JP2011186844A - Alarm device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise the sound pressure of alarm sound, that is, the volume of the alarm sound by using sound output from the front of a speaker and sound output from the rear of the speaker. <P>SOLUTION: An alarm device includes a detecting part 1, the speaker 2 and a housing 3. The detecting part 1 detects surrounding abnormal conditions. The speaker 2 outputs alarm sound and a voice to notify the abnormal conditions detected by the detecting part 1. Frequency bands are different between the alarm sound and the voice. In the housing 3, an internal space 36, a front side sound hole 34 and a lateral sound hole 37 are formed. The internal space 36 houses the speaker 2. A path from the front of the speaker 2 to the front side sound hole 34 is a first path, and a path from the rear of the speaker 2 to the lateral sound hole 37 through the internal space 36 is a second path. The housing 3 is formed so that a path difference between the second path and the first path may be 1/2 wavelength of a wavelength to a desired frequency included in the frequency band of the alarm sound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an alarm device that outputs an alarm sound and sound in order to notify an abnormality occurring in a predetermined area.

  Conventionally, various alarm devices that output an alarm sound in order to notify an abnormality that has occurred in a predetermined area have been developed and are commercially available (see, for example, Patent Document 1). In the alarm device of Patent Document 1, a speaker storage space in which a speaker is stored is formed by a member that holds the speaker and a cover provided in front of the speaker. The speaker of Patent Document 1 is provided at a position deviated in the peripheral direction from the center of the speaker storage space. In the speaker storage space, a side shielding part is provided on the side where the speaker is installed, and an opening is formed on the side opposite to the side.

  According to the alarm device of Patent Document 1, when the sound output from the rear surface of the speaker circulates in front of the speaker in the external space as a result of the distance from the speaker to the opening being increased, it is output from the rear surface of the speaker. Is out of phase with the sound output from the front of the speaker by 180 ° or more. Thereby, the sound output from the front surface of the speaker is less likely to be canceled out by the sound output from the rear surface of the speaker.

JP 2009-157424 A

  However, the alarm device disclosed in Patent Document 1 is configured such that the sound output from the front surface of the speaker is less likely to be canceled out by the sound output from the rear surface of the speaker. Even if the interference was reduced, the volume could not be increased from the sound output from the front of the speaker.

  The present invention has been made in view of the above points, and an object of the present invention is to increase the sound pressure of an alarm sound, that is, the volume of an alarm sound, using a sound output from the front surface of the speaker and a sound output from the rear surface of the speaker. It is to provide an alarm device that can be raised.

  The alarm device of the present invention includes a detection unit that detects a surrounding abnormality, a speaker that outputs a sound in a frequency band different from the warning sound and the warning sound in order to notify the abnormality detected by the detection unit, A housing to which the detection unit and the speaker are attached, wherein the housing includes an internal space in which the speaker is accommodated and a first sound wave generated on the front surface of the speaker to propagate to the external space. 1 opening and a second opening through which the second sound wave generated on the rear surface of the speaker propagates to the external space through the internal space are formed from the front surface of the speaker. A path from the rear surface of the speaker to the second opening through the internal space is defined as a second path, and the housing includes the second path. Path difference between the serial first path, characterized in that it is formed to have a half wavelength of the wavelength with respect to a desired frequency included in the frequency band of the alarm sound.

  In the alarm device according to the present invention, it is preferable that the housing has a silencer that attenuates a sound wave having a specific frequency included in the frequency band of the sound in the second sound wave.

  In the alarm device of the present invention, it is preferable that the silencer is provided in the housing so as to face a rear surface of the speaker.

  In the alarm device of the present invention, it is preferable that the housing has a plurality of the muffler portions.

  In the alarm device according to the present invention, the housing includes a first silencer and a second silencer as the plurality of silencers, wherein the first silencer and the second silencer are The specific frequencies are preferably different from each other.

