This standard applies to instruments (sound level meters) that measure sound pressure levels with certain frequency weighting and time weighting. This standard is the technical basis for the design, production and use of sound level meter products, and is also the basis for formulating product standards for various types of sound level meters. GB 3785-1983 Electrical and acoustic properties and test methods of sound level meters GB3785-1983 standard download decompression password: www.bzxz.net

UDC681.89:621.317.08
National Standard of the People's Republic of China
GB3785-83
Electric, sonic properties and measuringmethods for sound level meters1983-06-25issued
1984-03-01implemented
Approved by the National Bureau of Standards
Terms·
Product classification…
Technical requirements·
Test methods·
Appendix A
Appendix B
Appendix C
Relationship between peak factor and pulse duty factor. Diffuse field sensitivity.
Theoretical response to burst:
(2)
(9)
National Standard of the People's Republic of China
Electrical, sonic properties and measuring methods for sound level meters
This standard applies to instruments (sound level meters) that measure sound pressure levels with certain frequency weighting and time weighting. UDC681.89:621
.317.08
GB3785-83
This standard is the technical basis for the design, production and use of sound level meter products, and is also the basis for the formulation of various types of sound level meter product standards. This standard is formulated with reference to the International Electrotechnical Commission (IEC) 651 "Sound Level Meter" standard. 1 Terminology
1.1 Weighted sound pressure level: referred to as sound level, which is the ratio of weighted sound pressure to reference sound pressure, multiplied by 20 with the logarithm of 10 as the base, expressed in dB (decibel), that is:
Lp=20log1o
Where:.1
Lp—weighted sound pressure level, dB;
p——weighted sound pressure, Pa;
P,—reference sound pressure, Pa.
The weighted sound pressure level should indicate the frequency weighting and time weighting used. Note: ① Weighted sound pressure, that is, the sound pressure being measured is weighted according to the frequency weighting A, B, C or D and the time weighting "fast (F)", "slow (S)", "pulse (1)" or "peak (Peak)" specified in this standard. ② P = 20uPa, which does not change with frequency weighting and time weighting. ③ 1Pa (Pascal) = 1N/m2 (Newton/meter2). 1.2 Crest factor: The crest factor of a signal is the ratio of the peak value to the effective value measured within a specified period of time. For continuous short pulses and burst sounds, the relationship between the crest factor and the pulse duty factor is shown in Appendix A. 1.3 Main range of indicator: It is a specified indication range, within which the sound level meter indication value is within the linear tolerance specified in 3.5.9 and 3.5.10. ||tt| |1.4 Linearity: The reading of the sound level meter is a linear function of the input signal level within the specified tolerance. 1.5 Reference direction: It is the direction of sound incidence specified by the manufacturer, in which the absolute sensitivity, directivity and frequency weighting of the sound level meter are tested.
1.6 Reference frequency: A frequency specified by the manufacturer in the range of 200 to 1000 Hz, used to check the absolute sensitivity of the sound level meter. It is recommended to use 1000 Hz.
1.7 Reference sound pressure level: A sound pressure level specified by the manufacturer for calibrating the absolute sensitivity of the sound level meter. It is recommended to use 94 dB. 1.8 Reference range: A range specified by the manufacturer for calibration, and the reference sound pressure level should be within this range. 1.9 Intrinsic error: Measured under reference conditions (see 4.3.1) The error of a certain working characteristic. 2 Product classification
2.1 This standard stipulates that sound level meters are divided into four categories according to the accuracy level, namely 0, 1, 2 and 3 types. 2.2 The technical requirements of each type of sound level meter have the same central value, only the allowable tolerance is different, and the tolerance is relaxed as the type number increases.
Published by the National Bureau of Standards on June 25, 1983
Implementation on March 1, 1984
GB3785—83
2.3.0 Type sound level meter is used as a laboratory reference standard. Type 1 sound level meter is used for use in laboratories and places where the acoustic environment can be strictly controlled. When used in general occasions, it often cannot achieve the accuracy that this instrument should have. Type 2 sound level meter is suitable for general measurement. Type 3 sound level The meter is mainly used for on-site noise survey.
3 Technical requirements
3.1 General characteristics
3.1.1 Sound level meters usually consist of microphones, amplifiers with frequency weighting and detection indicators with certain time weighting characteristics. Accessories necessary to meet certain requirements (such as extension rods, extension cables, random incidence calibrators, etc.) should be considered as components of the sound level meter.
