JPH03174198A - Silencing system - Google Patents

Abstract

PURPOSE:To obtain the silencing system having sufficient silencing performance over a wide range by combining and disposing plural sets of acoustic reflecting surfaces consisting of passive elements and acoustic reflecting surfaces including acoustic conductance connected in parallel with the active elements or the pipelines equiv. thereto in a pipeline system in which the sounds to be controlled propagate. CONSTITUTION:The several reflecting surfaces A to F are disposed by combining the passive silencers 2 and the branch pipelines 3 including the active elements 4 in the main pipeline 1 system where the sounds to be controlled flow. The active elements 4 are constituted by using sound collecting microphones 5, secondary sound sources 6 and signal processing amplifiers 7 in the branch pipelines 3. The sound waves radiated from a sound source 8 propagate in the main pipeline 1 and are reflected respectively on the passive reflecting surfaces A, C, E and the active reflecting surfaces B, D formed in the branch pipes 33, by which interference is generated between the advancing waves and the retreating waves. If there is a reflection at the sound source 8 as well, the reflection by the reflecting surface F contributes to this reflection as well. The waves are partly absorbed by the active reflecting surfaces B, D. The silencing characteristic of the wide range is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sound deadening system. More specifically, the present invention relates to a silencing system that controls pipeline noise.

(Prior technology) Until now, expansion type, resonance type,
Passive silencers classified into interference type, sound absorption type, etc. have been used. Variable silencers provide a discontinuous surface of acoustic impedance in the pipe through which the target noise propagates, making it an acoustic reflecting surface, reflecting part of the acoustic energy between the sound sources, and reducing the amount of sound waves within the pipe. Obtaining a silencing effect by using the interference of
Furthermore, in recent years, active noise control technology using active elements has been developed, and its practical application is expected.

This active control method is for the sound to be silenced (-next sound).
- It was proposed in 1934 as a technology for silencing by superimposing a sound with the opposite phase to the next sound as a pre-secondary sound.
Patented by P. Lueg in 2010 (U.S.
, P, No, 2043416>, Kono method h'KF
If operated in one way, a perfectly reflective surface covering a wide range of noise frequencies will be formed, resulting in complete noise reduction.

Many of the active control methods currently in use for pipe system noise are based on the application of Lueg's method to pipes.
The sound pressure of the primary sound on the secondary sound source is predicted using digital signal processing from the upstream reference signal, and the pre-secondary sound in phase opposite to the -order sound is output to cancel this out. In this case, the ideal goal is to assume that the secondary sound has the same amplitude and opposite phase as the primary sound, and that there is complete cancellation, that is, a perfect reflective surface is formed on the secondary sound source. ing. This means that an acoustic impedance short-circuit surface is formed in the secondary sound source section. If a perfectly reflective surface is formed, theoretically sound waves will not propagate downstream from this surface.
According to this way of thinking, elements other than the secondary sound source section are not considered.

Furthermore, as an active control method that is not easily affected by changes in the propagation conditions of the conduit system and is easy to configure, a tightly coupled monoball with a microphone for collecting the reference signal and a speaker for the secondary sound source placed at the same position is available. (Tight-Coupled Hono
pole (hereinafter abbreviated as TCM) was established in 1983 as Kh
,Eghtesadl], 14. Hong, H, G
, Leventha. This method was proposed by Olsen in 1953.
The principle is similar to that of c 5ound absorber.

(Problem to be solved by the invention) However, with passive elements, the band in which complete reflection occurs is narrow, and sound absorption cannot be performed sufficiently. Therefore, due to the relationship between the properties and arrangement of the anti-qt surface and the frequency, a negative sound silencing effect may occur. There is a band that shows (increase in noise).

Furthermore, in order to obtain a sufficient silencing effect, the structure of the pipe element becomes complicated and pressure loss becomes large.

In addition, in the case of active noise control technology using active elements, although it is theoretically possible to form a completely reflective surface, it is impossible in actual equipment, and it is impossible to create a completely reflective surface through the secondary sound source. The desired performance may not always be obtained due to the effects of reflected waves between the downstream of the sound waves and sound waves re-reflected from between the sound sources.

