Microphones Flashcards
(55 cards)
Which microphone design works on the electrostatic principle?
Condenser
Microphone
A transducer which changes
acoustical energy into electrical
impulses
Dynamic Microphones
An electrical signal is produced by moving a conductor within a magnetic field
(Electromagnetic Theory of Induction)
2 Basic Designs of Dynamic Microphones
Moving Coil
Ribbon
Which microphone needs a special cable between the mic and power supply?
Tube type condensers
(Cable contains extra conductors which carry the voltage separate from the
audio)
Phantom Power
The audio and DC supply voltage travel
in the same conductors (48 Vdc)
Electret-Condenser
The polarizing charge is stored permanently within the diaphragm or
back plate
✤ No form of powering is required to charge the diaphragm
✤ The pre-amp will still require power
Polar Charts
A graph showing a mics relative sensitivity to sounds
originating at various locations
Omni-Directional
(Pressure) Microphone
Reacts equally to all sound sources, regardless of direction
Contains a diaphragm and a sealed enclosure
Bi-Directional Microphone
Pressure Gradient
✤ Equally sensitive to sounds originating 0° and 180°
✤ Least sensitive to sounds originating from 90° and 270°
✤ Both sides of the diaphragm are exposed
(Figure-8)
Uni-Directional Microphone
Phase Shift
Known as a Cardioid, due to its “heart” shape
✤ Most sensitive at 0°
✤ As the mic is rotated through a 360° arc the level continually decreases until 180° then increases again from 180° to 360°
Specialty Microphones
Parabolic Reflector
Boundary
Lavalier
Shotgun
Direct Box
Direct Injection (DI) box
✤ Reduces line level source to mic
level
✤ Change a high-Z source to low-Z
✤ Isolation of audio signals
Frequency Response
On axis frequency response curve is the measurement of the output over the audible range at a constant input
✤ Output vs. frequency
Proximity Effect
✤ A build up in the bass response of a directional mic used at close proximity
(Many directional microphones have a hi-pass filter to compensate for the proximity effect)
Sensitivity
Tells about the efficiency of converting acoustic energy to electrical energy at a specific standardized input level
Tells the degree of amplification required to raise the signal to operating line level (-10 dBV or +4 dBm)
Typical ratings for Sensitivity
✤ Condenser = -45 dBm per Pa
✤ Dynamic = -55 dBm per Pa
or
✤ Condenser = -65 dBV per µbar
✤ Dynamic = -75 dBV per µbarMicrophone Impedance
The opposition to current flow- measured in ohms
Output or source impedance: How easily the audio power will flow from the source.
Input or load impedance: How much power the input will tend to draw
Low-Z Mic Impedance
50 ohms, 150, or 250
Low-Z mics are fairly insensitive to electrostatic noise
High-Z Impedance
20k ohms to 50k
Decca Tree
Left and right mic pair placed 3 feet apart, and a third mic is placed 1.5ft in front and panned to the center
Ambient Miking
Places the pickup at such a distance that the reverberant or room sound is equally more prominent than the direct signal. The ambient pickup is often a cardioid stereo pair or crossed figure-8 (Bumlein) pair that can be mixed into a stereo or surround-sound production to provide a natural reverb and/or ambience
Stereo Miking Technique
The use of two microphones in order to obtain a coherent stereo image.
4 Fundamental Stereo Miking Techniques
Spaced Pair
X/Y
M/S
Decca Tree
