JPH08185189A - Silencing system of active noise control system - Google Patents

Abstract

PURPOSE: To provide a silencing system of an active noise control type which exerts a remarkable silencing effect on a wide range of frequencies by connecting plural pieces of silencers of Helmholtz type consisting of connecting pipe and cavity chambers in series and mounting a speaker at the cavity chamber of the last end. CONSTITUTION: An air duct 1 is provided with the connecting pipe 2, the cavity chamber 3, the connecting pipe 4 and the cavity chamber 5 in series and the speaker 6 is mounted at the cavity chamber 5 and is controlled by a controller 7. Amplified frequencies having plural (two in this embodiment) peaks are obtd. with the sound pressure of the speaker 6 and the frequency band of a wide silencing effect is obtd. The silencing system having the remarkable silencing effect on the certain broad frequencies is obtd. particularly if the two peaks are set in proximity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control type muffler which muffles noise transmitted through an air duct by causing a speaker to generate sound pressures having the same frequency and opposite phases to muffle or reduce noise.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Utility Model Laid-Open No. 4-11247, a speaker is attached to an air duct, for example, an intake duct of an internal combustion engine, and a sound pressure having the same frequency as the engine intake side noise but opposite phase is produced. It is known to generate noise to cancel noise.

In this case, in the case where the speaker is directly attached to the wall of the air duct, the diameter of the speaker cannot be increased and the output energy in the low frequency range cannot be increased.

Therefore, as shown in FIG. 4, there is a structure in which a Helmholtz type silencer 23 is constituted by a connecting pipe 21 attached to an air duct 20 and a cavity 22 and a speaker 24 is provided in the cavity 22. If the muffler 23 is set to resonate at a low frequency, the sound pressure output to the air duct 20 can be increased for a specific low frequency.

[0005]

It is said that it is effective to muffle or attenuate the noise of the internal combustion engine caused by the operation of the intake and exhaust valves, especially in the low frequency range. However, in the above-mentioned conventional one, since the output is amplified only to a specific frequency by one resonance chamber for the low frequency component of the noise sound pressure, the output is increased to a wide range of the low frequency. The muffling effect cannot be increased.

[0006]

[Means for Solving the Problems] A plurality of resonance-type silencers consisting of a connecting pipe and a hollow chamber are connected in series, a connecting pipe at the tip is connected to an air duct, and a speaker is attached to the hollow chamber at the rear end. The sound pressure having the same frequency and opposite phase as the noise frequency to be silenced is generated from the speaker.

[0007]

The noise of the noise source is detected, the speaker is controlled, and a sound pressure having the same frequency as the noise to be silenced but in the opposite phase is generated in the speaker to muffle the noise. In this case, there is a peak in which the sound pressure is amplified depending on the number of hollow chambers. Therefore, due to the amplified frequency of the peak, the silencing effect becomes particularly large for a plurality of frequency ranges of noise.

Further, by making the set frequencies to be amplified close to each other, the silencing effect can be enhanced in a certain wide frequency range of the noise frequency. Each set frequency to be amplified is calculated by a known calculation formula from the lengths and inner diameters of a plurality of connecting pipes and the volume of each cavity, or is experimentally determined. For example, it is said that it is effective to set the frequency to be amplified to a low frequency range for noise of an automobile engine, etc.
If the frequency difference is set to approach 30% in the range of about 200 Hz, the peak becomes relatively flat and the width of the amplified frequency range becomes wide.

[0009]

EXAMPLE FIG. 1 shows an example. The air duct 1 is an intake duct of an internal combustion engine for automobiles, and connects an air cleaner and an intake manifold. A composite Helmholtz-type sound deadening in which the connection pipe 2, the cavity chamber 3, the connection pipe 4, and the cavity chamber 5 are connected in series to the side wall of the air duct 1 in series to circulate the inside and the cavity chambers 3 and 5 serve as resonance chambers. Make up a container.

A speaker 6 controlled by a controller 7 is installed in the cavity 5. The control method of the speaker 6 by the controller 7 is publicly known, and the speaker 6 generates a sound pressure having the same frequency as the noise to be silenced but the opposite phase by the input signals 8 and 9 of the rotation speed and the intake air amount. It is what makes me. FIG.
The sound pressure generated from the speaker 6 due to the presence of the hollow chambers 3 and 5 is amplified at a specific frequency portion, and generally two peaks a and b are generated as shown in FIG.

In the case of the configuration of FIG. 1, as an example, the connecting pipe 2
Inner diameter 29 mm, length 8 mm, cavity chamber 3 2850c
c, the inner diameter of the connecting pipe 4 is 27 mm, the length is 200 mm, and the cavity 5 is 370 cc, the two peaks c and d of the frequencies come close to each other as shown in FIG.
z, 173 Hz (frequency difference: about 43%), and the peak portion connecting the two peaks c and d becomes relatively flat.
That is, the sound pressure of the speaker 6 is amplified in a wide range in the low frequency range, and it is effective for silencing and reducing the low frequency noise in a wide range.

In the example shown in FIG. 3, the air duct 1 is connected to the connecting pipe 1.
0, cavity chamber 11, connection pipe 12, cavity chamber 13, connection pipe 1
4. The cavity chambers 15 are connected in series, and the number of cavity chambers is three. Mounting the speaker 6 and its controller 7 in the hollow chamber 15 at the final end is similar to that in FIG.
In this example, the peaks of the sound pressure of the speaker 6 to be amplified appear at three places as indicated by e, f, and g in FIG. 3B. The frequencies of the peaks e, f and g are the respective connecting pipes 10, 12, 1
4 and the cavity chambers 11, 13, 15 can be set experimentally by changing the dimensions and volumes,
The sound pressure range to be amplified can be set to a continuous wide range by arranging at appropriate intervals.

[0013]

According to the present invention, a plurality of cavity chambers are connected in series so that the active noise control type silencer has a plurality of frequency regions having a remarkable silencing effect and can be widened. Further, by bringing these points close to each other, a remarkable silencing effect can be exerted on a continuous wide frequency range.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

2A and 2B are diagrams showing the characteristics of the silencer of FIG. 1, where FIG. 2A is a general case, and FIG. 2B is a case where set frequencies are close to each other.

3A is a diagram showing another embodiment, and FIG. 3B is a diagram showing its characteristics.

FIG. 4 is a diagram showing a conventional silencer.

[Explanation of symbols]

 2, 4, 10, 12, 14 Connection pipe 3, 5, 11, 13, 15 Cavity chamber 6 Speaker 7 Controller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G10K 11/16 15/04 302 A

Claims (1)

[Claims] 1. A plurality of Helmholtz type silencers consisting of a connecting pipe and a hollow chamber are connected in series, a connecting pipe at the tip is connected to an air duct, and a speaker is attached to the hollow chamber at the rear end and noise is reduced. An active noise control silencer equipped with a controller that causes a speaker to generate a sound pressure that has the same frequency and opposite phase as the sound pressure to be detected and silenced.