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Live Sound > Basic PA/AC 3 Phase/Cables > Flashcards

Basic PA/AC 3 Phase/Cables Flashcards

1
Q

7 things to create basic PA

A
  1. AC power
  2. Input Device
  3. Mixer or Board
  4. EQ
  5. Crossover
  6. Power Amp
  7. Speaker
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2
Q

AC Power

A

This is first because without this, nothing else works

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3
Q

Input Device

A

Typically microphone, instrument, laptops, DI box

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4
Q

Board/Mixer (B)

A

Puts all the input devices toward the output (bus) and brings the input devices to line level

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5
Q

Graphic EQ (E)

A

Change level of frequency that flows to next component

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6
Q

Instead of increasing what you want, you might want to

A

Cut what you don’t want

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7
Q

Crossover (CR)

A

Basic concept of separating frequency to feed frequency specific speakers; feed high frequencies to the tweeters, and low frequencies to the subwoofers

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8
Q

Power Amp (A)

A

Increase line level to speaker level

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9
Q

Speakers (S)

A

Obvious lol

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10
Q

After AC power and Input device, how can BE CRAS help you remember basic PA?

A

AC power and Input device are first two things in PA signal flow; afterward, B is board/mixer, E is graphic EQ, CR is crossover, A is power amp, and S is speaker

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11
Q

Single phase AC

A

Single source of alternating current, and is the type of current households receive

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12
Q

3 elements of single phase power

A

1 hot, 1 ground, 1 neutral

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13
Q

On two hots in a household coming from two separate breaker lines, what’s the vAC?

A

240vAC

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14
Q

On two hots in a household coming from the same breaker lines, what’s the vAC?

A

0vAC

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15
Q

IEC

A

International Electrical Connector

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16
Q

What is IEC and where is it commonly seen?

A

It’s a standard male and female connector used in cables for electrical devices such as computers, laptops, printers, etc

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17
Q

PowerCon

A

SOLID BLUE; has a locking device; most commonly used for entertainment system power distribution

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18
Q

3 phase AC

A

3 separate sources of alternating current

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19
Q

5 elements of 3 phase power

A

3 hots, 1 neutral, 1 ground

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20
Q

What are the colours of 3 hots in 3 phase power?

A

Black, blue, red

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21
Q

What is the vAC from hot to hot in 3 phase power?

A

208vAC

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22
Q

Why hot to hot in 3 phase power 208vAC and not 360vAC?

A

Because when one phase is at it’s peak (120vAC), the other two phases are only at 88vAC. So 88vAC+120vAC=208vAC

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23
Q

Feeder cable

A

Connects main power from venue to the AC Distro using camlock connectors

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24
Q

How many amps in each feeder cable?

A

400amps

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25
Q

Why must you be careful when measuring current in feeder cables?

A

Because 400amps will surely kill you

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26
Q

What provides AC power for all audio equipment in Live Sound?

A

3 phase AC Distro

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27
Q

Green feeder cable to White feeder cable vAC?

A

0vAC

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28
Q

Green feeder cable to Black, Red, or Blue?

A

120vAC

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29
Q

White feeder cable to Black, Red, or Blue?

A

120vAC

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30
Q

Black feeder cable to Red or Blue?

A

208vAC

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31
Q

Red feeder cable to Blue?

A

208vAC

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32
Q

Nema L21-30

A

Locking, 120/208 volt, 30 amp, 4 pole, 5 wire connector, 3 phase

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33
Q

Improper grounding can create a __________

A

Lethal hazard

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34
Q

Ground

A

A conducting connection, whether intentional or accidental between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth

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35
Q

Earth grounding vs Equipment grounding

A

Earth grounding: intentional connection from a circuit conductor, usually the neutral to a ground electrode placed in the earth
Equipment grounding: to ensure that operating equipment within a structure is properly grounded

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36
Q

Ground loops

A

Duplicate ground paths form the equivalent of a loop antenna, which very efficiently pick up interference currents; lead resistance transforms these currents into voltage fluctuation - which is noise that becomes part of the program signal
Ground reference in the system is no longer a stable potential

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37
Q

Ground loops can occur when _______

A

There is a shared audio ground path, from two or more different earth ground potentials

There is more than one ground connection path between two pieces of equipment

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38
Q

Every audio cable that we use has a g_______

A

Ground

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39
Q

What should you NEVER REMOVE when trying to get rid of a ground loop?

