Noise reduction earmuffs

Abstract

The present invention discloses a noise reduction earmuff, comprising an earmuff shell forming an earmuff cavity, a partition installed in the earmuff cavity and forming an independent cavity, and a conduit installed on the partition; one of the two end openings of the conduit is located in the cavity, and the other extends out of the cavity and is located in the earmuff cavity; the cavity and the conduit form a low-frequency resonator, and its resonance frequency is equivalent to the turning frequency of the low-pass filter formed by the earmuff. In solving the problem of earmuff isolation noise, the present invention adopts the method of arranging a low-frequency resonator in the earmuff cavity, and utilizes the resonance sound absorption effect of the low-frequency resonator to absorb the noise energy of passive sound insulation in the earmuff cavity near the resonance frequency of the low-frequency resonator, thereby avoiding the noise lifting and amplification problem in the low-frequency part of passive sound insulation, and realizing the balance of noise attenuation energy and attenuation frequency band in the earmuff cavity, which can not only protect human ears, but also reduce the overall size of the earmuff and improve the comfort of the wearer.

Description

Technical Field

[0001] The invention belongs to the technical field of noise protection, and in particular relates to a protective earmuff or earphone product for isolating external noise. Background Art

[0002] In the field of high-frequency noise protection, protective earmuffs can achieve good high-frequency noise isolation effect. For people working in special environments, wearing protective earmuffs can effectively protect the ears.

[0003] At present, in order to effectively isolate low-frequency noise, traditional protective earmuffs often use thick earmuff shells to form large-sized earmuff cavities. The earmuff shell and the earmuff cavity can form a low-pass filter to greatly isolate the high-frequency noise from the outside world, so that the noise that passes through the earmuff shell and enters the earmuff cavity mainly comes from the low-frequency part of the external noise that is lower than the turning frequency of the low-pass filter. The thicker the earmuff shell and the larger the earmuff cavity, the lower the turning frequency of the low-pass filter, and the more frequency bands of noise can be filtered out by the earmuff, which makes the noise isolation effect of the earmuff better. However, this traditional design of protective earmuffs not only makes the earmuffs bulky and unsightly, but also bulky and uncomfortable to wear, which seriously affects the wearer's experience. In addition, the passive sound insulation entering the earmuff cavity will cause the noise to rise and amplify near the turning frequency point. When the amplified frequency band energy exists in the ambient noise for a long time, it will cause fatigue to the wearer, and long-term use will also cause irreversible hearing damage. Summary of the invention

[0004] The object of the present invention is to provide a noise reduction earmuff, which can effectively control the volume of the earmuff and reduce the weight of the earmuff by adding a low-frequency resonator in the earmuff cavity to absorb the low-frequency noise energy in the earmuff cavity, thereby improving the noise isolation effect of the earmuff.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] In one aspect, the present invention provides a noise reduction earmuff, comprising an earmuff shell forming an earmuff cavity, a partition installed in the earmuff cavity and forming an independent cavity, and a duct installed on the partition; the duct has two openings, one located in the cavity and the other extending out of the cavity and located in the earmuff cavity; the cavity and the duct form a low-frequency resonator, and its resonance frequency is equivalent to the turning frequency of the low-pass filter formed by the earmuff.

[0007] Furthermore, an opening is formed on the side of the earmuff shell facing the human ear, and an earmuff is installed on the earmuff shell at the opening to improve the wearing comfort of the earmuff; for the earmuff installed with the earmuff, the corner frequency of the low-pass filter can be determined by the equivalent inductance of the earmuff shell and the equivalent capacitance of the earmuff cavity and the earmuff.

[0008] In order to expand the cavity space of the low-frequency resonator, it is preferred to fill the cavity with sound-absorbing material to increase the equivalent capacitance value of the cavity and further reduce the resonance frequency.

[0009] In the case where the earmuff is an earmuff in a headphone, the rear cavity of the speaker in the earmuff can be directly selected as the chamber, and a baffle is set in the rear cavity of the speaker. When the speaker outputs sound, the baffle blocks the opening of the conduit in the chamber to prevent the low-frequency energy in the audio signal or the communication signal from being offset; when the speaker has no sound output, the baffle is away from the opening of the conduit in the chamber, and the low-frequency resonator formed by the rear cavity of the speaker and the conduit is used to absorb the low-frequency noise energy in the earmuff, thereby reducing the low-frequency noise.

