It is often taught that "sound is vibrations in the air." We are able to enjoy music because we sense these vibrations in the air as sound.
Microphones convert these vibrations into electrical signals. Here are the two main types of microphone:
(1) Dynamic microphones
Construction is simple and comparatively sturdy. No power supply is required. Relatively inexpensive.
(2) Condenser microphones
Good sensitivity at all frequencies. Power supply is required. Vulnerable to structural vibration and humidity.
<Reference> Which type of microphone should I choose?
Condenser microphones may have greater appeal because they have "good sensitivity at all frequencies". However, they are not always the most practical choice.
Often during recording, a "pop shield" filter is required to protect against noise caused by the vocalist's breath hitting the condenser microphone. This is because condenser microphones are able to react to more subtle sounds. On the other hand, condenser microphones are not suited for high-volume recording, so dynamic microphones are mainly used in situations where loud audio is to be picked up.
Condenser microphones are used with PA systems in cases where a wide band of frequencies, ranging from low to high, is to be picked up for choir vocals, acoustic pianos, hi-hat cymbals (which are known for their sensitive and high frequency), or for use "overhead" to pick up sounds from the entire drum set.
Microphones have directionality that indicates from which direction they best pick up sound. Microphones that do not have any specific directionality (called "omnidirectional" microphones) will pick up sounds from all directions, thus sounds other than those of the intended instruments will go into the microphone. Particularly with PA systems, many instruments will often be played together on a stage, so it is necessary to have a good understanding of directionality. Some microphones have switches to select the preferred directional pattern.
This type of microphone features directionality to the front only and is also known as "cardioid" (because of its heart shaped directional pattern). Cardioid mics are most often used with PA systems for vocals, instruments, etc. In the diagram, 0°indicates the front of the microphone.
This type of microphone features directionality to the front and rear. Because bidirectional microphones will also pick up audio to the rear, they are rarely used with PA systems. They are often used to record audio between two people who are face to face, such as during radio interviews.
As mentioned above, this microphone type has no directionality. "Omni" mics are used to pick up all or wide range audio. For example, they are used for choirs, when many instruments are played at once, or to pick up all audio on the stage.
<Reference> What directionality should I choose?
A unidirectional microphone is generally used when picking up vocal and instrument performances with a PA system. Only choose an omnidirectional microphone when picking up vocals or performances from many people, or all sounds from the stage. However, omnidirectional microphones have a wide directionality, so they will also pick up sounds from the main speakers and monitor speakers on the stage, and feedback can easily occur. Therefore, use caution with the placement and volume of these microphones.
<Tips> If the microphone is covered, feedback will occur more easily: don't cover the grille with your hand
When a squealing or howling kind of feedback occurs at karaoke or other amateur singing events, some people cover the microphone instinctively. However, this actually has the opposite effect: If a microphone is covered, even a unidirectional microphone will behave like an omnidirectional microphone. It will pick up more sound from the speakers around it and cause more feedback. There are also some people who hold the microphone at the tip, but be careful because this, too, will increase the risk of feedback.
Selecting a microphone
This section has explained that dynamic microphones are generally used with PA systems, and that unidirectional microphones are the most suitable in this case. It also explained that condenser microphones are used with hi-hat cymbals and as drum kit overheads. Now, let's consider the actual selection of microphones for PA systems, including the microphones discussed above.
Here are two other types of microphone, each designed for specific uses.
(1) Wireless microphones
Wireless microphones can be moved around freely, without the cables getting in the way. These microphones require a transmitter and a receiver in order to broadcast sound. In general, handheld wireless microphones contain a built-in transmitter, whereas headset and clip-on microphones include a cable that attaches to the belt-pack transmitter.
The transmitters for both types are powered by batteries (either dry-cell or rechargeable), so always make sure that ample battery power is available.
It's also necessary to set the transmitter of the broadcasting microphone and the receiver to the same channel. Make sure that when you are using more than one wireless microphone, the transmitting and receiving channels are set differently for each microphone.
(2) Headsets and lapel microphones
Microphones worn on one's head are called headsets, while microphones worn on clothing not far from one's mouth are called lapel (or lavalier) microphones. Either can be used so that both hands are free. Headsets are often used while singing or dancing, while lapel microphones are often used by presenters on television. These headsets and lapel microphones are often used wirelessly.
<Note> Many headset and lapel microphones are omnidirectional, so extreme caution should be applied when using them with PA systems. Try using a unidirectional headset microphone to reduce the risk of feedback.