Sound Reinforcement Final

What are the different types of distortion in a sound system?

overdriven sound, harmonic distortion, intermodulation

Can you describe the difference between a personal PA, band PA, and touring PA?

Personal - small, 1-12 people, 10-20ft, “plug and play”

Band- Small-large venues, 10-2,000 people

Touring- extreme PA, requires small army and trucks, more set up time and knowledge

What is the difference between a point source and a line source?

point source: single speaker or multiple spaces out speaker, sound travels spherically, less range

line array: multiple speaker lined (usually vertically) distributing sound more linearly with mroe range/coverage

What are the three different uses of a sound system?

Public announcement, dirct public address, relaying art

What are the advantages/disadvantages of a portable and permanently installed system?

Portable

advantage: easily altered & disadvantage: more knowledge and set up time required

Fixed

advantage: less knowledge and set up time required for each use

disadvantage: not easily altered for various purposes

What is a “distributed” sound system?

connects into multiples spaces/rooms, often for public announcements (requires in places like malls and schools)

What is the power alley?

sections at which lowest frequencies are most audible in environment

How is power ally created and at what frequencies is it most noticeable?

subwoofers are at opposite ends of stage and phase cancellation/destructive interference causes dead spots, most noticeable at 50-100Hz

Can you describe phase time and how it affects your sound?

two or more speakers sound interference, can double (additive) or cancel (destructive) sound varying by frequency and some frequencies can cause “dead spots” in the room

What is RT60?

amount of time it take for the reverberation of a room to decay 60dB below inital SPL of direct sound

What is the absorption coefficient and what do the numbers represent?

measure how absorbent sound surface is, varies based on frequency, numbers represent percent of sound absorbed. 0=not absorbed to 1=fully absorbed

What is White noise?

equal energy for every frequency

What is Pink noise?

equal energy for every octave

How does a room’s acoustics play into the way we set up our system?

room size, shape, surfaces affect which speaker and angles/placement, and how we Eq/alter

What is the inverse square law?

For point source, intensity of sound decreases 6dB for each doubling of distance from the source

Why would we place our subs together and in mono at the center of the stage rather than in stereo?

to avoid destructive interference & power ally, instruments in subs usually panned center anyways

What equipment/information does a stage plot show?

Backline, mics/input channel, input box/snake, monitors, power inputs

What does a system diagram (line diagram) show?

signal path through one o rmore devices, document each line in a signal chain

What information needs to be put onto an input list?

instruments/inputs into console (for each band), mics & channel into console, sub snake & +48v

Can you identify the locations on a stage using common stage terms?

upstage, downstage, stage left, stage right, center stage, apron, thrust, house/audience

Can you identify different icons on a system diagram?

Yes (amp, faders, pan, ect).

Can you describe the different types of cable shielding?

Braided - woven copper, 70-95% coverage, adds cost and size, reduces flexibility

Spiral- copper spiral around conductor, cheaper, more flexible, less coverage

Foil- thin layer of aluminum that completely covers conductor

Can you identify different cables via photo?

Yes, practice cables and connectors

What is an optical cable, how is signal transmitted through it?

uses fiber optic cables to transmit video/audio, transmitted via laser light

What is EMI?

electromegnatic interference, any frequency of electrical noise

What is RFI?

radio frequency interference, interference from radio broadcast (specific subset of EMI frequencies)

How do we prevent EMI and RFI?

shielding

What are the frequencies of VHF in wireless systems?

Very High Frequencies, 30-300MHz

What are the frequencies of UHF wireless systems

Ultra High Frequencies, 300 MHz - 3GHz (less dropout/interference but cost more)

What are the best practices for Wireless Antenna placement?

mount 8-10ft high, at least ½ wavelength apart, direct line of sight between transmitted and receiver but at least 10ft apart, antennas should be off axis

What frequency bands (ranges) are illegal to operate wireless microphone systems? (hint: there are 2 bands)

600MHz and 700MHz range

What are the components to a wireless system?

transmitter and receiver

How does squelch affect my wireless signal? What does it do?

mutes the receiver when no signal present

Can you explain compansion and how it works?

fits audio signal into smaller radio signal bandwidth, transmitter compresses dynamic range and receiver expands it

Why is antenna diversity important in a wireless system?

prevent dropout in case one antenna picks up interference

Where should I place my monitor in relation to various microphones’ polar pattern for the greatest reduction in feedback?

Cardioid: directly behind mics

Supercardioid: monitors at 120 degree angle (slightly off from directly behind)

What is condensation effect and what mics are most/least susceptible to it?

moisture forms on capsule from dew, spit, sweat

condensers are most susceptible and can lead to pop, clicks, total failure

dynamic mics are least susceptible (good for rainy days)

What is transient response?

speed the mic responds to quick amplitude peaks

What is frequency response?

the mics ability to replicate frequencies at certain amplitudes

How can I reduce Proximity effect?

roll off low frequencies, mic further or off axis, use omni-directional mic

What microphones are not susceptible to wind noise?

omnidirectional

How does the mic’s pattern change over frequency?

lower frequencies are more omnidirectional (scattered), higher frequencies are more directional (beaming)

Can you identify different microphones’ pattern, manufacture, model, and transducer by a photo?

Yes, practice mics

How does cupping a mic affect it’s sound?

covering ports changes pick-up pattern of mic, typically less rejection in back and more likely to feedback

Can you describe the differences between a Mixer bussing and matrix sections?

Buss - routed from channel inputs to combine channels/duplicate signal/add effects then routed to output

Matrix - combines outputs of busses

What is a DCA and a VCA? How do they differ from a standard Bus on a console?

Digital Controlled Amplifier and Voltage Controlled Amplifier, NOT combine signal and NO audio pass through, mono channels controlled by 1 fader to maintain fader balance (works like a remote)

Understand the differences between PFL and AFL, and destructive vs Non-destructive solo.

PFL- Pre-fade listen after (eq, compression, ect.) but before fader (and effects), nondestructive, great for gain/processor adjustments

AFL - After-fader listen hear everything and monitor gain, nondestructive, great for mix adjustments

SIL - Solo in place, hear everything about signal, destructive (uses main mix bus as solo bus)

What are the basic audio components of a drive rack?

Eq, Compression, Delay

What is the basic signal flow of a drive rack?

Stereo Eq, Stereo Compressor/Limitor, Crossover, Eq/compressor/limiter/delays on each frequency range

What is an active crossover?

frequencies set by user, adjustable, before power amp

What is a passive crossover?

frequencies, non-adjustable, after power amp/inside speaker

What is the crossover slope?

rate at which frequencies attenuate at “crossover point” set by manufacture/2 filters

A 10 band, 15 band, and 31 band graphic EQ can affect how much of an octave per slider?

10 band - 1 octave per slider

15 band - 2/3 octave per slider

31 band - 1/3 octave per slider

How do you calculate delay times for speakers? Can you calculate delay?

distance between speakers (ft) / speed of sound (1130 ft/s) then convert to milliseconds (move decimal left 3 times

What is a 2 way, 3 way, or 4 way crossover network? What is a complex crossover network?

2 way - woofer and tweeter

3 way - woofer, midrange, tweeter

4 way - woofer, midrange, tweeter, super tweeter

complex - has more crossover points/drivers

What is a transistor and how does it work?

electronic component that can act as a amp or switch, audio signal goes into base, reservoir of power capacitors take electrical energy to make it consistent or store power to be released on demand - pass through the emitter to speaker

Can you calculate impedance load for speakers hooked up in series and parallel?

Series = S1 + S2

Parallel = 1/(1/S1) + 1/(1/S2)

complex amp uses series & parallel = find series then put in parallel

Can you identify the differences between amplifier classes?

Class A - 1 transistor, most common, add bias signal, master studio & permenant installs, low distortion & high quality audio, wastes a lot of energy cause doesn’t turn off

Class B- push-pull configuration, compression to top, rarefaction to bottom, 2 transistors each responsible for ½ the signal, crossover distortion (1 transistor off then other on)

Class A/B - push pull with bias turned on briefly for each transistor, fm and transistor radios, eliminate crossover distortion, uses more energy, 65-70% efficient (both transistor on then other turns off)

Class D - switch mode map, 2 transistors, series of pulses represent amplitude of waveform, similar to A-D conversion, most efficient 80-90%, portable/lightweight, less accurate sound/shaky wave (don’t completely recreate waveform)

Define the difference between Continuous, Program, and Peak power output.

continuous - sin wave or pink noise

program - RMS, 1 min

Peak - less than 1 second

how long a speaker can play something at high amplitude/what it can continuoisly play

How do you connect an NL4 to a bridged amplifier? What does it mean to have a bridged amp?

1+ (Positive), 2+ (Negative) a bridged amp takes 2 channels and turns into mono (doubles)

What is dampening and how does it affect your sound?

overdriving speaker causing it to not replicate sound properly, specifically effects low end

Can you calculate the wattage delivered to a speaker(s) in a circuit?

power = voltage² / impedance (may need many circuits to avoid overloading, can’t make single device send to multiple circuits)

Why is a baffle/enclosure needed for a speaker to function properly?

keep sound from front and back of drivers from colliding and causing interference

What is a coaxial speaker and what are its advantages/disadvantages?

woofer and tweeter share centerpoint

advantage - easy to install, affordable

Disadvantage- not as good sound quality as component speaker

What are the types of enclosures?

Acoustic suspension- dynamic, tight transient response, self limiting, not very power efficient

Ported enclosure- bass reflex, efficient power, less efficient trasnient response, easily damaged

Passive radiator- compromise between sealed and ported - drone cone, deeper low frequency rolloff

How do the following types of drivers work? Dynamic, Compression, Piezo, Ribbon

Dynamic - moving coil, coil and magnet interect electromagnetically to move speaker back and forth

Compression- moving coil, driver coupled with compression chamber - phase plug directs energy through throat and horm flare, sometimes wave guide

Piezo- bimorph crystal coupled to diapragm, changes shape with waveform - not widest frequency response, cheap but limited, no crossover, typically tweeter

Can you identify the parts of a moving coil and compression driver?

moving coil: voice coil (wire), magnet (creates magnetic field), diaphragm/cone (produces sound wave), suspension (on outside of diapragm), spider (on outside of coil), basket (on outside of spider) *driver shaped

compression driver: rear cover, membrane, phase plug, cavity, top plate & ring magnet (at top), suspension and voice coil (at bottom), driver exit and horn (middle) *horn shaped

Can you read the pinout of a power amplifier and hook it up for a speaker in Bi-Amp or Bridged mode?

Yes, the amp tells you

What does a speakers polar plot show you and why is it important?

vertical and horizontal dispersion of a speaker, varies by frequency, important for choosing speaker based on purpose and placing in right spot

What does the horn do to the sound of a speakers driver?

controls dispersion of sound, increases drivers efficiency, reduces midrange spread of driver

What happens when I place my subs close to a wall? How can I take advantage of this effect?

will cause boost in bass (1 wall = 3dB boost and add 3dB per wall added), use to get louder bass like if have smaller subwoofers

What is the Haas Effect (Precedence effect)?

psychoacoustics effect say that listener will percieve something coming from the same place if something louder from back and closer speaker is delayed

What does it mean to run my speaker in bi-amp mode?

hook 2 amps to speaker, 1 for lower frequencies and 1 for higher frequencies

What is a digital signal processor?

real world audio data and mathematically manipulate to achieve specific effects (algorithms)

What is the difference between a hard patch and a soft patch?

hard patch - physically plugging into outboard gear channel

soft patch - digitally assigning a channel

What is “Local I/O”?

connected directly to the processor elements

What is bit depth?

measure of the available dynamic range in audio

What is sample rate?

measure the avaliable bandwidth of frequency

What is clocking?

process by which an A-D convertor collector audio samples to synch devices an be in accurate timing (sample rate and bit depth must match between devices)

What is Occlusion and how does it affect my musicians?

outer ear is fully covered making peoples voices louder in their heads and noticeably boosts low frequency perception

What are Side fill monitors? Why do we use them?

full range speaker on side of stage providing additional coverage across stage, allow musicians to move around and hear everywhere (instead of being stuck in front of wedge)

What are the different types of monitor setups?

wedge, side fills, IEM (in ear monitors)

Can you calculate the amount of power needed for your equipment?

Amps (current) * voltage = power (watts) (P=VI)

What is “ground” and how does it affect my audio signal?

drains excess electricity to ear, protection from EMI/RMI & protects people from getting shocked

What happens when we have a ground loop?

EMI/RMI travel back to original source instead of ground because another source is hooked up to ground at different voltage

What is the ground wire used for in electrical systems?

provide low -resistance path to earth for user safety

How can you safely prevent a ground-loop in your system?

remove break shield for one of them, ground lift switch, cable adapters with ground connected only to one, connect both sources to same power outlet so grounds aren’t combining, NEVER REMOVE GROUND PIN

Can you use Ohms Law calculation to calculate the Wattage, Amperage, or Voltage of a circuit?

watts = volts * amps

amps = watts/volts

volts = amps/watts

Can you determine if there is enough power for your system?

Yes, how many circuits and how much power you need.

What is Three Phase Power and how many connections do you have when using this system?

high voltage system with 5 wires (3 carry 120volts each) other 2 are neutral and ground, all running together

What is Line level? How many volts is line level?

audio signal used to transmit sound between 2 devices. 1.228 or 1.24 volts

 What is the difference between a consumer and professional “line level” signal?

consumer = -10dbV

Professional = +4dBu

What is dBSPL?

Sound Pressure Level

What is dBA weighting?

uses filter that greatly reduces level reading of low frequencies, for low level measurements 

What is dBB weighting?

for medium level sound

What is dBC weighting?

no low frequency correction, for measuring high level sound sources

TS Pinout

Tip (positive), Sleeve (negative/ground)

TRS Pinout

Tip (positive), Ring (negative), Sleeve (ground)

XLR Pinout

Pin 1 (ground), Pin 2 (positive), Pin 3 (negative)

NL4 Pinout

1 (+/-), 2 (+/-)