JP2924586B2 - Secondary sound generator for silencing ducts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for generating a secondary sound for canceling a noise propagating in a duct such as an intake pipe or an exhaust pipe, and more particularly, to reducing the output of a speaker as a secondary sound source. It can be used to the fullest extent.

[0002]

2. Description of the Related Art As a conventional apparatus for generating a secondary sound for canceling a noise propagating in a duct, for example, Japanese Patent Application Laid-Open No. 2-503219 (first conventional example) and Japanese Patent Application Laid-Open No.
There is one described in Japanese Patent Application Laid-Open No. 7-97899 (second conventional example). That is, the first conventional example is a device for reducing exhaust noise particularly emitted from an exhaust pipe of an automobile,
As shown in FIG. 14 and FIG. 15 which is a cross-sectional view taken along the line XV-XV of FIG. 14, the waveguide 2 is provided so as to open coaxially at the opening end of the exhaust pipe 1, and Two loudspeakers 3 and 4 capable of radiating a sound wave into the pipe 2 and enclosures 5 and 6 covering the back of the loudspeaker are arranged at target positions with the exhaust pipe 1 interposed therebetween. Exhaust sound emitted from the exhaust pipe 1 and transmitted from the speakers 3 and 4 through the waveguide 2 while avoiding harm.
The next sound is superposed at the end of the exhaust pipe opening to reduce noise.

In the second conventional example, as shown in FIG. 16, a secondary sound generator comprising a waveguide 2, a speaker 3 and an enclosure 5 is provided at the end of a duct 7. It is connected to the acoustic mixer 8.

[0004]

However, the conventional apparatus described above has the following disadvantages. First, in the first conventional example, in order to efficiently use the secondary sounds emitted from the speakers 3 and 4 for noise reduction, it is necessary to increase the diameter of the waveguide 2 especially at the opening. When the diameter of the waveguide 2 is increased, the entire diameter becomes extremely large due to the double tube structure of the exhaust pipe 1 and the waveguide 2, and the degree of freedom in design is reduced. . In addition, since the opening end of the exhaust pipe 1 is a superposition point, and at the superposition point, the exhaust sound and the secondary sound are in a so-called dipole control method in which the exhaust sound and the secondary sound are in opposite phases, the exhaust gas flow rate is particularly low. If it is large, even if a silencing effect is obtained in the vicinity of the opening end of the exhaust pipe 1, the silencing effect diminishes as the distance from the opening end decreases, and in practice, a sufficient silencing effect cannot be obtained. Further, since the open end of the waveguide 2 is exposed to the outside, there is also a problem of flooding.

On the other hand, in the second conventional example, the primary sound (noise) propagating in the duct 7 is superimposed on the secondary sound in the acoustic mixer 8, and after the two have completely canceled each other, the external sound Therefore, a good noise reduction effect can be expected even when the flow velocity of the medium is large. However, since it is necessary to make the waveguide 2 longer to avoid heat damage, the waveguide 2 is
Interposed between the speaker 3 and the acoustic mixer 8 in such a manner as to reduce the excitation area of the
The secondary sound is attenuated in the waveguide 2 before reaching the acoustic mixer 8, so that in order to obtain a sufficient noise reduction effect, a large loudspeaker capable of generating a large volume secondary sound must be used. In addition, the size and cost of the device are increased, and mounting is sometimes difficult when the space is small like a vehicle.

The present invention has been made in view of such unresolved problems of the prior art, and has a structure in which the speaker output is not reduced as much as possible so that the speaker output can be reduced to a maximum for noise reduction. It is an object of the present invention to provide a duct noise-reducing secondary sound generator that can be used.

[0007]

In order to achieve the above object, the present invention provides an expansion chamber formed in the middle of a duct or at an open end, and a waveguide having one end communicating with the expansion chamber. And a speaker for radiating sound waves into the waveguide. In the secondary sound generating device for silencing a duct, the width direction dimension of the waveguide is made larger than its thickness direction to be equal to the diameter of the speaker. Or more, the speaker is disposed on the surface side of the waveguide, and the cross-sectional area of the expansion chamber by a plane orthogonal to the waveguide axis direction is equal to or equal to the area of the speaker. I did more.

