Sound level meter - Frequently Asked Questions

1. DC output in normal range

The specifications are as follows:

• Full-scale output level: 2.5 V ±10 mV
• Scale factor 0.5 V ±10 mV/10 dB

Therefore, when a steady-state sine wave is input, the DC output at the upper limit of the bar indicator will be 2.5V. The scale factor is 0.5V/10 dB. Thus, the output when the display level is adB above the upper limit of the bar indicator is expressed by the following formula:

2.5+0.5×a/10 V

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.)

2.5+0.5×(-20)/10 = 1.5 V

The electrical calibration signal is -6 dB above the upper limit of the bar indicator. Therefore, the DC output will be as follows:

2.5+0.5×(-6)/10 = 2.2 V

(If the level range is 60-120 dB, this corresponds to 114 dB.) Also, when the DC output level is aV, the indicated value is from the upper limit of the bar indicator.

(a-2.5)/0.5×10 dB

This will result in a distance of only that much. For example, if the DC output is 1.65 V, the indicated value will be from full scale.

(1.65-2.5)/0.5×10 = -17 dB

It is separated by only a few units, and corresponds to 103 dB when the level range is 60-120 dB, and also corresponds to 103 dB when the real-time range is 40-120 dB. The maximum output level of the DC output is 3 V, which is the same as the level of a sine wave that is 10 dB higher than full scale. If the steady sine wave exceeds this value, an over-mark will be displayed.

2. Wide-range DC output

The specifications are as follows:

• Full-scale output level: 2.5 V ±5 mV
• Scale factor 0.25 V ±5 mV/10 dB

Therefore, when a steady-state sine wave is input, the DC output at the upper limit of the bar indicator will be 2.5V. The scale factor is 0.25 V/10 dB. Thus, the output when the display level is adB above the upper limit of the bar indicator is expressed by the following formula:

2.5+0.25×a/10 V

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.)

2.5+0.25×(-20)/10 = 2 V

The electrical calibration signal is -16 dB above the upper limit of the bar indicator. Therefore, the DC output will be as follows:

2.5+0.25×(-16)/10 = 2.1 V

(This corresponds to 104 dB when the level range is 30-120 dB.) Also, when the DC output level is aV, the indicated value is from the upper limit of the bar indicator.

(a-2.5)/0.25×10 dB

This will result in a distance of only that much. For example, if the DC output is 1.2925 V, the indicated value will be from full scale.

(1.2925-2.5)/0.25×10 = -48.3 dB

This distance corresponds to 71.7 dB when the level range is 30-120 dB. The maximum output level of the DC output is +2.75 V, which is the same as the level of a sine wave that is 10 dB higher than full scale. If the steady sine wave exceeds this value, an over-mark will be displayed.