  In the alarm device of the present invention, it is preferable that the silencer is an acoustic tube whose cavity communicates with the internal space of the housing.

  In the alarm device according to the present invention, it is preferable that the silencer is a Helmholtz resonator whose cavity communicates with the internal space of the housing.

  In the present invention, the first sound wave generated on the front surface of the speaker and the second sound wave generated on the rear surface of the speaker in the frequency band of the alarm sound can be superimposed in the same phase, so that the sound of the alarm sound in the external space The pressure, that is, the volume of the alarm sound can be increased.

It is sectional drawing of the alarm device which concerns on Embodiment 1. FIG. It is a block diagram which shows the electric structure of the alarm device which concerns on the same as the above. It is a disassembled perspective view of the housing which concerns on the same as the above. It is sectional drawing of the speaker and housing which concern on the same as the above. It is a figure explaining the sound pressure of the alarm sound of the alarm device which concerns on the same as the above. It is a figure which shows the sound pressure characteristic of the alarm device which concerns on the same as the above. It is a perspective view of the alarm device which concerns on the modification same as the above. It is sectional drawing of the speaker and housing which concern on a modification same as the above. It is an alarm device which concerns on Embodiment 2, Comprising: (a) is sectional drawing, (b) is a front view of a 2nd housing member. It is a figure explaining the sound pressure of the audio | voice of the alarm device which concerns on the same as the above. It is a figure which shows the sound pressure characteristic of the alarm device which concerns on the same as the above. It is an alarm device which concerns on Embodiment 3, Comprising: (a) is sectional drawing, (b) is a front view of a 2nd housing member. It is an alarm device which concerns on Embodiment 4, Comprising: (a) is sectional drawing, (b) is a front view of a 2nd housing member. It is an alarm device which concerns on Embodiment 5, Comprising: (a) is sectional drawing, (b) is a front view of a 2nd housing member. It is an alarm device which concerns on Embodiment 6, Comprising: (a) is sectional drawing, (b) is a front view of a 2nd housing member.

(Embodiment 1)
The alarm device according to the first embodiment is a device that outputs an alarm sound and a sound in order to notify an abnormality that has occurred in a predetermined area. As shown in FIGS. 1 and 2, the alarm device of the present embodiment includes a detection unit 1, a speaker 2, and a housing 3.

  As shown in FIG. 2, the detection unit 1 includes a sensor 11, a control unit 12, a signal output unit 13, an amplifier 14, a power supply unit 15, and a storage case 16 (see FIG. 1). Installed in place. The detector 1 detects an abnormality in the area (surrounding) where the sensor 11 is installed.

  The sensor 11 detects a physical quantity related to the environment of the area where the sensor 11 is installed. For example, when the alarm device is a smoke detector, the sensor 11 is a smoke detector and detects the presence or absence of smoke in the area where the sensor 11 is installed.

  The control unit 12 is configured by, for example, a microprocessor, and determines whether an abnormality has occurred in the area where the sensor 11 is installed, using the detection result of the sensor 11. When the physical quantity detected by the sensor 11 is equal to or higher than a predetermined level, the control unit 12 determines that an abnormality has occurred in the area where the sensor 11 is installed. When the alarm device is a smoke detector, the control unit 12 determines that a fire has occurred in the area where the sensor 11 is installed if the amount of smoke detected by the sensor 11 is equal to or greater than the threshold. The threshold value is a preset value.

  The signal output unit 13 is configured by, for example, a microprocessor, and outputs a sound signal to the speaker 2 via the amplifier 14 when the control unit 12 determines that an abnormality has occurred in the installation area of the sensor 11. The sound signal includes an alarm sound signal for causing the speaker 2 to output an alarm sound and an audio signal for causing the speaker 2 to output sound.