[0010] Preferably, the armature in the electromagnetic relay can be used as the baffle to block the opening of the conduit, that is, when the speaker receives an audio signal, the electromagnetic relay generates a magnetic field to attract the armature to move, thereby blocking the opening of the conduit in the chamber; when the speaker has no audio signal connected, the electromagnetic relay releases the armature to move the armature away from the opening of the conduit in the chamber.

[0011] In order to control the accurate action of the electromagnetic relay, the present invention further provides a comparator in the noise-proof earmuffs, and utilizes the two input ends of the comparator to receive the trigger voltage and the audio signal respectively, and the output end is connected to the control end of a switch element, and the switch path of the switch element is connected to the power supply circuit of the coil of the electromagnetic relay; the amplitude of the trigger voltage is lower than the amplitude of the bias voltage in the audio signal, and when an audio signal is connected, the comparator output level controls the switch element to conduct, connects the power supply circuit of the coil of the electromagnetic relay, and energizes the coil to generate a magnetic field, attracts the armature to move, and blocks the opening of the catheter in the chamber. At this time, the rear cavity of the speaker and the catheter cannot form a low-frequency resonator, and will not absorb the low-frequency energy in the earmuffs, so the normal output of the low-frequency energy in the audio signal or communication signal can be ensured.

[0012] In another aspect, the present invention also proposes a noise reduction earmuff, comprising an earmuff shell forming an earmuff cavity, a partition installed in the earmuff cavity and forming an independent chamber, and a passive radiator installed on the partition; the chamber and the passive radiator form a low-frequency resonator, and its resonance frequency is equivalent to the turning frequency of the low-pass filter formed by the earmuff.

[0013] In yet another aspect, the present invention provides another noise-reducing earmuff, comprising an earmuff shell forming an earmuff cavity, a partition installed in the earmuff cavity and forming an independent cavity, a passive radiator and a duct installed on the partition; the duct has two end openings, one located in the cavity and the other extending out of the cavity and located in the earmuff cavity; the cavity, the passive radiator and the duct form a low-frequency resonator, and its resonance frequency is equivalent to the turning frequency of the low-pass filter formed by the earmuff.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: in solving the problem of earmuffs isolating noise, the present invention abandons the traditional structural design of thickening the earmuff shell and enlarging the earmuff cavity, and instead adopts a method of arranging a low-frequency resonator in the earmuff cavity, and utilizes the resonant sound absorption effect of the low-frequency resonator to absorb the noise energy of passive sound insulation in the earmuff cavity near the resonant frequency of the low-frequency resonator, thereby avoiding the noise lifting and amplification problem in the low-frequency part of passive sound insulation, and achieving the balance of noise attenuation energy and attenuation frequency band in the earmuff cavity, which is not only beneficial to protecting the wearer's hearing, but also can reduce the overall size of the earmuff and improve the wearer's comfort.

[0015] Other features and advantages of the present invention will become more apparent after reading the detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the partial structure of a traditional earmuff;

[0017] Figure 2 This is the equivalent circuit schematic diagram of traditional earmuffs after wearing;

[0018] Figure 3 It is a partial structural schematic diagram of an embodiment of the noise reduction earmuff proposed by the present invention;

[0019] Figure 4 yes Figure 3 The equivalent circuit schematic diagram of the noise reduction earmuffs after being worn is shown;

[0020] Figure 5 It is a comparison chart of passive sound insulation attenuation curves in the earmuff cavity;

[0021] Figure 6 is a partial structural schematic diagram of an embodiment of providing a low-frequency resonator in a headphone;

[0022] Figure 7 yes Figure 6 A circuit schematic diagram of an embodiment of an electromagnetic relay control part;

[0023] Figure 8is a partial structural schematic diagram of another embodiment of the noise reduction earmuff proposed by the present invention;

