Frequently Asked Questions about Microphones

Question number FAQ-1243

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

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, along with the microphone sensitivity, determine the maximum sound pressure level.

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

The output of the MI-3170 is amplitude-limited to above 2V relative to ground and within 2V relative to the power supply.

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

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

With a bias voltage of 10 V, the upper limit is +18 V and the lower limit is +2 V.

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

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

With a bias voltage of 12V, the upper limit is +16V and the lower limit is +4V.

With a bias voltage of 10 V, the upper limit is +16 V and the lower limit is +2 V.

With a bias voltage of 14 V, the upper limit is +16 V and the lower limit is +6 V.

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

With a bias voltage of 12 V, the voltage range is ±4 V (2.82 Vrms/9 dBVrms).

94 + 26 + 9 = 129 dB.

With a bias voltage of 10 V, the voltage range is ±6V (4.24 Vrms/12.6 dBvrms).

94 + 26 + 12.6 = 132.6 dB.

With a bias voltage of 14 V, the voltage range is ±2 V (1.41 Vrms / 3.01 dBVrms).

94 + 26 + 3 = 123 dB.

How to convert the output voltage (V) of the MI-8100 Directional Microphone to sound pressure level (dB).
From equation (1): (Assume SR-2210 gain 0 dB, preamplifier insertion loss 0 dB, and reference sound pressure level 94 dB.)

Calculating with a microphone sensitivity of 50 (mV/Pa), we get 1.41 V/(50 mV/Pa) = 28.2 Pa. The reference sound pressure is 20 μPa, so 20 Log(28.2 Pa/20 μPa) gives us 123 dB.

-reference-

For MI-1235/1433

Calculating with a microphone sensitivity of -29 dB, the result is 94 dB - (-29 dB) + 3 dB = 126 dB. (*94 dB is the reference sound pressure level)

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

*For MI-3170 please see here.

*For SR-2210 please see here.

Last updated: 2017-09-11