  The amplifier 14 amplifies the amplitude of the sound signal output from the signal output unit 13 to a size suitable for the speaker 2. The power supply unit 15 is, for example, a primary battery or a secondary battery, and supplies power to each unit of the detection unit 1. The storage case 16 is a member formed in, for example, a bottomed cylindrical shape, and stores the sensor 11, the control unit 12, the signal output unit 13, and the amplifier 14. The power supply unit 15 is not limited to a primary battery and a secondary battery. For example, the power supply unit 15 may be a device that is connected to a commercial power source and converts AC power supplied from the commercial power source into power suitable for each unit. Good.

  The speaker 2 is a dynamic speaker. When an alarm sound signal is input from the signal output unit 13 via the amplifier 14, the speaker 2 converts an alarm sound signal that is an electric signal into an alarm sound. When an audio signal is input from the signal output unit 13 via the amplifier 14, the speaker 2 converts the audio signal, which is an electrical signal, into audio. Thereby, the speaker 2 can output an alarm sound and a sound in order to notify the abnormality (outside the housing 3) detected by the detection unit 1 to the outside (outside the housing 3).

  The alarm sound and the sound are sounds in different frequency bands. As an example, the frequency band of the warning sound is around 3 kHz, and the frequency band of the voice is a lower frequency band (500 Hz to 1200 Hz) than the warning sound. However, the frequency bands of the alarm sound and the sound are not limited to the above-described bands, and are appropriately set according to the application. For example, the alarm sound frequency band may be lower than the sound frequency band.

  The alarm sound output from the speaker 2 includes a sound “view, view, view”, for example. The sound output from the speaker 2 includes, for example, a sound “fire”. Residents can be informed of the occurrence of a fire by the above warning sound and voice. Note that the speaker 2 outputs a notification sound “battery exhausted” when the remaining power of the power supply unit 15 is low.

  As shown in FIG. 3, the housing 3 includes a first housing member (front housing) 31 and a second housing member (rear housing) 32. Each of the first housing member 31 and the second housing member 32 is a member formed in a disk shape by a resin such as a thermoplastic material. The detection unit 1 is attached to the second housing member 32 (see FIG. 1).

  The first housing member 31 is provided with a cylindrical portion 312 that protrudes from the vicinity of the center of the bottom surface portion 311 to the rear surface side (the lower side in FIG. 3). As shown in FIG. 4, the speaker 2 is attached to the first housing member 31. In the present embodiment, a plurality of screw grooves are formed at the tip of the cylindrical portion 312 (lower end in FIG. 4), and a plurality of through holes (or screw grooves) are formed in the outer peripheral portion of the speaker 2. Each screw 33 passes through the through hole (or screw groove) of the speaker 2 and is fitted (screwed) into the screw groove of the cylindrical portion 312, so that the speaker 2 is attached to the first housing member 31 (screw). Will be stopped). Note that the method of holding the speaker 2 by the housing 3 is not limited to the above, and any method that does not cause problems such as chatter noises may be used.

  As shown in FIG. 3, a plurality of front sound holes 34, 34... Are formed in a region 313 surrounded by the cylindrical portion 312. Sound waves generated on the front surface of the speaker 2 (hereinafter referred to as “first sound waves”) propagate from the front sound holes 34 to the external space (see FIG. 1). Each front sound hole 34 corresponds to a first opening of the present invention.

  The first housing member 31 is provided with a plurality (four in the illustrated example) of projecting portions 314, 314, 314, and 314 projecting from the bottom surface portion 311 to the rear surface side (lower side in FIG. 3). . Each protrusion 314 is formed with a thread groove 315. The second housing member 32 has a plurality of (four in the illustrated example) through-holes 321, 321, 321, 321. A plurality of (four in the illustrated example) screws 35, 35, 35, 35 are fitted into (threaded into) the screw grooves 315 of the projecting portions 314 through the through holes 321, respectively, so that the first housing member 31 and the second housing member 32 are coupled.

