Buying Guide: Microphones
There are many microphones to choose from and a wide range of prices. While it's true with microphones that price generally reflects quality, in recent years, many mics have become available that are both moderately priced and capable performers for many applications. Many of these modestly priced models copy the basic structures of microphones costing many times more.
Table of Contents
- Polar Patterns
- Understanding the specs
- Polar Patterns
- Multi-pattern microphones
- Frequency response
- Sensitivity and SPL capability
- Response curve
- Proximity effect
- Type of microphones and their applications
- Dynamic mirophones
- Condenser microphones
- • Boundary microphones
The most important thing is to choose a microphone that is appropriate for the use you plan. Is it to be used onstage for vocals or to mic an instrument? Is to be used for recording? Or perhaps you want a microphone that can do both. There are numerous mics that are used for both live sound and in the studio. The Shure SM57, for example, is both a stage and studio staple.
You should match the mic to the environment it is to be used in and the gear it will be used with. It doesn't make much sense to spend thousands on a Neumann studio mic if you plan to use it for home recording in a room where the acoustics are less than perfect. In this case, a less sensitive and more affordable mic may be a better choice. On the gear side, even the finest microphone's performance is to a large extent dependent on the quality of the mic preamps it is connected to. Unless you have high-quality mic preamps, the virtues of a high-end mic will be wasted.
Understanding the specs and the terminology will help in selecting a mic that suits your needs. Here are the primary specs and terms you often see in mic descriptions.
The polar pattern is the shape of a mic's field of sensitivity or the directions from which it accepts or ignores incoming sounds. An omnidirectional mic responds to sounds coming from all directions. A bidirectional mic picks up sounds from east and west while excluding sounds from north and south. A unidirectional mic primarily hears sounds from one direction and excludes sounds from other directions.
Unidirectional mics are most common and come in three polar patterns: cardioid, supercardioid, and hypercardioid. All three are patterns that reject rear-axis and off-axis sounds coming from behind the mic or from the sides. The cardioid pattern is roughly a heart shape (hence its name), which makes the mic most sensitive from straight on and from the sides but rejects sounds from 180 degrees opposite the direction the mic is aimed. The supercardioid mic accepts a little more sound from a 180-degree direction but rejects more from each side. The hypercardioid allows yet more sound from 180 degrees but rejects more of the sound coming from 90 or 270 degrees.
These polar patterns can be important when you use the mic in a noisy setting such as a vocal mic used by a singer in a band context. The cardioid, supercardioid, and hypercardioid mics will tend to exclude all the sounds except the voice of the user, thus keeping the sound from becoming muddied and allowing more gain before feedback.
Some condenser microphones are multi-pattern. Their polar pattern can be changed by means of a switch or by interchangeable capsules from one pattern to another-from omni to cardioid, for example. This capability gives the mic added versatility in the studio.
This is the range of frequencies from low to high that a microphone will respond to and is stated as a range such as 80Hz to 15kHz. This would be a decent range for a vocal mic. For miking snares and toms, you would look for a range that starts around 50Hz, and for a kick drum mic, a low-end of 40Hz or even 30Hz is desirable.
Sensitivity refers to how quiet a sound the mic can detect and is expressed using different systems. For the nontechnical person, it is perhaps enough to know that the lower the number, the more sensitive the microphone is.
SPL stands for sound pressure level and is expressed in dBs. It describes the maximum volume of sound that a mic can handle and so is, in a way, the opposite of sensitivity. This is important if the mic must deal with loud instruments such as drums. An average level is around 100dB; a high SPL is 130dB.
An example of a frequency response curve: the Shure SM 58.Frequency response only tells you the range a mic can reproduce. The response curve refers to the shape of its frequency responsiveness. Because it starts out from zero at the low end and drops off to zero at the high end, it takes the form of a curve when graphed. Within this general curve there will be peaks and dips in certain places that give the mic a certain character and make it more suited to certain applications. For example, a mic intended for vocals may have a spike in its upper midrange that results in a smoother or more intelligible reproduction of voices.
Proximity effect is not given as a specification but is an important mic characteristic that is sometimes mentioned in descriptions. Condenser mics generally have more proximity effect than dynamic mics. Proximity effect causes bass frequencies to become more pronounced as the sound source moves closer to the mic. This is desirable for singers who "work the mic" to create effects. A recording engineer might select a mic with a strong proximity effect for close miking an instrument to bring out its bass tones.
More than specs determine the characteristics of a mic—its structure, the kind of metals used, and manufacturing precision can all affect performance. Because some manufacturers fudge the numbers, specs alone often don't distinguish a $50 mic from one that costs hundreds. It's fair to say that price itself is a significant specification. Listening is the best way to really know the differences between a great mic and a lesser one.
Most microphones fall into one of two categories: dynamic or condenser. Dynamic mics require no power source while condenser mics do. Their operating principles, the different kinds in each category, and their applications are explained below.
How they work: Dynamic microphones use an inductive coil connected to a diaphragm and placed within the field of a permanent magnet. As the diaphragm moves, it moves the coil, thus varying the voltage the coil produces.
