This standard specifies the measurement method of microporous exhaust silencer performance in anechoic chambers, reverberation chambers, and work sites. The measurement parameters specified in this standard are mainly the A and C weighted insertion loss and gas flow loss rate of microporous exhaust silencers. This standard is applicable to small microporous silencers made of powder metallurgy, ceramics, plastics or other materials. This standard is not applicable to the measurement of silencing performance of pipe exhaust silencers. JB/T 6972-1993 Microporous Exhaust Silencer Measurement Method JB/T6972-1993 Standard Download Decompression Password: www.bzxz.net

J93 | | tt | | JB | Published
Ministry of Machinery Industry of the People's Republic of China
Published
Implemented on 1994-07-01
Machine Industry Standard of the People's Republic of China
Micro-hole exhaust muffler Measurement method
1 Subject content and scope of application
JB/T 697293
This standard specifies the performance of microporous exhaust mufflers (hereinafter referred to as microporous mufflers) in anechoic chambers and mixing chambers. Measurement methods in sound rooms and work sites. The measurement parameters specified in this standard are mainly the A and C weighted insertion loss and gas flow loss rate of the microporous exhaust muffler. This standard applies to small microporous mufflers made of powder metallurgy, ceramics, plastics or other materials (generally limited to axis length L≤0.25m). This standard does not apply to the measurement of silencing performance of duct exhaust mufflers. 2 Reference standards
GB3241
GB3785bzxZ.net
GB3947
GB4759
GB4760
JJG176
3 Terminology||tt| |Electrical and acoustic properties and measurement methods of 1/1 and 1/3 times the rated range filter sound level meter for sound and vibration analysis
Measurement method of internal combustion engine exhaust muffler
Muffler Measurement method
Acoustic calibrator
Microhole exhaust silencer
3.1 lines
The pressure and speed of the airflow through the hole material are reduced to reduce the exhaust noise.
3.2 Insertion loss
The difference in the sound power radiated by the exhaust port measured before and after the muffler is installed is called the broadcast value of the muffler. Insertion loss. Symbol: D; Unit: dB Note: When the shape of the nozzle and the sound field distribution remain basically unchanged, the insertion loss is equal to the difference in sound pressure level before and after the silencer is installed at the original measuring point, 3.3 Gas flow loss. Rate
The gas flow loss rate is the ratio of the difference in gas flow before and after the muffler is installed and the gas flow when the muffler is not installed. Symbol: Q. The common reference sound pressure level of 3.4 octave band
is 20uPa. The frequency band sound pressure level when the frequency width is 1 octave is called the octave band sound pressure level. 4 Measuring instrument exposure
4.1 Sound level meter
The measurement accuracy of the sound level meter must at least meet the requirements of GB3785 1 Type instrument requirements. The performance of 4.2 octave and 1/3 octave filters
octave and 1/3 octave filters meet the requirements of GB3241, 4.3 calibrator
The calibrator should meet the requirements of JJG176. Each calibration period is one year. The measuring instrument should be calibrated before and after each on-site measurement
4.4 Gas Flow Meter
Approved by the Ministry of Machinery Industry on 1993-07-27. | |tt | Maximum upper limit flow rate, nominal pipe diameter, etc.) gas flow 5 measurement method
5.1 Overview
Insertion loss is the basic parameter to evaluate the performance of microporous mufflers. This section describes the measurement of the sound attenuation performance of microporous mufflers. Rate anechoic chamber, reverberation chamber and on-site measurement method
5.2 Semi-anechoic chamber measurement method
5.2.1 The air source for measuring the sound attenuation performance of the microporous muffler is installed in the semi-anechoic chamber. The air source device for measuring the microporous muffler is shown in Figure 1. Check-back
Air source
?
Gas storage
Overpass device
5.2 .2 Preparation of experimental equipment
Electric device research
Gas flow meter
Jie Gaoyue
Figure 1 Gas source device for measuring muffler
MMA | |tt |
8kg/cm*);
Repeatedly adjust the flow adjustment switch to achieve the required measurement air pressure in the pipe: b.
