How can I test how much voltage an electret microphone output?

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scream_er

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I want to know how much voltage an electret microphone can output when I scream into it at very close proximity. Can I connect the microphone directly to oscilloscope with BNC to probe wire. With +ve of microphone connected to +ve of BNC to prove and -ve of microphone connected to -ve of BNC to probe.
 

Yes, you can do that. It will be best if you set the oscilloscope input to AC mode. Otherwise, the DC offset on the microphone's output will push the trace way off the screen, making it necessary to make a large adjustment to the vertical centering control. That is, if a DC blocking capacitor is not already in place at the mic's output.
 

At which vertical Volts/Division do I set the oscilloscope to get a better output. uV would do right? Mostly how much does an electret microphone output (100uV to 500uV)?
 

If you install the capacitor (per post #2) then it will remove all DC component. You can easily center the signal. You can use the most sensitive setting (or almost the most sensitive).

WIthout the capacitor, there is mostly a DC voltage. You will need to try less sensitive settings in order to locate the trace. The audio waveform will be small bumps on the DC component.

I have used electret mics. They can operate on a wide range of voltage.

I made one to use a 1.5V battery. When talking loudly the signal clipped severely. A type of distortion known as 'shatter'.

I should have applied a higher supply voltage to the mic. It would have allowed greater amplitude of the audio.
 
Last edited:

@BradtheRad, i meant to say whats the average output voltage of an electret microphone, not the supply voltage needed by the microphone.
 

scream_er said:
@BradtheRad, i meant to say whats the average output voltage of an electret microphone, not the supply voltage needed by the microphone.
Click to expand...

Hi, I went back to edit my previous post while you posted yours.

To watch mic output I use the most sensitive settings. From 1mV to 10mV per division. The typical AC excursion for a mic is up to about 50mV.
 

You can start with the sensitivity setting mentioned by Brad and then change the scale as needed based on what you observe.

A microphone output can vary widely depending on how loud and how close the sound source is. Normal speech several inches away may produce an output of a few millivolts while a loud scream (which you seem to like doing :smile: ) close to the mic can be more than a hundred times stronger.

If, when you scream, you notice that the tops and/or bottoms of the waveforms are flat, it indicates that the signal is clipped. This means that the mic is trying to put out more than the limit set by the power supply but can't, which results in a distorted output.
 

Electret microphones usually needs bias voltage.
The electret is a modified version of the classic capacitor microphone, which exploits changes in capacitance
due to mechanical vibrations to produce a small voltage proportional to sound waves.
The electret does not need an applied (or phantom) voltage like the condenser microphone -- as it has a built-in charge --
but a few volts are still required to power the internal Field Effect Transistor (FET) buffer.

The bias is needed for the small built-in FET follower which converts the very high impedance of the electret element
(tens of megohms) to an acceptable level (several kohms).

below : different ways to connect the bias voltage

 
In the attached photo is the +ve pin of capacitor connected to +Ve pin of electret microphone? And the -ve pin connected to oscilloscope?
 

scream_er said:
In the attached photo is the +ve pin of capacitor connected to +Ve pin of electret microphone? And the -ve pin connected to oscilloscope?
Click to expand...

Supply ground and oscilloscope ground go to the 0V line on all the schematics (post #8).

Your capacitor may have a leg marked for polarity. The + sign on the capacitor goes toward the resistor which is closest to supply +. If the capacitor has a minus sign on it, then that leg should be away from the supply +.

There are different setups that can be used with an electret mic. Post #8 shows the most common ones. There will almost certainly be one of them that you will find will work with your equipment.
 

You should also be aware of the Sound Pressure limits of the electret capsule itself, if 'screaming' very close to the microphone, which won't necessarily show as clipping of the output waveform should the amplifier not be overloaded but will be more apparent as a rounded 'limiting' as the mechanical limits of the diaphragm are approached. (hope I've explained this well enough!)

hope this assists
Mik
 

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