Measurable maximum sound pressure level when using the MI-3170 (preamplifier) and SR-2210 (microphone preamplifier) in combination.

SR-2210: Constant current power (constant current drive) Current 2.4 mA

Applied voltage 18 V

MI-3170: DC bias voltage 12 V±2 V (The voltage swings around the DC bias voltage as the center)

The measurable maximum sound pressure level is determined by the specification of above microphone amplifier and preamplifier and microphone sensitivity.

The MI-3170 is a single power drive (constant current drive) from the SR-2210.

The MI-3170 can output voltages of 2V or more from the ground and 2V or less from the current voltage.

The applied voltage of SR-2210 is 18V, so the upper limit of the amplitude voltage is 16V which is 2V lower than the applied voltage.

The original output voltage range of the MI-3170 is ±8V, so the output voltage in the calculation is as follows;

When the DC bias voltage is 12V, the upper limit is +20V and the lower limit is +4V.

When the DC bias voltage is 10V, the upper limit is +18V, and the lower limit is +2V.

When the DC bias voltage is 14V, the upper limit is +22V, and the lower limit is +6V.

However, the voltage is limited to 2V or less of the applied voltage when using the SR-2210, so upper limit of the output voltage is +16V.

When the DC bias voltage is 12V, the upper limit is +16V, and the lower limit is +4V.

When the DC bias voltage is 10V, the upper limit is +5V, and the lower limit is +2V.

When the DC bias voltage is 14V, the upper limit is +16V, and the lower limit is +6V

The calculate the measurable maximum sound pressure level in the stationary sine wave with the MI-1271 microphone sensitivity -26 dB (1V/Pa);

When the DC bias voltage is 12V,

The upper limit of the voltage output is 16V, so the amplitude of one side is limited to 4V (16-12). Which means that the measurable voltage is ±4V. The rms value and dB value of ±4V are 2.82Vrms and 9dBVrms.

The calculation formula to give an allowance up to the measurable 9 dBVrms: 9-(-26)=35 dB

Measurable output voltage is 94+35=129 dB.

In the same way,

When the DC bias voltage is 10 V, ±6V (4.24 Vrms/ 12.6 dBVrms)

94-(-26)+12.6=132.6 dB

When the DC bias voltage is 14 V, ±2 V (1.41 Vrms/3.01 dBVrms)

94-(-26)+3=123 dB

https://www.onosokki.co.jp/English/hp_e/c_support/faq/mi/mi8100_2.htm

From the (1) formula in the above FAQ; SR2210: Gain 0dB, insertion loss of preamplifier: 0 dB, reference sound pressure level: 94 dB

When calculate it with the microphone sensitivity 50 (mV/Pa); 1.41 V/(50 mV/Pa)=28.2 Pa
Reference sound pressure is 20µPa; the measurable sound pressure level is 123 dB from 20 Log (28.2 Pa/ 20µPa)

-Remarks-

When using the MI-1235/1433

When calculating with the microphone sensitivity of -29 dB;

94 dB-(-29 dB)+3 dB=126 dB (*94 dB is the reference sound pressure level)

When calculating with the microphone sensitivity: 36 (mV/Pa)

1.41 V/(36 mV/Pa)=39.2 Pa

The reference sensitivity is 20µPa, so 20 Log (39.2 Pa/20µPa)=126 dB

Revised:2017.09.11

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