c
Use a filter with a filter The sound level meter uses "slow gear" to measure A, C sound pressure levels and frequency band sound pressure levels. 5.2.3 Position and direction of the microphone
The microphone is placed at the specified measuring point. The measuring points should be evenly distributed on a horizontal circle with the exhaust port as the center and a radius of 0.5m (see Figure 2). Generally Take 4 to 6 measuring points. Each measuring point should be 1.0m higher than the ground. The direction of the microphone points to the center of the exhaust port, and the muffler
5.2.4 Calculation of insertion loss
Figure 2 Measuring points Position
Measuring point quantity
The sound pressure level of the frequency band should be measured at the "slow gear" of the sound level meter, and the average value should be taken within a certain observation time. The observation time is specified as: Center frequency 2
JB/T6972-93
≥200Hz is 10s, center frequency ≤160Hz is 30s. The frequency band sound pressure level is averaged according to the energy law and Lpr is calculated according to formula (1): 110ls-g/n
Ler = 10lg[
where: N—the total number of measuring points: ||tt| |Lrt-
—the octave band sound pressure level measured at the center frequency of the factory at the measuring point;—the octave band background noise correction value measured at the center frequency at the 1st measuring point (see Table 1) . Kpe
The average sound pressure level L and A, C-weighted insertion loss in each frequency band are calculated by connecting to equation (2): D=Ln-Lr
where: D—the measured micropore muffler Insertion loss: Ln - measured exhaust port frequency band and A, C weighted sound pressure level without micro-hole muffler, dB; Ln - measured exhaust port frequency band and A, C-weighted sound after installing micro-hole muffler Pressure level, dB. 5.3 Reverberation room measurement method
5.3.1 Position and direction of microphone
(1)
(2)
The position of the microphone is as per 5.2 .3 stipulates that the measuring point should be selected and the distance from any reflecting surface in the room should not be less than 1.0m, and the direction of the microphone should be pointed at the center of the exhaust port
5.3.2 Insertion loss of the average sound pressure level of each frontal band. The sound pressure level of each preband is calculated according to formula (1), and the insertion loss is calculated according to formula (2). 5.3.3A, C-weighted insertion loss
A, C-weighted insertion loss connection formula of micro-tie muffler ( 2) Calculation, 5.4 On-site measurement method
5.4.1 Background noise correction value
When measuring the muffler on site, other noises except exhaust noise are considered background noise. If the difference in noise level is less than 3dB, the measurement result is invalid. If it is higher than 3dB, it will be corrected according to Table 1 (that is, the measured noise level minus the correction value), Table 1 Background noise correction value
Measured noise The difference between the loudest pop sound level and the back volume (dB) correction value (dB)
5.4.2 Microphone position and direction
<3
Invalid measurement
3
3
4~5
2
6~9
1
10
0||tt| |The microphone is placed 0.5m away from the exhaust port at an angle of 45° to the airflow axis of the exhaust port. In order to reduce the influence of reflected sound, the distance between the measuring point and each reflecting surface should be greater than 0.5m. 1.0m, the microphone position remains unchanged before and after the muffler device, see Figure 3
Note: In on-site measurements, there are fewer reflectors around the microhole muffler and the reflected sound field is weak, so the "free field" should be used type microphone; if there are many reflections around the microporous muffler and no sound cleaning measures are taken, a "pressure type" microphone should be used
Noise reduction recommendation||tt| |Figure 3 Microhole muffler on-site measurement point location
5. 4. 3
Insertion loss of each frequency band
The sound pressure level of each frequency band when measured at the work site is according to the formula (1 ) is calculated, and the insertion loss is calculated according to formula (2). 5.4.4 Measurement method of A, C weighted insertion loss 3
JB/T ·697293
When measuring on-site, the average value should be taken when the noise is stable, and the insertion loss connection (2) Count the numbers. Note: If there is obvious impulse noise, it should be stated in the test report. 5.5 Gas flow loss rate (AQ)
The gas flow loss rate is a parameter that reflects the circulation performance of microporous materials. Calculate QQ
Q according to equation (3). -Q:
Q
Gas flow rate, m\/h. 6 Test report
......
++(3)
The measurement record of the microporous muffler includes the measurement conditions and measurement data Two parts. The measurement conditions mainly include measurement location, measurement time, measurement instrument, measurement environment, gas flow, exhaust pressure, etc. The measurement data records are shown in Table 2. Table 2 Measurement data record table
Unit: dB| |tt||Weighted sound pressure level
Doubled sound pressure level
(center rate Hz)
Note
Measurement location:
Measurement time:
Measuring person:
Additional notes:
Lrx
Le
31.5
63
125| |tt||250
500
1K
2K
4K
8
Background noise
Background noise correction Value
This standard is proposed and managed by the Institute of Environmental Protection Technology of the Machinery Industry. This standard is drafted by the Institute of Environmental Protection Technology of the Machinery Industry. The main drafter of this standard is Xie Dehai
4||tt| |Ln
Lan
No.:
D
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