[0024] Fig. 9 It is a partial structural schematic diagram of another embodiment of the noise reduction earmuff proposed by the present invention. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0026] Existing protective earmuffs for isolating noise generally include a headband 1, an earmuff shell 2, an earmuff 6 and other parts, such as Figure 1 As shown. Among them, the earmuff shell 2 includes two, which are connected together by a headline 1, and are respectively used to be worn on the left ear and the right ear of the human body to protect the human ear. Each earmuff shell 2 forms an earmuff cavity 7, and the earmuff shell 2 forms an opening 4 on the side facing the human ear. The wearer's auricle 3 extends into the earmuff cavity 7 through the opening 4, and the earmuff shell 2 is used to block external noise to protect the human ear hearing. In order to improve the comfort of wearing the earmuffs, earmuffs 6 are often installed at the position where the opening 4 is formed on the earmuff shell 2. The earmuffs 6 are preferably made of a highly compliant material that is softer than muscles. The earmuffs 6 fit the facial muscles 5, which can eliminate the discomfort caused by the hard earmuff shell 2 directly contacting the skin to the wearer.

[0027] Figure 2 for Figure 1 The equivalent circuit schematic diagram of the protective earmuffs after wearing is shown. Among them, M1 is the equivalent acoustic mass of the earmuff shell 2, which is equivalent to the electrical inductance; C1 is the equivalent acoustic compliance of the earmuff 6, which is equivalent to the electrical capacitance; R1 is the equivalent acoustic resistance of the earmuff 6, which is equivalent to the electrical resistance; C2 and R2 are the equivalent acoustic compliance and acoustic resistance of the human face muscle 5 respectively; C3 is the equivalent acoustic compliance of the earmuff cavity 7. Figure 2 It can be seen that the sound mass M1 and the sound compliance C1, C2, C3 form a low-pass filter circuit, and its corner frequency f0 can be calculated by the following formula:

[0028]

[0029] Wherein, C is the equivalent capacitance of the low-pass filter circuit, which is jointly determined by the equivalent acoustic compliance C1 of the earmuff 6, the equivalent acoustic compliance C2 of the human face muscle 5, and the equivalent acoustic compliance C3 of the earmuff cavity 7. The equivalent acoustic compliance C1 is connected in parallel with C2, and then connected in series with the equivalent acoustic compliance C3 of the earmuff cavity 7. Considering that the equivalent acoustic compliance C2 of the human face muscle 5 is much smaller than the equivalent acoustic compliance C3 of the earmuff cavity 7, and plays a very small role in the equivalent capacitance C, the size of the equivalent capacitance C can be determined only by the equivalent acoustic compliances C1 and C3 of the earmuff 6 and the earmuff cavity 7. L is the equivalent inductance of the low-pass filter circuit, which can be determined by the equivalent acoustic mass M1 of the earmuff shell 2.

[0030] pass Figure 2 It is not difficult to see that since the earmuff shell 1, the earmuff 6 and the earmuff cavity 7 can form a low-pass filter (for protective earmuffs without earmuffs 6, the earmuff shell 1 and the earmuff cavity 7 can form a low-pass filter), the protective earmuffs can have a good high-frequency noise isolation effect. However, when the external noise P0 enters the earmuff cavity 7 through the earmuff shell 1, the passive sound insulation of this protective earmuff will cause noise lifting and amplification near the turning frequency f0 of the low-pass filter, as shown in FIG. Figure 5 The curve L1 in the figure generates a large amount of low-frequency noise energy, which may cause irreversible hearing damage to people who need to wear such protective earmuffs for a long time.

[0031] Depend on Figure 5 From the curve L1 in FIG. 1 , it can be seen that the noise entering the earmuff cavity 7 shows a second-order attenuation trend (12 dB per octave) in the frequency band greater than the turning frequency f0. Therefore, the lower the turning frequency f0, the more effective the passive noise isolation of the protective earmuff is.

[0032] In order to reduce the transition frequency f0 and improve the noise isolation effect of the protective earmuffs, the traditional design method is to thicken the earmuff shell 2 and enlarge the earmuff cavity 7, thereby increasing the equivalent inductance L and equivalent capacitance C of the low-pass filter circuit to reduce the transition frequency f0. However, this traditional design method will make the protective earmuffs larger and heavier, making them inconvenient to wear.