  As shown in FIG. 1, an internal space 36 is formed between the coupled first housing member 31 and second housing member 32. In the internal space 36, the speaker 2 is accommodated. Side sound holes 37 are formed in the entire outer periphery of the first housing member 31 and the second housing member 32. A sound wave generated on the rear surface of the speaker 2 (hereinafter referred to as “second sound wave”) propagates from the side sound hole 37 to the external space via the internal space 36. The side sound hole 37 corresponds to the second opening of the present invention.

  A path from the front surface of the speaker 2 to each front sound hole 34 is defined as a first path. A path from the rear surface of the speaker 2 to the side sound hole 37 through the internal space 36 is defined as a second path.

  In this embodiment, the length D from the center O of the housing 3 to the side sound hole 37 is set to 50 mm. That is, both the first housing member 31 and the second housing member 32 have a radius of 50 mm. Therefore, the path length of the second path is 50 mm. In the present embodiment, since the path length of the first path is negligibly short compared to the path length (50 mm) of the second path, the path difference between the second path and the first path is equal to the second path length. It can be approximated to the path length of the path and is 50 mm. As described above, the housing 3 is configured such that the path difference between the second path and the first path is a half wavelength (1/2) λ of the wavelength λ with respect to a desired frequency included in the frequency band of the alarm sound. Is formed. In the present embodiment, the wavelength λ with respect to a desired frequency is a wavelength obtained in advance through experiments or the like so that the output of the alarm sound is maximized. That is, in the alarm device of the present embodiment, the wavelength for the frequency that is most effective in improving the maximum sound pressure is set to λ.

  As described above, the alarm device according to the present embodiment includes a so-called bass reflex type speaker system as shown in FIG. When the speaker 2 outputs an alarm sound (sound in a frequency band around 3 kHz), the sound speed is 340 m / s, and the wavelength λ for a desired frequency is 340 (m / s) / 3400 (Hz) = 0.1 (m ), The half wavelength (1/2) λ of the wavelength λ is 50 mm. Therefore, the second sound wave having a frequency of 3.4 kHz is generated on the rear surface of the speaker 2 in a phase opposite to that of the first sound wave. However, when the second sound wave propagates to the side sound hole 37 through the internal space 36, each front sound hole It becomes the same phase as the first sound wave propagated to 34. That is, the first sound wave and the second sound wave propagate in the same phase in the external space. Even in the vicinity of the frequency of 3.4 kHz, the first sound wave and the second sound wave are superimposed in a form close to the same phase. As a result, as shown in FIG. 5, the alarm device of the present embodiment can increase the sound pressure of the alarm sound, that is, the volume of the alarm sound, as compared with the case of only the first sound wave (the left diagram of FIG. 5). Yes (right figure in FIG. 5). In FIG. 5, the first sound wave is indicated by a broken line, and the second sound wave is indicated by a solid line.

  Next, the sound pressure characteristics of the alarm device according to the present embodiment will be described with reference to FIG. FIG. 6 shows the sound pressure-frequency characteristics (solid line in FIG. 6) of the alarm device of the present embodiment, and the sound pressure-frequency characteristics (broken line in FIG. 6) of the alarm device having a sealed speaker system as a comparative example. It is shown. The sound pressure in FIG. 6 is a value measured at a point 0.3 m ahead from the alarm device. At the measurement point, it can be approximated that the distance from the measurement point to the front sound hole 34 and the distance from the measurement point to the side sound hole 37 are substantially the same. In the alarm device of the present embodiment, the path difference between the second path and the first path is a half wavelength (50 mm) of the wavelength (100 mm) for a desired frequency included in the frequency band of the alarm sound. The housing 3 is designed. Therefore, the alarm device of the present embodiment improves the sound pressure in the frequency band around 3 kHz (particularly around 3.4 kHz) as shown in FIG. 6 compared to the alarm device of the comparative example. That is, the volume of the alarm sound increases.

  As described above, the alarm device according to the present embodiment can superimpose the first sound wave generated on the front surface of the speaker 2 and the second sound wave generated on the rear surface of the speaker 2 in the same phase in the frequency band of the alarm sound. The sound pressure of the alarm sound, that is, the volume of the alarm sound can be increased in the external space.

