Transcript Intro to Electronic

Intro to Electricity
What is electricity?
How is it created?
How is it transmitted?
Electricity

Electricity is a form of energy
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Generally defined as the flow of electric charge
from one place to another
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This is not entirely accurate, but the metaphor works
Two sub-atomic particles
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Protons
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Positive charge. Large relative mass
Electrons
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Negative charge. Very little relative mass
Electricity
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Electric power is created by detaching electrons
from an atom
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This leaves behind a net positive charge
This positive charge pulls electrons from neighboring
atoms and a “flow” begins
Not all atoms easily allow their electrons to break
free
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Good conductors – easily freed electrons
 Copper, aluminum, gold, platinum
Insulators – electrons are VERY hard to break free
 Most plastics, silicone rubber, porcelain, glass
Alternating current
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Voltage will change with
time
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Voltage is a “relative”
measurment
In most instances, it
happens very fast
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50 cycles per second (Hz)
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Europe and most of Asia
60 cycles per second (Hz)
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United States, some of Asia
and some South America
Alternating current
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James Clerk Maxwell
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Discovered that electricity and magnetism are two forms of the same physical phenomenon.
Maxwell’s laws
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“A changing magnetic field will produce an electric field”
“A changing electric field will produce a magnetic field”
How a generator works
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3 massive coils of wire which are caused to spin around a permanent magnet.
Coils are moving through a magnetic field and this causes electrons to begin moving
While moving from north to south, electrons flow one way. From south to north they move the other way
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Causes three phase electricity. The number of times per sec that the coil revolves will determine the frequency of the
electric current
Induced current
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As the voltage rises and falls in an AC circuit, there will be a varying magnetic field produced around
the conductor. This magnetic field will in turn produce an electric current in any conductors which
are nearby
Lighting cable, motor cable, sound power feeds, building air conditioning power…
Induces noise in sound lines
Direct current
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Often the product of a chemical reaction
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Batteries
Can be generated using an alternator
Can be converted from AC current
Voltage stays constant over time.
Ohms Law
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Voltage, current and resistance
are all related
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Voltage
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The potential charge between
two points
It is a relative measurement

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We usually measure voltage
with respect to “ground” or
“earth”
Requires a complete path
back to ground in order to
“flow”
Current
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The “flow” of electrical charge
carriers
Current Flow
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Water analogy
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Wire = hose
Voltage = water pressure
Current = flow of water
Resistance = resistance to water flow
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Kink in the hose
A larger hose connected to a smaller hose
Ohms Law
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V=IR
P=VI
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V= voltage (volts)
I = current (amps)
R = resistance (ohms)
P = power (watts)
VIRP
Ohms Law
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These two formulas allow us to relate
voltage, current resistance and power to each
other.
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If you know any 2, you can now the other 2.
Strictly speaking this is only for DC circuits
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For AC circuits, resistance is replaced with
impedance
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Takes into account capacitors and inductors
Circuits
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Series
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Electricity flows through
each component
RT=R1+R2+R3…
Circuits
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Parallel
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The current breaks up,
with some flowing along
each parallel branch and
re-combining when the
branches meet again.
1
1
1
1
 
 ....
RT R1 R2 R3
Electricity and Sound
Transducers
Audio Signals
Cables and Shielding
Sound Environments
Physical and Virtual - Working Definitions
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Physical = Sound we hear
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Physical environment of the audience / performers.
World of physics and acoustics
Virtual (electronic) = Audio Systems
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Electrical signals that are representations or facsimiles of
sounds
Technical Environment of equipment, wires and “techie”
Sound Environments
Physical and Virtual - Working Definitions
Transducers - Link Sound and Audio Environments
Equipment System
Microphone
Virtual Environment
Speaker
Audio
Performers
Physical Environment
Sound
Simple System Block Diagram
Audience/Performed
Sound Environments
Physical and Virtual - Working Definitions
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Worlds meet at “transducers”
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Transducers are devices that convert energy from one
form to another.
In the theatre:
 Convert sound to electrical signals. • Microphones
 Convert electrical signals to sound. • Speakers
Sound Environments
Physical and Virtual - Working Definitions
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Every time a transducer is used, some
information is lost
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No transducers are 100% efficient.
The sound represented will change
Clipping will occur
Audio Signals
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Microphone level
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Typically around 2mV
The signal created by a microphone and other low power input devices
Typically uses XLR connectors or ¼” TRS (Tip-Ring-Sleeve)
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Line level
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Standard voltage for signals between pieces of equipment
Ranges between .316V and 1.23V
The audio signal from CD players, DAT decks, MD players, mixers
Typically uses
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TRS also referred to as ¼” Stereo plug, ¼” Balanced
1/8” or 1/4” phone plug
1/8” TRS (mini-stereo)
RCA (cinch)
Speaker level
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Much higher voltages depending upon the power ratings of the amplifier and load
The signal from power amplifiers to loudspeakers
Typically uses
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Speakon connectors
Twist lock
Bare wires
Audio Signals
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Impedance (Z) matching
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When interconnecting equipment it is important to match
levels
 Sending a line level signal into an input which is expecting a
microphone level signal will cause distortion
High impedance (High Z)
 Generally line level signals on unbalanced lines
 Line outs from audio equipment
 Outputs from electronic instruments
 Outputs from mixing desks
Low impendence (low Z)
 Generally microphone level signals on balanced lines
 Outputs from microphones or Direct Injection Boxes
Audio Signals
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Direct Injection Box
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Used to convert an unbalanced Hi-Z speaker or
instrument level output to a balanced lo-Z mic
level output
Usually used to enable an electronic instrument to
be delivered long distances on lo-Z lines to
minimize noise
Balanced vs. Unbalanced
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Unbalanced – 2 conductors. Hot and return
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Often the return is a screen or braid around an
inner conductor
Low levels of noise resistance
Good for short cable runs at line level or
speaker level
Balanced – 3 conductors. Hot, return and
shield
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Shield is a braid or metallic foil around two inner
conductors
Sometimes inner conductors are a “twisted pair”
Shield is connected to ground and bleeds off
any induced current
High levels of noise resistance
Good for long cable runs. Typically at
microphone level.
Using a Multi-Meter
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Used to measure
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Voltage
Resistance
Continuity
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The same as resistance, only simpler
Current
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Requires a change in setup