JJG 188-2017Sound Level Meters (English PDF)

3.1 Sound pressure

The difference between the instantaneous total pressure and the corresponding static pressure.

3.2 Sound pressure level

The logarithm to the base 10 of the ratio -- of the time mean square of the sound pressure signal to the square of the reference value -- multiplied by 10.

3.3 Frequency weighting

The difference -- between the frequency-weighted signal level indicated on the display device and the corresponding constant amplitude sinusoidal input signal level, which is a specific function of frequency.

3.4 Time weighting

A time exponential function with a specified time constant, that weights the square of the sound pressure signal.

3.10 Time-average sound level

Equivalent continuous sound level

5.1 Indication sound level adjustment

It shall be performed at the reference sound pressure level in the reference level range and at the verification check frequency in the range of 160 Hz ~ 1250 Hz.

5.2 Frequency weighting

5.2.1 The sound level meter shall have frequency weighting A; the Class 1 sound level meter shall also have frequency weighting C. The sound level meter that measures the

C-weighted peak sound level shall also be able to measure the C-weighted time average sound level.

5.2.4 For sound level meters and configurations with nominal operating modes

specified in the instruction manual, the relative frequency-weighted free-field response and relative frequency-weighted random-incidence response (if applicable) shall comply with the corresponding frequency weightings and acceptance limits in Table 1.

5.3 Frequency weighting at 1kHz

At the reference sound pressure level within the reference level range, for a 1 kHz steady-state sinusoidal electrical signal, the difference -- between the indicated sound level measured on C weighting and Z weighting and the indicated sound level measured on A weighting -- shall not exceed ±0.2 dB. This requirement does not apply to the indication of peak sound level.

5.4 Level linearity

5.4.1 Within the reference level range, the level linearity range at 1 kHz frequency shall be at least 60 dB.

5.6 Time weightings F and S

5.6.1 The design target for the exponential time constant of the sound level meter time weighting F is 0.125 s and the time weighting S is 1 s. The decay rate of the indicated sound level shall be measured by suddenly terminating the input 4 kHz steady-state sinusoidal electrical signal. The decay rate of the time weighting F shall be between

31.0 dB/s and 38.5 dB/s; the time weighting S shall be between 3.6 dB/s and 5.1 dB/s.

5.7 Toneburst response

5.8 Repeated toneburst response

5.8.1 The requirements for repeated toneburst response apply to A-weighting as well as

C and Z-weighting. The deviation of the measured time-averaged sound level from the time-averaged sound level calculated for the corresponding toneburst sequence, using a 4 kHz repeated electric toneburst sequence of the same amplitude and duration, shall be within the acceptance limit specified for the sound exposure level toneburst response in Table 2.The measurement shall be made on the reference level range of the sound level meter, 3 dB below the upper limit of the corresponding 4 kHz level linearity range, with the duration of the toneburst of 0.25 ms ~ 1 s.

7.1 Verification conditions

7.1.1 Environmental conditions

The verification environmental conditions of the sound level meter are as follows.

7.1.2 Reference environmental conditions

The reference environmental conditions of the sound level meter are as follows.

allowable measurement uncertainty in Appendix A.

7.1.3 Measurement standards and main supporting equipment

7.3 Verification method

7.3.1 Appearance inspection

Visual inspection or manual operation.

7.3.3 Frequency weighting

7.3.3.1 Overview

Among the frequency weightings provided by the sound level meter, at least one shall be tested with an acoustic signal; the other frequency weightings may use either an acoustic signal or an electrical signal. For the first verification of the sound level meter, at least one frequency weighting shall be used to calibrate the acoustic signal and the electrical signal.

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