  As a modification of the present embodiment, a plurality of circular side sound holes 37, 37... Are formed on the side surface provided on the outer peripheral portion of the first housing member 31 as shown in FIG. May be formed. Also, a plurality of slit-shaped (oval-shaped) side sound holes 37, 37,... As shown in FIG. Each side sound hole 37 in FIGS. 7A and 7B corresponds to a second opening of the present invention. The same applies to the following second to sixth embodiments.

  As another modification of the present embodiment, a claw portion may be provided on the cylindrical portion 312 of the first housing member 31, and the speaker 2 may be fitted to the first housing member 31. In this case, the first cushion member 38 may be fitted into the first housing member 31 together with the speaker 2 as shown in FIG. Further, as shown in FIG. 8B, the second cushion material 39 may be sandwiched between the rear surface of the speaker 2 and the second housing member 32. Furthermore, as a method of holding the housing 3 on the speaker 2, a method using a screw and a method of a modification may be combined as in this embodiment. The method of holding the speaker 2 by the housing 3 is not limited to the above, and any method that does not cause problems such as chattering sound may be used. The same applies to the following second to sixth embodiments.

  As a modification of the present embodiment, the alarm device may be a crime prevention device (intrusion detection siren) that outputs an alarm sound when an intruder is detected. In this case, the sensor 11 is a human sensor and detects the presence or absence of a person in the detection area. When a person is detected by the sensor 11, the control unit 12 determines that a suspicious person has entered the detection area of the sensor 11. The speaker 2 outputs an alarm sound and sound in order to notify the intrusion of a suspicious person. The same applies to the following second to sixth embodiments.

  The alarm device may be a heat sensor. In this case, the sensor 11 is a thermal sensor and detects heat in the detection area. When heat is detected by the sensor 11, the control unit 12 determines that a fire has occurred in the detection area of the sensor 11. The speaker 2 outputs an alarm sound and sound to notify the occurrence of a fire. The same applies to the following second to sixth embodiments.

  Further, the alarm device may be a gas alarm device. In this case, the sensor 11 is a gas detection sensor and detects the presence or absence of gas in the detection area. When gas is detected by the sensor 11, the control unit 12 determines that a gas leak has occurred in the detection area of the sensor 11. The speaker 2 outputs an alarm sound and sound in order to notify the occurrence of gas leakage. The same applies to the following second to sixth embodiments.

(Embodiment 2)
The alarm device according to the second embodiment is different from the alarm device according to the first embodiment (see FIG. 1) in that it includes a silencer that attenuates the sound output from the rear surface of the speaker 2. The silencer attenuates a sound wave having a specific frequency included in the frequency band of the sound among the second sound wave (sound wave generated on the rear surface of the speaker 2). The alarm device according to the present embodiment is the same as the alarm device according to the first embodiment except for the points described above.

  As shown in FIG. 9, the housing 3 according to the present embodiment includes a plurality of (four in the illustrated example) acoustic tubes 4, 4, 4 and 4 in the second housing member 32 as silencers. Specifically, each acoustic tube 4 is provided on the bottom surface of the second housing member 32. Each acoustic tube 4 is formed integrally with the second housing member 32. The same resin as that of the second housing member 32 is used for each acoustic tube 4 due to advantages in the manufacturing process. Each acoustic tube 4 is a tube whose internal cavity communicates with the internal space 36 at the opening 41. Each acoustic tube 4 attenuates a sound wave having a specific frequency included in the sound frequency band in the second sound wave. The housing 3 of the present embodiment is the same as the housing 3 of the first embodiment (see FIG. 1) except for the points described above.

