Sound level meter - Frequently Asked Questions

1. AC output in normal range

The specifications are as follows:

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

Therefore, when a steady-state 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 measured level of the steady signal is a dB above the upper limit of the bar indicator is expressed by the following formula:

0.707×10^a/20 Vrms = -3+a dBV

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

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 354 mVrms or -9 dBv. (This corresponds to 114 dB if the level range is 60-120 dB.) Also, when the AC output level with a steady signal input is b Vrms or adBV, the indicated value is from the upper limit of the bar indicator.

20 × Log10 ^(b/0.707) dB or a + 3 dB

This will result in a distance of 100 mVrms = -20 dBV. For example, the indicated value when the AC output is 100 mVrms = -20 dBV will be from full scale.

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

The difference is only 103 dB when the level range is 60-120 dB, and 103 dB when the real-time range is 40-120 dB. The maximum output level of the AC output is ±1.00 V, and linearity is guaranteed up to this level. However, if the value exceeds ±3.16 V, which is the maximum value of a sine wave that is 10 dB greater than the full scale, the A/D converter will overflow and an over-mark will be displayed. Also, the LA-5110 and LA-2110 will be disabled if the input sound pressure exceeds 140 dB, and the LA-5120 will be disabled if the input sound pressure exceeds 130 dB.

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-state 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 measured level of the steady signal is a dB above the upper limit of the bar indicator is expressed by the following formula:

2.234×10^a/20 Vrms = 7+a dBV

For example, if the measured level is -20 dB below the upper limit of the bar indicator, the output will be as follows: (This corresponds to 100 dB if the level range is 30-120 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 if the level range is 30 to 120 dB.) Also, when the AC output level with a steady signal input is b Vrms or adBV, the indicated value is from the upper limit of the bar indicator.

20 × Log10 ^(b/2.234) dB or a -7 dB

This will result in a distance of only that much. For example, if the AC output is 8.61 mVrms = -41.3 dBV, the indicated value will be from full scale.

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

This distance corresponds to 71.7 dB when the level range is 30-120 dB. The maximum output level of the AC output is ±3.16 V, and the maximum value of a sine wave that is 10 dB above full scale is ±10.0 V. An over-mark will be displayed if this value is exceeded. Because the wide range has an AC output level of only 70 V at the lower limit of the linearity range, low-noise recorders and analyzers are required to cover the entire linearity range.