A

NEVER REMOVE AC GROUND/EARTH GROUND

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40
Q

What does removing AC/Earth ground risk??

A

It places the artist at risk for electrical shock by causing the artist to become the earth ground (people have died on stage because of this)

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41
Q

What can you use to get rid of Ground Loops?

A

A DI box; use ground lift switch on it

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42
Q

+4dBu to dBv/vAC?

A

1.2dBv / 1.2vAC

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43
Q

-10dBu to dBv/vAC?

A

0.3dBv / 0.3vAC

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44
Q

Two common operating line levels

A

+4dBu & -10dBu

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45
Q

Why must we match operating line levels between output of one component and input of another component?

A

It’s all about attaining proper gain-staging; it is necessary to set an input sensitivity of the device that matches the output sensitivity of the connected output

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46
Q

What component inside an analog splitter system blocks DC?

A

Transformer

47
Q

Every time you add a console to an analog split, the signal decreases or increases to each console?

A

Decreases

48
Q

Standard color for neutral in single phase power in the US?

A

White

49
Q

Pin 1 on XLR

A

Ground/Shield

50
Q

IECs supply what conductors?

A

Ground, Neutral, Hot

51
Q

Amount of active crossover points used on Club PA

A

1

52
Q

Standard color for ground in single phase power in the US?

A

Green / bare copper

53
Q

Can you change a crossover point on a passive crossover?

A

No

54
Q

Standard color for hot in single phase power in the US?

A

Black

55
Q

What type of solo splits before the fader?

A

Pre Fader Listen

56
Q

Pin 3 on XLR

A

Negative/Cold

57
Q

Mic pre must be _______ for it to function at optimal level with the microphone

A

10 times the output impedance of the mic

58
Q

Voltage supplied at a standard American wall outlet?

A

120vAC

59
Q

Splitter system that loses no mic signal while splitting?

A

Digital

60
Q

Pin 2 on XLR

A

Positive/Hot

61
Q

What are NEMA L21-30 cables typically used for?

A

High-density rack system connections to the rack power bus where 120/208 volt, 30 amp, three phase service is provided

62
Q

Pre-Fader

A

For the monitor to be heard by the artist

63
Q

Pre-Fader Listen

A

Soloing - also used to adjust input levels on the channel

64
Q

Post-Fader

A

For effects to be heard by everyone

65
Q

After-Fader Listen

A

Soloing

66
Q

Hi shelving

A

Boosts or cuts high frequency

67
Q

Peaking EQs

A

Hi Mid and Low Mid

You choose frequency that you can cut/boost

68
Q

Low shelving

A

Boosts or cuts low frequency

69
Q

Aux used for AFL

A

Aux 5 & 6 are post

70
Q

Outboard Graphic EQ

A

Used to cut unwanted frequencies to make speakers sound good in Live Sound
20Hz-20kHz, 31 bands

71
Q

Outboard Graphic EQ octaves

A

Every 3 sliders is an octave from 2nd slider

There are 10 octaves

72
Q

Outboard EQ for Monitor

A

Used to cut out feedback

73
Q

Importance of crossover

A

Woofer cones need to move 2” to produce sound aka. can’t move fast enough to produce highs, so the voice coil will overheat = speakers on fire
Tweeter cones need to move 1/32” to produce sound, so if you send too low of a frequency, it will break it/blow it

74
Q

Active crossover

A

Works at line level
Variable crossover points
Requires AC power
Does not display insertion loss

75
Q

Passive crossover

A

Works at speaker level
Not variable - fixed crossover points
Does not require AC power
Creates insertion loss

76
Q

Active crossover point

A

80Hz:
20Hz - 80Hz (Low)
80Hz - 20kHz (High)

77
Q

Power amps 3 modes

A
  1. Stereo
  2. Dual mono
  3. Bridge mono
78
Q

Power amp: Stereo

A

2 in & 2 out

can be left/right, but Club PA sends hi/low, then 2 speakers for 2 hi/2 low

79
Q

Power amp: Dual mono

A

1 in & 2 out

80
Q

Power amp: Bridge mono

A

1 in & 1 out

81
Q

Speaker cables

A

Speakon connectors: NL2, NL4, NL8

82
Q

Power supply converts what voltage

A

AC to DC

83
Q

In Club PA, what type of connectors are used for the speaker wires?