[0033] In order to solve the above problems, this embodiment adopts a low-frequency resonator set in the earmuff cavity 7, and utilizes the resonant sound absorption effect of the low-frequency resonator to absorb the noise energy near the resonance frequency in the earmuff cavity 7, so as to achieve the design purpose of reducing the noise in the earmuff cavity 7.

[0034] The specific structural design of the noise reduction earmuffs provided with low-frequency resonators is described in detail below through two specific embodiments.

[0035] Embodiment 1, as Figure 3As shown, in order to form a low-frequency resonator in the earmuff, a partition 10 is added to the earmuff cavity 7 surrounded by the earmuff shell 2, and an independent chamber 8 is surrounded in the earmuff cavity 7 by the partition 10, and a conduit 9 is installed on the partition 10. The conduit 9 is hollow and has openings at both ends, and one opening 17 extends into the chamber 8, and the other opening 18 extends out of the chamber 8 and is located in the earmuff cavity 7.

[0036] Figure 4 This is a schematic diagram of the equivalent circuit of a noise-reducing earmuff equipped with a low-frequency resonator after being worn. Figure 4 In the figure, M1 is the equivalent acoustic mass of the earmuff shell 2; C1 and R1 are the equivalent acoustic compliance and acoustic resistance of the earmuff 6 respectively; C2 and R2 are the equivalent acoustic compliance and acoustic resistance of the human face muscle 5 respectively; C3 is the equivalent acoustic compliance of the earmuff cavity 7; M2 is the equivalent acoustic mass of the conduit 9, which is equivalent to the electrical inductance; C4 is the equivalent acoustic compliance of the cavity 8, which is equivalent to the electrical capacitance. Figure 4 It can be seen that the acoustic mass M2 and the acoustic compliance C4 can form a low-frequency resonator, and its resonant frequency f1 can be calculated by the following formula:

[0037]

[0038] Wherein, C' is the equivalent capacitance of the low-frequency resonator, which is determined by the equivalent acoustic compliance C4 of the chamber 8. L' is the equivalent inductance of the low-frequency resonator, which can be determined by the equivalent acoustic mass M2 of the conduit 9.

[0039] Since the low-frequency resonator has a resonant sound absorption effect for absorbing sound energy near its resonant frequency f1, the resonant frequency f1 of the low-frequency resonator can be changed by adjusting the spatial size of the chamber 8 and / or the shape of the conduit 9. By adjusting the resonant frequency f1 of the low-frequency resonator to be equivalent to (i.e., the same as or close to) the turning frequency f0 of the low-pass filter formed by the earmuff, the resonant sound absorption effect of the low-frequency resonator near its resonant frequency f1 can be utilized to absorb the noise energy of the passive sound insulation near the turning frequency f0 of the low-pass filter. This can solve the problem of noise lift and amplification generated by the passive sound insulation in the earmuff cavity 7 near the turning frequency f0, so that the low-frequency noise in the earmuff cavity 7 is effectively attenuated, thereby achieving the purpose of noise reduction and protection.

[0040] Figure 5The curve L2 in the figure is the noise attenuation curve after the low-frequency resonator is installed in the earmuff. It can be seen from the curve L2 that the noise is obviously absorbed near the resonance frequency f1 of the low-frequency resonator. Although the noise in the frequency band greater than the resonance frequency f1 is higher than that without the addition of the low-frequency resonator, the increase amplitude and bandwidth are very small, and the noise isolation in the high-frequency part has reached dozens of dB. Therefore, the impact of the noise increase problem here on the wearer can be ignored, achieving effective protection of the wearer's hearing.

[0041] In this embodiment, the chamber space of the low-frequency resonator can be expanded by filling the chamber 8 with sound-absorbing materials such as sound-absorbing sponge or glass wool felt, that is, increasing the equivalent acoustic compliance C4 of the chamber 8, so as to reduce the resonance frequency f1 of the low-frequency resonator. The conduit 9 can be selected from various air ducts that can produce sound quality, such as hoses and hard pipes, and its form can be a straight pipe, a curved pipe, and the cross-sectional shape can be circular, square or other shapes. As a preferred design of this embodiment, the equivalent acoustic compliance C4 of the chamber 8 can be set to 20cc (cubic centimeters), and the conduit 9 can be selected from a round tube with a diameter of 1.5mm and a length of 10mm.

