KR20010038462A - Method for measuring of noise transmission loss in a duct-systems - Google Patents

Abstract

PURPOSE: A noise transmission loss measuring method for a duct system is provided to simplify the measurement of the transmission loss of noise by computing only incident waves which participates in the transmission loss by mounting respective two microphones in input and output parts of the system. CONSTITUTION: In a duct system, a muffler(10) to test is mounted between first and second ducts(11,12), a sound source(13) is mounted at an end of the first duct for generating noise, two microphones(14a,14b) are mounted in the first duct for measuring the size of the noise before the noise passing through the muffler, and two microphones(14c,14d) are mounted in the second duct for measuring the size of the noise after passing through the muffler, wherein a noise transmission loss generated in the duct system is measured on the basis of pressures(P1,P2,P3,P4) obtained by the microphones respectively mounted in input and output parts according to a formula, wherein the noise transmission loss(TL)=20log10xabsolute value of ((ejks-H12)/(H13(ejks-H34)), wherein H12=(P2/P1)H13=(P3/P1)H34=(P4/P3).

Description

METHOD FOR MEASURING OF NOISE TRANSMISSION LOSS IN A DUCT-SYSTEMS

The present invention relates to a method for measuring the transmission loss of the noise generated in the duct system, and more particularly, to model the intake and exhaust machine including the silencer of the vehicle by measuring the transmission loss of the noise by the four-terminal water purification method using four microphones. The present invention relates to a method for measuring the noise transmission loss of a duct system that can be helpful for noise and noise prediction.

In general, when designing an automobile silencer, the shape of the expansion tube, the temperature gradient, the flow flow, and the influence of the air gap tube are considered in order to increase the transmission loss caused by the silencer from an acoustic point of view. Influence of the geometric shape of the expansion pipe, the number of bulkheads, the area of the expansion pipe, the expansion ratio, etc. on the permeation loss, literature Yang Yang Han, Byung Deok Lim, "Experimental Study on the Permeation Loss of the Silencer for a Passenger Car," , Vol. 7, No. 5, 94-101 (1988), Yang Han-han, "A Study on the Silencer Design through Acoustic Analysis," Journal of the Korean Society of Mechanical Engineers, Vol. 29, No. 4, 496-506 (1989). have.

On the other hand, the literature, Kwan-ju Kim et al., "Measurement and Analysis of Transmission Loss of Passenger Mufflers", published in the Journal of Korean Society of Automotive Engineers, 1994, describes the transmission loss of the silencer for passenger cars. The characteristics of transmission loss using GSA, a program, are described, and the results of comparative verification with experimental data using the 2-microphone method are described.

On the other hand, Korean Patent Application Publication No. 98-10402 has been filed a patent by Kia Motors Co., Ltd. under the name of "transmission loss measuring apparatus of automobile silencer (application date 1996.7.12 Application No. 96-28115)".

The above-described patent application is to reduce the noise more efficiently by accurately measuring the transmission loss of the noise passing through the muffler in a simpler manner, the configuration of the measuring device is schematically shown in FIG.

According to FIG. 1, the silencer 1 to be tested is installed between the first duct 2 on the inlet side and the second duct 3 on the outlet side, and on the first duct 2 and the second duct 3. A sound source 4 is installed at one end of the first duct 2 to generate noise, and the first duct for measuring the noise level before the noise generated from the sound source 4 passes through the muffler 1. The first microphone 5 is installed in (2), the second microphone (6) is installed in the second duct (3) in order to measure the size of the noise after passing through the silencer (1), the second duct ( 3) The end of the second duct 3 to prevent the reflection of the noise passing through is made to form a fallopian tube.

On the other hand, the interval ΔX between the microphones 5 and 6 is ΔX <C / 2 f _MAX , (C is the sound velocity, f _MAX is f _CUTOFF, f _CUTOFF = λnm C / πD maximum frequency measured) Is determined by.