A

NL4

84
Q

Power amps are turned on first, last, anytime?

A

Last

85
Q

Power amps are turned off first, last, anytime?

A

First

86
Q

Passive splitter needs power. T/F

A

False - Passive = no need for power

87
Q

Active splitter needs power. T/F

A

True - Active = needs power

88
Q

Transformers are active. T/F

A

False - they are passive

89
Q

Stereo PA has 2 high boxes, 2 low boxes, and a stage monitor. How many amp channels are needed to power them?

A

5

90
Q

Power supply accepts what type of voltage

A

AC

91
Q

Power supply provides what type of voltage

A

DC

92
Q

Concept of -10 and +4 when dealing with an equipment’s specifications?

A

Output levels vs Input Sensitivity

93
Q

Snakes

A

Cables used to connect all microphones onstage to the mixing console at FOH
Could be over 100ft apart

94
Q

Passive splitters

A

Nothing more than an XLR “Y” cable (splitter)
Single end of cable: Microphone on stage (female)
Double end of cable: to FOH console (male), to Monitor console (male)

95
Q

Stage box

A

Mics on stage plug into stage box

W-2 connects to splitter

96
Q

Patch master

A

W-2 ports with XLR snake head outputs that will plug into splitter inputs

97
Q

W-2 multi-pin connector

A

Comes in two sizes:
W1 - 39 solder type contacts, used for cables with 12 pairs or fewer
W2 - 61 solder type contacts, used on 16 and 20 pair cables
Male and female

98
Q

Transformer isolated splitters

A

Level cuts in half when split
Microphone input in and will split
One path will go through a transformer and then to the transformer isolated output
Other path will go straight to the direct output

99
Q

Transformer isolated splitter turns ratio

A

1:1, which is why it’s called isolated

100
Q

Transformers pass and block which voltages?

A

Pass AC audio signal, but will block DC voltage in either direction

101
Q

Do transformer isolated splitters affect impedance?

A

No, it does not lower impedance, therefore it does not allow for an increased number of splits over parallel splitting

102
Q

Why would a transformer isolated splitter need a direct out?

A

Because this direct leg will need to go to the console that will be providing phantom power (vDC)

103
Q

W-4 MASS connector

A

Asexual connectors with equal number of pins and sockets

176 pin MASS connector

104
Q

W-4 to fan out

A

One end of the W-4 will have XLR snakes (fan out)

105
Q

In single phase power, why would there be two hots? What is the voltage and colours?

A

There would be two hots on two different breakers/circuits. Voltage between two different hots is 240vAC, between two hots on the same circuit is 0vAC, and the two colours are black and red.

106
Q

Three phase power is out of phase by how many degrees?

A

120 degrees

107
Q

120 degree offset in three phase power causes how much cancellation in voltage?

A

32vAC resulting in 208vAC total

120+120-32

108
Q

In TRS, which sections are ground, negative, positive?

A

Tip - positive
Ring - negative
Sleeve - ground

109
Q

What makes a balanced cable balanced?

A

The positive and negative waveforms are equal energy, on separate wires, and are isolated

110
Q

In TS, which sections are ground, negative, positive?

A

Tip - positive

Sleeve - negative + ground

111
Q

What makes an unbalanced cable unbalanced?

A

The negative waveform and ground are on the same wire, therefore are not isolated

112
Q

U in dBU

A

Undetermined, undefined

113
Q

Why do we lose level after every analog split?

A

Because with every new split, we are lowering the total resistance, and the mic pre must be 10 times the output impedance of the microphone. So with lowered impedance, mic level drops, and now we have to crank up the mic pre even higher.

114
Q

On an XLR, which pin carries phantom power?

A

Pin 1

Live Sound (7 decks)

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