Under reference conditions, the sound level meter is placed in a sound field composed of plane traveling waves, so that the sound wave with a frequency of the reference frequency and a sound pressure of the reference sound pressure level reaches the microphone along the reference direction. After the preheating time specified by the manufacturer, the inherent error of the absolute sensitivity of the sound level meter is shown in Table 1. The inspection and calibration methods should be provided in the product standards. Table 1 Intrinsic errors of various types of sound level meters
Intrinsic errors
3.1.3 The manufacturer should provide a method for testing using electrical signals. So that the whole machine can be tested without microphone. 3.2 Directional characteristics
3.2.1 The manufacturer shall specify the reference direction, which is generally the reference axis of the microphone. dB
3.2.2 The maximum change in sensitivity of the sound level meter within the range of ±30° from the reference direction shall not exceed the value specified in Table 2. The maximum change in sensitivity within the range of ±90° from the reference direction shall not exceed the value specified in Table 3. The microphone shall be installed according to the normal use method specified by the manufacturer. The observer shall not affect the sound field at the microphone. The values ​​in Tables 2 and 3 should be checked using the same microphone setup: dB
31.5~1000
1000~2000
2000~4000
4000~8000
8000~12500
31.5~1000
10002000
2000~4000
4000~8000
800012 500
Maximum sensitivity change within the range of ±30° from the reference direction Type 0
Maximum sensitivity change within the range of ±90° from the reference direction Type 0
GB3785-83
3.2.3 The manufacturer shall provide at least directional responses including 1000, 2000, 4000, 8000Hz (for Type 2 and 3 sound level meters) and 12500Hz (for Type 0 and
1 sound level meters), and calculate the diffuse field sensitivity according to Appendix B. 3.3 Frequency weighting and amplifier characteristics
3.3.1 The sound level meter shall have one or more frequency weighting characteristics called A, B and C. It may also include D weighting characteristics for aircraft noise measurement and linear characteristics with flat response. When measuring in the reference direction, the frequency response and tolerance of the weighting characteristics are shown in Table 4 and Table 5 respectively.
A sound level meter with a linear response characteristic can measure sound pressure level (unweighted) or be used as a preamplifier. The manufacturer shall specify its frequency range and frequency response tolerance, which shall not be greater than the tolerance of the weighted characteristic. Note: The response and tolerance of the D-weighted characteristic are the same as those of the IEC537 standard. 3.3.2 The amplifier shall have sufficient peak factor capacity to meet the requirements of 3.5.1. For Type 0 sound level meters, an overload detector shall be provided between amplifier stages and an indication shall be given when the peak factor capacity is exceeded. It is recommended that Type 1 and Type 2 sound level meters also use overload detectors. Any type of sound level meter that includes a "pulse" characteristic shall be provided with an overload detector. 3.3.3 When the microphone is replaced by an equivalent electrical impedance, for each weighting characteristic, the reading shall be at least 5 dB lower than the specified minimum measurable weighted sound pressure level.
Frequency weighting characteristic
Relative free-field frequency response in the reference direction Nominal frequency*
Accurate frequency*
*Nominal frequency is the same as ISO 266 standard.
A weighting
B weighting
**Accurate frequency is given with 4 significant figures and is equal to 1000×10\, where n is a positive or negative integer. C weighting
D weighting
Nominal frequency
Nominal frequency
Accurate frequency
GB3785—83
Continued Table 4
A weighting
B weighting
Tolerances of frequency weighting characteristics of various types of sound level meters Type 1bzxZ.net
+3, -8
*The tolerances for all weighting characteristics are the same and are based on the readings at the reference frequency. 4 | | tt | 2, -3
+2, -3
+2, -3
GB3785—83
continued table 5
+1.5, -2
+3, -6
+3, -80
+5, -0
+5, -8
+ 5, -
If an output signal is available at the filter connection and the AC output, the total harmonic distortion of the output should be less than 1% when a sinusoidal signal in the frequency range of 31.5 to 8000 Hz is input, and the level of the test signal is at most 10 dB lower than the upper limit of the equivalent level of the measurable weighted sound pressure level.
At the upper limit of the sound pressure level specified by the manufacturer, input sound of any frequency in the range of 200 to 1000 Hz. The total harmonic distortion measured at the output should be less than 10%.
3.3.5 For various frequency weightings, at the upper limit of each indicator main range, the manufacturer should indicate the lowest frequency at which the error caused by nonlinear distortion between the sound input and the signal output is ±1 dB. It is recommended that this error should be less than ±1 dB at all frequencies greater than or equal to 31.5 Hz.
3.4 ​​Range controller
When the sound level meter is equipped with a range controller, the error introduced by all other range positions relative to the reference range position shall not be greater than the values ​​listed in Table 3.4.1
6.
