JPH02226023A - Method for measuring transfer function used in active control of noise - Google Patents

Abstract

PURPOSE:To obtain a transfer function permitted in the fluctuation of the number of rotations by measuring the transfer function between a compressor and a sound receiver by driving the compressor at predetermined power supply frequency effectuating at least one of data corresponding to integral multiple the number of rotations of the compressor and data integral multiple power supply frequency among measuring data to interpolate the effective data. CONSTITUTION:The transfer functions between a speaker 13/a compressor 8 and a microphone 12/an auxiliary microphone 15 are measured and, on the basis of these functions, noise having a phase reverse to that of the noise emitted from the compressor 8 is generated from the speaker 13 to perform sound arresting control. The transfer functions between the compressor 8 and the microphone 12 as well as the auxiliary microphone 15 are measured by operating the compressor 8 at predetermined power supply frequency and at least one of the data integral multiple the number of rotations of the compressor and the data integral multiple power supply frequency among measuring data is made effective and the effective data is interpolated to calculate said functions.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention actively cancels noise from a machine room housing a compressor! ! This invention relates to an AI determination method for a transfer function used in active control of lg-.

(Prior Art) Cooling devices that use compressors, such as refrigerators, are often installed in the living space of ordinary households.
Moreover, since they are operated continuously regardless of the season, reducing noise has become an issue. in this case,
The most problematic noise source for refrigerators is the noise from the machine room in which the compressor and the piping system connected thereto are housed. That is, in the machine room, the compressor itself generates relatively large noises (operating noise of the compressor motor, fluid noise due to the compressed gas, mechanical noise from the 1-iJ moving elements on the side of the compressor, etc.). The piping system connected to the compressor also generates noise due to its vibrations, and such machine room noise accounts for most of the refrigerator noise. Therefore, suppressing the noise from the machine room greatly contributes to reducing the noise of the entire refrigerator.

Therefore, in the past, noise reduction from the machine room χ,I
As a countermeasure, in addition to reducing the noise of the compressor itself (for example, adopting a rotary type compressor), we have also improved the vibration-proof support structure of the compressor and modified the shape of the piping system to reduce vibration damping in the vibration propagation path. Alternatively, attempts are being made to increase sound absorption and noise transmission loss within the machine room by arranging sweat absorbing members and sound insulating members around the compressor and piping system.

However, in general, the machine room of a refrigerator has multiple openings for heat dissipation because it is necessary to release the heat generated by the compressor to the outside. There will be a lot of noise. For this reason, the conventional noise reduction measures as described above naturally have a limit, and the effect of reducing the noise level can only be expected to be about 2 dB (A) at most.

In contrast, in recent years, with the development of electronics application technology, especially acoustic data processing circuits and T8 sound control technology, sound wave interference has been developed. ;1v1
Note: Application of active noise control technology to reduce noise
1 has been done. That is, this active 1. Basically, it is! The sound from the gl sound source is converted into electricity (No. 3) by a control sound receiver (for example, a microphone) installed at a specific position, and this electrical signal is added to the signal by a computing unit and used for control purposes. By operating a sound generator (for example, a speaker), the generator generates an artificial sound that is in the opposite phase to the original sound (the sound from the noise source), has the same wavelength, and the same amplitude. The purpose is to attenuate the original sound by interfering with the original sound, and the principle of ll!I sound by such active control will be schematically explained below with reference to FIG.

That is, in FIG. 8, Xs is the noise generated by the compressor S, which is the noise source, Xm is the sound generated by the speaker 8, which is the control sound generator, and which is received by the microphone ν1, which is the XaS control sound receiver, and the control target point. Let the sound at O be Xo, and furthermore, the first to fourth valleys of the sound output and input points as described above.
The acoustic transfer function of GAM, GAO, GSM, GSO
Then, the following equation holds true for a two-man power two-output system. In addition, each of the above acoustic transfer functions CAM, G^0. GSM, G
The meaning of SO is that the subscript in the first stage corresponds to the input end, and the subscript in the second stage corresponds to the output side (response (lIIl). For example, CAM
represents the acoustic transfer function when the input terminal is the human input signal to the speaker A, and the output signal from the microphone M is set as the output terminal.