[0042] By applying the design principle of the low-frequency resonator of this embodiment to the current headphone, the headphone can have the function of noise reduction protection. Figure 6 As shown, current headphones generally include a headline 1 and two left and right earmuff shells 2. Each earmuff shell 2 surrounds an earmuff cavity 7 with an opening 4 on one side. A partition 10 is provided in each earmuff cavity 7. The partition 10 is preferably arranged parallel to the opening 4. The earmuff cavity 7 is divided into two parts by the partition 10, wherein one cavity with the opening 4 can be called an earphone front cavity 11, and the other cavity can be called a speaker rear cavity 12, which is used to accommodate the sound-generating device of the earphone, namely a speaker 13 (or loudspeaker). The speaker 13 is connected to the host through an earphone lead 14 to receive the audio signal emitted by the host. In this embodiment, a conduit 9 is provided on the partition 10, and an opening 17 at one end of the conduit 9 is located in the speaker rear cavity 12, and an opening 18 at the other end is located in the earphone front cavity 11. The speaker rear cavity 12 and the conduit 9 form a low-frequency resonator to absorb low-frequency noise near the resonance frequency in the earphone. The spatial size of the speaker rear cavity 12 and the shape design of the conduit 9 can be imitated from the above-mentioned Figure 3 Related description.

[0043] Considering that when the earphone is working normally, most of the audio signals output through the speaker 13 are low-frequency signals, and inevitably include audio signals near the resonance frequency. If the low-frequency resonator formed by the speaker back cavity 12 and the conduit 9 is allowed to work when the earphone is working normally, the audio signals near the resonance frequency will be absorbed, resulting in the inability to output the sound normally. In order to solve this problem, this embodiment adds a baffle 16 in the speaker back cavity 12, such as Figure 6 As shown. When the speaker 13 outputs sound, the baffle 16 is designed to block the opening 17 of the conduit 9 in the speaker rear cavity 12, thereby destroying the low-frequency resonator, thereby preventing the low-frequency energy in the audio signal or communication signal from being offset. When the speaker 13 does not output sound, the baffle 16 can be designed to be away from the opening 17 of the conduit 9 in the speaker rear cavity 12, and then the low-frequency resonator formed by the speaker rear cavity 12 and the conduit 9 is used to absorb the low-frequency noise energy in the earmuff cavity 7, so as to achieve the noise reduction protection function of the earphone.

[0044] As a preferred structural design of this embodiment, the armature in the electromagnetic relay 15 (the armature is used to drive the movable contact to close or disconnect in the electromagnetic relay) can be used as the baffle 16 to block the opening 17 of the conduit 9. Specifically, the electromagnetic relay 15 can be designed to be energized when the speaker 13 receives an audio signal, so that its coil generates a magnetic field, attracts the armature to move (for example, close to the coil) to block the opening 17 of the conduit 9 located in the speaker rear cavity 12. Conversely, when there is no audio signal connected to the speaker 13, the electromagnetic relay 15 is designed to be de-energized, at which time its coil no longer generates a magnetic field, releases the armature (for example, the armature moves in a direction away from the coil), and moves the armature away from the opening 17 of the conduit 9 located in the speaker rear cavity 12. At this time, the opening 17 of the conduit 9 is exposed to the speaker rear cavity 12, and forms a low-frequency resonator with the speaker rear cavity 12 to absorb the low-frequency noise in the earmuff cavity 7, thereby achieving a noise reduction effect.

[0045] In order to control the accurate movement of the armature in the electromagnetic relay 15, a relay control circuit is also provided in the speaker rear cavity 12 in this embodiment, such as Figure 7 As shown, it can be specifically set on the PCB board of the headset to achieve accurate control of the electromagnetic relay. Specifically, a comparator U1 is set in the relay control circuit, and the inverting input end of the comparator U1 is connected to the speaker 13 through the resistor R1 to receive the audio signal Ui transmitted to the speaker 13. The non-inverting input end of the comparator U1 is connected to a trigger voltage U through the resistor R2. RThe output end of the comparator U1 is connected to the control end of a switch element through a resistor R3, for example, connected to the base of a PNP transistor Q1, and the switch path of the switch element is connected to the power supply circuit of the coil K of the electromagnetic relay. For example, the collector of the PNP transistor Q1 is grounded through the coil K of the electromagnetic relay connected in series, and the emitter is connected to a DC power supply VCC through a current limiting resistor R4.