Furthermore, in many conventional methods, a reference signal for predicting the sound pressure of the primary sound on the secondary sound source is obtained from a microphone installed at a position away from the secondary sound source upstream I11 in the conduit. There is. However, the propagation characteristics of sound waves between the microphone and the secondary sound source change depending on the temperature, flow rate, etc. in the pipe. This change causes an error when estimating the second blow sound, which has the same amplitude and opposite phase as the -blow sound. Conventionally, this problem has been addressed using adaptive signal processing. However, there is a problem in that there is a delay in following sudden changes, and the signal processing system becomes complicated.

Furthermore, conventional active noise control methods for pipeline systems using conventional TCMs also aim to create a fully reflective surface. For this reason, it is necessary to invert the phase of the collected sound signal and output it through an amplifier with infinite gain. When attempting to realize this, oscillations occur in actual systems due to the phase characteristics of the system. Therefore, the condition of perfect reflection cannot be achieved. Nevertheless, the design does not take into account the effects of interference with other conduit elements when complete reflection is not achieved.

The problems with the conventional noise reduction techniques described above can be summarized as follows.

■Passive silencers have complicated pipe element structures and have large pressure losses.

■Passive silencers, in principle, become larger for low frequency ranges.

■Passive silencers produce a band that exhibits an in principle silencing effect (1!! sound increases) against broadband noise.

■The goal of conventional active silencers is to form a completely reflective surface. However, this is not practical and is affected by other conduit elements such as the end of the conduit, making it impossible to obtain sufficient performance over a wide band.

■In a conventional active silencer in which the reference signal sound collection section and the secondary sound source section are placed apart on the main pipe, the propagation characteristics of the sound waves between the two are affected by the temperature, flow velocity, etc. in the main pipe. In order to avoid this, complex adaptive signal processing is required, but even then it cannot be avoided sufficiently, making it difficult to put it into practical use.

(2) In the method using TCM, which is a method that solves the above-mentioned problem (2), when trying to obtain the necessary silencing effect, oscillation occurs due to the phase characteristics of the system, which tends to make the operation unstable.

■For conventional active silencers that have active elements placed in the main pipe, it is necessary to develop active elements that can withstand the conditions (temperature, flow rate, etc.) of the gas flowing through the main pipe.

For example, microphones and speakers such as those currently used cannot be installed in pipe systems through which high-temperature gas or corrosive gas flows.

An object of the present invention is to solve the above-mentioned problems (1) to (4) and provide a sound deadening system having sufficient sound deadening performance over a wide band.

(Means for Solving the Problem) In order to achieve the above object, the silencing system of the present invention has the following features:
A plurality of combinations of acoustic reflecting surfaces made of passive elements and acoustic reflecting surfaces including active elements or equivalent acoustic conductance are arranged in a conduit system through which the sound to be controlled propagates.

Here, the acoustic reflecting surface by the passive element is a passive reflecting surface at the end of a pipe, or a component of a passive layer muffler, such as an expansion type muffler, which is further filled with a sound absorbing material, etc. It is.

Further, the acoustic reflecting surface including an active element or an acoustic conductance equivalent thereto is not intended to be a completely reflective surface, but is a reflecting surface that allows a portion of sound waves to pass through. The acoustic conductance that forms this active reflective surface is, for example, a branch pipe provided at one or more locations in the middle of a pipe or an expanded muffler, and each branch pipe has a sound collection sensor and a sensor for this sensor. It is an element in which a secondary sound source is placed that is driven by signal processing the sound collected by the sensor, or the sound collection sensor and the secondary sound source are placed at almost the same position, and a signal processing system with a relatively small gain is installed. element (L
(TCN), and further includes one whose gain is about 0.5 and which operates as a non-reflection branch pipe. Alternatively, the active reflective surface is a secondary sound source at one or more locations in the main pipe or an extended silencer that is driven by signal processing the sound collected by a sound collection sensor in the pipe, Or, it is an LTCM installed at one or more locations in the main pipeline.