Here, the term "equivalent" means that even if they are substantially the same, they include a case where they are completely identical numerically and also a case where they are slightly (about several%) larger or smaller. According to a second aspect of the present invention, in the first aspect of the present invention, the waveguide communicates with the expansion chamber such that a thickness direction of the waveguide coincides with an axial direction of the duct. According to a third aspect of the present invention, in the first or second aspect of the invention, a plurality of waveguides are communicated with the expansion chamber, and a speaker is provided for each of the waveguides. is there.

Further, according to a fourth aspect of the present invention, in the first to third aspects of the present invention, a plurality of expansion chambers are provided, and a waveguide is communicated with each of the expansion chambers. A speaker is provided in each of the waveguides. According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the back of the speaker is covered with an enclosure, and the volume of the enclosure is variable.

According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, at least one of the length and the sectional area of the waveguide is variable. Further, the invention according to claim 7 is the invention according to claims 1 to 6, wherein at least one of the length of the expansion chamber and the cross-sectional area thereof is variable.

[0011]

First, an apparatus as shown in FIG. 7 is considered. This means that the speaker 11 is fixed on the surface 10a side of the thin rectangular parallelepiped volume 10 so as to radiate sound waves into the volume 10 and the speaker 10 is mounted on one end face 10b of the volume 10 in the volume 10 The tube 12 is connected so as to communicate with the tube 12, and the end of the tube 12 opposite to the volume 10 is open. The numerical values shown in FIG. 7 are the dimensions of each part, and the unit is mm (the same applies to other drawings). In such a device, the speaker 11 emits the light via the volume 10 and the tube 12. When the flow of the sound wave emitted to the outside was examined, it could be experimentally confirmed that the model is as shown in FIG. FIG.
FIG. 7 is a diagram illustrating frequency characteristics of sound pressure at the opening end of the tube 12 when the voltage applied to the speaker 11 is constant, where A is an experimental value and B is a calculated value.

By the way, a calculation model as shown in FIG. 10 is considered, which includes a speaker, an enclosure that covers the back of the speaker and acts as an air spring, and a waveguide through which sound waves emitted from the speaker are transmitted. This is a model including a sound transmission path of a pipe or the like, and m in FIG.
Coil, the weight of the cone paper of the speaker, [phi] D _m is the speaker diameter, k is a spring constant of the speaker, c is the attenuation constant of the speaker, [phi] D _a enclosure of diameter, L _a is the enclosure thickness, φD ₁ ~φD ₃ is the diameter of each element of the sound wave transmission path, and L _{1 to} L ₃ are the lengths of each element of the sound wave transmission path. Moreover, the force of P _in per unit area coil of the loudspeaker occurs, the equivalent cross-sectional area of the speaker S _m, the equivalent cross-sectional area of the enclosure S _a, S ₁ equivalent cross-sectional area of each element of the acoustic pathway ~S _3. Assuming that the wave number is W and the density of the medium is ρ, the sound pressure Pr at a position separated by a distance r from the open end of the sound wave transmission path is _expressed by the following equation (1).

[0013]

(Equation 1)

(1) That is, considering the device as shown in FIG. 7, the speaker 11 and the volume 10 are separated by a plane parallel to the area of the speaker 11 and the surface 10a of the volume 10. The volume 10 and the tube 12 are
The cross-sectional area in a plane parallel to the side surface 10b of the volume portion 10 is not connected by the ratio of the cross-sectional area of the tube 12 to the cross-sectional area in the plane parallel to the surface 10a, as shown in FIG. And the cross-sectional area of the tube 12.

When sound waves are transmitted from the speaker 11 to the volume 10, if the area of the volume 10 to which the speaker 11 is fixed is equal to or larger than the area of the speaker 11, It can be seen that the sound wave hardly attenuates. In addition, it can be seen that the sound wave is hardly attenuated in the volume part 10 unless the shape of the volume part 10 is a shape that narrows the transmission path of the sound wave.

When the sound wave is transmitted from the volume 10 to the tube 12, it is desirable to increase the cross-sectional area of the tube 12 so that the transmission path of the sound wave is not narrowed. 8 can be expressed by a model as shown in FIG. 8, that is, it can be considered that the speaker 11 and the tube 12 are opposed to each other with the thin rectangular parallelepiped volume 10 therebetween. If the area is equal to or larger than the area of the speaker 11, after all, the sound wave transmitted from the speaker 11 to the tube 12 via the volume 10 is hardly attenuated. For example, the cross-sectional area of the tube 12 is
9C, the frequency characteristics as shown in FIG. 9C were obtained.