Next, the silencing by each acoustic tube 4 will be described. The specific frequency (frequency of the sound wave to be silenced) is f (Hz), the sound speed is c (m / s), the opening end correction by the diameter of the cavity of the acoustic tube 4 is ΔL (m), and the cavity length of the acoustic tube 4 is When L (m) is established, Expression 1 is established.
L + ΔL = (c / f) × (1/4) (Formula 1)
The frequency fn of the sound wave that is actually silenced is expressed as shown in Equation 2 using the specific frequency f.
fn = f × (2n + 1) (n = 0, 1, 2,...) (Formula 2)
In order for the alarm device of the present embodiment to attenuate the sound wave of around 500 Hz of the second sound wave, the length L of the cavity of each acoustic tube 4 may be designed to be about 180 mm. In order for the alarm device of the present embodiment to attenuate the 800 Hz sound wave of the second sound wave, the length L of the cavity of each acoustic tube 4 may be designed to be about 100 mm. Thereby, the design freedom of an alarm device can be raised.

  From the above, as shown in FIG. 10, the alarm device according to the present embodiment is lower in sound pressure of the sound due to the second sound wave, that is, the sound of the sound, as compared with the alarm device not provided with the acoustic tube (the left diagram in FIG. 10). Volume reduction can be suppressed (the right diagram in FIG. 10). In FIG. 10, the first sound wave is indicated by a solid line, and the second sound wave is indicated by a broken line.

  Next, the sound pressure characteristics of the alarm device according to the present embodiment will be described with reference to FIG. FIG. 11 shows a sound pressure-frequency characteristic (solid line in FIG. 11) of the alarm device according to the present embodiment and a sound pressure-frequency characteristic (broken line in FIG. 11) of the alarm device according to the first embodiment as a comparative example. ing. The sound pressure in FIG. 11 is a value measured at a point 0.3 m ahead from the alarm device. At the measurement point, it can be approximated that the distance from the measurement point to the front sound hole 34 and the distance from the measurement point to the side sound hole 37 are substantially the same. Since the alarm device of this embodiment attenuates the sound wave of the specific frequency contained in the frequency band of an audio | voice among the 2nd sound waves by each acoustic tube 4, compared with the alarm device of a comparative example, as shown in FIG. It is possible to suppress a decrease in sound pressure in a sound frequency band (particularly a frequency band of 1 kHz or less).

  As described above, the alarm device according to the present embodiment can mute the sound of the specific frequency by attenuating the second sound wave generated on the rear surface of the speaker 2 with the acoustic tube 4 at the specific frequency of the sound band. Therefore, it is possible to prevent the sound output from the front surface of the speaker 2 from being canceled by the sound output from the rear surface of the speaker 2. Thereby, the alarm device according to the present embodiment can suppress a decrease in sound pressure of the sound, that is, a decrease in sound volume, in a state where the sound pressure of the alarm sound is increased.

  Further, the alarm device according to the present embodiment has a plurality of acoustic tubes 4, 4, 4, and 4, so that the sound of the sound can be compared with the case where the housing 3 includes only the single acoustic tube 4. The effect of suppressing the volume reduction can be further enhanced.

  Furthermore, the alarm device of the present embodiment can easily determine the frequency of the sound to be muted, that is, the specific frequency, by setting the length L of the cavity of each acoustic tube 4.

  The housing 3 is not necessarily provided with a plurality of acoustic tubes 4, 4, 4, and may include only one acoustic tube 4. Also in this case, the alarm device can mute the sound of the specific frequency by attenuating the second sound wave generated on the rear surface of the speaker 2 with the acoustic tube 4 at the specific frequency of the sound band. The sound output from the front surface can be suppressed from being canceled out by the sound output from the rear surface of the speaker 2. The alarm device can easily determine the frequency of the sound to be muted, that is, the specific frequency, by setting the length L of the cavity of the acoustic tube 4.

  As a modification of the present embodiment, each acoustic tube 4 may be molded separately from the second housing member 32 and attached to the second housing member 32 after molding. In this case, the same resin as that of the second housing member 32 may be used for each acoustic tube 4, or a resin different from that of the second housing member 32 may be used. The same applies to the following third to fifth embodiments.