Furthermore, a reflective surface equivalent to the active element using the LTCM described above or an acoustic reflective surface including an equivalent acoustic conductance can also be realized using an acoustic damper. Here, the term "acoustic damper" refers to something that deforms itself due to changes in sound pressure associated with noise and can absorb energy through the resistance associated with the deformation. For example, the cone part of a loudspeaker that has equivalent viscosity against vibrations. This includes things like viscous rubber membranes or pistons. It is preferable to install this acoustic tamper in the middle of the main pipe, in the middle of the expansion type muffler, or in the branch pipe.

(Function) Therefore, the silencing system of the present invention uses active elements to configure reflective surface elements with characteristics that cannot be obtained with passive elements, and actively uses passive elements together with active elements to provide reflective surface elements with different properties. By appropriately arranging the surfaces, the sound waves propagating through the main pipe are interfered with and absorbed, thereby silencing the sound.
In other words, active elements are used as reflective surfaces (reflects part of the incident wave, and transmits and absorbs part of the incident wave) within a achievable range, and passive elements By combining the reflective surfaces with reflective elements and allowing the plurality of reflective surfaces to appropriately perform interference and absorption, the pipe system as a whole constitutes one silencing system.

For example, when a branch pipe is provided in the main pipe connected to the sound source, and a sound collection sensor and a secondary sound source that is driven by appropriately processing the signal are placed inside the branch pipe, the branch pipe section allows the sound to propagate through the main pipe. It acts as an element that partially reflects and absorbs noise. This element has characteristics that cannot be achieved with passive layer mufflers. Further, the characteristics of this element can be easily varied by changing the length of the branch pipe, the positions of the sensor and secondary sound source, and the characteristics of the signal processing system. By arranging such elements at one or more locations in the main pipe, a noise reduction effect can be obtained by interference of the reflected waves circulating within the main pipe. Moreover, if this branch pipe is arranged on the same circumferential surface of the main pipe, the effect of the reflective surface can be further increased. It is noted that such an active reflective surface has properties not available with the reflective surface of the passive elements of a passive layer muffler. For example, a relatively large energy absorption can be obtained compared to passive elements. A muffler is constructed by arranging such reflective surfaces so that the sound muffling characteristics of the entire system are improved.

Therefore, if the reflective surface of the active element described above and the reflective surface conventionally used as the passive element are appropriately combined and arranged, the performance of the two will complement each other and will be even better than simply combining the characteristics of both. Good silencing properties can be obtained.

A reflective surface consisting of an active element in a conduit is generally equivalent to a circuit containing a controlled power source. However, as a special case, an LTCM with a secondary sound source and a sound collection sensor placed in close proximity and negative feedback with relatively low gain does not include a control power source.
It is equivalent to acoustic conductance. LTCM can achieve high performance acoustic conductance by being controlled by active elements. The acoustic conductance element forms a lossy reflective surface, which is desirable as a reflective surface for use in the present invention.

Similar to LTCM, it is also possible to use an acoustic damper as an element that can be regarded as acoustic conductance. LTCM
If instead, an acoustic damper is installed in the main pipe, an expanded muffler, or a branch pipe, the viscosity of the acoustic damper acts as a conductance in the pipe, forming a lossy reflective surface similar to the LTCM.

(Example) Hereinafter, the configuration of the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an embodiment of the present invention. This silencing system combines a passive muffler 2 and a branch pipe 3 that passes through an active element 4 to the main pipe #11 system through which the sound to be controlled flows, and has several reflecting surfaces A, B, C, D, E, In the six-branch conduit 3 in which the F is disposed, an active element 4 is constructed using a sound collection microphone 5, a secondary sound source 6, and a signal processing/amplifier 7.

Here, F, A, C, and E are passive reflective surfaces, and reflective surfaces B and D made using active elements are active reflective surfaces. Furthermore, the active reflective surfaces B and D are generally not perfect reflective surfaces.

In this specification, LTCM refers to low gain tight-coupled monoball.
dNonet) 010), which includes a reference signal sound collection sensor such as a microphone 5 and a secondary sound source such as a speaker 6.
are placed at the same position, and the gain is set relatively low, for example, about 20 a.
8 or less and operates within a range where oscillation does not occur.This is easy to operate stably, unlike the conventional tightly coupled monoball or aiming for a perfect reflective surface, which has the problem of instability. There are some that act as imperfectly reflecting surfaces.

