Poff 2560 Sound Reinforcement Final

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

- Overdriven Sound

- Harmonic distortion

- Intermodulation

Describe the differences between a personal PA, a band PA and a touring PA.

Personal - small, can fit in a car - meant for 1 to 12 people, range of 10-20 ft., "plug and play"

Band - Reinforces small to large venues, easily scaleable, meant for 10-2,000 people

Touring - Extreme end of PA's, requires small army of people and trucks, more set up time and knowledge

What is a "distributed" sound system?

connects into multiple spaces/rooms, often for public announcements - required in places like malls for emergencies

3 different uses of sound systems

Public announcement, direct public address, relaying art

Pros and cons of portable/permanently installed systems

Portable (+) easily altered (-) more knowledge and setup time required

Fixed (+) less knowledge and setup time required for each use (-) not easily altered for various purposes

Difference between point source and line source

A point source is a single speaker or multiple speakers spaced out, sound travels in a spherical shape; therefore, less range

A line array has multiple speakers lined up (usually vertically), distributes sound more linearly with more range/coverage

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

Measure of how absorbent of sound a surface is, varies based on frequencies; numbers represent percent of sound that gets absorbed - "1" = fully absorptive

White noise v. pink noise

White noise has equal energy per every frequency, pink noise has equal energy per octave

Phase time and how it affects sound

When two or more speaker's sounds interfere, they can cause additive or destructive interference, varies by frequency, can cause "dead spots" in the room for certain frequencies

What is the power ally? How is it created and what frequencies is it most noticeable in?

The power ally represents the sections at which the lowest frequencies are most audible in an environment - it is created when subwoofers are at opposite sides of the stage causing "dead spots" due to destructive interference- most noticeable at 50-100Hz

What is RT60?

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

How does a room's acoustics play into the way we setup a system?

Room size, shape and surfaces can affect which loudspeakers we want to work with (read manual and look at dispersion pattern), where we place them, and how we alter our EQ

What is the inverse square law?

For a point source, the intensity of sound decreases by around 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 and the "power ally" - instruments in subs (kick and bass) are usually panned center anyway

What equipment/information does a stage plot show?

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

What does a system diagram (line diagram) show?

signal path through one or more devices, documents each link in signal chain

What information needs to be put onto an input list?

- List of Instruments/Inputs into Console w/Each Band

- Mics & Channel into Console

- Sub Snake if needed, & 48v

Can you describe the different types of cable shielding?

Braided - woven mesh of copper wires, typically 70-95% coverage, adds cost and size and reduces flexibility

Spiral - copper spirals around conductor, cheaper and more flexible with less coverage

Foil - thin layer of aluminum that completely covers around conductor

Pinout of TS

Tip (+), Sleeve (-/ground)

Pinout of TRS

Tip (+), Ring (-), Sleeve (ground)

Pinout of XLR

Pin 1 (ground), Pin 2(+), Pin 3 (-)

Pinout of NL4

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

Pinout of NL8

1 (+/-), 2 (+/-), 3 (+/-), 4(+/-)

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 and RFI? How do we prevent it in our cabling?

EMI = electromagnetic interference, any frequency of electrical noise

RFI = radio frequency interference, specific subset of EMI frequencies dedicated to radio broadcast

Prevented by shielding

What are the frequencies of VHF and UHF wireless systems?

VHF - Very High Frequencies - 30-300MHz

UHF - Ultra High Frequencies - 300 MHz-3 GHz

- less dropout/interference, more cost

What are the best practices for Wireless Antenna placement?

Mount antennas 8-10 ft high and at least 1/2 wavelength apart, direct line of sight between transmitter and receiver, they should be at least 10 feet apart, antennas should be off axis

What frequency bands (ranges) are illegal to operate wireless microphone systems?

600 MHz and 700 MHz 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 there's no signal present

Can you explain compansion and how it works?

Fits audio signals onto smaller radio signal bandwidth,

transmitter compresses dynamic range, and receiver expands it

Why is antenna diversity important in a wireless system?

Prevents dropouts in case one antenna picks up interference etc

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

Cardioid - Place monitors directly behind microphone

Supercardioid - place monitors at a 120 degree angle

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

Moisture forms on capsule from dew, spit or sweat, condensers are most sensitive to it and can cause pops, clicks and total failure

What is transient response and frequency response?

