted to the first sound pressure level, the second sound pressure level adjustment circuit unit outputs a third audio signal in which the sound pressure level of the second audio signal has been adjusted to a second sound pressure level that is lower than the first sound pressure level, and the earphone unit emits the third audio signal as an adjusted sound.

[0015] Moreover, in the automatic noise reduction device of the present invention, the first sound pressure level adjustment circuit section does not have a diode circuit that clamps the first audio signal at a set sound pressure level or higher.

[0016] In the automatic noise reduction device of the present invention, the adjustment sound includes the noise and a sound within the factory or the work site that overlaps with the noise.

[0017] In the automatic noise reduction device of the present invention, the second sound pressure level adjustment circuit varies the second sound pressure level in multiple stages and outputs the second sound pressure level as the third audio signal.

[0018] Furthermore, in the automatic noise reduction device of the present invention, when the sound pressure level of the first audio signal is lower than 85 dBspl, the variable level control circuit of the first sound pressure level adjustment circuit unit is not driven, and the first sound pressure level adjustment circuit unit outputs the first audio signal to the second sound pressure level adjustment circuit unit.

[0019] In the automatic noise reduction device of the present invention, a transistor constituting the second sound pressure level adjustment circuit section is driven by a control voltage output from the first sound pressure level adjustment circuit section. [Effects of the Invention]

[0020] The automatic noise reduction device of the present invention uses a first sound pressure level adjustment circuit and a second sound pressure level adjustment circuit to compress and attenuate the sound pressure level of a first audio signal collected from a microphone in two stages. This control method allows sounds such as emergency broadcast announcements that overlap with noise generated at the work site to remain at a level audible to workers and is emitted from the earphone unit as adjusted sound. As a result, workers can quickly grasp the situation at the work site, such as an accident, and evacuate, ensuring their own safety and the safety of surrounding workers.

[0021] Furthermore, the automatic noise reduction device of the present invention does not use a diode circuit that clamps external sound signals above a predetermined set sound pressure level, and prevents loss of external sound signals such as emergency broadcast announcements contained in noise within a factory, etc. This enables workers to hear the announcements without loss and accurately grasp the situation of the accident at the site, etc.

[0022] Furthermore, with the automatic noise reduction device of the present invention, noise is also emitted from the earphone unit as an adjustment sound at a sound pressure level that is unlikely to cause hearing damage to the worker. This control method allows the worker to proceed with their work while being aware of the source of the noise, thereby ensuring safety at the workplace.

[0023] Furthermore, in the automatic noise reduction device of the present invention, the second sound pressure level adjustment circuit outputs a third audio signal in which the second sound pressure level is varied in multiple stages. This control method allows the worker to hear from the automatic noise reduction device 10 an adjusted sound with a sound pressure level that is suited to the worker, depending on the type of work, the working time, the worker's own hearing condition, etc.

[0024] Furthermore, in the automatic noise reduction device of the present invention, when the noise generated at the workplace is less than 85 dBspl, the first audio signal is emitted from the earphone unit. With this control method, the worker hears audio and noise equivalent to when their ear canal is open, allowing them to continue working safely without removing the earphone unit, thereby improving work efficiency.

[0025] In the automatic noise reduction device of the present invention, the transistor constituting the second sound pressure level adjustment circuit is driven by a control voltage output from the first sound pressure level adjustment circuit. This control method enables attenuation control corresponding to a wide range of sound pressure levels, even 85 dBspl or higher. Furthermore, when the sound pressure level of the external sound signal is lower than 85 dBspl, the external sound signal is emitted from the earphone without driving the variable level control circuit of the second sound pressure level adjustment circuit. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a perspective view illustrating an automatic noise reduction device according to an embodiment of the present invention. [Figure 2A] 1 is a side view illustrating an automatic noise reduction device according to an embodiment of the present invention. [Figure 2B] 1 is a schematic diagram illustrating a state in which an automatic noise reduction device according to an embodiment of the present invention is used. [Figure 3] 1 is a circuit diagram illustrating a sound pressure level adjustment circuit incorporated in an automatic noise reduction device according to an embodiment of the present invention. [Figure 4] 3 is a characteristic diagram illustrating a first sound pressure level adjustment circuit section incorporated in an automatic noise reduction device according to one embodiment of the present invention. FIG. [Figure 5] 3 is a characteristic diagram illustrating a second sound pressure level adjustment circuit section incorporated in an automatic noise reduction device according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] An automatic noise reduction device 10 according to one embodiment of the present invention will now be described in detail with reference to the drawings. In describing this embodiment, the same reference numerals will be used for the same components, and repeated explanations will be omitted.

[0028] FIG. 1 is a perspective view illustrating an automatic noise reduction device 10 of this embodiment. FIG. 2A is a side view illustrating a first mounting portion 12 of the automatic noise reduction device 10 of this embodiment. FIG. 2B is a schematic diagram illustrating a state in which the first mounting portion 12 of the automatic noise reduction device 10 of this embodiment is in use. FIG. 3 is a circuit diagram illustrating a sound pressure level adjustment circuit incorporated into the automatic noise reduction device 10 of this embodiment. FIG. 4 is a characteristics diagram illustrating sound pressure level adjustment in a first sound pressure level adjustment circuit unit 31 incorporated into the automatic noise reduction device 10 of this embodiment. FIG. 5 is a characteristics diagram illustrating sound pressure level adjustment in a second sound pressure level adjustment circuit unit 32 incorporated into the automatic noise reduction device 10 of this embodiment.

[0029] 1, automatic noise reduction device 10 mainly comprises a main body 11, and a first mounting part 12 and a second mounting part 13 connected to main body 11 via wiring 14. Automatic noise reduction device 10 is used in a factory or at an outdoor work site, and a worker uses it by inserting first mounting part 12 and second mounting part 13 near the entrance of ear canals 24 (see FIG. 2B) of each of their left and right ears 20 (see FIG. 2B), respectively.

[0030] As will be described in detail later, the automatic noise reduction device 10 attenuates the sound pressure level of external sounds, including noise and voices, generated at the workplace, and then emits adjusted sounds that have been adjusted for the external sounds to the worker. As a result, the worker's left and right ears 20 are covered by the first and second mounting parts 12 and 13, preventing them from directly hearing noises of 85 dBspl or more generated at the workplace. The worker is less likely to suffer from hearing damage by hearing the adjusted sounds, the sound pressure levels of which have been emitted from the first and second mounting parts 12 and 13.

[0031] Furthermore, the automatic noise reduction device 10 emits, as the adjustment sound, noise and voice that have been processed to reduce the external sound, from the earphone unit 23. By listening to the adjustment sound from the automatic noise reduction device 10, the worker can proceed with work while understanding the source of the noise, thereby ensuring safety at the work site. Meanwhile, if an accident or the like occurs at the work site, the worker can understand the audio of emergency broadcast announcements such as evacuation instructions, which are included in the adjustment sound.

[0032] In other words, in the automatic noise reduction device 10 of this embodiment, at least the first sound pressure level adjustment circuit unit 31 described below does not have a diode circuit (hereinafter referred to as a "clamp diode circuit") that clamps the external sound signal S1 contained in noise that is equal to or greater than a desired set sound pressure level, as in the conventional automatic noise reduction device described above, thereby preventing the announcement from being cut off in the emergency broadcast.The worker can then hear the announcement in its uncut state through the earphone unit 23 and accurately understand its content.

[0033] As a result, workers can quickly grasp the situation of an accident at the work site and evacuate, thereby ensuring the safety of themselves and other workers in the vicinity.

[0034] 2A, the first wearing unit 12 includes, for example, a cylindrical housing 21, a microphone 22 disposed inside the housing 21 at the rear end, and an earphone 23 disposed at the front end of the housing 21. The earphone 23 has a speaker 23A disposed inside the housing 21 and an earpiece 23B inserted into the ear canal 24 of the worker.

[0035] 2B , when the first attachment unit 12 is attached to the ear canal 24 of the worker's ear 20, the microphone unit 22 is positioned outside the worker's ear 20. The microphone unit 22 collects external sounds, such as noise and voice, that reach the worker's ear, converts the collected external sounds into an electrical signal, and generates an external sound signal S1. The first audio signal of the present invention corresponds to the external audio signal S1 of this embodiment.

[0036] Meanwhile, the earpiece 23B of the earphone unit 23 is inserted into the ear canal 24 of the worker and is brought into close contact with the ear canal 24, thereby maintaining the first fitting unit 12 in a state of being fitted to the ear canal 24. The speaker unit 23A then converts the external sound signal S1, which has been attenuated in the automatic noise reduction device 10, from an electrical signal back into an adjusted sound, and emits the adjusted sound into the ear canal 24.

[0037] In the automatic noise reduction device 10 of this embodiment, for example, the first mounting part 12 is mounted on the right ear 20 of the worker via the earphone part 23, and the second mounting part 13 is mounted on the left ear 20 of the worker via the earphone part 23. The worker's ear canal 24 is then blocked by the first mounting part 12 and the second mounting part 13, preventing the worker from directly hearing noise of 85 dBspl or more generated at the workplace. The second mounting part 13 has the same structure as the first mounting part 12, and the above description of the first mounting part 12 should be referred to, and a description thereof will be omitted here.

[0038] 1, the main body 11 is formed with a first sound pressure level adjustment circuit 31 and a second sound pressure level adjustment circuit 32 for adjusting the sound pressure level of external sound, as shown in FIG. 3, which will be described later. An external sound signal S1 generated by the first wearing part 12 and the second wearing part 13 is input to the main body 11 via a wiring 14. The main body 11 is also provided with a volume adjustment part 25, which can be operated by an operator, for example, by rotation. As will be described in detail later, when the operator rotates the volume adjustment part 25, the sound pressure level to be attenuated by the second sound pressure level adjustment circuit 32 (see FIG. 3) is adjusted in stages.

[0039] 3, the automatic noise reduction device 10 mainly includes a microphone unit 22 that collects external sound and generates an external sound signal S1, a first sound pressure level adjustment circuit unit 31 that attenuates the external sound signal S1 for external sounds of 85 dBspl or more and generates a first adjusted sound signal S2 at a constant first sound pressure level, a second sound pressure level adjustment circuit unit 32 that attenuates the sound pressure level of the first adjusted sound signal S2 to a second sound pressure level below the first sound pressure level and generates a second adjusted sound signal S3, an amplifier circuit 38 that amplifies the second adjusted sound signal S3, and an earphone unit 23 that converts the external sound signal S1 into an external sound at the same sound pressure level as when it was input and emits the sound, or converts the second adjusted sound signal S3 into an adjusted sound and emits the sound. The second sound signal of the present invention corresponds to the first adjusted sound signal S2 of this embodiment, and the third sound signal of the present invention corresponds to the second adjusted sound signal S3 of this embodiment.

[0040] The first sound pressure level adjustment circuit unit 31 is an ALC (Automatic Level Control) circuit. The first sound pressure level adjustment circuit unit 31 mainly includes a variable level control circuit 31A in the preceding stage and an audio signal level detection circuit 34 in the succeeding stage. The first sound pressure level adjustment circuit unit 31 is formed downstream of the microphone unit 22, and receives an audio signal S1 converted from an external sound by the microphone unit 22.

[0041] Unlike the conventional automatic noise reduction device described above, the first sound pressure level adjustment circuit unit 31 does not use a clamp diode circuit that clamps the external sound signal S1 that is equal to or higher than a predetermined set sound pressure level, but instead converts the external sound signal S1 input from the microphone unit 22 into a first adjusted sound signal S2 using a variable level control circuit 31A and outputs the first adjusted sound signal S2 to the second sound pressure level adjustment circuit unit 32. The first sound pressure level adjustment circuit unit 31 of this embodiment converts the external sound signal S1 with a sound pressure level of 85 dBspl or higher into the first adjusted sound signal S2 with a constant sound pressure level that is equal to or lower than the sound pressure level of the external sound signal S1, for example, a sound pressure level of 85 dBspl.

[0042] In other words, the variable level control circuit 31A of the first sound pressure level adjustment circuit unit 31 is a circuit that adjusts the input voltage V1 of the external sound signal S1 and automatically controls the output voltage from the amplifier circuit 33 to become the voltage V2 set by the audio signal level detection circuit 34. As described above, the voltage V2 is a constant voltage lower than the input voltage V1.

[0043] The variable level control circuit 31A has a transistor 35 that is automatically controlled by an audio signal level detection circuit 34. Meanwhile, the audio signal level detection circuit 34 receives an external sound signal S1 via an amplifier circuit 33, detects the signal, and detects a detection voltage V4. The audio signal level detection circuit 34 then applies the detected detection voltage V4 to the base of the transistor 35, driving the transistor 35 and controlling the collector impedance of the transistor 35. The variable level control circuit 31A controls the output voltage divided by the collector impedance and resistor 40 to become the set voltage V2.

[0044] Here, the detection voltage V4 in this embodiment is a voltage that is detected when the sound pressure level of the external sound signal S1 is 85 dBspl or more, and is a voltage that indicates a sound pressure level of 85 dBspl or more generated by the first sound pressure level adjustment circuit unit 31.

[0045] When the input voltage V1 of the external sound signal S1 is greater than the preset voltage V2, the audio signal level detection circuit 34 automatically attenuates the external sound signal S1 so that the output voltage becomes the voltage V2. In other words, in this embodiment, the voltage V2 is a preset value for a sound pressure level of 85 dBspl. When the sound pressure level of the external sound signal S1 is 85 dBspl or higher, the audio signal level detection circuit 34 is activated. The audio signal level detection circuit 34 then activates the transistor 35 and attenuates the external sound signal S1 using the variable level control circuit 31A. When the sound pressure level of the external sound signal S1 is 85 dBspl or higher, the first sound pressure level adjustment circuit 31 generates a first adjusted sound signal S2. The first sound pressure level adjustment circuit 31 then outputs the first adjusted sound signal S2 to the second sound pressure level adjustment circuit 32.

[0046] 4, in the first sound pressure level adjustment circuit unit 31, when the input voltage V1 due to the external sound signal S1 is equal to or lower than a set voltage V2, the audio signal level detection circuit 34 and the transistor 35 are not driven, and the external sound signal S1 is output as is to the second sound pressure level adjustment circuit unit 32. As shown in the figure, in the first sound pressure level adjustment circuit unit 31, when the sound pressure level of the external sound signal S1 is 85 dBspl or higher, the sound pressure level of the external sound signal is compressed to 85 dBspl and attenuated.

[0047] The second sound pressure level adjustment circuit 32 is mainly configured using a transistor 36, a collector resistor 37 connected to the collector of the transistor 36, and a resistor 39, and forms a variable level control circuit. The second sound pressure level adjustment circuit 32 is formed downstream of the first sound pressure level adjustment circuit 31, and receives the first adjustment sound signal S2 or the external sound signal S1 from the first sound pressure level adjustment circuit 31. When the first adjustment sound signal S2 is input, the second sound pressure level adjustment circuit 32 attenuates the first adjustment sound signal S2 using the detection voltage V4 detected by the audio signal level detection circuit 34 so that the output voltage becomes voltage V3. Note that the second sound pressure level adjustment circuit 32 is also configured without using a clamp diode circuit that clamps the external sound signal S1 or the first adjustment sound signal S2 above a predetermined set sound pressure level, as in the conventional automatic noise reduction device described above.

[0048] As described above, the detection voltage V4 detected by the audio signal level detection circuit 34 is applied to the base of the transistor 36, thereby driving the transistor 36. Then, the second sound pressure level adjustment circuit unit 32 controls the output voltage divided by the collector resistor 37 and the resistor 39 to become the set voltage V3, thereby generating the second adjustment sound signal S3.

[0049] In the automatic noise reduction device 10 of this embodiment, the sound pressure level attenuated by the second sound pressure level adjustment circuit 32 is continuously and stepwise adjusted by the operator's rotation of the volume adjustment unit 25. As shown in FIG. 5 , the second sound pressure level adjustment circuit 32 varies the resistance value Rc of the collector resistor 37 selected by the operator, thereby adjusting the amount of attenuation of the sound pressure level. For example, the sound pressure level of the second adjustment sound signal S3 is continuously adjusted between 50 dBspl and 70 dBspl. Note that the adjustable sound pressure level can be arbitrarily modified by design. The sound pressure level of the second sound pressure level adjustment circuit 32 may also be adjusted stepwise.

[0050] Thereafter, the second sound pressure level adjustment circuit 32 outputs the second adjustment sound signal S3 to the speaker 23A of the earphone 23 via the amplifier circuit .

[0051] Here, the Ministry of Health, Labour and Welfare's "Revision of the Guidelines for Preventing Noise Disturbances (Basic Notification 0420 No. 2: April 20, 2023)" states the following:

[0052] Noise in the workplace is considered a harmful working environment, and in order to prevent health problems, the Industrial Safety and Health Regulations (Ministry of Labour Ordinance No. 32 of 1972) require the implementation of work environment measurements in designated workplaces, the clear indication of noise-emitting locations, the prevention of noise transmission, and the provision of protective equipment.In addition, in Basic Notification No. 546 dated October 1, 1992, entitled "Regarding the Revision of the Guidelines for the Prevention of Noise Disturbances," the "Guidelines for the Prevention of Noise Disturbances" (hereinafter referred to as the "Old Guidelines") were established, which systematized noise disturbance prevention measures that employers are encouraged to take voluntarily, and efforts have been made to establish these guidelines.

[0053] The above guidelines, for example, state in "Measurement of equivalent sound pressure levels by fixed point measurements (Appendix 2)" that, as measures based on the measurement results, employers should "strive to continuously maintain the working environment at the location if the level is below 85 dBspl," and "if the level is between 85 dBspl and 90 dBspl, (a) inspect the facilities, equipment, work processes, or work methods, and based on the results, take necessary measures to improve the working environment, such as installing or maintaining facilities or equipment, improving work processes or methods, or otherwise striving to keep the equivalent sound pressure level below 85 dBspl, and (b) require workers engaged in noisy work to use hearing protection as necessary." Based on these, the Ministry of Health, Labour and Welfare has adopted "85 dBspl" as the standard value for sound pressure levels of noise.

[0054] As described above, the first sound pressure level adjustment circuit section 31 of this embodiment performs a first-stage attenuation process of the automatic noise reduction device 10 by uniformly compressing and attenuating the sound pressure level of external sounds, including noise generated at the work site, to 85 dBspl, without limiting the frequency band of the external sounds. Then, the second sound pressure level adjustment circuit section 32 performs a second-stage attenuation process of the automatic noise reduction device 10 by uniformly compressing and attenuating the sound pressure level to a sound pressure level that is set in multiple stages in response to the operation of the volume adjustment section 25 by the worker.

[0055] 3, in the second sound pressure level adjustment circuit section 32, the base of the transistor 36 is connected to the audio signal level detection circuit 34 of the first sound pressure level adjustment circuit section 31. With this circuit configuration, when the audio signal level detection circuit 34 is driven, a control voltage is applied to the base of the transistor 36, and the transistor 36 is driven.

[0056] On the other hand, as described above, in the first sound pressure level adjustment circuit unit 31, when the input voltage V1 due to the external sound signal S1 is equal to or lower than the set voltage V2, the audio signal level detection circuit 34 is not driven, and therefore the transistor 35 is not driven. The transistor 36 of the second sound pressure level adjustment circuit unit 32 is also not driven, and the input external sound signal S1 is output directly to the speaker unit 23A via the amplifier circuit 38. In this case, noise with the same sound pressure level as the noise input to the microphone unit 22 is emitted into the ear canal 24. Since the sound pressure level of the noise is less than 85 dBspl, this is in compliance with the Ministry of Health, Labour and Welfare guidelines mentioned above.

[0057] In the automatic noise reduction device 10 of this embodiment, the sound pressure level of the external sound, including noise, is uniformly attenuated in two stages in response to the external sound signal S1 converted by the microphone unit 22 using the first sound pressure level adjustment circuit unit 31 and the second sound pressure level adjustment circuit unit 32, without being limited to a certain frequency band.

[0058] External sounds may include emergency broadcast announcements overlapping with high-sound-pressure-level noise, and the announcements are intended to alert workers to danger and are expected to have sound pressure levels close to those of the actual noise. Therefore, the automatic noise reduction device 10 of this embodiment does not have the clamp diode circuit of the conventional automatic noise reduction device described above, and therefore the first sound pressure level adjustment circuit unit 31 and the second sound pressure level adjustment circuit unit 32 clip the announcement audio, preventing any loss of part of it.

[0059] As a result, the audio of the announcement is compressed and attenuated to a conversational level of about 70 dBspl, allowing workers to hear and recognize the entire audio of the announcement contained in the noise as an adjusted sound. This allows workers to quickly grasp the situation of an accident at the work site and evacuate, ensuring the safety of themselves and surrounding workers.

[0060] Furthermore, the sound pressure level of noise varies depending on the work site, and the hearing condition of the worker also varies depending on factors such as the worker's age. Therefore, the automatic noise reduction device 10 uses a second sound pressure level adjustment circuit unit 32 as a second-stage sound pressure level attenuation processing means. This control method allows the worker to select the sound pressure level of the adjusted sound output from the speaker unit 23A based on the type of work, the working time, the worker's hearing condition, etc. As a result, by hearing the adjusted sound at a sound pressure level that suits the worker from the automatic noise reduction device 10, the worker can identify the source of the noise and proceed with the work while being prepared for an emergency, thereby ensuring safety at the work site. Furthermore, the worker's hearing function is also protected.

[0061] In this embodiment, the audio signal level detection circuit 34 of the first sound pressure level adjustment circuit section 31 is driven to drive the transistor 36 of the second sound pressure level adjustment circuit section 32, but the present invention is not limited to this. For example, a separate audio signal level detection circuit may be formed in the second sound pressure level adjustment circuit section 32, and a control voltage may be applied to the base of the transistor 36.

[0062] In addition, in the first sound pressure level adjustment circuit unit 31, the sound pressure level of the external sound signal S1 is attenuated to 85 dBspl as the first stage of attenuation processing, but this is not limited to this case. For example, in a work site where noise of 120 dBspl or more is generated, the sound pressure level of the external sound signal S1 may be attenuated to 90 dBspl as the first stage of attenuation processing. As described above, the automatic noise reduction device 10 adjusts the sound pressure level in two stages, thereby ensuring the safety of the worker by keeping the voice of the emergency broadcast announcement that overlaps with the noise at a level that the worker can hear. Various other modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0063] 10 Automatic noise reduction device 11 Main body 12 First mounting part 13 Second mounting part 14 Wiring 20 ears 21 Housing 22 Microphone section 23 Earphone section 23A Speaker section 23B earpiece 24 External auditory canal 25 Volume control section 31 First sound pressure level adjustment circuit section 31A variable level control circuit 32 Second sound pressure level adjustment circuit section 33 Amplification circuit 34 Audio signal level detection circuit 35 transistors 36 transistors 37 Collector resistor 38 Amplification circuit 39 Resistance 40 Resistance

Claims

1. An automatic noise reduction device for use in a factory or work site where noise is generated, The device includes a microphone unit, a first sound pressure level adjustment circuit unit, a second sound pressure level adjustment circuit unit, and an earphone unit, When the sound pressure level of the first audio signal collected and generated by the microphone unit is 85 dBspl or more, the first sound pressure level adjustment circuit unit automatically adjusts the sound pressure level of the first sound signal to a first sound pressure level and outputs a second sound signal; the second sound pressure level adjustment circuit unit outputs a third sound signal obtained by adjusting the sound pressure level of the second sound signal to a second sound pressure level that is lower than the first sound pressure level; The automatic noise reduction device is characterized in that the earphone unit emits the third audio signal as an adjustment sound.

2. 2. The automatic noise reduction device according to claim 1, wherein the first sound pressure level adjustment circuit does not include a diode circuit for clamping the first audio signal at a sound pressure level equal to or higher than a set sound pressure level.

3. 3. The automatic noise reduction device according to claim 2, wherein the adjustment sound includes the noise and a sound within the factory or the work site that overlaps with the noise.

4. 4. The automatic noise reduction device according to claim 3, wherein the second sound pressure level adjusting circuit varies the second sound pressure level in multiple stages and outputs the second sound pressure level as the third audio signal.

5. If the sound pressure level of the first audio signal is less than 85 dBspl, 5. An automatic noise reduction device according to claim 1, wherein the first sound pressure level adjustment circuit outputs the first audio signal to the second sound pressure level adjustment circuit without driving a variable level control circuit of the first sound pressure level adjustment circuit.

6. 6. An automatic noise reduction device according to claim 5, wherein a transistor constituting said second sound pressure level adjustment circuit section is driven by a control voltage output from said first sound pressure level adjustment circuit section.

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