(Embodiment 3)
The alarm device according to the third embodiment is different from the alarm device according to the second embodiment (see FIG. 9) in that the length of the cavity of the acoustic tube 4 is different as shown in FIG. Note that the alarm device of the present embodiment is the same as the alarm device of the second embodiment in points other than the above.

  The housing 3 of the present embodiment includes a first acoustic tube 4a and a second acoustic tube 4b having different cavity lengths as a plurality (four in the illustrated example) of acoustic tubes 4, 4, 4 and 4. ing. The length of the cavity of the first acoustic tube 4a is L1, and the length of the cavity of the second acoustic tube 4b is L2 (L2> L1). Since the first acoustic tube 4a and the second acoustic tube 4b have different cavity lengths, the specific frequencies f are different from each other according to Equation 1. The housing 3 of the present embodiment is the same as the housing 3 of the second embodiment (see FIG. 9) in points other than the above.

  In the alarm device of the present embodiment, the first acoustic tube 4a and the second acoustic tube 4b attenuate the second acoustic wave (the acoustic wave generated on the rear surface of the speaker 2) having different specific frequencies f. Can be made.

  From the above description, the alarm device of the present embodiment can mute the sounds having different frequencies by the first acoustic tube 4a and the second acoustic tube 4b, so that the frequency band of the muffled sound can be expanded. it can.

(Embodiment 4)
The alarm device according to the fourth embodiment is different from the alarm device according to the second embodiment (see FIG. 9) in that an acoustic tube 4 is provided facing the rear surface of the speaker 2 as shown in FIG. Note that the alarm device of the present embodiment is the same as the alarm device of the second embodiment in points other than the above.

  The housing 3 of the present embodiment is provided with one acoustic tube 4 facing the rear surface of the speaker 2. That is, the opening 41 of the acoustic tube 4 faces the rear surface of the speaker 2. The housing 3 of the present embodiment is the same as the housing 3 of the second embodiment (see FIG. 9) in points other than the above.

  From the above description, in the alarm device of the present embodiment, when the acoustic tube 4 is provided facing the rear surface of the speaker 2, the acoustic tube 4 is provided at a position away from the rear surface of the speaker 2. As compared with the above, it is possible to further enhance the effect of suppressing the sound volume reduction.

  As a modification of the present embodiment, the alarm device may be provided with a plurality of acoustic tubes 4 facing the rear surface of the speaker 2.

(Embodiment 5)
The alarm device according to the fifth embodiment is different from the alarm device according to the fourth embodiment (see FIG. 13) in that the acoustic tube 4 extends in the horizontal direction as shown in FIG. The alarm device according to the present embodiment is the same as the alarm device according to the fourth embodiment except for the points described above.

  In the acoustic tube 4 of the present embodiment, the opening 41 faces the rear surface of the speaker 2 in the same manner as the acoustic tube 4 of Embodiment 4 (see FIG. 13). However, the acoustic tube 4 of this embodiment is not a straight tube but extends in the radial direction from the center of the second housing member 32 and further extends in the circumferential direction of the second housing member 32. That is, the acoustic tube 4 of the present embodiment extends in the horizontal direction of the housing 3 rather than in the front-rear direction of the housing 3 (vertical direction in FIG. 14A). The length L of the cavity of the acoustic tube 4 of the present embodiment is the length of the alternate long and short dash line in FIG. In addition, the acoustic tube 4 of this embodiment is the same as that of the acoustic tube 4 of Embodiment 4 in points other than the above.

  From the above description, in the alarm device of the present embodiment, when the acoustic tube 4 is provided in the horizontal direction of the housing 3, the acoustic tube 4 is provided as a straight tube in the front-rear direction of the housing 3 (see FIG. 13). In comparison, the length of the alarm device in the front-rear direction can be shortened.

