Introduction to microphones and techniques Microphones convert ACOUSTICAL energy (sound waves) into ELECTRICAL energy (audio signal)

Types of microphones Condenser Microphones Also referred to as capacitor or electrostatic Require a power source (Battery or +48v) Audio signal is stronger than that of a dynamic mic Have a flatter FREQUENCY RESPONSE than dynamics More sensitive and responsive than dynamics NOT ideal for high-volume work as their sensitivity makes them prone to distort

How Condenser Microphones work

Types of Microphones Dynamic Microphones Do not require an external power source Better suited to handling high volume levels Weaker audio signal than condenser mics Do not usually have the same flat frequency response as condensers; instead have a tailored frequency response for particular applications A “backwards speaker”

How a dynamic microphone works

Suggest some uses Taking into consideration the characteristics of each microphone type, suggest practical applications for: Dynamic Microphones Condenser Microphones Situations where EITHER type could be used

Directional Properties Describes sensitivity to sound from various directions Divided into 3 main categories: Omni-directional Omni meaning “all” or “every” Unidirectional from predominantly one direction Bidirectional Two opposite directions Graphically represented on a graph, known as a Polar-Pattern

Common Polar Patterns

Omni-directional Captures sound equally from all directions Capturing ambient noise; Situations where sound is coming from many directions; Situations where the mic position must remain fixed while the sound source is moving. Although omni-directional mics are very useful in the right situation, picking up sound from every direction is not usually what you need. Omni sound is very general and unfocused - if you are trying to capture sound from a particular subject or area it is likely to be overwhelmed by other noise.

Cardioids Cardioid means "heart-shaped", which is the type of pick-up pattern these mics use. Sound is picked up mostly from the front, but to a lesser extent the sides as well. Emphasizing sound from the direction the mic is pointed whilst leaving some latitude for mic movement and ambient noise. The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioid.

Hyper-Cardioid This is exaggerated version of the cardioid pattern. It is very directional and eliminates most sound from the sides. Due to the long thin design of hyper-cardioids, they are often referred to as shotgun microphones. Isolating the sound from a subject or direction when there is a lot of ambient noise; Picking up sound from a subject at a distance. Can sound un-natural as no “space” is present.

Bi-directional Uses a figure-of-eight pattern and picks up sound equally from two opposite directions.(- and +) As you can imagine, there aren't a lot of situations which require this polar pattern. One possibility would be an interview with two people facing each other (with the mic between them). Used as the “side” microphone in the “mid-side” technique.

Microphone Sensitivity Sensitivity expresses the microphones ability to convert acoustical energy into electrical energy. Measurements are usually done using a certain SPL, namely ONE PASCAL, which is equal to 94dBSPL. This information is usually available in the user manual for the microphone. If not, a test can be conducted using 94dB of white noise.

How to Calculate sensitivity If a sensitivity of -33dBv is given we use the following formula: 10 (dBV/20) 10 (-33/20) = 0.023 = 23mV

How to Calculate Sensitivity If a transform factor of 23mV/Pa is given, use the following formula. REMEMBER 23mV = 0.023V 20log(voltage) 20log(0.023) =-33dBV

Sensitivity The sensitivity rating tells us how sensitive the microphone is to SPL’s. The HIGHER the dBV value, the more sensitive the microphone is. Generally, the greater the pressure sensitivity the more sensitive the microphone is to quieter sounds. Also the greater the signal will be produced relative to noise in cables, etc. This means that less gain will be needed to bring the electrical signal up to “line level (0dBV), therefore less NOISE will be created from the power amp.

Frequency Response The Frequency Response of the microphone indicates the level in dB of frequencies that it can capture. This is usually demonstrated using a Frequency Response graph like the one below.

What can we tell from the graphs?

Frequency Response It is important that we look at this data before choosing a microphone for a specific purpose. The frequency of the audio to be captured must be understood in order to pick the right microphone. Eg. A Bass Drum would benefit from a microphone that has better response in the lower frequencies / bass frequencies.

Research Task In groups, you are to decide which microphones to use for a range of activities: Vocal Recording Snare Drum (metal drummer) Bass Guitar through an amp (jazz player) Violin Kick Drum Choir (multiple voices) Using the technical data in the manual, make notes about the polar pattern, sensitivity and frequency response. Select a spokesperson for the group and share your findings with the class.