[0046] Setting the trigger voltage U R The amplitude of is smaller than the amplitude of the bias voltage in the audio signal Ui. When the speaker 13 does not receive the audio signal Ui, the voltage at the non-inverting input terminal of the comparator U1 is higher than the voltage at its inverting input terminal. At this time, the comparator U1 outputs a high level, that is, Figure 7 Uo in is a high level and is equivalent to the amplitude of the DC power supply VCC. At this time, the PNP transistor Q1 is in the cut-off state, no current flows through the coil K of the electromagnetic relay, no magnetic field is generated around the coil K, and the armature in the electromagnetic relay remains in a default position away from the coil K. The armature is designed to be away from the opening 17 of the conduit 9 in the default position, so that the conduit 9 and the speaker back cavity 12 form a low-frequency resonator to eliminate the low-frequency noise in the earmuff cavity 7. At this time, the earphones can be used as noise protection earmuffs to isolate external noise. When the speaker 13 receives the audio signal Ui, since the bias voltage in the audio signal Ui is higher than the trigger voltage U R , so the voltage Uo output by the comparator U1 is low level. At this time, the PNP transistor Q1 is saturated and turned on, and the DC power supply VCC is used to power the coil K in the electromagnetic relay, so that a magnetic field is generated around the coil K, and the armature is attracted to move toward the direction close to the coil K, thereby blocking the opening 17 of the conduit 9, so that the conduit 9 and the speaker rear cavity 12 cannot form a low-frequency resonator, preventing the low-frequency energy of the audio signal or the communication signal from being offset, ensuring that the audio signal is normally output through the speaker 13, and the communication signal can be reliably transmitted.

[0047] Of course, the comparator U1 can also receive the trigger voltage U through its inverting input terminal. R , the in-phase input terminal receives the audio signal Ui. At this time, the switching element Q1 can be a NPN transistor connected to the power supply circuit of the coil K of the electromagnetic relay, which can also achieve accurate control of the on and off of the coil K.

[0048] In this embodiment, the resistors R1, R2, and R3 are protective resistors for protecting the comparator U1 from being damaged by the impact of abnormal current, and by adjusting the resistance values ​​of the protective resistors R1, R2, and R3, the sensitivity of the comparator U1 can be reduced, ensuring that the alternating voice signal can stably control the triggering of the comparator U1.

[0049] A voltage stabilizing diode Dz can be further connected to the output end of the comparator U1. When the voltage of the audio signal Ui is less than the trigger voltage U R When the voltage Uo output by the comparator U1 is clamped at a high level corresponding to the reverse conduction voltage drop of the voltage zener diode Dz by using the voltage zener diode Dz, the switch element Q1 is controlled to remain in the off state, so that the armature is away from the opening 17 of the conduit 9, and the low-frequency resonator formed by the conduit 9 and the speaker rear cavity 12 is used to absorb more low-frequency noise energy in the earphone.

[0050] Embodiment 2, as Figure 8 As shown, in order to form a low-frequency resonator in the earmuff, the present embodiment firstly arranges a partition 10 in the earmuff cavity 7 surrounded by the earmuff shell 2, and uses the partition 10 to enclose an independent chamber 8 in the earmuff cavity 7. Then, a passive radiator 19 is installed on the partition 10, and a low-frequency resonator is formed by the passive radiator 19 and the chamber 8 to absorb low-frequency noise near the resonance frequency in the earmuff cavity 7. With this structural design, when calculating the resonance frequency f1 of the low-frequency resonator, the equivalent capacitance C' of the low-frequency resonator is determined by the equivalent acoustic compliance of the chamber 8, and the equivalent inductance L' of the low-frequency resonator is determined by the equivalent acoustic mass of the passive radiator 19. Since the equivalent acoustic mass of the passive radiator 19 is usually larger than the equivalent acoustic mass of the conduit 9, the formation of a low-frequency resonator by the passive radiator 19 and the chamber 8 can obtain a lower resonance frequency, which is conducive to absorbing lower frequency noise.

