ABSOLUTE

SOUND

PRESSURE

[dBPa]

-94dB

SENSITIVITY

[dBV/Pa]

SOUND

PRESSURE

[dB SPL]

VOLTAGE

[dBV]

A-WEIGHTED FILTER

5pF

LMV1031

SNOSAP8B – SEPTEMBER 2005 – REVISED MAY 2013

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MEASURING NOISE AND SNR

The overall noise of the LMV1031 is measured within the frequency band from 10 Hz to 22 kHz using an A-

weighted filter. The input of the LMV1031 is connected to ground with a 5 pF capacitor.

Figure 14. Noise Measurement Setup

represents a sound pressure level of 94 dB with a standard ECM sensitivity. No input capacitor is connected.

SOUND PRESSURE LEVEL

The volume of sound applied to a microphone is commonly stated as the pressure level with respect to the

threshold of hearing of the human ear. This sound pressure level (SPL) in decibels is defined by:

where

•

•

In order to be able to calculate the resulting output voltage of the microphone for a given SPL, the sound

pressure in dB SPL needs to be converted to the absolute sound pressure in dBPa. This is the sound pressure

level in decibels which is referred to 1 Pascal (Pa).

The conversion is given by:

dBPa = dB SPL + 20*log 20 µPa

dBPa = dB SPL - 94 dB

Translation from absolute sound pressure level to a voltage is specified by the sensitivity of the microphone. A

conventional microphone has a sensitivity of

−44 dBV/Pa.

Figure 15. dB SPL to dBV Conversion

8

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