There are literally thousands of different microphones available for broadcasting and recording applications. How does one pick the right microphone for a particular sound source? It’s a complex question. Here’s a guide.
It might sound primitive, but it helps to understand the various types of microphones and how they work. Of course, all microphones convert analog sound waves into electrical energy. How they go about it is what differs. There are dynamics, condensers, ribbons and other types of mics. Each type has various pickup patterns, which determine how it is used.
A dynamic, or moving coil, microphone has a coil attached to a diaphragm. It vibrates in opposition to a surrounding magnet, turning the sound waves into electricity. Dynamic mics are very robust for live performances and are staples of music groups.
The basic construction of a dynamic microphone resembles that of a loudspeaker--a coil of wire surrounding a magnet. When the diaphragm moves, a small voltage is generated in the coil. Dynamic microphones are good solutions when ruggedness is an important factor. Image: Courtesy B&H Photo
Dynamics handle loud transients and are resonant between one and 4 kHz. They tend to roll off high frequencies above 10 kHz or so, and are often used for both vocals and musical instruments. The venerable Shure SM58, which have been run over by trucks and still work, is probably the most popular dynamic microphone in the world today.
A ribbon microphone relies on a very thin strip of corrugated foil made into a ribbon that vibrates between two magnets. Providing an accurate and natural sound, they are a good choice for studio work. While today's ribbon mics are more rugged than their predecessors, few engineers would assign them to a 'run-and-gun' news type application. Image: Courtesy B&H Photo.
A variant of the dynamic is the ribbon mic. Instead of a moving coil, it uses a very thin strip of corrugated foil made into a ribbon that vibrates between magnets. Ribbon mics are more accurate and natural sounding than moving coils, but also more sensitive to physical damage. Modern ribbons are far more rugged than older models and are widely used today in digital recording due to their flattering, natural sound.
Condenser microphones use a thin, typically a gold-plated, Mylar diaphragm suspended in front of a solid metal backplate. As sound pressure moves the Mylar sheet a small voltage is generated representing the audio. True condenser microphones require an external power supply. Courtesy B&H Photo.
Another category, condenser microphones, act as a two-plate capacitor with a voltage between them. In a condenser mic, one of these plates is made of very light material — usually gold-sputtered Mylar — and acts as the diaphragm. The other plate is solid metal. When sound waves hit the diaphragm, it moves back and forth relative to the solid backplate. This changes the distance between the two plates, converting the sound waves into an electrical signal.
Neumann, a maker of condenser mics, notes that condenser mics produce almost no current, because so little energy is stored in this small capacitor. This requires condensers to have what is called an “impedance converter,” a circuit that buffers between the capsule and the outside world. The impedance converter makes the signal more robust by making more signal current available.
This converter requires external power to operate. Typically this is 48-volt phantom power, though many more modern electret condensers — which apply an electrostatic equivalent to a permanent magnet — can operate on batteries.
Neumann condenser capsule.
Condenser microphones come in a wide range of shapes and sizes, from top-end studio mics to tiny lavs. Some condensers have specific colorations, particularly in the highs and high-midrange. These colorations can be heard on vocals, where they engender a very present, silky sound. This is why there are so many “favorite” condensers for their unique sound. Condenser mics recorded on analog media also often sound different when recorded digitally.
When we get past microphone types, pickup patterns must be considered. There are omnidirectional, cardioid, hyper-cardioid, figure-of-eight and a host of middle ground patterns. There are also specialty mics like PZMs for wide angle pickup and shotgun mics for a very specific sound, like motion picture dialog.
Essentially an omni pattern captures sound from all around it, while a cardioid is a heart-like pattern around the front of the microphone with minimal response coming from the rear. Cardioid mics comes in various directional characteristics, which is the subject of continuous experimentation.
The AEA N22 ribbon microphone is targeted at singer-songwriters, musicians and studio applications. While the manufacturer claims the mic is rugged, like any ribbon microphone, it should not be placed in 'plosive' applications without a pop filter.
Figure-of-eight, or bidirectional, mics pick up audio in front of the capsule and directly behind it. There is virtual rejection of audio on the sides. This polar pattern can be quite useful when trying to get separation among live musical instruments in tight spaces.
Learning which type of mic and which pattern to use with a specific sound source is one of the great black arts and mysteries of audio recording. It is often what separates great recording engineers from others. It usually comes with acquiring the skills of what works and what doesn’t over a long period of time.
Use the Room
The room being used for the broadcast or recording is also very important and can affect the sound. B&H Photo and Video, a major pro audio dealer in New York City, offers this tip: When in an unfamiliar space, walk around while clapping your hands, listening for flutter echoes.
Use the higher and lower registers of your voice to test out low and high-frequency responses. Once a pleasurable spot is found, set up there. This way, B&H said, you’ll be more inclined to use the sound of the room to your advantage, using off-axis positioning with confidence. This applies to both interviews and music recording.
Always try to move the microphone around and find the sweet spot, no matter what you are recording. Don’t correct mic problems with electronic gadgetry or computer plug-ins. It will sound fake in the end and cause problems. Great sound has always come through trial and error mic placement. Computers make it easier but comes at the price of authenticity.
This mic placement also includes vocals, whether spoken word or singing. If you find yourself de-essing recorded vocals, place the mic capsule at a slight angle to the speaker or singer. Again, avoid using electronics to correct the problem if you can. The same goes for a piercing brass instrument or an alto or soprano saxophone. Always try to fix it first with mic placement.
Today's audio engineers have hundreds of choices when it comes to microphones. Fortunately, the judicious purchase of several different types of microphones will ensure a good solution is always at hand.
If at all possible, avoid putting a mic very close to the source. Give the sound a little air to breathe, especially if you’re in a great acoustical space. Use proximity effect to your advantage. The closer one gets to a microphone, the more low-mid range will be elicited. Using proximity effect is where announcers get that “voice of God” effect that makes them sound so rich on the air. On musical instruments, bring the mic closer to get deeper, more beefy sound.
Use figure-of-eight patterns to reject undesired sounds. The sides of the mic are virtually dead and the microphone can be angled in such a way that anything on its sides are out of the line of pickup. Since most ribbons have figure-of-eight patterns and can work far from the source, these are excellent choices to avoid excessive bleed in small spaces.
When recording anything, there are a complex range of microphone choices to be made to get the sonic signature being sought. Microphones become like artist’s paint brushes, each offering a sonic difference of their own. This is where the art of shaping sound comes in. The only way to learn it is with practice. It is what separates the pros from the amateurs.
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