[0051] Of course, you can also Figure 8 Based on the earmuff structure design shown in FIG. 1 , a conduit 9 is further provided on the partition 10, such as Fig. 9 As shown, one of the two end openings of the conduit 9 is extended into the chamber 8, and the other is extended out of the chamber 8 and is located in the earmuff cavity 7. A low-frequency resonator is formed by using the passive radiator 19, the conduit 9 and the chamber 8 to offset the low-frequency noise with lower frequency and wider bandwidth.

[0052] When the low-frequency resonator is composed of a passive radiator 19, a conduit 9 and a chamber 8, the equivalent inductance L' in the calculation formula for the resonant frequency f1 of the low-frequency resonator should be determined by the equivalent sound masses of the passive radiator 19 and the conduit 9, while the equivalent capacitance C' of the low-frequency resonator is determined by the equivalent acoustic compliance of the chamber 8.

[0053] The spatial dimensions of the chamber 8 or the shapes of the passive radiator 19 and the conduit 9 are adjusted so that the resonance frequency f1 of the low-frequency resonator is equal to or close to the turning frequency f0 of the low-pass filter formed by the earmuff (for the earmuff equipped with the earmuff 6, f0 is determined by the equivalent inductance of the earmuff shell 2 and the equivalent capacitance of the earmuff cavity 7 and the earmuff 6) to absorb the noise energy near the resonance frequency f1 and prevent the noise in the earmuff cavity 7 from being raised and amplified near the resonance frequency f1.

[0054] Considering the limited space of the earmuff cavity 7, the present embodiment preferably adopts a method of filling the cavity 8 with sound-absorbing materials such as sound-absorbing sponge or glass wool felt to expand the space of the cavity 8.

[0055] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A noise reduction earmuff, the earmuff being an earmuff in a headphone, characterized in that: include: An earmuff shell, which forms an earmuff cavity; A partition plate is installed in the earmuff cavity and forms an independent chamber, which is the rear chamber of the speaker in the earmuff; A conduit is mounted on the baffle, and one of the two openings of the conduit is located in the cavity, and the other one extends out of the cavity and is located in the earmuff cavity; the cavity and the conduit form a low-frequency resonator, and its resonance frequency is equivalent to the turning frequency of the low-pass filter formed by the earmuff; A baffle is arranged in the rear cavity of the speaker; when the speaker outputs sound, the baffle blocks the opening of the conduit in the cavity; when the speaker does not output sound, the baffle is away from the opening of the conduit in the cavity.

2. The noise reduction earmuff according to claim 1, characterized in that: The earmuff shell has an opening on one side facing the human ear, and an earmuff is installed on the earmuff shell at the opening. The turning frequency of the low-pass filter is determined by the equivalent inductance of the earmuff shell and the equivalent capacitance of the earmuff cavity and the earmuff.

3. The noise reduction earmuff according to claim 1, characterized in that: The chamber is filled with sound absorbing material.

4. The noise reduction earmuff according to any one of claims 1 to 3, characterized in that: The baffle is an armature in an electromagnetic relay. When the speaker receives an audio signal, the electromagnetic relay generates a magnetic field to attract the armature to move and block the opening of the catheter in the chamber. When no audio signal is connected to the speaker, the electromagnetic relay releases the armature and moves the armature away from the opening of the catheter in the chamber.

5. The noise reduction earmuff according to claim 4, characterized in that: It also includes a comparator, wherein the two input ends of the comparator receive the trigger voltage and the audio signal respectively, and the output end is connected to the control end of a switch element, and the switch path of the switch element is connected to the power supply circuit of the coil of the electromagnetic relay; the amplitude of the trigger voltage is lower than the amplitude of the bias voltage in the audio signal, and when the audio signal is connected, the comparator output level controls the switch element to turn on, connects the power supply circuit of the coil of the electromagnetic relay, generates a magnetic field through the coil, attracts the armature to move, and blocks the opening of the catheter in the chamber.

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