  As a modification of the present embodiment, the alarm device may be provided with a plurality of acoustic tubes 4 as in the present embodiment.

  As another modification of the present embodiment, the acoustic tube 4 may not be provided to face the back surface of the speaker 2.

(Embodiment 6)
The alarm device according to the sixth embodiment is different from the alarm device according to the first embodiment (see FIG. 1) in that a Helmholtz resonator 5 is provided as a silencer as shown in FIG. The alarm device according to the present embodiment is the same as the alarm device according to the first embodiment except for the points described above.

  The Helmholtz resonator 5 is integrally provided on the bottom surface of the second housing member 32. That is, the Helmholtz resonator 5 of the present embodiment is provided on the bottom surface portion of the second housing member 32. The Helmholtz resonator 5 is formed with a cavity 51 and a circular opening 52. The cavity 51 communicates with the internal space 36 through the opening 52.

The resonance frequency f _H (Hz) of the Helmholtz resonator 5 of the present embodiment is expressed as Equation 3. In Equation 3, c (m / s) is the speed of sound, S (m ² ) is the cross-sectional area of the opening 52, V ₀ (m ³ ) is the volume of the cavity 51, l (m) is the length of the opening 52, r (m) is the radius of the opening 52. That is, when the volume V _{0 of the} cavity 51, the cross-sectional area S of the opening 52, the length l and the radius r of the opening 52 are determined, the resonance frequency f _H is obtained by Equation 3.
f _H = (c / 2π) {S / [V ₀ (l + r)]} ^1/2 (formula 3)
Alarm device of the present embodiment, by setting sufficiently higher than the resonant frequency f _H of the Helmholtz resonator 5 in a particular frequency f, the specific frequency f of the second sound wave (sound wave generated on the rear surface of the speaker 2) The sound wave can be attenuated.

From the above description, the alarm device according to the present embodiment designs the structure of the Helmholtz resonator 5 (for example, the volume V _{0 of the} cavity 51, the cross-sectional area S of the opening 52, etc.), and the frequency of the sound to be muted (specific frequency) by sufficiently high resonance frequency f _H of the Helmholtz resonator 5 with respect to f), it can readily determine the frequency of the sound to be muted.

DESCRIPTION OF SYMBOLS 1 Detection part 2 Speaker 3 Housing 34 Front sound hole (1st opening part)
36 Internal space 37 Side sound hole (second opening)
4 Acoustic tube 5 Helmholtz resonator

Claims (7)

A detection unit for detecting surrounding abnormalities;
A speaker that outputs a sound of a frequency band different from the warning sound and the warning sound in order to notify the abnormality detected by the detection unit;
A housing to which the detection unit and the speaker are attached;
The housing has an internal space in which the speaker is accommodated, a first opening for transmitting a first sound wave generated in front of the speaker to the external space, and a second in the rear surface of the speaker. And a second opening for propagating the sound wave to the external space through the internal space,
A route from the front surface of the speaker to the first opening is a first route, a route from the rear surface of the speaker through the internal space to the second opening is a second route,
The housing is formed so that a path difference between the second path and the first path is a half wavelength of a desired frequency included in the frequency band of the alarm sound. Features alarm device.   The alarm device according to claim 1, wherein the housing has a silencer that attenuates a sound wave of a specific frequency included in the frequency band of the sound among the second sound wave.   The alarm device according to claim 2, wherein the silencer is provided in the housing so as to face a rear surface of the speaker.   The alarm device according to claim 2, wherein the housing includes a plurality of the silencers. The housing has a first silencer and a second silencer as the plurality of silencers,
The alarm device according to claim 4, wherein the first silencer and the second silencer have different specific frequencies.   The alarm device according to any one of claims 2 to 5, wherein the silencer is an acoustic tube whose cavity communicates with the internal space of the housing.   The alarm device according to any one of claims 2 to 5, wherein the silencer is a Helmholtz resonator whose cavity communicates with the internal space of the housing.

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