What kind of signal level from a Magnetic microphone?

Thread Starter

Wendy

Joined Mar 24, 2008
21,919
@Audioguru
I am about to design a simple audio amp. I'm wondering what the typical signal strength from a microphone (in mv)? So, I can adjust the gain of the circuit accordingly. If I were able I would just hook up a mic to an Oscope and measure it. For now I just have to fake it.
 

Veracohr

Joined Jan 3, 2011
694
Find the specs of your microphone, it should have a sensitivity listed somewhere. The below mic outputs 1.85mV per 94dB SPL at 1kHz. 94dB SPL is a bit loud for sustained sound, but close-miked loud instruments (like kick drums) can reach much higher at the mic, so you'll find them able to handle over 170 dB SPL for certain purposes. A quick search for a dB SPL chart gives conversational speech at 1m distance a level of 60dB SPL, and the "threshold of pain" is 120dB SPL.


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DickCappels

Joined Aug 21, 2008
6,014
It depends on how loud you yell into the microphone, but generally 2 or 3 mv is accepted as normal. I will yield to AudioGuru as the final authority.
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,919
OK, What I have been doing is setting limits. I'm going to treat the 2 mv number as RMS. I am going for a 10V P-P signal which works out to 3.535Vrms. So the gain needed would be around G= 3.545 Vrms / 2 mvrms, G = 1767.5. I will use a pot in the final design to set the exact gain.

I will pick up this design in another thread. Guess AG wasn't interested.
 

Audioguru

Joined Dec 20, 2007
11,251
Sorry Wendy, I was in the hospital for a couple of weeks with blood poisoning and intravenous antibiotics when you posted, but I survived while I chased the nurses around, no internet there. The food in the hospital was awful.

A dynamic mic (coil and magnet) and an electret (condenser mic with 48VDC stored in its electret material and a Jfet impedance converter) both have an output of about 10mV RMS at normal conversation level 10cm from your mouth. But audio levels vary a lot, leave enough headroom for louder sounds.
 

DickCappels

Joined Aug 21, 2008
6,014
Sorry Wendy, I was in the hospital for a couple of weeks with blood poisoning and intravenous antibiotics when you posted, but I survived while I chased the nurses around, no internet there. The food in the hospital was awful.

A dynamic mic (coil and magnet) and an electret (condenser mic with 48VDC stored in its electret material and a Jfet impedance converter) both have an output of about 10mV RMS at normal conversation level 10cm from your mouth. But audio levels vary a lot, leave enough headroom for louder sounds.
Glad you made it back. It must have been a very unpleasant experience.

I am just curious about that 10 mv RMS. In the case of typical speech, if such a thing exists, how does that 10 mv RMS translate into peak-to-peak?
 

Audioguru

Joined Dec 20, 2007
11,251
As you know Dick, the level of speech varies all over the place and is different with different people. Also the 10cm distance of the mic from the lips is crucial. Avoid talking to a mic with it under your chin. A real VU meter will show the average level as 10mV RMS which is 28.4mV p-p.
 

sghioto

Joined Dec 31, 2017
1,038
Output levels on dynamic mics will depend on whether they are high or low impedance. I would agree the high impedance type will deliver about 10mv on average but the low impedance type (600 ohms or less) only 1 or 2mv on average from experience.
SG
 
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