Here, the efficiency of the model shown in FIG. 11 is compared with the efficiency of the model shown in FIG. That is, FIG.
1 (a) is a front view, and FIG. 1 (b) is a side view of FIG. 1 (a).
Is fixed so that sound waves can be radiated from the end of the cylindrical waveguide 14 to the inside thereof, and the other end of the waveguide 14 is connected to be able to communicate with the extension chamber 15.

FIG. 12 (a) is a front view, FIG. 12 (b) is a side view of FIG.
The speaker 11 covered with is fixed to the inside of the flat waveguide 14 so that sound waves can be radiated from the front end thereof, and one end face of the waveguide 14 is connected to the expansion chamber 15 so as to communicate therewith. The end face of the waveguide 14 opposite to the extension chamber 15 is closed.

The specifications of the speaker 11 are as follows.
When the mass was 20 g, the spring constant was 1623 N / m, and the frequency characteristics of only the speaker 11 and the enclosure 13 were measured, the result was as shown in FIG. 13A. And
When the frequency characteristics of the sound pressure in the expansion chamber 15 are measured with the configuration of FIG. 11, the result is as shown in FIG. 13B, and the efficiency is considerably deteriorated as apparent from comparison with FIG. This is because, in the configuration of FIG. 11, the sound waves emitted from the speaker 11 are greatly attenuated in the waveguide 14.

On the other hand, when the frequency characteristics of the sound pressure in the expansion chamber 15 are measured in the same manner in the configuration of FIG.
, Which is much more efficient than B,
A sound pressure level equal to or higher than that of A can be obtained. This is because, in the configuration of FIG. 12, the waveguide 14 is formed in a thin rectangular parallelepiped shape, the width dimension thereof is made equal to the diameter of the speaker 11, and the speaker 11 is fixed on the surface side of the waveguide 14. , The cross-sectional area of the expansion chamber 15 by a plane orthogonal to the axial direction of the waveguide 14 (250 mm × 84 mm = 21000 m
m ² ) to the area of the speaker 11 ((164 mm / 2) ² × π ≒ 21
113 mm ²⁾ and because of the equal, because the same effect as when the diameter of the tube 12 was equal to the diameter of the speaker 11 in the model of Figure 8 is obtained. However, the volume 10 in FIG. 8 corresponds to the waveguide 14 in FIG. 12, and the tube 12 in FIG. 8 corresponds to the expansion chamber 15 in FIG.

As is apparent from the above description, according to the first aspect of the present invention, since the sound wave emitted from the speaker reaches the expansion chamber with almost no attenuation, the speaker output is maximized. Used for Then, the noise that has propagated through the duct in the expansion room and the secondary sound interfere with each other, and after the noise is reduced in the expansion room, the noise is emitted to the outside of the duct.

According to the second aspect of the present invention, since the waveguide can be communicated with an extremely narrow range in the longitudinal direction of the expansion chamber, for example, the position where the waveguide communicates is set to the position of the expansion chamber. It is possible to concentrate on a portion where stagnation occurs, such as a corner, and heat intrusion from the expansion chamber into the waveguide can be minimized.
According to the third aspect of the present invention, the acoustic characteristics of a plurality of sets of resonance systems are different from each other by, for example, making the characteristics of a plurality of speakers provided in each of the plurality of waveguides different. And they can be used independently. As a result, it is also possible to generate a secondary sound in accordance with the frequency characteristics of the generated noise, and it is possible to reduce noise satisfactorily in a wide frequency band.

Similarly, in the invention according to claim 4,
Since there are a plurality of waveguides and loudspeakers, it is possible to use them independently by making the characteristics of the resonance system constituted by the waveguides and loudspeakers different. According to the fifth aspect of the invention, if the volume of the enclosure changes, the acoustic characteristics of the speaker covered by the enclosure change, so that one resonance system can operate with a plurality of characteristics. Thus, a secondary sound can be generated in accordance with the frequency characteristics of the generated noise.