Therefore, the 'flXa that should be generated by speaker 8 is calculated from the above equation as Xa=(-GSO-Xm+03M・Xo)/(G
SM@GAO-G50e CAM), but in this case, since the goal is to make the tone level at control target point 0 zero, it can be set as Xa-0. As a result, X a =Xm ◆GSO/ (GSO
#GAM-GSM・GAO). As can be understood from this equation, in order to make 3Xo at the control target point 0 zero, the Xm received by the microphone M is given by G-GSO/ (GSO-GA)4- GSM-GA0
)(]) If the sound Xa processed through a filter according to the transfer function G is generated from the speaker A, the control target point O
Active control can be performed to theoretically reduce the sound level to zero, and a computing unit H is provided to carry out such processing.

Therefore, in order to determine the transfer function G, the first to fourth acoustic transfer functions GAM, GAO, GSM,
It is necessary to measure GSO, and a transfer function measuring device using fast Fourier transform (FFT) is used to determine flFJ. Also, in this case, the first degree and the second degree
The measurement of the acoustic transfer functions CAM and GAO was performed with speaker A being driven by a white noise signal with a frequency bandwidth subject to active control. The Q transfer functions C3M and GSO are measured with the compressor S actually being driven. Incidentally, for such measurements, an auxiliary microphone M' serving as a receiver for determining the lpj is provided at the control target point O.

In this case, the above formula (1) is expressed as G −1
/ (CAM-(GS)l/G50) GAO)-1/
(CAM-GOM・G AO) ・・・・・・(
2), so the 3rd. Regarding the fourth acoustic transfer functions GSM and GSO, the output signal from the auxiliary microphone M' provided at the control target point O is used as the input terminal, and the output signal from the microphone M is set as the input terminal. If we measure the equivalent acoustic transfer function GUM with the signal on the output side, we can calculate the 8-tube transfer function G
It is equivalent to measuring SM and GSO.

Then, the acoustic transfer function G
A.M.

The transfer function G of the arithmetic unit H is determined based on GOM and GAO.

(Problem to be Solved by the Invention) The noise spectrum /Ii generated by driving the compressor S is as shown in FIG. 9, and the noise spectrum is:
It exists only in each frequency band that is an integral multiple of the rotation speed of the compressor S and an integral multiple of the power supply frequency. For this reason, in the conventional 11FI determination method, correct AI constant data can only be obtained for the acoustic transfer function GO and the part corresponding to the frequency where the spectrum is present.

Therefore, when performing the active control using the transfer function G determined based on the i-star acoustic transfer function GON, etc., if the rotation speed of the compressor S fluctuates during operation (the rotation speed If the acoustic transfer function GOH differs between the time of measurement and the time of actual operation), the active control becomes meaningless, and no silencing effect can be obtained at all.

In addition, when measuring the acoustic transfer function as described above, at frequencies where there is no noise spectrum from the compressor S, the signal at the input end (output No. t:i from the auxiliary microphone M') also changes from No. 13 (No. 13) on the output side. The output signal from microphone M) also becomes a noise signal. Therefore, the transfer function +1
! In the first error, calculations are performed using numerical data close to zero as a denominator, and depending on the case, the measurement result of the acoustic transfer function may become abnormally high. The measurement data obtained in this way is actually meaningless and does not play a role in determining the transfer function G, but since the dynamic range of the transfer function measuring instrument is constant, the influence of the above meaningless measurement data The accuracy of other relatively small-level effective Mf9 transfer function C1 constant data will be inadvertently reduced, which may lead to insufficient silencing effect during active control.

The present invention has been made in view of the above circumstances, and the present invention has been made in view of the above circumstances.
First, it is possible to improve the i+p+ constant accuracy of the transfer function, which is necessary when noise from a compressor is suppressed by active control, over a wide frequency band that allows for fluctuations in the rotation speed of the compressor. An object of the present invention is to provide an API method for determining a transfer function used in active noise control, which provides an effect such as always being able to obtain an optimal silencing effect even when the rotational speed of a compressor varies.

[11X5 structure of the invention] (Means for solving the problem) In order to achieve the above object, the present invention provides a control sound receiver that converts sound from a compressor provided in a machine room into a 7-air signal. , a transfer function of the arithmetic unit that is necessary when active control of noise is performed by a combination of an arithmetic unit that processes the electrical signal using a predetermined transfer function, and a control sound generator that is operated based on the processed signal. In a method of measuring
i The first acoustic transfer function between the control sound receiver and the second sound transfer function between the control sound receiver and the measurement sound receiver are set to a predetermined frequency band for the control sound receiver, respectively. The third B+5 transfer function between the compressor and the control sound receiver and the fourth acoustic transfer function between the compressor and the measurement sound receiver are measured while inputting a white noise signal of , the measurement is performed with the compressor driven at a predetermined power supply frequency, and among the measurement data obtained, a group of δN constant data corresponding to frequencies that are integral multiples of the rotational speed of the compressor and frequencies that are integral multiples of the power supply frequency are measured. enable at least one of them to interpolate their valid measurement data, and calculate the pre-tpi calculator based on the thus interpolated third and fourth acoustic transfer functions and the first and second acoustic transfer functions. The transfer function is determined.