Is the zero value of the first derivative of the Bessel function, and D is the diameter of the silencer inlet and outlet.

For example, when the inlet and outlet diameters (D) of the silencer are 49 mm and the usable frequency range is 50 to 2000 Hz, the zero derivative of the first derivative of the Bessel function is λ ₁ = 1.84 at room temperature (27 ° C), and the speed of sound (C) = Since 343m / s, f _CUTOFF = λnm C / πD = 1.84 × 343 / π × 0.049 ≒ 4100 (Hz). At this time, since the usable frequency range is 50 to 2000 Hz, the maximum frequency f _max actually measured is determined by the smaller of these values, so f _max is 2000 Hz. Therefore, since the space | interval (DELTA) X between microphones is (DELTA) X <C / 2fMAX, (DELTA) X <343 / 2x200 _, (DELTA) X <85.7, (DELTA) X is determined to be 60-80.

Such a conventional measuring apparatus uses a 4-pole parameter method using a transfer matrix to obtain a transfer loss of a silencer.

On the other hand, the conventional measuring apparatus has to measure twice in different conditions in order to obtain the transfer matrix, that is, when the end of the duct system is a non-reflective end and the end of the duct system is blocked. The 4-terminal integer had to be obtained from the measurement data.

By the way, in the conventional noise transmission loss measuring device to the shape of the exit end of the duct system to the shape of the fallopian tube to exclude the influence of the reflected wave to be a non-reflective end, but actually there is a problem that causes a lot of errors due to the reflected wave.

Accordingly, the present invention is to solve such a conventional problem, and to calculate the transmission loss by calculating only the incident wave involved in the transmission loss at the sound pressure measured by the four microphones without using the four-terminal integer method in analyzing the sound level meter The purpose is to provide a measurement method that can be performed.

In addition, the present invention obtains the four-terminal constant from the sound pressure measured in the four-microphone to connect the transmission matrix 2 × 2 transmission matrix to the system to predict the noise noise transmission loss of the duct system for more accurate modeling of the system The purpose is to provide a measurement method.

In order to achieve the above object, the present invention provides a method for measuring the noise transmission loss of a duct system, the sound pressure obtained by using two microphones each installed at the input and output of the system. With the formula below

(here, Provides a method for measuring the noise transfer loss of the calculated duct system.

In addition, the present invention is a method for measuring the transmission loss of the noise generated in the duct system, the sound pressure obtained by using two microphones each installed at the input and output of the system ( ) Into the formula below

(here ; Pressure and speed when the tip is non-reflective, ; Pressure and speed when the end is closed) Provides a method for measuring the noise transmission loss of a duct system using 4-terminal constant

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

1 is a schematic diagram showing a conventional noise transmission loss measuring apparatus,

Figure 2 is a schematic diagram showing a noise transmission loss measuring method according to the present invention.

<Description of the code | symbol about the principal part of drawing>

10; Silencer (duct system)

11; First duct

12; 2nd duct

13; soundtrack

14; microphone

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a schematic diagram showing a noise transmission loss measuring method according to the present invention.

As shown, the muffler 10 to be tested is installed between the first duct 11 and the second duct 12, and the first duct 11 and the second duct 12 to generate noise A sound source 13 is installed at one end of the first duct 11, and two noises are provided on the first duct 11 to measure the noise level before the noise generated from the sound source 13 passes through the muffler 10. Microphones 1 and 2 (14a and 14b) are installed, and after passing through the silencer 10, two microphones 3 and 4 (14c and 14d) are installed in the second duct 12 to measure the magnitude of the noise.

On the other hand, the measurement frequency band is limited to the in-plane plane wave region (0 <f <f _cutoff Hz), and the interval ΔX between the two microphones 14 installed in the first duct 11 and the second duct 12 is determined according to ΔX <C / 2 f _max, of the condition. (C is the speed of sound, f _max is f _cutoff, f _cutoff = λ _nm maximum frequency measured by C / πD) where λ _nm is the zero value of the first derivative of the Bessel function, and D is the diameter of the inlet and outlet of the silencer 10. to be.

