Basic PA/AC 3 Phase/Cables Flashcards
1
Q
7 things to create basic PA
A
- AC power
- Input Device
- Mixer or Board
- EQ
- Crossover
- Power Amp
- Speaker
2
Q
AC Power
A
This is first because without this, nothing else works
3
Q
Input Device
A
Typically microphone, instrument, laptops, DI box
4
Q
Board/Mixer (B)
A
Puts all the input devices toward the output (bus) and brings the input devices to line level
5
Q
Graphic EQ (E)
A
Change level of frequency that flows to next component
6
Q
Instead of increasing what you want, you might want to
A
Cut what you don’t want
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
8
Q
Power Amp (A)
A
Increase line level to speaker level
9
Q
Speakers (S)
A
Obvious lol
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
11
Q
Single phase AC
A
Single source of alternating current, and is the type of current households receive
12
Q
3 elements of single phase power
A
1 hot, 1 ground, 1 neutral
13
Q
On two hots in a household coming from two separate breaker lines, what’s the vAC?
A
240vAC
14
Q
On two hots in a household coming from the same breaker lines, what’s the vAC?
A
0vAC
15
Q
IEC
A
International Electrical Connector
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
17
Q
PowerCon
A
SOLID BLUE; has a locking device; most commonly used for entertainment system power distribution
18
Q
3 phase AC
A
3 separate sources of alternating current
19
Q
5 elements of 3 phase power
A
3 hots, 1 neutral, 1 ground
20
Q
What are the colours of 3 hots in 3 phase power?
A
Black, blue, red
21
Q
What is the vAC from hot to hot in 3 phase power?
A
208vAC
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
23
Q
Feeder cable
A
Connects main power from venue to the AC Distro using camlock connectors
24
Q
How many amps in each feeder cable?
A
400amps
25
Why must you be careful when measuring current in feeder cables?
Because 400amps will surely kill you
26
What provides AC power for all audio equipment in Live Sound?
3 phase AC Distro
27
Green feeder cable to White feeder cable vAC?
0vAC
28
Green feeder cable to Black, Red, or Blue?
120vAC
29
White feeder cable to Black, Red, or Blue?
120vAC
30
Black feeder cable to Red or Blue?
208vAC
31
Red feeder cable to Blue?
208vAC
32
Nema L21-30
Locking, 120/208 volt, 30 amp, 4 pole, 5 wire connector, 3 phase
33
Improper grounding can create a __________
Lethal hazard
34
Ground
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
35
Earth grounding vs Equipment grounding
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
36
Ground loops
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
37
Ground loops can occur when _______
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
38
Every audio cable that we use has a g_______
Ground
39
What should you NEVER REMOVE when trying to get rid of a ground loop?
NEVER REMOVE AC GROUND/EARTH GROUND
40
What does removing AC/Earth ground risk??
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)
41
What can you use to get rid of Ground Loops?
A DI box; use ground lift switch on it
42
+4dBu to dBv/vAC?
1.2dBv / 1.2vAC
43
-10dBu to dBv/vAC?
0.3dBv / 0.3vAC
44
Two common operating line levels
+4dBu & -10dBu
45
Why must we match operating line levels between output of one component and input of another component?
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
46
What component inside an analog splitter system blocks DC?
Transformer
47
Every time you add a console to an analog split, the signal decreases or increases to each console?
Decreases
48
Standard color for neutral in single phase power in the US?
White
49
Pin 1 on XLR
Ground/Shield
50
IECs supply what conductors?
Ground, Neutral, Hot
51
Amount of active crossover points used on Club PA
1
52
Standard color for ground in single phase power in the US?
Green / bare copper
53
Can you change a crossover point on a passive crossover?
No
54
Standard color for hot in single phase power in the US?
Black
55
What type of solo splits before the fader?
Pre Fader Listen
56
Pin 3 on XLR
Negative/Cold
57
Mic pre must be _______ for it to function at optimal level with the microphone
10 times the output impedance of the mic
58
Voltage supplied at a standard American wall outlet?
120vAC
59
Splitter system that loses no mic signal while splitting?
Digital
60
Pin 2 on XLR
Positive/Hot
61
What are NEMA L21-30 cables typically used for?