31.5~8000
2012500
Tolerance of sound level range controller accuracy
For manual range controllers, when the steps are 10dB, the ranges shall overlap by at least 5dB. If the steps are larger, the overlap shall be at least 10
3.4.3 In order to reduce the chance of overload and to have the widest dynamic range at high sound pressure levels, the sound level meter may be equipped with independent dual adjustable range controllers to operate the attenuators placed before and after the weighting circuit. The manufacturer shall explain the operation of the controller. If an automatic range control system is used, its settling time shall be stated. 3.5 Characteristics of detectors and indicators
3.5.1 Sound level meters with "fast" and "slow" detection indicator characteristics should indicate the effective value of the measured signal and specify the averaging time respectively. Sound level meters with "impulse" characteristics should indicate the maximum value of the short-time effective value of the measured signal. For various signal crest factors, the maximum allowable error of the effective value detection indicator system is listed in Table 7. 6
Integer factor
GB3785-83
Maximum allowable error of the effective value detection indicator system 3
Note: ① The symbol 0I type refers to the 0 type sound level meter including the impulse characteristic. ② For 3I type, see 3.5.3.
3.5.2 The principle block diagram of the "fast" and "slow" detection indicators is shown in Figure 1. Their time weighting characteristics in response to burst sound should be derived from the provisions of Table 8. The overshoot caused by the sudden application of signals or step signals shall comply with the provisions of Table 9. When the applied signal is suddenly cut off, the time for the indicator value to drop by 10dB shall not exceed 0.5s for the "fast" characteristic; and not exceed 3s for the "slow" characteristic. Input
Detection indicator
*See ​​Appendix C.
Squaring circuit
Duration of test sound burst
Exponential averaging circuit
F: time constant 125ms
S: time constant 1000ms
With continuous signal response
as reference, the maximum response of the test
S
Response to sound burst
Indicator in decibel scale
Tolerance of maximum response of various types of sound level meters
Detection indicator characteristics
GB3785—83
Maximum overshoot
The principle block diagram of the "pulse" detection indicator is shown in Figure 2. The time constant of the exponential averaging circuit is the same for charging and discharging. The rise time constant of the peak detector shall be very small compared with the 35 ms time constant of the averaging circuit, but its fall time shall be very long and the decay rate shall be 2.9 dB/s with a tolerance of ±0.5 dB/s for Type 0 and 1 sound level meters and ±1 dB/s for Type 2 and 3. This corresponds to time constants of 1500 ± 250 ms and 1500 ± 500 ms respectively. Input
Squaring circuit
Single-pole exponential averaging circuit
B-interval constant 35 m
Bee detector decay
Time constant 1500 ms
Indicator scaled in decibels
The response of the "pulse" detector indicator to single and continuous sound bursts shall conform to the values ​​in Tables 10 and 11 respectively. If a Type 3 sound level meter incorporates an "impulse" feature, the requirements for the Type 2 sound burst test shall be met. Table 10 Response to single sound burst
Duration
Repetition frequency
*See ​​Appendix C.
With continuous response signal as reference
Maximum response to test sound burst*
Type 0, 1
Table 11 Response to continuous sound burst
With continuous response signal as reference
,
Maximum response to test sound burst*
Type 0, 1
Not tested
GB3785-83
3.5.4 In the frequency range of 31.5～8000Hz, the indication of steady-state sinusoidal signal by “fast”, “slow” and “impulse” detection indicators shall not deviate more than 0.1dB for Type 0, 1 and 2 sound level meters and not more than 0.2dB for Type 3 sound level meters. 3.5.5 If the sound level meter is equipped with peak measurement, the rise time of its detector shall be specified by the manufacturer. For type 0 sound level meters, the indication produced by a single pulse of any polarity with a duration of 50μs shall be at most 2dB lower than the indication produced by a single pulse of the same peak amplitude and a duration of 10ms; for other types of sound level meters, the indication produced by a single pulse of 100μs duration shall be at most 2dB lower. 3.5.6 The indicator range of various sound level meters shall be at least 15dB, and the main range of the indicator shall be at least 10dB. 3.5.7 For analog indicators (electric meters or recorders), its scale divisions shall be at least 1dB per division within a range of at least 15dB, and the 1dB division shall be at least 1mm wide.
