Frequently Asked Questions about Microphones

Question number FAQ-1243

About the maximum sound pressure level when using the MI-3170 (preamp) in combination with the SR-2210 (microphone amplifier).

SR-2210: Constant current power supply (constant current drive) Current 2.4 mA Applied voltage 18 V

MI-3170: DC bias voltage 12 V ± 2 V

These two specifications and the microphone sensitivity determine the maximum sound pressure level.

The MI-3170 operates with constant current from a single power supply (constant current drive) compared to the SR-2210.

The output of MI-3170 is limited to an amplitude of more than 2 V with respect to ground and within 2 V with respect to the power supply.

The MI-3170 has a maximum output amplitude of ±8 V, so the calculated output amplitude is,

In the case of a bias voltage of 12 V, the upper limit is +20 V and the lower limit is +4 V.

In the case of a bias voltage of 10 V, the upper limit will be +18 V and the lower limit will be +2 V.

In the case of a bias voltage of 14 V, the upper limit is +22 V and the lower limit is +6 V.

When driven by SR-2210, the applied voltage is 18 V.

In the case of a bias voltage of 12 V, the upper limit will be +16 V and the lower limit will be +4 V.

In the case of a bias voltage of 10 V, the upper limit will be +16 V and the lower limit will be +2 V.

In the case of a bias voltage of 14 V, the upper limit will be +16 V and the lower limit will be +6 V.

Calculating the maximum sound pressure level for a steady-state sine wave with a microphone sensitivity of -26 dB for the MI-1271.

For a bias voltage of 12 V, ±4 V (2.82 Vrms/9 dBVrms)

94 + 26 + 9 = 129 dB.

For a bias voltage of 10 V, ±6V (4.24 Vrms/12.6 dBvrms)

94 + 26 + 12.6 = 132.6 dB.

For a bias voltage of 14 V, ±2 V (1.41 Vrms / 3.01 dBVrms)

94 + 26 + 3 = 123 dB.

How to convert the output voltage value (V) of the MI-8100 Directional Microphone to sound pressure level value (dB)
from equation (1). (SR-2210 gain 0 dB, insertion loss of the preamp 0 dB, reference sound pressure level set to 94dB.)

Calculating with a microphone sensitivity of 50 (mV/Pa), 1.41 V/(50 mV/Pa) = 28.2 Pa, the reference sound pressure is 20 μPa, so from 20 Log(28.2 Pa/20 μPa), it becomes 123 dB.

-Reference-

in the case of MI-1235/1433

When calculated with a microphone sensitivity of -29 dB, it results in 126 dB from 94 dB - (-29 dB) + 3 dB. (*94 dB is the reference sound pressure level.)

Calculating with a microphone sensitivity of 50 (mV/Pa), 1.41 V/(36 mV/Pa) = 39.2 Pa, and the reference sound pressure is 20 μPa, thus 20 Log(39.2 Pa/20 μPa) results in 126 dB.

*Please see here for MI-3170.

Please see here for SR-2210.

Last updated date: 2017-09-11