sound level meter Frequently Asked Questions

1. Normal range AC output

The specifications are as follows.

• Full-scale output level 0.707 Vrms ±15%
• Offset voltage within ±10 mV

Therefore, when a steady sine wave is input, the AC output at the upper limit of the bar indicator will be as follows.

±1 V = 0.707 Vrms = -3 dBV

The output when the measurement level of the steady signal exceeds the upper limit of the bar indicator by a dB is expressed by the following formula.

0.707×10^a/20 Vrms = -3+a dBV

For example, if the measurement level is -20 dB below the upper limit of the bar indicator, the output will be as follows: it corresponds to 100 dB when the level range is 60 to 120 dB, and it also corresponds to 100 dB when the real-time level range is 40 to 120 dB.

0.70×10^（-20）/20 = 70.7 mVrms
-3+（-20） = -23 dBV

The electrical calibration signal is -6 dB from the upper limit of the bar indicator. Therefore, the AC output will be 354mVrms or -9 dBv. (This corresponds to 114 dB when the level range is 60 to 120 dB.) Additionally, the indicated value of the AC output level during steady signal input is b Vrms or adBV from the upper limit of the bar indicator.

20×Log10 ^(b/0.707) dB or a+3 dB

It will be separated only. For example, the indicated value for an AC output of 100 mVrms = -20 dBV is from full scale.

20×Log10^{（0.1/0.707）} = -17 dB
-20+3 = -17 dB

It is only separated, and when the level range is 60 to 120 dB, it corresponds to 103 dB, and in real-time at 40 to 120 dB, it also corresponds to 103 dB. The maximum output level of the AC output is ±1.00 V, and linearity is guaranteed up to this level. However, if the maximum value of a sine wave exceeds ±3.16 V, which is 10 dB greater than full scale, the A/D converter will overflow, resulting in an overmark being displayed. Additionally, for the LA-5110 and LA-2110, input sound pressure exceeding 140 dB, and for the LA-5120, exceeding 130 dB will also be invalid.

2. Wide range AC output

The specifications are as follows.

• Full-scale output level 2.234 Vrms ±15%
• Offset voltage within ±10 mV

Therefore, when a steady sine wave is input, the AC output at the upper limit of the bar indicator will be as follows.

±3.16 V = 2.234 Vrms = +7 dBV

The output when the measurement level of the steady signal exceeds the upper limit of the bar indicator by a dB is expressed by the following formula.

2.234×10^a/20 Vrms = 7+a dBV

For example, if the measurement level is -20 dB below the upper limit of the bar indicator, the output will be as follows. (In the case of a level range of 30 to 120 dB, this corresponds to 100 dB.)

2.234×10^（-20）/20 = 223.4 mVrms
7+（-20） = -13 dBV

The electrical calibration signal is -16 dB from the upper limit of the bar indicator. Therefore, the AC output will be 354 mVrms or -9 dBV. (This corresponds to 104 dB when the level range is 30 to 120 dB.) Additionally, the indicated value when the AC output level is b Vrms or adBV during steady signal input is from the upper limit of the bar indicator.

20×Log10 ^(b/2.234) dB or a-7 dB

It will be separated only. For example, the indicated value for an AC output of 8.61 mVrms = -41.3 dBV is from full scale.

20×Log10^{（0.00861/2.234）} = -48.3 dB
-41.3-7 = -48.3 dB

The level is only separated, and in the case of a level range of 30 to 120 dB, it corresponds to 71.7 dB. The maximum output level of the AC output is ±3.16 V, and the maximum value of the sine wave, which indicates a value 10 dB higher than full scale, is ±10.0 V. Exceeding this value will display an overmark. The wide range has an AC output level of only 70 µV at the lower limit of the linearity range, so to cover the entire linearity range, it is also necessary to have recorders and analyzers with low noise levels.