Microphone sensitivity and the output voltage

[CHL]

Hello

I have a question about microphone's sensitivity

1) For the sensitivity, the reference is 0dB which means 1V. Is it always same even though the microphone supply voltage is different?(e.g. 1.5V microphone VS 3.3V microphone)

2) If the question above is correct, does it mean all of the microphones cannot achieve 1Vrms output signal? Are the output signals always mV range?

 

[betwixt]

1. Where do you find a reference to 0dB being 1V? Please bear in mind that decibels are based on the ratio of two values so you need more information on what those values are. For conversion of sound to voltage you need one of them to be a reference to sound pressure level.

2. It would be a very unusual microphone that could achieve 1V RMS output, most are in the mV to 10s of mV range.

Brian.

 

[mdyusuf]

Where do you find a reference to 0dB being 1V? Please send me the link.

 

[D.A.(Tony)Stewart]

Hello

I have a question about microphone's sensitivity

1) For the sensitivity, the reference is 0dB which means 1V. Is it always same even though the microphone supply voltage is different?(e.g. 1.5V microphone VS 3.3V microphone)

2) If the question above is correct, does it mean all of the microphones cannot achieve 1Vrms output signal? Are the output signals always mV range?

All your assumptions are incorrect re:
0dB is not 1V
Nor is it, a mic output.

But 0dBmV=1mV and 0dBV = 1V

mic sensitivity varies with sound pressure , frequency ( and distance to source )

 

[Audioguru]

An electret microphone produces an average of about 10mV when it is about 10cm from your mouth and you speak at normal conversation level. Usually an electret mic is fed 0.5mA through a resistor that powers the Jfet inside. If the supply is 9V then the resistor is about 10k then the output level is what is expected because the 10k resistor does not load the Jfet much to reduce its output level and the voltage across the Jfet is about 9V - (0.5mA x 10k)= 4.0V so its gain is what is expected.

If the mic supply is 3.3V then the 0.5mA current for the Jfet requires a resistor value of about (3.3V/2)/0.5mA)= 3.3k ohms which loads the mic reducing its level, the Jfet voltage is low reducing its gain and the maximum sound level is reduced causing loud sounds to be distorted.

If the mic supply is only 1.5V then the electret mic barely works with a very low level and a low maximum sound level causing distortion.

A preamp with a gain of 100 is needed to amplify the 10mV to 1V. Usually a preamp has much more gain (about 300) so that its sensitivity can be high when needed and its output level can be turned down with a volume control when the sound levels are normal or loud.

 

[CHL]

It is not 'dB', it's 'dBV'.
That's my mistake
sensitivity[dBV] = 20log(sensitivity[mV/Pa]/Output_AREF)
The Output_AREF is 1V/Pa reference, so I said 0dBV means 1V.
I use "ADMP401" made by Analog Devices

Thank you for your help

 

[Audioguru]

The Analog Devices microphone produces no low frequency bass sounds and no very high audio frequency sounds, since it is made to be used in a narrow bandwidth telephone.
It has a preamp in it and its output is 1V RMS when its input has a very loud 94dB of sound. The gain of its preamp is 42dB which is about 180 times.
A consumer line level of 150mV is about -15dB. Its sound input level for a consumer line level output is 94dB - 15dB= 79dB but without its distance stated from the sound source (maybe when very close to your mouth like a telephone).
The datasheet does not say if or how much its output level changes when the supply voltage is reduced.

 

[CHL]

Can you tell me where you got the preamp gain?
I cannot fine the value in the datasheet.
Thank you!

 

[FvM]

I read the datasheet differently. It specifies an output level of typically -42 dBV (8 mV) at 1 Pa (94 dB) sound pressure. It also says the maximum sound pressure is 120 db which refers to 160 mV signal level.

 

[Audioguru]

I read the datasheet differently. It specifies an output level of typically -42 dBV (8 mV) at 1 Pa (94 dB) sound pressure. It also says the maximum sound pressure is 120 db which refers to 160 mV signal level.

True, I was completely wrong. It does not have a preamp, it has an impedance converter instead. 42dB is not 180 times, it is about 125 times so when the input sound level is loud at 94dB its output level is 1Vref/125= 8mV.

It is very similar to an electret mic because its output level is almost the same. But it is smaller, it uses less voltage and it uses less current.

 

[CHL]

Thank you so much guys