Similarly, in the invention according to claim 6 or claim 7, since the volume of the waveguide or the expansion chamber changes, one resonance system can be operated with a plurality of characteristics. Thus, a secondary sound can be generated in accordance with the frequency characteristics of the generated noise.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a first embodiment of the present invention. FIG. 1 is a front view, and FIG. 2 is a sectional view taken along line II-II of FIG. First, the structure will be described. This is an example in which the present invention is applied to a device for reducing exhaust noise emitted from an exhaust pipe 1 of an automobile. A cylindrical expansion chamber 15 is formed to increase the diameter. Therefore, the exhaust gas flowing through the exhaust pipe 1 once reaches the expansion chamber 15 from the introduction duct 1A, and is discharged therefrom to the outside via the extraction duct 1B.

On the lower surface side of the expansion chamber 15, one end of a thin rectangular parallelepiped waveguide 14 is fixed so as to be able to communicate with the axial direction thereof being directed vertically. Note that the lower end surface of the waveguide 14 is sealed. Further, in this embodiment, the width direction (the left-right direction in FIG. 1) of the waveguide 14 matches the axial direction of the exhaust pipe 1. The two loudspeakers 11 are inserted into the lower end of the waveguide 14 so as to be sandwiched from the front and back sides.
A and 11B are fixed, and the speakers 11A and 11B are fixed.
The sound wave emitted from 11B is radiated into the waveguide 14. That is, the speakers 11A and 11B
Are fixed not on the end face or side face of the waveguide 14 but on the front face side. The back surfaces of the speakers 11A and 11B are covered by box-shaped enclosures 13A and 13B.

Here, the width dimension of the waveguide 14 is larger than its thickness direction (horizontal direction in FIG. 2), so that the speakers 11A and 11B do not protrude from the front and back surfaces. It is larger than the diameter of the speakers 11A and 11B. Further, the waveguide 14 is connected to the speaker 1.
The same cross-sectional shape is maintained from the portion where 1A and 11B are fixed to the expansion chamber 15.

Further, in this embodiment, the inner diameter of the expansion chamber 15 in the horizontal direction (horizontal direction in FIG. 2) has a sectional area in a horizontal plane (a plane orthogonal to the axial direction of the waveguide 14) of the speaker 11.
The dimensions are set to be sufficiently larger than the area of A, 11B. Next, the operation of this embodiment will be described. Exhaust pipe 1
Exhaust noise propagating through the inside of the chamber extends from the introduction duct 1A to the expansion chamber 15A.
The sound wave emitted from the speakers 11A and 11B is transmitted to the inside of the expansion chamber 15 through the waveguide 14 and reaches the interior of the expansion chamber 15 as a secondary sound. Therefore, the exhaust sound and the secondary sound interfere in the expansion chamber 15. Therefore, if the secondary sound is a sound wave having a phase opposite to that of the exhaust sound in the expansion chamber 15 and having the same power, the exhaust sound is canceled in the expansion chamber 15 and released from the outlet duct 1B to the outside. The exhaust noise is extinguished or at a very low level.

Since the exhaust noise is generated in synchronization with the rotation of the crankshaft of the engine, feedforward control (preferably, control based on an adaptive algorithm such as an LMS algorithm) is performed based on the rotation of the crankshaft. If the speakers 11A and 11B are driven by the execution, a desired secondary sound can be generated, and the exhaust sound propagating through the exhaust pipe 1 can be canceled to reduce the noise level.

In this embodiment, the speaker 1
The width of the waveguide 14 is larger than the diameter of the speakers 1A and 11B, and the waveguide 14 is not shaped so as to be squeezed on the way. The sound waves emitted from the speakers 11A and 11B reach the expansion chamber 15 with little attenuation (increased depending on the frequency) because they are sufficiently larger than the area.

As described above, according to the configuration of the present embodiment, the outputs of the speakers 11A and 11B can be utilized very efficiently, and the secondary sound having the same power as the exhaust sound can be compared with the conventional device. And can be easily generated. In other words, if you want to generate a secondary sound of the same power,
Inexpensive speakers having a smaller diameter than conventional devices can be used. In particular, if only small speakers are used, there is an advantage that mounting is easy even in a case where a space margin is small like a vehicle.