The active element 4 is configured to appropriately process a signal collected by a sound collection sensor (such as a microphone) 5, and then radiate the signal from a secondary sound source (such as a loudspeaker) 6 via an amplifier 7. For example, in the case of this embodiment, an LTCM is adopted in which a microphone 5 as a sound collection sensor is installed above a speaker 6 as a secondary sound source, and this is installed in each branch pipe F#I.
3,3. It is installed at the end of... It is preferable that the active element 4 limits the gain of the amplifier 7 to a relatively low value, for example, about 20 dB or less, and operates within a range in which oscillation does not occur. Note that the arrangement between the speaker 6 and the microphone 5 (the system is not particularly limited to that described above, and may be installed slightly upstream of the speaker 6 depending on the case).

Also, this active element is about 173 [?] of the length between the two reflective surfaces from upstream or downstream between the two reflective surfaces. [It is preferable to provide [[]. In this case, as shown in FIG. 8, there is an effect of eliminating valleys in the attenuation characteristics over a wide range. still,
In Fig. 8, only an expansion chamber is provided;
is at the 1/2 position, □ is at the 1/3 position, and -m
- indicates the transmission loss when LTCM is placed in 1/4.

In addition, this active element is not limited to the above-mentioned LTCM, but for example, the main pipe 1 rather than the speaker 6
It is also possible to employ other active elements etc. that collect the reference sound in the open state.

It is also possible for branch line 3 to include passive elements.

For example, it is also possible to provide a passive element, such as a conduit or another branch, between the microphone 5 and the secondary sound source 6 in the branch 3.

A reflective surface B formed by this active element 4.

D is a reflective surface that partially reflects, absorbs, and transmits instead of complete reflection, which is difficult to achieve, and is a reflective surface formed by other active elements or a reflective surface formed by passive elements A, C,
It actively utilizes the interference of reflected waves from a plurality of reflecting surfaces such as E and F.

Note that the sound collection sensor 5 and the secondary sound source 6 are not limited to the above-mentioned microphones, microphones, and speakers, and may be appropriately selected depending on the purpose and the like.

Further, the branch pipe 3 containing the active element 4 is for isolating the active element 4 from the flow in the main pipe line 1 and forming an active reflective surface in the main pipe line l. This branch pipe 3
In order to avoid the influence of the airflow flowing through the main pipe 1, especially the temperature, a heat insulating material 9 and/or a cooler are placed in the main pipe 1.
It is preferable to protect the sound collection sensor 5 and the secondary sound source 6 from the influence of air currents.Furthermore, if corrosive gas, high temperature gas, etc. flow in the main pipe 1, the intrusion of these gases is prevented and only the sound passes through. It is preferable to provide a means at the inlet of the branch pipe 3 to cause this. This can be easily achieved using glass wool, for example. In addition, the length of the branch pipe 3 is determined based on the necessary silencing characteristics,
It is selected as appropriate depending on the degree of influence of the airflow in the main pipe. If the influence of airflow is negligible, the length of the branch pipe 3 can be O and the LTCM can be placed directly in the main pipe 1.

In this case, it becomes easy to increase the amount of silence.

Furthermore, by placing the sensor 5 upstream of the secondary sound source 6 in place of the LTCM and incorporating a passive element between them, the estimation error of the transmission system can be reduced compared to the conventional method of obtaining a fully active reflective surface. It is also possible to simplify the processing system of the active element system and stabilize its operation. For example, as shown in FIG.
and the sensor 5. In this case, the signal processing can operate stably simply by providing a delay characteristic of 1/C. However, C is the speed of sound in the main pipe.9 In addition, acoustic reflecting surfaces by passive elements expand or reduce the cross-sectional area of the pipe, such as expansion type, resonance type, interference type, sound absorbing type silencers, etc. Acoustic impedance failure 3! It includes not only the continuation surface but also the open surface E at the end of the conduit.

Since the silencing system of the present invention is configured as described above, it operates as follows.

