A Hot Mic can disrupt your whole day

For most people, microphones are mystical black boxes, really cylinders, that magically capture sound. But every mic has a key stat that defines how well it converts acoustic vibrations into electrical signals: sensitivity. Measured in decibels or millivolts, sensitivity indicates how much volume a microphone picks up from a given source. Hot mics with high sensitivity can overload your speakers if you’re not careful. And hot, in this case, does not mean good-looking.

Condenser mics like the Shure SM86 tend to be extra sensitive compared to dynamics like the venerable SM58. That’s because condensers use a thin diaphragm that vibrates readily in response to sound waves. Ribbon mics are often the hottest of all due to their ultrathin ribbon element. Lav mics need boosted sensitivity to cope with distant sources.

Mic Specs

Condenser and dynamic are the two main categories of microphones in any system. Basically speaking, condenser mics well, condense or compress the sound going into it. That provides for a more even loudness level. Dynamic mics do not. They take what they get and transfer it down the line. Another key distinction between dynamic and condenser mics is that wired condenser microphones need Phantom Power. This is not a ghostly electrical force. It’s power that goes back down the mic cable to the microphone.

But why do the specs list sensitivity in confusing dBV and millivolts? It’s because mic sensitivity is measured against a standard 1kHz tone at 94dB SPL (sound pressure level). Hotter mics produce more voltage from this source sound. So a sensitivity of -50dBV means the mic puts out a signal 50dB lower than 1 volt when blasted with that 94dB tone. Translated to millivolts, that’s around 3mV.

Hot Mic and What to Do

Understanding these sensitivity ratings allows smarter mic selection. Need lots of gain before feedback for a distant talker? Choose a hot condenser or ribbon. But for close-miking drums and guitars, a lower sensitivity dynamic may be safer to avoid distortion. Sensitivity graphs the delicate balance between clean gain and clipping. Turn it up, but not too far.