General characteristics: Dynamic mics are rugged and often have a high SPL capability, internal shockmounting to allow hand use, and a polar pattern that rejects off-axis sounds. They tend to be used for live sound applications, for vocals and instruments, and some are also used for recording. The Shure SM57 has been both a studio and stage staple for many years. As a group, dynamic mics are relatively affordable, and many of the big-name mic manufacturers have economy series mics that give you great performance for a low price.
» Unlike other dynamic mics, ribbon mics are extremely delicate. They operate by the same principle as the other dynamic
mics, but instead of a diaphragm, they employ a thin ribbon that vibrates to vary voltage. Ribbon mics are used in the studio for recording voices and a broad range of instruments. They soften the sound and impart a warmth to recorded material. They have high SPL capabilities and so can be placed very close to a sound source.
» In recent years, microphone manufacturers have begun producing dynamic microphone models designed for specific instruments. Here are a few examples:
- Drum microphones» Because drum kits make so many different sounds, mics have been tailored for kick drums, snares and toms, and cymbals. Each mic will have a response range and profile suited to the drum it is used on. Drum mics are often sold in special packs of four, five, or more. They usually save you money, are convenient, and each mic is tailored to its job.
- Horn microphones» These are typically small size, lightweight, have a frequency response tailored to the instrument, and employ a special mounting system that attaches to the horn's bell or body. They move with the horn and thus maintain a set distance for greater volume consistency. An attached horn mic also allows the player more freedom to move.
An example of a bullet microphone: the Shure 520DX.Bullet microphones » These are used by harp players. They have a short round casing that can be cupped in the player's hands along with the harmonica, and their crystal diaphragm elements produce a distorted sound beloved by blues harp players.
- Wireless microphones » These are essentially the same as wired microphones with a transmitter added.
How they work: In these mics, a thin conductive diaphragm is located close to a metal plate called a backplate, creating a capacitor. The capacitor is supplied with a small electric charge, either from phantom power or from a battery. When the pressure of soundwaves cause the diaphragm to vibrate, it changes the distance between it and the backplate, thus causing variations in the output voltage. This varied output is the microphone's signal.
General characteristics: Condenser microphones either have an external power supply, internal batteries, or use phantom power supplied by the mixer input. These days, most mixers have phantom power on mic inputs, but if you are using an older mixer, make sure it has phantom power before buying a condenser that requires it.
An example of a big recording mic: the Audio-Technica AT3035.
There are many different types of condenser mics, and most of them are used for recording. A few are used for live sound applications such as overhead miking of choirs, pianos, acoustical string instruments, and certain percussion instruments. Often a condenser is used for overhead cymbal miking. Here are the main types of condenser microphones:
Large-diaphragm condenser microphones» These are the big recording microphones with diaphragms from three quarters to an inch in diameter. Usually very sensitive, they require external power and suspension mounting. Their large size and need for suspension makes them unsuited for such applications as miking drum kits where placement is tight, but they are excellent for recording voices and many instruments. They often serve as the studio's all-purpose microphone, and the best can be very expensive. A number of affordable large-diaphragm condensers have become available in recent years that mimic the design of the expensive models and work quite well for nonprofessional recording.
An example of a large side address mic: the Shure KSM27.
Side address condenser microphones» These are a type of large condenser mic. They usually have a wide, flat windscreen over a large diaphragm positioned horizontally and aimed toward the side at a 90-degree angle. If the mic is vertical, a singer seems to be addressing the mic from the side, hence the name.
Dual-diaphragm condensers» Usually these are side-address mics and have two diaphragms aimed in opposite directions. They are effective for recording duets or larger groups, or for room ambience applications. A dual condenser mic makes it easier to keep two simultaneous sources balanced than using two single-diaphragm mics.
Tube condenser microphones
» These are the vintage recording mics used in recording and broadcast studios decades ago. Because they impart a special quality to recorded material—much like a tube guitar amp colors the instrument's sound—they are still made and used in professional studios to this day. They require a dedicated power supply, and it is the tubes in this power supply that warm up and color the sound.
An example of a small diaphragm condenser mic: the MXL 993 Pencil Mic
Small-diaphragm condenser microphones» These microphones have a diaphragm that is one-half inch or less in diameter and are used in many recording applications and a few live applications as well. They do especially well at reproducing higher frequency sounds and sound sources that change quickly in volume or have sudden attack. One common application is overhead miking of cymbals. Like other condensers, they depend on phantom power or a battery to operate.
An example of a boundary mic—the Crown Sound Grabber II PZM.
Shotgun microphones» These are condenser mics with a very narrow and extended polar pattern. They are often used for broadcasts—at sporting events, for example—because they excel at picking up specific sound sources from a distance.
Boundary microphones» Boundary mics are quite versatile, used on podiums, at conferences, and in the studio. These mics are usually placed on a flat surface—the floor, ceiling, or wall—which helps gather the sound. They are good for stereo applications and for general miking of musical groups.
Probably the most helpful thing you can do in selecting a mic is good old-fashioned research. Ask others about the mics they use. Refer to the customer comments on specific mics on our website, or read the Reviews. Harmonycentral.com is another great place to go on the web for reviews and comments regarding specific products. TapeOp magazine features articles on home recording techniques and gear. These sources of information can provide the knowledge you need to choose the right microphones.