According to the present invention, the transmission loss can be measured in two ways.

First, a method of measuring the transmission loss in one measurement test without using the 4-terminal integer will be described.

In Figure 2 : Sound pressure measured at each microphone 14 position;

Incident incident pressure at the microphone 14 positions 1 &3;

: Reflected pressure at microphone 14 positions 1 &3;

: Distance between two microphones 14;

As shown, for each plane wave propagation of the duct system, each incident wave and reflected wave can be represented as follows.

here, = Wave number

=> Static variable

Likewise

The total sound pressure and particle velocity at microphone 1 14a are

The total total pressure and particle velocity in microphone 2 (14b)

Equation 1 -Equation 1,

Similarly from the total sound pressure at microphone 3 14c and the total sound pressure at microphone 4 14d.

(If the tip is antireflective Becomes)

On the other hand, since the transmission loss only concerns the incident wave

( : transmission coefficient

here,

As described above, according to the present invention, two microphones 14 are installed at both ends of the sound level meter system, and the transmission loss can be measured using the sound pressure measured by only one measurement test. In addition, since the calculation is performed using only incident wave components without reflecting wave components, the accuracy of data may be improved. In addition, the measuring device is simplified since it is not necessary to provide a separate means for making the end of the second duct 12 non-reflective.

On the other hand, a method of measuring the transmission loss using a four-terminal integer will be described.

In the present invention, the transfer matrix method, which is a method of modeling the propagation characteristics of sound by introducing the impedance concept used in the electric field to obtain the 4-terminal constant, is used. As is well known, this method has a merit that the calculation of the matrix is simple and can be applied to a sound system combined in an arbitrary form, and the design sound system is modeled for each element and configured as a whole system, so that the design can be easily changed.

The two state variables used in the transfer matrix method are the sound pressure p and particle velocity v on both sides of the acoustic element, and a four-terminal constant (also called transfer matrix coefficient) can be obtained according to the conditions on both sides.

First, when the end of the second duct is an antireflection end (impedance of the end If

Is the state vector at the inlet of the duct system, Is the state vector at the outlet of the duct system. Equation 3 is a relation of particle velocity

Substituting in an expression

Similarly, Equation 4 is a relation of particle velocity

Substituting in an expression

If the end is blocked next (impedance at the end If

Similarly, using the transfer matrix method for the sound pressure and velocity on both sides of an acoustic element

Substituting Equations 3 and 4 into Equations 7 and 8, respectively,

Becomes

The following four complex equations are established from Equations 5 and 6.

here Are already calculated values, and since there are four unknowns in four equations, we can get 4-terminal integers and transfer losses using them as follows.

here,

: Pressure and speed when the tip is non-reflective

: Pressure and speed when the tip is blocked

In the above description, it should be understood that those skilled in the art can make modifications and changes to the present invention without changing the gist of the present invention as merely illustrative of a preferred embodiment of the present invention.

As described above, according to the present invention, two microphones are provided at the system input unit and the output unit, respectively, and only the incident wave related to the transmission loss can be calculated to measure the transmission loss, thereby simplifying the measurement.

In addition, the four-terminal constant is obtained from the sound pressure measured by the four-microphone, and the transmission matrix is connected to the system by a 2 × 2 transmission matrix to predict the noise, thereby enabling more accurate modeling of the system.

Claims (2)

In the method of measuring the transmission loss of the noise generated in the duct system, Sound pressure obtained by using two microphones installed at the input and the output of the system With the formula below (here, ) Measurement of noise transmission loss of calculated duct system. In the method of measuring the transmission loss of the noise generated in the duct system, Sound pressure obtained by using two microphones installed at the input and the output of the system ) Into the formula below (here ; Pressure and speed when the tip is non-reflective, ; Pressure and speed when the end is blocked) Noise transfer loss measurement method of duct system using 4 terminal constant.