(Operation) As is clear from equation (1) shown in the section (Conventional Example) above, the transfer function of the arithmetic unit can be determined based on the first to fourth acoustic transfer functions. In this case, the first and second T8g transfer functions are measured by manually applying a white noise signal of a predetermined frequency bandwidth to the respective control sound generators, so the measurement accuracy is high over a wide frequency band. Becomes good. On the other hand, since the third and fourth acoustic transfer functions are Al constant when the compressor is driven at a predetermined power supply frequency, the noise spectrum accompanying the drive is Frequency bands corresponding to integral multiples of the number and integral multiples of the power supply frequency)
Any other data will be inaccurate. However, in this case, among the data of the transfer function determined by API as described above, ΔP1 corresponding to a frequency that is an integral multiple of the rotation speed of the compressor and a frequency that is an integral multiple of the power supply frequency is
The third and fourth acoustic transfer functions are obtained by optimizing at least one of the constant data rJ1, that is, the data n1 of the frequency band in which the noise spectrum from the compressor exists, and interpolating their self-effect ΔP + constant data. Since the third and fourth 'F89 transfer functions after the interpolated data are obtained, the noise spectrum from the compressor is
It is relatively accurate even in a frequency band where there is no t. Therefore, the calculation is determined based on the third and fourth acoustic transfer functions obtained in this way and the first and second 6g transfer functions that provide good measurement accuracy over a wide frequency band as described above. The transfer function of the compressor has improved accuracy over a wide frequency band that allows for fluctuations in the compressor rotational speed.

(Example) Hereinafter, please refer to Figures 1 to 7 for an example of the present invention. .

First, in Fig. 3 showing the overall configuration of the refrigerator, ] is the refrigerator main body, and inside this, from the top, there are two freezer compartments.
．． A refrigerator compartment 3 and a vegetable compartment 4 are provided. 5 is a cooler disposed at the back of the freezer compartment 2; 6 is a fan that directly supplies cold air generated by the cooler 5 to the freezer compartment 2 and the refrigerator compartment 3. Reference numeral 7 denotes a machine room formed at the lower part of the back side of the refrigerator body 1, and inside this, a rotary compressor 8, a condenser vibe 9, and a defrost water evaporation device 10 using so-called ceramic fins are housed. .

Now, as shown in FIG. 4 (here, the illustration of the condenser vibrator 9 and the defrost water evaporator 10 is omitted), the machine room 7 has a rectangular shape with only its back side open. This opening portion is closed by a machine room cover 11. At this time, machine room cover 1
1 is installed so that its peripheral edge is airtight with respect to the opening edge of the machine room 7, and the left edge in the figure has an 11+1 rectangular heat dissipation opening 11.1 extending in the vertical direction. a is formed. In other words, when the machine room cover 11 is covered with rock,
The machine room 7 is in a closed state leaving a heat radiation opening 11a. The machine room cover 11 is made of a material with excellent thermal conductivity and high secondary transmission loss (for example, metal such as iron).
It is formed in

Further, in FIG. 4, 12 is a control sound receiver, such as a microphone, which is placed in the machine room 7, and this is located on the opposite side of the compressor 8 from the heat dissipation opening 11a (on the right side in the figure). They are arranged so as to face each other from the side), and are provided so as to convert the sound from the compressor 8, which is a noise source, into an electrical signal. Reference numeral 13 denotes a speaker serving as a control sound device disposed in the machine room 7;
It is mounted and supported in a buried manner in a portion of the back wall portion (corresponding to the bottom wall portion of the refrigerator body 1) near the heat radiation opening 11a.

As shown in FIG. 6, the speaker 13 is operated by a signal obtained by processing the electrical signal from the microphone 12 by the arithmetic unit 14. This is done based on the principle of silencing through active control as described in the section (Conventional Example).