3.5.8 When a digital indicator or other discontinuous display indicator (such as a sound level lamp) is provided, the sound level meter shall have a hold function to display the maximum weighted sound pressure level during the measurement. A method of automatically holding the display at fixed time intervals or on command may be added. If it is an average mode, the effective sound level should also be indicated. When the sound level meter provides an automatic display mode, its cycle time should be one time per second. When an electrical output in digital form is provided, the output rate should be given. The digital display should have a resolution better than 0.1dB. For discontinuous analog displays, it is allowed to reduce the resolution, which should not be less than 0.2dB for type 0 and 1 sound level meters, 1dB for type 2, and 3dB for type 3. When the resolution is too low, a special test method is required to prove that all the requirements of this standard can be met. 3.5.9 A system consisting of a manual or automatic range controller of a detection indicator. With reference to the reference sound pressure level, its linearity should meet the requirements of Table 12.
Level linearity tolerance with reference to the reference sound pressure level Table 12!
Indicator main range
Outside the indicator main range
3.5.10 In both the cases of inside and outside the main range of the indicator, the linear tolerances allowed for each type of sound level meter for points separated by 1 dB and 10 dB are shown in Table 13.
Table 13 Linear tolerances of different levels
Points separated by 1 dB within the main range of the indicator
Points separated by 10 dB within the main range of the indicatorPoints separated by 1 dB outside the main range of the indicator
Points separated by 10 dB outside the main range of the indicatorType 0
3.6 Environmental impact
3.6.1 For a 10% change in static pressure, the sensitivity change of the whole machine between 200 and 1000 Hz shall not be greater than ±0.3 dB for Type 0 and 1 sound level meters; and shall not be greater than ±0.5 dB for Type 2 and 3.
3.6.2 Replace the microphone with an equivalent electrical impedance, place the sound level meter in the sound field from the reference direction, the test sound pressure level is 100dB, and its response is at least 20dB lower than the reading obtained in normal use. For all sine wave signals with frequencies in the range of 31.5 to 8000Hz, this requirement shall be met.
GB3785—83
3.6.3 When the sound level meter is working, the influence of mechanical vibration shall be reduced as much as possible. The manufacturer shall give the influence of sinusoidal vibration with an acceleration of 1m/s2 between 20 and 1000Hz on the sound level meter. If the microphone is not installed on the extension cable in normal use, this data shall apply to the entire sound level meter. Otherwise, the influence on the microphone assembly shall be given. 3.6.4 When the sound level meter is working, the influence of magnetic and electric fields shall be reduced as much as possible. The sound level meter equipped with a microphone is placed in a magnetic field with an intensity of 1Oe (Oersted) at 50Hz for testing. For each weighting characteristic, the influence of the magnetic field should be given by the manufacturer. 3.6.5 Sound level meters powered by an AC power supply should be able to ensure normal operation under the conditions of a power supply voltage of 220V±10% and a power supply frequency of 50Hz±4%.
For sound level meters operated by batteries, the manufacturer should state the specifications of the battery and the number of hours or working current to ensure continuous normal operation, and provide appropriate methods to check whether the battery is sufficient to enable the sound level meter to operate normally. 3.6.6 After the preheating time specified by the manufacturer (not more than 10 minutes), under constant test conditions, the change in the sound level meter reading within one hour of continuous operation shall not be greater than the value shown in Table 14. Table 14 Maximum change in reading within one hour of continuous operation Type 0
3.6.7 The sound level meter should be able to withstand the temperature test specified in the product standard. Within the rated use range, the change in calibration of the whole machine (including microphone) relative to the indication at 20°C shall not exceed ±0.5dB for Type 0 and 1, and not exceed ±1dB for Type 2 and 3. The test shall be carried out at a frequency between 200 and 1000Hz.
3.6.8 The sound level meter shall be able to withstand the humidity test specified in the product standard. Within the rated use range, the change in sensitivity of the whole machine (including microphone) relative to the indication at 65% relative humidity shall not exceed ±0.5dB for Type 0, 1 and 2, and not exceed 1dB for Type 3. The test shall be carried out at a frequency between 200 and 1000Hz. 4 Test methods
Test items
Measurement of the inherent error of the absolute sensitivity of the sound level meter; measurement of the directional characteristics;
Test of the frequency weighting and amplifier characteristics; measurement of the accuracy of the range controller;
Test of the detector and indicator characteristics;
Measurement of the system linearity;
Measurement of the influence of atmospheric pressure changes on the sensitivity of the sound level meter; measurement of the influence of the sound field;
Measurement of the influence of mechanical vibration on the operation of the sound level meter; measurement of the influence of the electromagnetic field;
Measurement of the influence of power supply voltage changes;
Measurement of continuous working stability.
4.2 Requirements for main instruments and equipment
4.2.1 Signal generator
Frequency range: 20～20kHz
Frequency error: ±2%
Output voltage: 0.1mV~100V
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