The sound waves emitted from the sound source 8 propagate within the main pipe 1i'31, and pass through the passive reflection surfaces A at the entrance, exit, and end of the pipe of the expansion chamber 2,
C, E and two branch pipes 3 arranged in the expansion chamber and outlet pipe
, are reflected at the active reflecting surfaces B and D formed in the three parts, and interference occurs between the forward wave and the backward wave. If there is reflection at the sound source, the reflection from the reflective surface F also contributes to this. In addition, a portion of the light is absorbed at the active reflection surfaces B and D (branch pipe portions). As a result, the sound is muted and radiated from the conduit end E.

Although the above-mentioned embodiment is a preferred example of real silicon of the present invention, it is not limited thereto, and various modifications can be made without departing from the gist of the present invention.6For example, the active reflection of the present invention Generally, a sound collection sensor 5 and a secondary sound source 6 are placed in the middle or at the end of the branch pipe 3, or in plural units. It is also possible to arrange the speaker 6 as a secondary sound source at a distance, to perform adaptive processing on the signal processing, or to arrange passive elements as an auxiliary arrangement.

In addition, the distance between the sound collection sensor 5 and the secondary sound source 6, their arrangement position, and signal processing (including passive methods) are as follows:
It is selected as appropriate depending on the required silencing characteristics. Branch pipe 3
Even if the length of the branch pipe 3 is constant, various characteristics such as changing the resonant frequency of the branch pipe 3 can be obtained by appropriately selecting them.

Moreover, as a special example of an active element including branch pipe 3,
There is a non-reflection end configuration in LTCM. This is the case where an LTCM is placed at the end of the branch pipe 3 and the gain of the LTCM is set to 0.5 for signal processing.

When the end of the branch pipe is made into a non-reflection end in this way, a broadband and substantially flat sound damping characteristic can be obtained, and there is no restriction on the length of the branch pipe, making it easy to reduce the influence of airflow on secondary sound sources.

By changing the characteristics of this pond and the signal processing section, the properties of the reflective surface of the branch pipe section can be varied in various ways.For example, if an LTCM is used at the end of the branch pipe and used under conditions other than the above-mentioned no-reflection condition, , the transmission loss of the branch pipe section becomes a resonance characteristic. By changing the gain of the LTCM, the sharpness of resonance and the reversal of resonance and anti-resonance can be achieved. Furthermore, it is also possible to tune the resonance frequency by changing the phase characteristics of the signal processing section.

Furthermore, a plurality of branch pipes 3 can be arranged on the same circumference of the main pipe line 1 and the passive muffler 2. This makes it possible to suppress an increase in the volume of the device and increase the silencing effect.

In addition, in this system configuration example, each active reflection surface is driven independently, but if you want to change the amount of silencing of the entire system when the characteristics of the sound source change significantly, you can use passive elements. Although this can be done by changing the length, the silencing characteristics can be changed by comprehensively controlling the amplifier gain of each active reflection surface and the characteristics of the signal processing section. Furthermore, by adaptively controlling the characteristics of the signal processing section, it can respond to the noise situation! & It can also have suitable characteristics.

Moreover, as shown in FIG. 2, the silencing system of the present invention
It is also possible to construct a system using only the passive reflecting surface E and the active reflecting surfaces B and D at the end of the conduit without placing the expansion chamber 2 in the middle of the conduit 1, which is a passive reflecting surface.

In addition, both the active element 4 and the passive element 2 can be used in combination with sound-absorbing materials. By filling in an appropriate arrangement, it is possible to increase the silencing effect and reduce the influence of airflow on sensors and secondary sound sources.

