Microphone Selection Demystified
the mic for an instrument and situation greatly influences the resulting sound
in both recording and live use. Every instrument and environment has certain
sound characteristics and obstacles so microphones are optimized differently
to enhance those varied characteristics of sound and have features that help
overcome the obstacles presented by the situation they are designed for. A
bass drum, for instance, mostly produces low and low mid frequencies so a
mic for a bass drum is optimized for that kind of sound. A bass drum mic's
job is to concentrate on the low frequencies. This works almost like an EQ
but is more a decision of how frequencies will be transduced (turned into
an electric signal) than later in the signal chain processing. EQ is processing
what's there, but a mic can greatly influence what is actually being translated
from the acoustic world. Also, a bass drum presents the obstacle of being
loud enough to easily overload many mics, so a mic being used for one must
be able to handle a high sound pressure level. (this is known as an SPL rating)
Choosing a mic for a bass drum is easy... um I'll take the bass drum mic please,
but for most instruments it's not quite so clearcut. There are not very many
mics at all that say they are for one specific type of instrument (other than
vocals) and the ones that do are often useful for others. A bass drum mic
is the standard for miking a bass guitar cabinet. A vocal mic often works
great on an acoustic guitar because of it's high and high mid frequency response.
The room itself can present challenges to miking a sound succesfully, like
being near a wall or other speaker, even another performer being too close
to your mic. (how dare they?) So how do you know what type of mic to use for
the zillion sounds and situations? Well that's the fun part... There are no
rules only guidelines.
First I'll start with a description of the two main types of mics engineers will encounter (there's definitely more than two, though). They are dynamic mics and condenser mics. This refers to the method with which the diaphragm inside the mic turns acoustic sound into signal. A diaphragm is a membrane that captures the initial acoustic waves by vibration. (Your ear drum is a diapghram, too). A dynamic mic's diaphragm vibrates within a voice coil who's vibration is then, in turn, transformed into an electric signal. This is much like a speaker in reverse. In fact, some dynamic mics are speakers too, like a policeman's radio. A condenser mic uses an electromagnetic charge to create a magnetic field between the diaphragm and a backplate. As the diaphragm vibrates, the magnetic field is altered and the change is measured and turned into signal. They also require phantom power, an electrical current supplied through the mic cable. This is obviously alot more complex and delicate of an operation than a dynamic mic. This makes condenser mics generally alot more expensive and fragile than dynamics. They are also alot more sensitive and reproduce sound much clearer. This is not always desirable though. Dynamics being less senstive are often much better for live use than condensers because of them being LESS sensitive. A condenser would be so sensitive it would often pick up just about every instrument on a small stage and often way too much sound of the floor monitors or sound bouncing off the walls causing everyone's best friend... feedback! Ahh feedback, that delightful squeal that can make everyone at the show cringe instantly. Dynamics have a much higher SPL rating too, so they are great for drums. Also, their highly directional sensitivity can be great for a snare drum mic not picking up too much cymbal for instance. Dynamics do not have as good of high frequency response as condensers, however, but that's not as big of an issue for live use. Snare drum and tom sounds, however, are usually more about tone than clarity so dynamics are the most common choice even in the studio, aided, too, by the high cost of having many condensers on your drum kit. In the studio, condensers are often used on cymbals and hats because of their high frequency response and brave live sound engineers who have alot of space onstage will too. Drums are an easy example to contrast distinct types of sound and they present a few challenges that are common to their unique situation for the purpose of describing some advantages of dynamic vs condenser. Mic choice however goes alot deeper than just which of the two to use.
Within the categories of dynamic and condenser are many types of unique mic sound characteristics and features. Besides just the transduction method, there are all sorts of mic electronics that give the mic it's character. Mic's sound can be described as warm, round, big, bright, thin, lot's of detail, bassy, tonal, and unlimited, more adjectives. Some expensive studio mics even have vacuum tubes in them that slightly distort in a pleasant way. This creates extra harmonics that can make a voice sound more full. A tube mic's sound is great for going for that full warm sound and can make someone sound larger than life, but that's not always desired. Music has only so much sonic real estate to give up and if you give too much sonic bigness to the wrong sound something else or the mix might suffer. Also, you might want a brighter thinner sound on something like an acoustic guitar. The way to choose a mic is to think about the sound you're capturing and then think about how you want it to sound. Whatever mic has the sound to get you the desired result is the one to use... and how do you know which mic that is? Your ear. The only real rule is: If it sounds good, use it. Knowing that condensers are clearer than dynamics helps and that tube mics are enhancing warmth and bigness, but within those categories there are literally hundreds of mics. One thing that helps, too, is if you know what a mic is specifically designed for, you can apply your knowledge of how that instrument (vocal is an instrument too) sounds to what you might want to use it on when you don't have a mic for your specific purpose. It's also good to have a nice general purpose mic or two that don't have a real lot of character so they can be used on a wider range of intruments.
Especially within the condenser mic category, there are an enormous variety of ways mics can sound. In fact every mic has a unique influence on sound, sometimes down to the particular mic vs another of the same exact model. Other things to consider are the features of the mic, like it's pickup pattern (the directional focus of the mic), if it has a pad which enables it to be used to capture higher SPLs, a low frequency rolloff switch can make the mic reject low frequency rumbling caused by commotion or backround noise from things like planes flying outside. As far as sound is concerned the real best way to choose is by trial and error and knowing what a wide variety of different mics sound like by actually hearing them. To give you a headstart on your new mission of knowing mic sounds and uses, I will list a few to get you started. Remember though these are only guidlines. If it sounds good, use it. Who knows? I bet Barry White would sound good singing in a bass drum mic.
Very popular studio condenser. Has a very big warm sound. Good for vocals and instruments for a high mid frequency sound
Studio condenser. Has a very bright clear and snappy sound. Can give life to dull sounds and make people with lot's of presence in their voice sound more balanced. Great also on studio snare drums, cymbals, and acoustic guitars.
Dynamic instrument mic. Limited frequency response helps shape tone. very common on drums of all types for live use, and snares/toms in the studio. Also a favorite for guitar cabinets.
Bass drum mic also good for bass guitars
Live vocal mics with super and hypercardiod pickup patterns. (does not pick up as much sound not aimed directly into mic) helps reduce feedback onstage.