How to find output voltage of microphone when sensitivity given is -38dBV . I want to compare volatges for various Sound pressure level. Link of datasheet is : https://store.invensense.com/datasheets/invensense/INMP404.pdf
\$\begingroup\$
\$\endgroup\$
1
-
\$\begingroup\$ More about decibels - for people who prefer text to videos. \$\endgroup\$– JRECommented Jul 18, 2018 at 14:47
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
We nomrally can hear a 100 decible or dB range at 1 kilohertz (kHz) from perfect silence to a loud stereo at 1m. ( more can be painful) The typical (1933) Fletcher Munson curves are below for human hearing.
This logarithmic pressure and frequency range in Sound Pressure Level (SPL) is plotted in dB SPL so 100dB spans 5 decades or 20dB per decade. How it is measured.
Talking loud at close range as possible to the mic. can achieve this high sound pressure level (SPL) used as a test reference 94 dB SPL @ 1kHz produces a voltage of -38dBV where 0dBV = 1 volt and and -40dBV is 1% of 1 Volt or 10mV which is what you expect at normal strong levels.
With a SNR of 62dBA , or A weighted quiet sounds defined for below 55 dB SPL . This means if the design is clean, the noise level is about 3 decades ( 20dB/decade in voltage below the test level of 94 dB SPL. ( since 60dB ~ 62dB)
So you should expect the mic to produce 10mV (rms) signal max and 10uV noise > minimum at 1 kHz when using their design guide.
The A weighted frequency response curve of the microphone indicates the weighted response after normalizing to the above human hearing response which is most sensitive in the 1000 Hz to 5 kHz range.
\$\begingroup\$
\$\endgroup\$
5
The sensitivity is -38 dBV for a 1 kHz sound pressure level of 94 dB (the data sheet tells you that) and -38 dBV is 12.6 mV RMS so you now know the signal level in volts, the frequency (1 kHz) and the sound pressure level (1 pascal = 94 dB SPL).
If the sound pressure level decreased by 10 dB the voltage output would fall by 3.162 to 4 mV because 10 dB is a ratio of \$10^{10/20}\$.
More assistance: -
answered Jul 18, 2018 at 13:23
-
\$\begingroup\$ Okay but how -38 dBV is 12.6 mV RMS ?? \$\endgroup\$ Commented Jul 18, 2018 at 13:30
-
\$\begingroup\$ Divide -38 by 20 and take the antilog (base 10). It's the reverse process of taking a voltage (say) 10 volts, taking the log (base 10) and multiplying by 20. \$\endgroup\$– Andy akaCommented Jul 18, 2018 at 13:33
-
\$\begingroup\$ @jagrutimahajan Do you understand what a dB ratio is? \$\endgroup\$ Commented Jul 18, 2018 at 13:33
-
\$\begingroup\$ @ElliotAlderson Not really, can you please explain. \$\endgroup\$ Commented Jul 18, 2018 at 13:34
-
\$\begingroup\$ @jagrutimahajan see this youtube video for more learning: youtube.com/watch?v=mMsGLz3fMr8 \$\endgroup\$– Andy akaCommented Jul 18, 2018 at 13:36