Further, in this embodiment, the exhaust sound and the secondary sound are superimposed in the expansion chamber 15 formed in the middle of the exhaust pipe 1, and are muted there. Therefore, even when the flow rate of the exhaust gas is high, the noise reduction effect is not reduced. Since the diameter of the outlet duct 1B does not need to be particularly large, the degree of design freedom of the outlet duct 1B, which is easily visible from the outside, is increased, and secondary sound is introduced into the expansion chamber 15 through the waveguide 14. With such a configuration, the waveguide 14 can be communicated with an arbitrary position in the expansion chamber 15, so that the degree of freedom in layout can be increased, and the problem of flooding can be solved accordingly.

Further, in this embodiment, the speaker 1
1A and 11B and two enclosures 13A and 13B, two resonance systems exist. Therefore, if the resonance points of the respective resonance systems are given a difference by, for example, making the masses and spring constants of the speakers 11A and 11B or the volumes of the enclosures 13A and 13B different between the resonance systems, one resonance system is used. Since the frequency band in which a high-power secondary sound is obtained is different from the frequency band in which the high-power secondary sound is obtained by the other resonance system, the high-power secondary sound is spread over a wide frequency band. It is easy to obtain, and there is an advantage that the frequency band in which a good noise reduction effect is obtained is widened.

FIGS. 3 and 4 show a second embodiment of the present invention. FIG. 3 is a front view, and FIG. 4 is a sectional view taken along line IV-IV of FIG. In this embodiment, the present invention is also applied to a device for reducing the exhaust noise emitted from the exhaust pipe 1 of the automobile. However, since the configuration is substantially the same as that of the first embodiment, the same configuration is adopted. Are denoted by the same reference numerals, and overlapping descriptions thereof will be omitted.

That is, in this embodiment, the waveguide 14 and the expansion chamber 1
5 is different from that of the first embodiment, and the waveguide 14 can communicate with the expansion chamber 15 so that the thickness direction of the waveguide 14 and the axial direction of the exhaust pipe 1 match. It is connected. Other configurations are the same as those of the first embodiment.
Here, when the exhaust gas flowing through the exhaust pipe 1 has the configuration in which the expansion chamber 15 is provided as in the present embodiment, the exhaust gas smoothly flows from the introduction duct 1A into the expansion chamber 15 and then to the discharge duct 1B.
Is swung in the expansion chamber 15 without being discharged from the chamber.
For this reason, in the expansion chamber 15, a portion where the flow rate of the exhaust gas is high and a portion where the exhaust gas stagnates are generated.

Therefore, for example, the introduction duct 1 of the expansion chamber 15
If you know that the exhaust gas is stagnant in the corner on the A side,
As shown in FIG. 3, by connecting the waveguide 14 to a position near the corner, the invasion of heat from the expansion chamber 15 to the waveguide 14 can be suppressed to some extent.
The effect of heat on A and 11B can be minimized.

That is, if the thickness direction of the waveguide 14 is made to coincide with the axial direction of the exhaust pipe 1 as in this embodiment, the expansion chamber 1
In the longitudinal direction of 5, the waveguide 14 and the expansion chamber 15 can be communicated only at the position where the exhaust gas stagnates, and the invasion of heat to the waveguide 14 can be suppressed. Other functions and effects are the same as those of the first embodiment.
Also in this embodiment, if a difference is given to the resonance points of the respective resonance systems, a high-power secondary sound can be easily obtained over a wide frequency band, as in the first embodiment. .

FIG. 5 is a view showing a third embodiment of the present invention. In this embodiment, the present invention is applied to an apparatus for reducing exhaust noise emitted from an exhaust pipe 1 of an automobile. Since the configuration is substantially the same as that of the first and second embodiments, the same components are denoted by the same reference numerals, and redundant description will be omitted. That is, in the present embodiment, one expansion chamber 15
The two loudspeakers 11A, 14B are connected to each of the waveguides 14A, 14B so as to be able to communicate with each other, similarly to the first and second embodiments.
11B and the enclosures 13A and 13B are fixed. The waveguides 14A and 14B are connected to the expansion chamber 15 so that the thickness direction thereof coincides with the axial direction of the exhaust pipe 1, as in the second embodiment.