(Example of actual measurement of noise reduction effect) (1) Example of actual measurement of noise reduction using only a pipe and two active reflective surfaces (
(See Fig. 2) The silencing effect was actually measured using the apparatus having the configuration shown in Fig. 2. Figure 3 (A) shows the prediction of the silencing effect based on calculations when only the pipe is used and when active reflective surfaces are used, and □ is when active reflective surfaces are used in three locations.・Scream■ is 2
-m- is the result for one location. Due to this,
In the case of a single active reflective surface, regions where no attenuation can be obtained periodically appear, but by arranging multiple active reflective surfaces at appropriate intervals, these characteristics can be corrected, and each active reflective surface It can be understood that even if the surface is not a perfect reflective surface, a large sound-damping effect can be obtained by combining multiple surfaces. Figure 3 (B)
This is the result of actually measuring the amount of silencing when active reflective surfaces are provided at two locations. In the figure, the calculation results shown in FIG. 3(A) are shown, and . . . are the results of actual measurements. The length of the branch pipe at this time was 10 mm, and the length of the branch pipe could be almost ignored within the measurement range. From this result, it can be understood that the predicted value and the actual value show a considerable correlation.

(2) Actual measurement of noise reduction using active elements in both the conduit and the expansion chamber Figure 4 shows the configuration of the device, and Figure 5 shows a comparison between the predicted calculation results and the actual measurements of the noise reduction effect. In the figure, -m- is a calculation result when only passive elements are used, and -m- is an actual measurement result when only passive elements are used.

□ is the calculation result when active elements are used together, and...
・・・・・・・・・・・・・・・・・・ is the result of actual measurement using active elements. It can be seen that the calculated results and the actual measurement results show a considerable correlation. It can also be seen that the area where no attenuation is obtained is smaller and the attenuation amount and attenuation band are wider and larger than in the case of only passive elements and the case of only active elements.

Further, an acoustic damper can be used as an acoustic reflecting surface equivalent to acoustic conductance.

For example, it is possible to omit the sound collection sensor, amplifier, and signal processing system of the LTCM described above, and to configure the system using only the secondary sound source. In this case, the acoustic damper undergoes viscoelastic deformation due to changes in sound pressure caused by noise, that is, vibrates with attenuation, changes the volume inside the pipe, and forms a reflective surface within the pipe by absorbing energy. . This acoustic damper can be used, for example, when a loudspeaker is used as a secondary sound source in LTCM, and when there is no sound collection sensor or amplifier (the speaker terminals are connected at low impedance).
This means that even in the event that these devices break down, a certain degree of noise reduction effect can be expected. Furthermore, an acoustic damper refers to something that deforms itself due to changes in sound pressure associated with noise and can absorb energy through the resistance associated with the deformation, such as the cone part of a loudspeaker that has equivalent viscosity against vibrations. Contains something like a viscous rubber membrane or piston.

In order to confirm the effect of this acoustic damper,
In the 70M silencing system, Figure 7 shows the noise analysis results at the outlet of the conduit when the amplifier is turned on and when the amplifier is turned off in the LTCM.In this measurement result,... . . . is a case where there is only a conduit, -m- is a case where the power of the LTCM amplifier is turned off, and □ is a state where it is working as an LTCM. As is clear from this result, the LT
It can be seen that CM is greatly attenuated. It can be seen that even when the amplifier is powered off, that is, when it operates as an acoustic damper, it has a significant damping effect.

(Effects of the Invention) As is clear from the above description, the present invention includes an acoustic reflecting surface made of a passive element and an active element or an acoustic conductance equivalent thereto in a conduit system through which the sound to be controlled propagates. By arranging multiple acoustic reflecting surfaces in combination, the active element is not intended to form a completely reflective surface, which is difficult to achieve, but to reflect a portion of the incident wave, and to By designing the properties and arrangement of each reflective element surface so that interference and absorption by multiple reflective surfaces are appropriately performed, it is possible to obtain a high silencing effect for the pipe system as a whole. can. Moreover, the present invention combines a plurality of acoustic reflecting surfaces made of passive elements and acoustic reflecting surfaces including active elements or equivalent acoustic conductance into one.
The system consists of two silencing systems, so it is possible to deal with noise with a large amount of change by leaving the passive elements as they are and controlling the characteristics of the active part appropriately according to the amount of change.
& Since it is possible to achieve appropriate effects and the structure of the pipe line can be simplified, pressure loss can be significantly reduced compared to conventional passive silencers.

The sound deadening system of the invention also uses the active element not as a fully reflective surface, but as one of the possible reflective surfaces that reflects part of the incident wave and transmits and absorbs part of it. Because of this, it is possible to expect interference and sound absorption effects that cannot be obtained with conventional active mufflers.It also improves the negative muffling bands of interference and resonance mufflers, and provides wide-band sound muffling that cannot be obtained with the muffling characteristics of passive mufflers. Sound deadening properties can be obtained.

