Unit 2: Microphones

Dynamic Microphones

In a dynamic microphone, the sound waves from the source hit a thin sheet of plastic called the diaphragm, inducing vibrations within a coil of wire attached beneath it. The back and forth movement of the coil makes it pass through a magnetic field created by a magnet below.

This then generates an electrical signal which directly influences the sound.

Pros

• Dynamic microphones are capable of handling very loud sounds without experiencing distortion.
• Since the sound waves have to cause the vibration of the diaphragm and the voice coil, they are good for vocals or horned instruments.

Cons

• They are not good for quiet or far sounds.
• Due to aforementioned reasons, although dynamic microphones are good at picking up on vocals or horned instruments, they struggle with some stringed instruments as a result of their limited high frequency detail.
• Since a dynamic microphone must contain a magnet, it is difficult to make them small. Therefore, this might cause issues with mounting options.

Condenser Microphones

Similarly to dynamic microphones, sound waves also impact a diaphragm and cause it to vibrate. However, in this scenario, the diaphragm is mounted just in front of an electrically-charged backplate. The vibrations of the diaphragm cause a change in the electrical field, inducing an electrical current which corresponds with the sound.

Pros

• Due to the absence of a voice coil, the sound waves in a condenser microphone only have to move the diaphragm. This is especially useful for picking up on high frequencies in detail. In turn, this makes them more useful for mic'ing stringed instruments, pianos, percussion and softer vocals.
• Since condenser microphones typically have a higher output than dynamic microphones, they are much better at picking up far or quiet sound sources.
• Condenser microphones do not require a magnet, therefore they can be made incredibly small, drastically increasing their mounting options and decreasing the visibility of the microphone.

Cons

• Condenser microphones often must be powered by phantom power to operate. There will rarely be a condenser microphone which runs on an internal battery.
• Due to the sensitivity of the electrical components in a condenser microphone, they are prone to being overloaded by very loud sounds, causing distortion or even damage to the microphone.

Frequency Response

What does frequency response mean? Frequency response essentially entails how a sound is heard via the range of frequencies (or pitches) that a microphone can reproduce. Some microphones may also amplify certain frequencies of sound and soften others for specific purposes.

Flat Response

A microphone with flat response responds equally to all frequencies. This is represented by a relatively straight line across a frequency response diagram. With flat response microphones, the sound remains original and unchanged, making it ideal for orchestras or acoustic instruments.

Shaped Response

A microphone with shaped response is more sensitive to certain frequency ranges than others. For example, a kick drum mic may have a larger frequency response on the lower end of the frequency spectrum, which assists it with picking up that sound in more detail.

Which one is better?

It is subjective whether a flat response or shaped response microphone is better and heavily depends on the scenario. Generally, a shaped response microphone is better for vocals as it increases clarity of the voice.

Some microphones might have the option to change between flat response and shaped response, usually in the form of a low frequency roll-off switch. A low frequency roll-off might be useful to alleviate background noise.

Polar Patterns and their Uses

Polar patterns show how far and in which direction sound is picked up from a certain microphone. This is important to factor in as your needs can differ from scenario to scenario. Choosing the microphone with the right polar pattern ensures the reduction of background noise and the enhancing of noise relevant to the recording.

Omnidirectional

Microphones may be omnidirectional. As its name infers, an omnidirectional microphone picks up sound from 360 degrees equally. On an polar pattern, an omnidirectional microphone will take the shape of a sphere.

This is useful when picking up something like a group of people sat around a table, but shows its weakness when it is intended to pick up a single source.

Unidirectional

Unidirectional microphones pick up sound from one direction with more sensitivity than other directions. This results in less background noise being picked up and reduces the risk of feedback. 

Unidirectional microphones have many polar patterns, the most popular of which being the cardioid microphone, named after its diagrammatical appearance of a heart.

The cardioid microphone is very sensitive to sounds in front of the it, but less sensitive to sounds behind it. The pickup angle of a cardioid microphone is 130 degrees, which is useful as it can accommodate 2 speakers or one speaker which moves around. 

The super cardioid microphone is similar to the cardioid, however, it is not only narrower (with a pickup angle of 110 degrees) but also picks up a bit of sound behind the microphone. This may be useful when there is background noise that could interfere with the recording and can minimise the risk of feedback. 

However, this requires the user to stay more within the range of the microphone and does not typically allow for multiple users.

Bidirectional

Finally, bidirectional microphones pick up sound from two directions (the front and the rear of the microphone). They tend to have a narrow pickup angle. Due to its ability to pick up sounds from the front and back, this might be useful in a podcast scenario where two speakers are sitting opposite.