The Difference Between Active and Passive Microphones

In the early days of pro audio, all microphones had a passive design. That means they needed no electricity to operate. The most common examples are dynamic mics, which work on electromagnetic induction, and vintage ribbon mics, a type that uses a thin, electrically conductive ribbon placed between the poles of a magnet that produces a voltage also by electromagnetic induction.

These two types of microphones have been popular since the 1930s, dominating all professional microphone sales for more than 85 years. Rugged dynamic models are still the best-selling microphones in the world, especially for music and voice-over production.

When condenser microphones became popular in the 1960s, they had to be powered by external means. This is because a condenser mic contains a diaphragm usually made of a thin metal and a backplate, second piece of metal. The electricity is supplied to create a static charge between the two parts. Once the sound hits the diaphragm, it vibrates and produces a small current. Phantom power was invented to electrify these condenser mics.

The differences between mic types are notable and are used to paint the subtle characteristics between various sounds. Dynamic mics are better for capturing loud, strong sounds (especially intense music and vocals). Ribbon mics, a type of dynamic, are typically richer, darker and more natural sounding, while condensers are better at acquiring more delicate sounds and higher frequencies.

The Launcher by Soyuz

In recent times, the mic’s preamp, whose sole job is to increase the microphone’s low gain, has become a factor. While condenser mics may work fine with the 30dB–50dB gain level of average preamps, low-output/high-impedance mics such as most dynamics and ribbon mics typically require much more gain — as high as 75dB. Until recently, few modern mic preamps had that level of gain and when pushed too hard became noisy.

To solve the low gain problem, Cloud Microphones in 2011 announced the Cloudlifter microphone activator. It’s an in-line amplifier that uses phantom power to provide passive dynamic or ribbon mics up to +25dB extra gain without passing phantom power on to microphone.

The Cloudlifter was a big hit and helped overcome the low gain issue with many mid-level preamps. Since then, many companies have introduced mic activators for passive microphones, which allows them to be used with any preamp. Soyuz, a Russian company, is now making The Launcher mic activator with 26dB of gain that purposely colors the mic with a warm sound, a new use for mic activators.

In 2022, a growing array of dynamic and ribbon microphones came with internal amplification. These are called active microphones. One of the reasons for this was to make components universally compatible and simplify the transition of audio recording away from professional studios to the home and office.

The Shure SM7B, long a popular large diaphragm dynamic mic with radio announcers, is now preferred for podcasting. It is desired because its low output rejects ambient noise and it works well in untreated acoustic spaces, such as makeshift studios. Many SM7B owners use Cloudlifters to boost the mic’s output.

SE Dynacaster

A new competitor to the SM7B is the DynaCaster by SE Electronics, a look-alike dynamic that uses in internal active preamp to the boost the signal. When supplying the mic with 48 volts of phantom power, the DynaCaster offers 30dB gain boost with very low noise. No mic activator is needed.

This is also true with a new generation of ribbon microphones, which are known as active ribbons. All have an internal amplifier matched to the microphone that boosts output level by supplied phantom power.

In addition to the boost in level, pairing a passive ribbon mic with a preamp that has a low input impedance can have a negative effect on the low-end, transient response and overall frequency response of the sound. The correct preamp allows a passive ribbon mic to operate at its best performance level.

Another reason for active mics of all kinds is for musicians on the road. They never know the kind of console or preamp they will be plugging into at various music venues, many of whom use the cheapest gear they can find.

AEA of Pasadena, Calif, a manufacturer of ribbon microphones, has transitioned much of its line to active microphones. Each has internal electronics that boost the mic’s output level and maintain a consistent impedance over the entire frequency spectrum.

AEA R44 Series

AEA makes a replica of the iconic RCA 44B, one of the most popular ribbon mics ever made. They now offer an active version with an additional 18dB of gain. It is used in recording studios all over the world.

Active microphones can be used with any preamp and their frequency response will be consistent. Engineers can add color and saturation using their preamps instead of worrying about whether the device will affect the bass response of the microphone.

As active mics are becoming more popular, so are mic preamps with higher gain. RØDE’s new RØDECaster Pro II, available this month, has preamps with a massive 75 dB gain. The preamps are so quiet, RØDE claims, a mic activator is not needed or even preferred. It would degrade the mic signal, the company said.

Others with high gain preamps include the Sound Devices MixPre series at 76dB and several Zoom models with 75db. As these high-gain preamps become more common, mic activators will become less necessary.

Though the types of microphones are slow to change, their amplification is a fast-moving new technology. Matching a microphone to its pre-amp is critical to successful audio. It is getting easier to make that match.

Writer at Broadcast Beat
Frank Beacham is a New York-based writer, director and producer who works in print, radio, television, film and theatre.

Beacham has served as a staff reporter and editor for United Press International, the Miami Herald, Gannett Newspapers and Post-Newsweek. His articles have appeared in the Los Angeles Times, Washington Post, the Village Voice and The Oxford American.

Beacham’s books, Whitewash: A Southern Journey through Music, Mayhem & Murder and The Whole World Was Watching; My Life Under the Media
Microscope are currently in publication. Two of his stories are currently being developed for television.

In 1985, Beacham teamed with Orson Welles over a six month period to develop a one-man television special. Orson Welles Solo was canceled after Mr. Welles died on the day principal photography was to begin.

In 1999, Frank Beacham was executive producer of Tim Robbins’ Touchstone feature film, Cradle Will Rock. His play, Maverick, about video with Orson Welles, was staged off-Broadway in New York City in 2019.
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