Moreover, from this, the silencing system of the present invention can easily construct silencing characteristics with a higher degree of freedom than passive silencers or conventional active silencers that aim for a completely reflective surface. For example, the silencing characteristic can be achieved by changing the pipe line, but it can also be easily achieved by changing the gain of the amplifier or the signal processing section.

In addition, since this system basically has an active part inside the branch pipe, the sound collection sensor and secondary sound source are not placed separately on the main pipe, so changes in sound velocity due to changes in the airflow conditions flowing through the main pipe, and flow velocity Since the silencing characteristics do not change much due to the influence of the noise, there is no need to modify the signal processing system of the active element, so a sufficiently wide band silencing characteristic can be obtained without using advanced adaptive processing. Moreover, the cooperation of the active elements improves the silencing effect in the low frequency band region, so that the passive elements such as the conduit and expansion chamber can be downsized.

In addition, since the noise reduction system of the present invention has an active part inside the branch pipe, it is possible to protect the sound collection sensor and the secondary sound source from the effects of temperature and flow velocity, etc. It reduces problems such as temperature and corrosion, and allows existing sensors (microphones, etc.) and secondary sound sources (speakers, etc.) to be used as is.

In addition, conventional active silencers, which collect sound upstream and consist of a completely reflective surface using a linear prediction filter, cannot be used for non-linear sounds such as car exhaust noise, but this system uses a branch pipe. When composing an active element within it,
Since the sensor and the secondary sound source are in the same position when viewed from inside the main pipe, it can also handle the generation of nonlinear waves.

Therefore, in addition to the normal piping system, it is also possible to
It can be used to reduce exhaust noise, and can also be used as an auxiliary means for existing noise reduction systems, and the non-reflective end can be used to counter resonance in pipes, etc. It is also relatively easy to change the characteristics of the silencing effect of the entire system, so compared to conventional active elements, the characteristics are less likely to deteriorate due to changes in the nature of the noise or the conditions inside the pipe. be.

Moreover, in order to achieve even more optimal operation, these characteristics can be improved by using an adaptive signal processing system (based on the LMS algorithm, etc.) in the signal processing system of each active element so that the characteristics of the entire system are optimized. Able to respond to change.

In the present invention, LTCM can be used as a preferred method for realizing a reflective surface consisting of active elements.

In LTCM, the active element acts as a control mechanism for property improvement, and in the conduit it is an element that equivalently acts as a passive conductance. Therefore, in active silencing systems, which are less likely to suffer from problems such as oscillation, which is one of the problems of conventional active silencing systems, there is a risk that noise will be amplified when the system fails. When an LTCM is used, even in the event of a failure, the LTCM acts as an acoustic damper, and as shown in FIG. 7, even if the performance is slightly degraded, it is possible to maintain a certain level of silencing effect. Furthermore, in applications where it is difficult to install microphones, loudspeakers, etc., it is possible to use acoustic dampers instead of LTCMs, and the present invention can also be applied to targets where conventional active silencing systems have been difficult to apply. Wide range of applications.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram showing an embodiment of the silencing system of the present invention. FIG. 2 is a principle diagram showing another embodiment. Figure 3 (A) is a graph predicting the silencing effect of the silencing system shown in Figure 2 when only a pipe is used and when an active reflective surface is used. It is a graph showing predicted calculated values and actual measurement results when FIG. 4 is a principle diagram showing another example of a real square color. FIG. 5 is a graph showing a comparison between the predicted calculation results and actual measured values of the silencing effect in the silencing system of FIG. 4. FIG. 6 is a principle diagram showing another embodiment of the present invention. Figure 7 shows L'r when the branch pipe length shown in Figure 2 is 0.
' In the CM silencing system, it is a graph showing the analysis results of noise at the conduit outlet when the power of the amplifier is turned on in the LTCM and when the power of the amplifier is turned off. FIG. 8 is a graph showing changes in attenuation characteristics due to differences in the position of the LTCM. 1... Piping system, 2... Passive element, 3... Branch pipe, 4... Active element, 5... Microphone (sound collection sensor), 6... Speaker (secondary sound source), 7... amplifier, 9... cooling means, A, C, E, F... passive reflective surface, B, D... active reflective surface.