High-density rack system connections to the rack power bus where 120/208 volt, 30 amp, three phase service is provided
62
Pre-Fader
For the monitor to be heard by the artist
63
Pre-Fader Listen
Soloing - also used to adjust input levels on the channel
64
Post-Fader
For effects to be heard by everyone
65
After-Fader Listen
Soloing
66
Hi shelving
Boosts or cuts high frequency
67
Peaking EQs
Hi Mid and Low Mid
| You choose frequency that you can cut/boost
68
Low shelving
Boosts or cuts low frequency
69
Aux used for AFL
Aux 5 & 6 are post
70
Outboard Graphic EQ
Used to cut unwanted frequencies to make speakers sound good in Live Sound
20Hz-20kHz, 31 bands
71
Outboard Graphic EQ octaves
Every 3 sliders is an octave from 2nd slider
| There are 10 octaves
72
Outboard EQ for Monitor
Used to cut out feedback
73
Importance of crossover
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
Active crossover
Works at line level
Variable crossover points
Requires AC power
Does not display insertion loss
75
Passive crossover
Works at speaker level
Not variable - fixed crossover points
Does not require AC power
Creates insertion loss
76
Active crossover point
80Hz:
20Hz - 80Hz (Low)
80Hz - 20kHz (High)
77
Power amps 3 modes
1. Stereo
2. Dual mono
3. Bridge mono
78
Power amp: Stereo
2 in & 2 out
| can be left/right, but Club PA sends hi/low, then 2 speakers for 2 hi/2 low
79
Power amp: Dual mono
1 in & 2 out
80
Power amp: Bridge mono
1 in & 1 out
81
Speaker cables
Speakon connectors: NL2, NL4, NL8
82
Power supply converts what voltage
AC to DC
83
In Club PA, what type of connectors are used for the speaker wires?
NL4
84
Power amps are turned on first, last, anytime?
Last
85
Power amps are turned off first, last, anytime?
First
86
Passive splitter needs power. T/F
False - Passive = no need for power
87
Active splitter needs power. T/F
True - Active = needs power
88
Transformers are active. T/F
False - they are passive
89
Stereo PA has 2 high boxes, 2 low boxes, and a stage monitor. How many amp channels are needed to power them?
5
90
Power supply accepts what type of voltage
AC
91
Power supply provides what type of voltage
DC
92
Concept of -10 and +4 when dealing with an equipment's specifications?
Output levels vs Input Sensitivity
93
Snakes
Cables used to connect all microphones onstage to the mixing console at FOH
Could be over 100ft apart
94
Passive splitters
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
Stage box
Mics on stage plug into stage box
| W-2 connects to splitter
96
Patch master
W-2 ports with XLR snake head outputs that will plug into splitter inputs
97
W-2 multi-pin connector
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
Transformer isolated splitters
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
Transformer isolated splitter turns ratio
1:1, which is why it's called isolated
100
Transformers pass and block which voltages?
Pass AC audio signal, but will block DC voltage in either direction
101
Do transformer isolated splitters affect impedance?
No, it does not lower impedance, therefore it does not allow for an increased number of splits over parallel splitting
102
Why would a transformer isolated splitter need a direct out?
Because this direct leg will need to go to the console that will be providing phantom power (vDC)
103
W-4 MASS connector
Asexual connectors with equal number of pins and sockets
| 176 pin MASS connector
104
W-4 to fan out
One end of the W-4 will have XLR snakes (fan out)
105
In single phase power, why would there be two hots? What is the voltage and colours?
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
Three phase power is out of phase by how many degrees?
120 degrees
107
120 degree offset in three phase power causes how much cancellation in voltage?
32vAC resulting in 208vAC total
| 120+120-32
108
In TRS, which sections are ground, negative, positive?
Tip - positive
Ring - negative
Sleeve - ground
109
What makes a balanced cable balanced?
The positive and negative waveforms are equal energy, on separate wires, and are isolated
110
In TS, which sections are ground, negative, positive?
Tip - positive
| Sleeve - negative + ground
111
What makes an unbalanced cable unbalanced?
The negative waveform and ground are on the same wire, therefore are not isolated
112
U in dBU
Undetermined, undefined
113
Why do we lose level after every analog split?
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
On an XLR, which pin carries phantom power?
Pin 1