By making one waveguide 14 longer than the other waveguide 14B, the waveguides 14
A and 14B have different acoustic characteristics. Further, in each of the waveguides 14A and 14B, the mass or the spring constant (or the volume of the enclosures 13A and 13B) of the speakers 11A and 11B is different.

Therefore, in this embodiment, the speaker 1
The numbers of 1A and 11B, that is, the resonance points of the four resonance systems are different from each other. Therefore, there are four individual frequency bands in which a high-power secondary sound can be obtained. By selecting the diameters of the speakers 11A and 11B so that they are appropriately dispersed, the frequency bands over a wide frequency band can be obtained. It is easy to get a high power secondary sound,
The frequency band in which a good silencing effect can be obtained is further expanded.

The other functions and effects are the same as those of the first and second embodiments.
This is the same as the embodiment. FIG. 6 is a view showing a fourth embodiment of the present invention. In this embodiment, the present invention is applied to a device for reducing exhaust noise emitted from an exhaust pipe 1 of an automobile. Since the configuration is substantially the same as that of each embodiment, the same reference numerals are given to the same components, and the overlapping description will be omitted.

That is, in this embodiment, two speakers 11A and 1A are connected to one waveguide 14 as in the above embodiments.
Instead of fixing the 1B, one speaker 11 and one enclosure 13 covering the back surface thereof are fixed to the waveguide 14. However, inside the enclosure 13, the space inside the first space 13a on the side where the speaker 11 exists and the second space 1a on the side where the speaker 11 does not exist.
3b, and a partition plate 17 is provided.
The partition plate 17 is provided with an opening / closing valve 18 for communicating or blocking the space on both sides thereof.

That is, in this embodiment, by switching the open / close valve 18 between the open state and the closed state,
Although the waveguide 14 is provided with only one speaker 11, there are two resonance systems. Therefore, by switching the open / close valve 18 so as to form a resonance system that matches the frequency of the exhaust sound propagating through the exhaust pipe 1, the exhaust valve 2 is suitable for silencing the exhaust sound.
A secondary sound can be generated, and a good silencing effect can be obtained. That is, for example, by providing a plurality of speakers having different characteristics, it is possible to obtain the same operation and effect as a structure having a plurality of resonance systems without incurring a significant increase in size and cost of the device due to the provision of a plurality of speakers. is there.

For example, when the thickness of the enclosure 13 is switched between 80 mm and 100 mm by applying the structure of FIG. 6 to the model having the dimensions shown in FIG. 12, as shown in FIG. The speaker efficiency at lower frequencies is further improved as compared with FIG. 13C which is a characteristic based on the model of FIG. Other functions and effects are the same as those in the above embodiments.

In this embodiment, the enclosure 13
Although the configuration is such that the volume is switched in two stages, a configuration in which the volume is switched in three or more stages may be employed, which allows finer control. In this embodiment,
Although the above-described operation and effect are obtained by making the volume of the enclosure 13 variable, the same operation and effect can also be obtained by making the length and cross-sectional area of the waveguide 14 and the expansion chamber 15 variable. Obtainable. Waveguide 14
Various methods can be considered as a specific measure for changing the length of the expansion chamber 15 and the expansion chamber 15. For example, a bypass pipe is provided in parallel with the waveguide 14, and an acoustic wave is generated between the waveguide 14 and the bypass pipe. This can be realized by providing a valve or the like for switching the transmission path of the signal.

In the above embodiments, the case where the expansion chamber 15 is provided in the exhaust pipe 1 has been described. However, the expansion chamber 15 may be formed at the end of the exhaust pipe 1. In particular,
It is good also as composition which omitted lead-out duct 1B. Further, in each of the above-described embodiments, the case where one expansion chamber 15 is formed in the exhaust pipe 1 has been described.
A configuration in which a resonance system including the enclosures 13A and 13B is connected may be adopted. Also in such a case, by making the frequency characteristics of the respective resonance systems different, it is easy to obtain a high-power secondary sound over a wide frequency band, and the frequency band in which a good silencing effect can be obtained is expanded.

Further, in each of the above-described embodiments, it has been described that when a plurality of resonance systems exist, a good noise reduction effect can be obtained over a wide frequency band by making their frequency characteristics different. But, for example,
When it is desired to generate a secondary sound having extremely high power at a specific frequency, the frequency characteristics of the respective resonance systems may be matched to obtain the maximum output of each resonance system at the specific frequency. .

