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MUSIC 109 > Microphones > Flashcards

Microphones Flashcards

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1
Q

Which microphone design works on the electrostatic principle?

A

Condenser

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2
Q

Microphone

A

A transducer which changes
acoustical energy into electrical
impulses

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3
Q

Dynamic Microphones

A

An electrical signal is produced by moving a conductor within a magnetic field
(Electromagnetic Theory of Induction)

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4
Q

2 Basic Designs of Dynamic Microphones

A

Moving Coil

Ribbon

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5
Q

Which microphone needs a special cable between the mic and power supply?

A

Tube type condensers
(Cable contains extra conductors which carry the voltage separate from the
audio)

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6
Q

Phantom Power

A

The audio and DC supply voltage travel

in the same conductors (48 Vdc)

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7
Q

Electret-Condenser

A

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

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8
Q

Polar Charts

A

A graph showing a mics relative sensitivity to sounds

originating at various locations

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9
Q

Omni-Directional

(Pressure) Microphone

A

Reacts equally to all sound sources, regardless of direction

Contains a diaphragm and a sealed enclosure

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10
Q

Bi-Directional Microphone

Pressure Gradient

A

✤ 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)

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11
Q

Uni-Directional Microphone

Phase Shift

A

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°

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12
Q

Specialty Microphones

A

Parabolic Reflector
Boundary
Lavalier
Shotgun

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13
Q

Direct Box

A

Direct Injection (DI) box

✤ Reduces line level source to mic
level
✤ Change a high-Z source to low-Z
✤ Isolation of audio signals

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14
Q

Frequency Response

A

On axis frequency response curve is the measurement of the output over the audible range at a constant input
✤ Output vs. frequency

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15
Q

Proximity Effect

A

✤ 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)

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16
Q

Sensitivity

A

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)

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17
Q

Typical ratings for Sensitivity

A 
✤ Condenser = -45 dBm per Pa
✤ Dynamic = -55 dBm per Pa
      or
✤ Condenser = -65 dBV per µbar
✤ Dynamic = -75 dBV per µbar
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18
Q

Microphone Impedance

A

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

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19
Q

Low-Z Mic Impedance

A

50 ohms, 150, or 250

Low-Z mics are fairly insensitive to electrostatic noise

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20
Q

High-Z Impedance

A

20k ohms to 50k

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21
Q

Decca Tree

A

Left and right mic pair placed 3 feet apart, and a third mic is placed 1.5ft in front and panned to the center

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22
Q

Ambient Miking

A

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

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23
Q

Stereo Miking Technique

A

The use of two microphones in order to obtain a coherent stereo image.

24
Q

4 Fundamental Stereo Miking Techniques

A

Spaced Pair
X/Y
M/S
Decca Tree

25
Q

Spaced Pair

A

Can be placed in front of an instrument or ensemble (in a left/right fashion) to obtain an overall stereo image.

26
Q

X/Y

A

An intensity-dependent system that uses only the cue of amplitude to discriminate direction. Facing at angles from 90 to 135 degrees

27
Q

M/S

A

Similar to X/Y technique, however, it requires the use of an external transformer, active matrix, or software plug-in in order to work

Two mics, cardioid that faces sound source, S (side) oriented sideways at 90 degrees and 270 degrees

28
Q

Ribbon Mic

A

Works on principle of electromagnetic induction

29
Q

Dynamic Mic

A

Uses electromagnetic induction

30
Q

Theory of Electromagnetic Induction

A

States that 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 that metal

31
Q

Specialty Microphones

A

Shotgun
Parabolic Reflector
Boundary
Lavalier

32
Q

Unbalanced Lines

A

A single conductor caries the positive (in phase) signal
✤ Shield carries the negative (return) signal to ground
✤ Susceptible to picking up noise

33
Q

Balanced Lines

A

Audio signal is carried by two conductors (positive and negative)
✤ Neither is tied to ground
✤ Ground is carried by the outer shield

34
Q

Sensitivity Refrences

A

10 dynes/cm2 = 10 ubars = 1 Pa = 94 DBSPL

1 dynes/cm2 = 1 ubar = 0.1 Pa = 74 DBSPL

35
Q

In a Moving Coil Microphone, attached to the diaphragm is the ______ which is suspended in a high flux magnetic field

A

voice coil

36
Q

resistive damping felt

A

achieve flat frequency response

37
Q

capacitance determined by

A

composition and surface areas of plates (fixed value)
dielectric or substance between the plates, air (fixed)
distance between the plates (variable with changing air pressure)

38
Q

In Condensor microphone, capsule consists of 2 thin plates

A 
one movable (diaphram)
one fixed (back plate)
39
Q

In condensor microphones, when distance between plate decreases

A

capacitance increases

vise versa

40
Q

FET

A

field effect transitor

41
Q

electret-condensor will stay charged for

A

about 10 years

predicted 30-100 years for capsule sensitivity to drop 3 dB

42
Q

directional characteristics

A

humans have selective hearing, even with distractions

mics do not and pick up and transmit anything in their path

43
Q

Anechoic Chamber

A

reflection free environment

used for testing mics

44
Q

potentiometer

A

ability to create many variable patterns

45
Q

cardioid + cardioid=

A

omni-

46
Q

cardioid - cardioid=

A

Bi-

47
Q

cardioid - cardioid (lesser value)=

A

super- to hyper-

48
Q

cardioid + 0 =

A

Cardioid

49
Q

In High Z, as cable length increases, so does its capacitance. what is the formula

A

f=1/2(pie)RC

50
Q

common mode rejection

A

eliminating any noise at the input transformer

51
Q

pin 1 in balanced lines is

A

always the shield

52
Q

never use more than how many microphones

A

2

53
Q

3-1 rule

A

every unit of distance measured between a mic should be at least 3 times unit of measure of the first mic

54
Q

2-1 Rule

A

every unit of distance measured between a mic should be at least 2 times the unit of measure of the first mic

55
Q

make sure mic lines are properly

A

shielded
balanced
terminated

MUSIC 109 (7 decks)

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