Here, in the case of the refrigerator configured as described above, the level of noise generated in the machine room 7 according to the drive of the compressor 8 is 700H7, as shown in FIG. In the band of ~5 KHz, the sound becomes audible. Among these noises corresponding to the 3% I/range, high-frequency noise can be attenuated by transmission loss in the machine room cover 11, etc., and appropriate sound-absorbing members can be installed in the machine room 7. Microphone 1 as mentioned above can be easily muted by
2. Active control of noise by the speaker 13 and the W14 may be performed with a target frequency of 700 Hz or less.

In addition, when performing active noise control as described above, it is important to configure the noise in the machine room 7 so that it becomes a one-dimensional plane traveling wave, both theoretically and technically. This becomes important in order to perform 4V4 accurately. Therefore, in this embodiment, among the three-dimensional depth (width) and height (j) dimensions in the machine room 7 shown in FIG. Measure W to other dimensions.

Set larger than H (specifically, W = 600 mm.

By setting D=H-20C1gm), the standing wave of sound in the machine room 7 is established only in the first mode. That is, for example, when the machine room 7 is assumed to be a rectangular cavity, the following equation holds true.

f −C−X LX + Ny I−y)
+(Nz/I,Z)2/2(2), f is the resonant frequency (
Hz), NX, Ny.

NZ is the th mode of X, Y, Zt & direction, LX, Ly,
Ll is the dimension in each of the x, y, and z directions (D, W,
H), C is the speed of sound. Therefore, from the above formula, x, y,
z Frequency of standing wave of one spout for each direction fx, fy,
fz can be found.

That is, as mentioned above, if the depth dimension D - 20011 width dimension W - 60011 height dimension H - 2υ0■ is set, the frequency f of the first standing wave in the X direction
x is Ny = Nz-Os speed of sound C = speed of sound - 340 m /
As seconds, fx -34010,2)' /2 -850 Hz roar.Similarly, the first constant (I:
The wave frequencies fy and fz are fy=340 1 . 6)'/2 =283Hz fz =340 1, -)'/2850H
It becomes z. As a result, the target frequency (-700H
z) From F, the standing wave of noise in the machine room 7 is in the Y direction (
This is true only for the mode in the width direction), and the noise in the machine room 7 is one-dimensional.

It can be considered as a plane traveling wave. For this reason, the above-mentioned speaker 13 etc. were used! When silencing the gl sound by active control, the theoretical handling of the wavefront becomes easy, and the silencing 1; q control can be easily performed with high precision.

Now, in the following, a method for measuring the transfer function G of the arithmetic unit 14 necessary for the above-mentioned active control will be explained with reference to FIGS. 1 and 2.

That is, in FIG. 1, the machine room 7 of the refrigerator to be measured includes a compressor 8. In addition to the microphone 12 and the speaker 13, an auxiliary microphone 15 is provided as a measurement sound receiver to monitor the sound at the heat radiation opening 11a, which is a point to be controlled during active control. Further, the power source of the compressor 8 is connected to an inverter device 16 which is an edible frequency 7u source, so that the number of revolutions of the compressor 8 can be adjusted continuously for one week by the inverter device 16. Furthermore, 17 is a noise signal generation circuit, which is provided to generate a white noise signal having the same power over the entire frequency bandwidth for which 11PI is to be determined. 18 is a transfer function measuring device that uses fast Fourier transform (FFT) by a CPU, for example, and what is connected to the human input signal terminal Ta and the output signal terminal 7'Tb, and what is the input signal to these input signals? Then, the transfer function between the human input signal and the output signal (between the ends TTa and Tb) is determined by /+111.

Here, the data necessary to determine the acting force, U of the device 14; and the connection function G are the data for the speaker 13 and the microphone 12, as is clear from equation (1) shown in the section (conventional example).
A first acoustic transfer function GAM between the speaker 13 and the auxiliary microphone 15, and a second acoustic transfer function GAM between the speaker 13 and the auxiliary microphone 15.
O, the third between the compressor tube 8 and the microphone 12
The acoustic transfer function G SM.

A fourth acoustic transfer function GSO between the compressor 8 and the auxiliary microphone 15. At this time, as is clear from Equation (2) shown in the section (Conventional example), the third and fourth acoustic transfer functions GSM and GSO are equal to (If[
i-like acoustic transfer function GOM, i.e. auxiliary microphone 15
If we define eight equivalent transfer functions GOM with the output signal from the microphone 12 as the input terminal and one output signal from the microphone 12 as the output side (response side), then their v1 lightning transfer function C
; It is equivalent to measuring SM and GSO. Therefore,
It suffices to measure the first and second acoustic transfer functions CAM, G^0, and equivalent acoustic transfer function GOM using the transfer frequency meter 18.

Therefore, the first acoustic transfer function CAM is 71! In the case of setting II, the white noise No. 13 from the noise signal generation circuit 17 is transmitted to the speaker 13 and the transfer function fill is fixed 2'':
The output signal from the microphone 12 is input to the input signal terminal Ta of the i18, and the output signal from the microphone 12 is input to the transfer function APE determiner 18.
When the noise signal generating circuit 17 is driven in such a connected state, measurement data by the transfer function measuring device 18 is obtained as the first acoustic transfer function CAM.

Furthermore, when measuring the second acoustic transfer function G^0,
The connection state between the noise/signal generation circuit 17 and the speaker 13 and the human signal terminal Ta of the transfer function measuring device 18 is left as is, and the output signal terminal Tb of the transfer function measuring device 18 is left as is.
The output signal from the auxiliary microphone 15 is connected to the auxiliary microphone 15 so that it is input manually, and the data measured by the transfer function measuring device 18 when the noise signal generating circuit 17 is driven in such a connected state is transmitted to the second lightning. Let j be the function GAO. In addition, these first. The second η transfer function CAM, GAO
Of course, the compressor 8 is stopped when dl11 is set.

On the other hand, when determining the equivalent acoustic transfer function GO)l A11l, the output signal from the auxiliary microphone 15 is inputted to the manual signal terminal Ta of the transfer function illuminator 18, and the output signal No. 13 from the microphone 12 is input manually. is the transfer function al
It is manually connected to the output signal terminal Tb of the LF device 18, and in this state, measurements are performed according to the procedure shown in the flowchart of FIG.

That is, the output frequency f of the inverter device 16 is the lower limit frequency f. (For example, the frequency is lower than the rated power frequency F!? of the compressor 8 by a predetermined amount) and the compressor 8 is driven at the rotation speed N. In step a), the dpI constant data obtained by the transfer function measuring device 18 in this state is , JPI is determined as the equivalent acoustic transfer function GOM at the rotation speed N0 (step b), then the output frequency f of the inverter device 16 is
Step C
), the measurement data by the transfer function illuminator 18 after this sweep is expressed as the equivalent acoustic transfer function G at the rotation speed N.
O) Measure as 1 (step d). After this, the sweep of the output frequency f as shown above and the measurement of the equivalent g-lo transfer function GOH are repeated, and the output frequency f of the inverter device 16 is set to the upper limit frequency fn (for example, the rated value of the compressor 8). When the frequency becomes higher than the power supply frequency P+? by a predetermined amount, the transfer function GOH with the above equal reef sound
Repetition 71? + end the determination (step e). Then,
Of all+constant data taken in steps b and d above, NRX is an integer multiple of the rated rotation speed N)l of the compressor 8.
Step f: Validate each A-1 constant data group corresponding to n (n is a natural number) and a frequency PRXn that is an integral multiple of the rated electrolytic corrosion frequency PR, and perform linear interpolation of the validation data. ), so 1iIlivf acoustic transfer function GO
The final measurement of H is completed.

In addition, in FIG. 7, the equivalent acoustic transfer function G is shown in (a) and (b).
In addition to showing examples of rough measurement data of OH, (c) and (d)
2 shows the data of the final equivalent acoustic transfer function GO)I that was linearly interpolated based on the above measurement data.

In summary, 1. Second acoustic transfer function G A)! .

Since the GAO measures the white noise signal with a predetermined frequency bandwidth manually applied to each speaker 13, the measurement accuracy is good over a wide frequency range. On the other hand, the equivalent acoustic transfer function GOM (and thus the third and fourth acoustic transfer functions GSM).

G So) is measured with the compressor 8 driven at a predetermined power supply frequency f, so the frequency band (corresponding to an integral multiple of the compressor rotational speed and an integral multiple of the power supply frequency) in which the noise spectrum associated with the drive exists is measured. Data other than the specified frequency band) will be inaccurate.

However, in this case, among the data of the acoustic transfer function GUH measured as described above, the frequency NRXn, which is an integral multiple of the rated rotation speed Nli of the compressor 8, and the frequency, which is an integral multiple of the rated power frequency 1'RX, are By activating the corresponding measurement data group, that is, the data group of the frequency band in which the noise spectrum from the compressor 8 exists, and linearly interpolating their effective illumination data, an equal acoustic transfer function GOX is obtained. Therefore, the noise spectrum from the compressor 8 after the interpolated data is relatively accurate even in a frequency band where the noise spectrum is not equal to /I;L. Therefore, the calculation determined based on the equi-fdli acoustic transfer function GOM obtained in this way and the first and second acoustic transfer functions CAM and GAO that provide good measurement accuracy over a wide frequency band as described above. The transfer function G of the compressor 8 can be treated as an accurate measurement value with improved precision over a wide frequency band that allows for fluctuations in the rotational speed of the compressor 8.

As a result, the noise active j;I based on the above transfer function G
In the case of performing J11, even if the rotational speed when the compressor 8 is actually operated is different from the lpJ fixed time of the transfer function G, the silencing effect by active control will be insufficient as in the past. This eliminates the fear.

In the above embodiment, among the data of the acoustic transfer function GOH measured while sweeping the power supply frequency f of the compressor 8, the data corresponding to frequencies that are integral multiples of the rotation speed of the compressor 8 and frequencies that are integral multiples of the power supply frequency are Both Δpj constant data groups are enabled to perform interpolation mj (linear interpolation), but if interpolation is performed for at least one Δp1 constant data group (for example, the one that has a large effect on reducing the accuracy of the transfer function G). It's good.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings; for example, the object of noise reduction is not limited to refrigerators, but may be applied to outdoor units of air conditioners, refrigerated showcases, etc. , various modifications can be made without departing from the gist thereof.

[Effects of the Invention] According to the present invention, as explained above, the compressor housed in the machine room is driven by 1? The transfer function of the above-mentioned arithmetic unit, which is necessary when performing active control in which the generated lines are actively canceled by interference with the artificial sound from the control sound generator operated by the signal processed by the arithmetic unit. The measurement accuracy can be improved over a wide frequency band that allows for fluctuations in the compressor rotation speed. It is effective.

[Brief explanation of the drawing]

Figures 1 to 7 show an embodiment of the invention, Figure 1 is a layout diagram schematically showing a method for measuring a transfer function, and Figure 2 shows details of the above measuring method. flowchart,
Fig. 3 is a vertical sectional view of the refrigerator, Fig. 4 is an exploded view of the main parts of the refrigerator, and a perspective view indicated by 4. Fig. 5 is a III! diagram for explaining the dimensional relationship of the main parts of the refrigerator. EI125 perspective view, FIG. 6 is a diagram schematically showing a configuration for active noise control in a refrigerator, and FIG. 7 is a waveform diagram showing a measurement example of the sound J transfer function. Further, FIG. 8 is a schematic configuration diagram showing the principle of silencing by active control, and FIG. 9 is a diagram showing an example of noise level characteristics in a refrigerator. In the figure, 1 is the refrigerator body, 7 is the machine room, 8 is the compressor, 10 is the defrosting water evaporator, 11 is the machine room cover 11a
is a heat radiation opening, 12 is a microphone (control sound receiver)
, 13 is a speaker (control sound generator), ]4 is a computing unit, 1
5 is an auxiliary microphone (measurement sound receiver), 16 is an inverter device, 17 is a noise signal generation circuit, and 18 is a transfer function measuring device. Applicant: Toshiba Corporation Figure 6 Figure 6

Claims (1)

[Claims] 1. The sound generated by the drive of the compressor installed in the machine room is converted into an electrical signal by a control sound receiver, and the control sound generator is operated based on the signal processed by this electrical signal by a computing unit. In the method of measuring the transfer function of the arithmetic unit used for active control in which sound radiated to the outside from the machine room is actively canceled by a first acoustic transfer function between the control sound generator and the control sound receiver, and a second acoustic transfer function between the control sound generator and the measurement sound receiver. are measured with a white noise signal of a predetermined frequency bandwidth being input to each of the control sound generators, and the third acoustic transfer function between the compressor and the control sound receiver as well as the compressor and the measurement sound receiver are measured. Measure the fourth acoustic transfer function between the Validate at least one of the measurement data groups corresponding to the doubled frequency, interpolate those valid measurement data, and interpolate the third
Measurement of a transfer function used for active control of noise, characterized in that the transfer function of the arithmetic unit is determined based on a fourth acoustic transfer function and the first and second acoustic transfer functions. Method.