Claims (21)

[Claims] (1) In the conduit system through which the sound to be controlled propagates, there are multiple acoustic reflecting surfaces made of passive elements and acoustic reflecting surfaces including acoustic conductance connected in parallel to active elements or equivalent conduits. A silencing system characterized by being arranged in combination. (2) The acoustic reflecting surface including the active element according to claim 1 or an acoustic conductance equivalent thereto is not a completely reflecting surface, but is a reflecting surface that intentionally allows a portion of sound waves to pass through. Sound deadening system. (3) A sound muffling system characterized in that the acoustic reflecting surface formed by the passive element according to claim 1 is a component of a passive muffler. (4) A silencing system, wherein the passive element according to claim 1 is a passive reflective surface at the end of a conduit. (5) A sound muffling system, wherein the passive muffler according to claim 3 is an expansion muffler. (6) A sound muffling system, characterized in that the expandable muffler according to claim 5 is filled with a sound absorbing material. (7) A branch pipe in which an acoustic reflecting surface including the active element according to claim 1 or 2 or an acoustic conductance equivalent thereto is provided at one or more locations in the middle of the pipe or in an expandable muffler. A sound deadening system characterized in that a sound collecting sensor and a secondary sound source driven by signal processing the sound collected by the sensor are arranged as active elements in each branch pipe. (8) A secondary sound source in which an acoustic reflecting surface including the active element according to claim 1 or 2 or an acoustic conductance equivalent thereto is provided at one or more locations in the middle of the main pipe or in the expanded muffler, The noise reduction system is characterized in that the secondary sound source is driven by signal processing of sound collected by a sound collection sensor in the pipe. (9) A noise reduction system characterized in that a plurality of branch pipes according to claim 7 are arranged on a circumferential surface at the same position with respect to the flow of the main pipe. (10) A silencing system characterized in that the active element inside the branch pipe according to claim 7 or 9 or an acoustic conductance equivalent thereto is placed at the end of the branch pipe. (11) A silencing system characterized in that a plurality of active elements inside the branch pipe according to claim 7 or 9 or acoustic conductance equivalent thereto are arranged in the middle and at the end of the branch pipe. (12) A sound silencing system, wherein the sound collection sensor and the secondary sound source according to claim 10 are elements placed at substantially the same position and driven using a signal processing system with a relatively small gain. (13) The gain of the active element according to claim 12 is about 0.5.
A noise reduction system that operates as a non-reflective branch pipe. (14) A silencing system characterized in that the signal processing system of the active element according to claim 12 has a phase characteristic and a resonant frequency is variable. (15) A noise reduction system characterized in that the secondary sound source and the sound collection sensor according to claim 8 are elements placed at substantially the same position and driven using a signal processing system with a relatively small gain. (16) A sound deadening system, characterized in that a passive element is disposed between the secondary sound source and the sound collection sensor according to claim 8. (17) A sound deadening system according to claim 16, wherein the passive element is a conduit having an equal length to the next reflecting surface on the downstream side of the secondary sound source. (18) A silencing system characterized in that the signal processing system of the active element according to claim 7, 8 or 10 is adaptive signal processing and operates while correcting the overall characteristics according to the nature of the noise. (19) A sound muffling device according to claim 1 or 2, characterized in that the acoustic reflecting surface including the acoustic conductance connected in parallel to the conduit is an acoustic damper installed in the middle of the conduit or the expansion type muffler. system. (20) The acoustic conductance connected in parallel to the conduit according to claim 1 or 2 is a branch pipe provided at one or more places in the middle of the conduit or in an expansion type muffler,
A noise reduction system characterized by an acoustic damper installed inside each branch pipe. (21) A sound damping system, characterized in that the active element inside the branch pipe according to claim 7 or 9 is placed at the end of the branch pipe, and an acoustic damper is installed in each branch pipe.