In each of the above embodiments, the present invention has been described as applied to a device for generating a secondary sound for canceling an exhaust sound propagating through the exhaust pipe 1 of an automobile. The present invention is not limited to this, and may be a device that generates a secondary sound for canceling noise that propagates through a duct other than the exhaust pipe 1, for example, an air conditioning duct in a building.

[0049]

As described above, according to the present invention, the width of the waveguide is made larger than the thickness of the waveguide so as to be equal to or larger than the diameter of the speaker, and the size of the speaker is reduced. Disposed on the surface side of the waveguide, and
Since the cross-sectional area of the expansion chamber by a plane perpendicular to the waveguide axis direction is equal to or larger than the area of the speaker, sound waves emitted from the speaker are supplied to the expansion chamber with little attenuation or sound increase. Therefore, there is an effect that the output of the speaker can be maximally utilized for noise reduction. In addition, since the noise and the secondary sound are superimposed in the expansion room, the noise reduction effect is not reduced even when the flow velocity is increased, and the degree of freedom in layout is increased, so that the effect of flooding is solved. .

In particular, according to the second aspect of the invention, there is an effect that heat intrusion from the expansion chamber side to the waveguide side can be suppressed to some extent, and heat damage can be prevented. According to the third to seventh aspects of the present invention, for example, if the frequency characteristics of the respective resonance systems are made different, there is an effect that a high-power secondary sound can be generated over a wide frequency band. .

[Brief description of the drawings]

FIG. 1 is a front view showing the configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a front view showing the configuration of a second embodiment of the present invention.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a front view showing the configuration of a third embodiment of the present invention.

FIG. 6 is a front view showing a configuration of a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of an apparatus for explaining the operation of the present invention.

8 is an equivalent model of the device shown in FIG.

FIG. 9 is a frequency characteristic diagram of discharge sound pressure based on the model of FIG. 8;

FIG. 10 shows a model used for calculation.

FIG. 11 is a model of a comparative example.

FIG. 12 is a model of the present invention.

FIG. 13 is a frequency characteristic diagram illustrating the effect of the present invention.

FIG. 14 is a front view showing a configuration of a conventional example.

15 is a sectional view taken along line XV-XV in FIG.

FIG. 16 is a front view showing the configuration of another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust pipe (duct) 1A Introductory duct 1B Outgoing duct 11, 11A, 11B Speaker 13, 13A, 13B Enclosure 14, 14A, 14B Waveguide 15 Expansion room 17 Partition plate 18 Opening / closing valve

Claims (7)

(57) [Claims] 1. A duct silencing device comprising: an expansion chamber formed in the middle of a duct or at an open end; a waveguide having one end communicating with the expansion chamber; and a speaker that emits a sound wave into the waveguide. In the secondary sound generator for use, the width dimension of the waveguide is made larger than its thickness dimension to be equal to or larger than the diameter of the speaker, and the speaker is placed on the surface of the waveguide. Wherein the cross-sectional area of the expansion chamber in a plane perpendicular to the waveguide axis direction is equal to or greater than the area of the speaker. apparatus. 2. The secondary sound generating device for muffling a duct according to claim 1, wherein the waveguide is communicated with the expansion chamber such that a thickness direction of the waveguide coincides with an axial direction of the duct. 3. The secondary sound generating device for muffling a duct according to claim 1, wherein a plurality of waveguides are communicated with the extension chamber, and a speaker is provided for each of the waveguides. 4. The apparatus according to claim 1, wherein a plurality of expansion chambers are provided, and a waveguide is connected to each of the expansion chambers, and a speaker is provided for each of the waveguides. 2. The secondary sound generator for silencing a duct according to item 1. 5. The secondary sound generating device for muffling a duct according to claim 1, wherein a rear surface of the speaker is covered with an enclosure, and a volume of the enclosure is variable. 6. The secondary sound generating device for muffling a duct according to claim 1, wherein at least one of a length of the waveguide and a sectional area thereof is variable. 7. The duct noise-reducing secondary sound generating apparatus according to claim 1, wherein at least one of the length of the expansion chamber and the cross-sectional area thereof is variable.