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Microphones for nature recording I.: types and arrays

The number of available microphones these days is quite overwhelming. They range in cost from $15 to more than $15,000. They range in dimensions from the size of a pencil eraser for lavaliere to more than 21 inches long for a shotgun mic. They vary in the basic way they pick up sound waves and transfer the waves to electric energy, and they vary in their pickup patterns. Most microphones are developed for the music and film industry, where the sounds are often louder and more controllable. Some of these mics are better than others for recording natural sounds, so some background on how different mics function is necessary to choose the best microphones for each situation. In this case, just choosing top of the line gear may not help you. For instance, Sennheiser makes 16 microphones in their highly-rated MKH series, which include omnidirectional, cardioids, supercardioids and figure 8 mics, as well as some with adjustable polar patterns.

In this section I will be discussing the different types of microphones, their polar patterns, and different arrays for stereo mics. I discuss specialty microphones, such as hydrophones, contact mics, and ultrasonic mics in the next section. If you want to skip the details and go straight to examples of microphones for specific applications, click here.

Types of microphones

Most microphones in use today for recording are one of three types: dynamic (electromagnetic induction), condenser (capacitance change), or piezoelectric generation. Dynamic microphones are robust, inexpensive and resistance to moisture. However, they do not respond linearly to all frequencies, so their use in natural sound recording is limited. Most field recordists stick with condenser microphones, which produce a higher quality signal, but require a power source. Electret microphones are small condensors. Consumer mics often use “plug-in power” supplied by batteries within the microphones and power from the recorder. Professional microphones use 48v “phantom power” supplied by the recorder or an additional mixer or power supply. Some consumer recorders supply phantom power (e.g., the Zoom H4n), but most don’t; likewise some professional recorders don’t have a plug-in power port. So you need to match the microphone to the recorder.

Polar patterns

Microphones differ in their pickup patterns – that area in which they can detect sound. They include omnidirectional (from all around), cardioid (in the front of the mic), hypercardioid (to the front and a little bit behind), and figure 8 (to the sides, but not the front or back). Lavaliers, those tiny microphones often pinned to the lapel of someone in front of a camera, are usually omnidirectional. Hypercardioid microphones include most shotgun mics, and they vary in how much they reduce the side (off-axis) noise. Although they are often compared to zoom lenses in photography, a better analogy is looking though a tube. Imagine looking through a short tube and comparing the field of view to looking through a long tube. That’s basically the hypercardioid microphones “fetch.” Sometimes shotguns are referred to as “supercardioid”, which means they restrict the side noise more than a hypercardioid mic. Long shotguns restrict more of the side noise than short shotguns. Note that for both of these, there is some pick up to the rear of the mic, so if you are hand-holding the mic or using it on top of a camera for video work, it can pick up some operator noise. If you want to record a bird in front of you or get closer to a person speaking, while reducing other noises, you would use a shotgun mic. One drawback to shotgun mics relative to others is that they are more sensitive to wind noise.

microphones

Four basic microphone patterns.  There are many variations of these, and individual microphones may show slight differences in patterns at different frequencies.

Polar patterns are not only important for the spatial quality of the individual microphones, but factor into how microphones may be combined in stereo arrays. Not all polar patterns mesh well when two or more microphones are used together.

For a more information on microphones, see: http://en.wikipedia.org/wiki/Microphone

Stereo Arrays

We hear in stereo (if our hearing isn’t damaged), so nature recordings often sound best when two or more mics are used together. If you want to record the entire soundscape around you, you need some form of stereo array. There are 4 basic ways mics are combined to achieve nice stereo results: XY, spaced pair, binaural, and Mid-side (M-S).

Commercially, off-the-shelf stereo microphones are typically XY or M-S. XY mics consist of two cardioid microphone capsules facing each other, usually at a 90° angle, although some mics, like the Audio-Technica AT2022, have adjustable capsules that include 90º or 130º. Some XY mics are enclosed and others have the capsules exposed. Some consumer recorders also have XY built-in mics.

Mid-Side arrays are typically more complicated, as the signals are split between the inputs, such that the hypercardioid signal goes to one input and the figure 8 goes to the other (rather than right and left signals for other arrays). This usually requires a matrix decoder in order to monitor the signal as stereo, and special software to properly combine the signals in processing. Stereo shotgun mics (e.g., Sennheiser MKH 418s) are M-S mics with two capsules in one housing. It is also possible to piggyback a cardioid and a figure 8 to create an M-S recording system; Sennheiser MKH 30 and MKH 40 are often used together in that fashion.

Binaural arrays (literally, “two ears”) consist of a dummy head with microphones mounted within the ear pinnae. Usually small omni capsules are used for this. A commercial version, (Neumann KU-100 appx. $8,000 USD), has been used in some symphony halls with great success. It has not been as successful for painting a good sonic “picture” outdoors, though. These arrays can be constructed relatively cheaply using a dummy head and omni lavaliers, but they are a bit bulky to use in the field. The results seem to work well with headphones, but not so well when the sound is played back through speakers.

The term “spaced pair” encompasses an almost endless variety of designs in which two omni or cardioid mics are separated. In the studio, spaced pairs are also referred to as “A/B” mic arrays, and are spaced 3-10 feet apart. Field recordists usually space mics a distance roughly equivalent to the width of a human head and most often with something solid between the mics, to mimic a dense human head and approach a binaural effect. These arrays are usually hand-made, with the goal being to create a natural sounding sonic environment, without necessarily attempting to record exactly they way we hear. Very good results have been obtained with these arrays.

For a more detailed treatment of spaced pair arrays, see DIY stereo boundary mics or Capertee Birder

microphones_arrays2

Common methods of setting microphones to record a stereo image.  For nature recording, spaced pairs are commonly set about 8 inches apart, with a solid object in between.

IN A NUTSHELL:
Before choosing microphones for field recording, it helps to have a good idea of what you want to record, and which polar pattern might best suit the recording. Condenser microphones tend to work better in field situations than dynamic mics. If you are interested in stereo recording, some microphones are stereo mics and others are mono mics that need to be rigged in stereo fashion.

Which stereo array is best is often a matter of personal preference. In the next section, I present some natural sounds that were recorded with different arrays and equipment.

Photo by Adam Ward, 2009.

Additional references:

Krause, B. 2002. Wild soundscapes. Wilderness Press, Berkeley.

Viers, R.  2008. The sound effects bible.  Michael Weise Productions, Studio City, CA.

Available from the Amazon link at the right.

Last modified June 2016.

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