Microphone – a transducer that
converts one type of energy (sound waves) into another corresponding form
of energy (electric signal).
The overall sound is only as good as the weakest link in the signal path.
The good rule:
Good musician + good acoustics + good mike + good placement = good sound
Dynamic microphones use electromagnetic induction to generate an output signal.
In theory: whenever an electrically conductive metal cuts across the flux lines of a magnetic field, a current of a specific magnitude and direction will be generated within the metal.
Similar principle to dynamic mic except that the diaphragm is made of extremely thin aluminum.
Because the diaphragm is light (compared to the coil of the dynamic mic), a step-up transformer must be used to bring the output impedance up from 2 ohms to the acceptable range of 150 – 600 W.
Operate on electrostatic instead of electromagnetic
principle. The capsule consists of two thin plates, one fixed and one movable.
The plates form a capacitor or condenser. A condenser is an electric device
capable of storing an electric charge.
Because the diaphragm’s output is of extremely high impedance, it is fed through an impedance conversion amplifier which is placed into the circuit at close proximity to the diaphragm in order to prevent hum and noise. This is why condenser microphones require a power supply voltage in order to operate.
Electret-Condenser microphones feature a permanently stored polarizing charge on the microphone’s back-plate or diaphragm. Since the capsule still has a very high output impedance, phantom power or n external power supply is still required.
Directional response refers to the mic’s output level at various angles of incidence with the respect to the front side of the mic.
Omnidirectional polar response – pressure sensitive device (mic) responsive to sound waves from all directions.
Directional microphones are pressure-gradient. They discern pressure differences coming from different directions.
Bi-directional microphone is one that is purely pressure gradient. Many ribbon mics are bi-directional.
Some very commonly known and used patterns are:
|Cardioid||The cardioid pattern, sometimes called unidirectional, looks like an upside-down heart. These highly directional microphones pick up sound from the front and reject sound from the rear. Thusly, this pattern is a favorite for live situations.||
A highly directional microphone whose minimum sensitivity begins at 110 degrees. Microphones called "line" or "shotgun"microphones which are used often on sound stages have a hypercardioid pattern.
|Omnidirectional||The omnidirectional pattern picks up sound equally from all directions. This pattern is an excellent choice for a “live” recording feel, acoustic bass and surround sound applications.||
Omni, Cardioid or Hypercardioid
The bidirectional microphone pattern picks up form the front and rear equally and eliminates sound from the left or right side. This mic is great when two people are facing each other while performing or in the case of a panel discussion when a performer or lecturer is interacting with the audience. A figure-8 polar pattern is an excellent esample of a bidirectional microphone.
Omni, Cardioid or Bidirectional
|Hemispheric||Also known as a "half-omni" pattern. A PZM zone pressure microphone is the most common example of a hemispheric pattern microphone. The hemispheric pattern picks up sound in the shape of a half-sphere. For this reason, PZM mics are often set on the studio glass at about 5 to 6 feet in height. This enable the hemispheric pattern to capture sound from floor to ceiling in a three-dimensional way.||
|Supercardioid||The supercardioid is similar to the cardioid except that this pattern adds sensitivity to the rear. This microphone is useful for picking up the direct sound and some of the reflections from the rear of the microphone. The supercardioid picks up a little more than 180° from the front. The supercardioid pattern pick up a very broad picture from the front. From the rear, the microphone picks up a narrow beam of sound waves. This microphone is very useful when recording a large horn section or vocal ensemble.||
Shure Beta 58
|Subcardioid||A highly directional microphone whose minimum sensitivity begins at 100 degrees.||
|Spherical|| The KU 100 dummy head is a binaural stereo
microphone. It resembles the human head and has two microphone capsules
built into the ears. When listening through high-quality headphones it
gives the illusion of being right at the scene of the acoustic events.
When using the KU 100 dummy head, the binaural stereo experience moves
the listener into the scene of the original performance, in contrast
to other space-related recording techniques, where the acoustic event
is moved to the listener. The dummy head is also used in many industrial
applications as a measuring device, for example in acoustic research.
The KU 100 can be operated with typical 48 V phantom powering, or from
an external power supply unit, or from the built-in battery. At the bottom
ofthe unit is a switch for the different power supply modes, as well
as connectors for balanced and unbalanced output signals. Inside the
head are additional switches for 10 dB attenuation and the high-pass
Schoeps MK-21 capsule and CCM21 microphone
For amzing discussions on
microphones, microphone images, sound clips, connectors and patterns, please
Vintage microphones history
Coutant.org (This is an amazing site with pictures and information)
Response is measured against the standard 20 - 20,000 Hz Frequency range.
Flat response means equal output at all levels.
Low freq. (3 – 25 Hz) can cause rumble. Use a shock mount to eliminate or reduce effect.
Proximity effect is an increased bass response when sound source is closer than 1’ to the mic.
Transient response – how quickly does mic react to the sound wave.
Dynamic mics, because they have large diaphragms, have slow responses producing rugged, gutsy and less accurate sound than smaller diaphragm mics.
Ribbon mics have very small diaphragms producing a very fast and accurate response.
Sensitivity rating – is the output level in volts that a microphone will produce given a specific and standardized input level (rated in dB). The measurement specifies the amount of amplification needed to raise the mic’s signal to line level (-10 or +4).
The higher the mic’s sensitivity level, the higher it’s output level.
EQUIVALENT NOISE RATING – the device’s electrical self-noise.
Overload Characteristics – at what point does the input level cause distortion. Condenser mics are very sensitive and therefore usually have a built in pad.
Dynamic mics are low impedance devices that use a built-in step-up transformer. These mics cables often pickup electrostatic noise. They use unbalanced lines.
Used because most mics can’t put enough signal for line level. A mic preamp is used to boost the signal (30 – 60 dB) to an acceptable level.
Most preamps today are very inexpensive and sound great. Most offer features such as:
Input gain, high-pass filtering and phantom power.
Phantom power supplies a positive DC supply voltage of 48+ V
to both conductors
(pins 2 and 3) of a balanced mic line. Most condenser mics need phantom power in order to work correctly.
All mics have a distinctive sound based on their design.
Distant placement – more than 3’ from source.
Close placement – 1’ – 3’ from source.
Leakage is defined as when sound from one instrument is picked up by a nearby microphone. Happens often with horn sessions and live rhythm section recordings.
Techniques used in avoiding leakage:
Whenever individual instruments are being recorded close or semi-close, it’s generally wise to follow the 3:1 distance rule. The rule states that in order to maintain phase integrity … for every unit of distance between a mic and its source, a nearby mic (or mics) should be separated by at least three times that distance.
Accent mic – a mic placed by an instrument or section, inside of a larger ensemble, in a close but not so close position as to record an unnatural sound. Used to add presence to those instruments without changing the balance or spatial relationship of the overall recording.
Ex. Placing a mic close to the double-reed section in an orchestra.
Ambient mic is placed at a distance so that the room sound is more prominent than the source sound.
Reasons for use of ambient mics:
The use of two microphones in one of three ways:
D.I. (direct injection) box serves to interface in the following ways: