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Intro to Electricity What is electricity? How is it created? How is it transmitted? Electricity Electricity is a form of energy Generally defined as the flow of electric charge from one place to another This is not entirely accurate, but the metaphor works Two sub-atomic particles Protons Positive charge. Large relative mass Electrons Negative charge. Very little relative mass Electricity Electric power is created by detaching electrons from an atom 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 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 Voltage will change with time Voltage is a “relative” measurment In most instances, it happens very fast 50 cycles per second (Hz) Europe and most of Asia 60 cycles per second (Hz) United States, some of Asia and some South America Alternating current James Clerk Maxwell Discovered that electricity and magnetism are two forms of the same physical phenomenon. Maxwell’s laws “A changing magnetic field will produce an electric field” “A changing electric field will produce a magnetic field” How a generator works 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 Causes three phase electricity. The number of times per sec that the coil revolves will determine the frequency of the electric current Induced current 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 Often the product of a chemical reaction Batteries Can be generated using an alternator Can be converted from AC current Voltage stays constant over time. Ohms Law Voltage, current and resistance are all related Voltage The potential charge between two points It is a relative measurement We usually measure voltage with respect to “ground” or “earth” Requires a complete path back to ground in order to “flow” Current The “flow” of electrical charge carriers Current Flow Water analogy Wire = hose Voltage = water pressure Current = flow of water Resistance = resistance to water flow Kink in the hose A larger hose connected to a smaller hose Ohms Law V=IR P=VI V= voltage (volts) I = current (amps) R = resistance (ohms) P = power (watts) VIRP Ohms Law These two formulas allow us to relate voltage, current resistance and power to each other. If you know any 2, you can now the other 2. Strictly speaking this is only for DC circuits For AC circuits, resistance is replaced with impedance Takes into account capacitors and inductors Circuits Series Electricity flows through each component RT=R1+R2+R3… Circuits Parallel 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 Physical = Sound we hear Physical environment of the audience / performers. World of physics and acoustics Virtual (electronic) = Audio Systems 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 Worlds meet at “transducers” 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 Every time a transducer is used, some information is lost No transducers are 100% efficient. The sound represented will change Clipping will occur Audio Signals Microphone level 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) Line level 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 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 Much higher voltages depending upon the power ratings of the amplifier and load The signal from power amplifiers to loudspeakers Typically uses Speakon connectors Twist lock Bare wires Audio Signals Impedance (Z) matching 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 Direct Injection Box 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 Unbalanced – 2 conductors. Hot and return 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 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 Used to measure Voltage Resistance Continuity The same as resistance, only simpler Current Requires a change in setup