Transient response is the speed at which the microphone responds to quick amplitude peaks such as snare hits

Frequency response is mic's overall response to different frequencies

How can I reduce Proximity effect?

Rolloff low frequencies, place mic further away or off axis, use omnidirectional mic

What microphones are not susceptible to wind noise?

omnidirectional

How does the mic's pattern change over frequency.

lower frequencies are more omnidirectional while higher frequencies are more directional

How does cupping a mic affect it's sound?

Usually will cover ports which make the mic directional :covering these will cause less rejection in the back of the mic and make it more likely to feedback

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

Busses are typically routed from channel inputs to combine channels, duplicate signals, or add effects, routed to output

Matrices are typically routed from the master or submaster, to other locations such as front/side fills, delays

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

voltage or digital controlled amplifiers - works like remote control; does not combine signals and no audio actually passes through - pair mono channels controlled by 1 fader, maintain fader balance

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

PFL - Pre-Fader Listen - used to monitor a signal after insert processing (EQ, Dynamic Processors etc.) but BEFORE any gain or attenuation by channel fader- Soloing in PFL will be non-destructive (won't affect the mains)

AFL - After-Fader listen - used to monitor a signal after the affect of any gain or attenuation by the channel fader and panning - soloing in PFL will be destructive and get rid of the sound of every other channel in the mains

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/Limiter , Crossover, EQ/Compressor/Limiter/Delays on each frequency range

What is an active and passive crossover? What are this differences between them, and where are they placed in the signal flow of a drive rack?

Active - Frequencies set by user, adjustable, before power amp

Passive - Frequencies non-adjustable - after power amp, inside of speaker

What is the crossover slope?

the rate at which the frequencies attenuate at the "crossover point" - set by manufacturer

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/speed of sound

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 and tweeter

4 way - woofer, midrange, tweeter and super tweeter

Complex= more?

What is a transistor and how does it work?

miniature electronic component that can act as amplifier 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 - passes through the emitter to the speaker

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

Series = S1+S2

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

Can you identify the differences between amplifier classes?

Class A - 1 transistor - most common and simple design, have to add bias signal - typically in master studios, permanent installs, high-end studios

(+) very low distortion, high quality audio

(-) very inefficient

Class B - push-pull configuration - compression to top, rarefaction to bottom, almost never use

(+) 2 transistors responsible for 1/2 signal each, 80% efficient

(-) crossover distortion

Class A-B - push-pull with bias turned on briefly for each transistor - FM and transistor radios

(+) eliminates crossover distortion - 65-70% efficient

(-) uses more energy

Class D - switch mode amp - only thing same is 2 transistors- series of pulses represents amplitude of waveform - similar to A-D conversion

(+) most efficient (80-90%) - lightweight/portable

(-) less accurate sound - shaky wave

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

Continuous - via Sine Wave or pink noise

Program - RMS, 1 min

Peak - <1 sec

How do you connect an NL4 to a bridged amplifier?

What does it mean to have a bridged amp?

1+ (Pos) 2+ (Neg)

A bridged amp takes 2 channels and turns into mono

What is dampening and how does it affect your sound?

the ability of the amplifier to control speaker motion once signal has stopped - well dampened speakers sound tighter in the low end

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

keeps sound from front and back of the drivers from colliding and causing interference

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

Woofer and tweeter share centerpoint - easy to install and more affordable, not as good of sound quality as component speakers

Different types of enclosure?

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

Ported enclosure- bass reflex - efficient power wise, less efficient transient 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- most common, moving coil, coil and magnet interact electromagnetically to move speaker back and forth

Compression - also moving coil design, Driver is coupled with compression chamber- phase plug directs energy through throat and horn flare, sometimes wave guide

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

Ribbon - ultra thin - efficient, light, responsive and directional, fast transient, can be fragile - typically tweeter

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

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

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

controls dispersion of sound, increases driver's 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 a boost in bass frequencies

What is the Haas Effect (Precedence effect)?

psychoacoustic phenomenon that can cause listener to perceive space and distance based on a slight delay between stereo channels

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

Hook two amps to the speaker, one for the lower frequencies and one for the higher frequencies

What is a digital signal processor?

DSPs take real world audio data, and mathematically manipulate it to achieve specific effects

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

Hard patch means plugging in outboard gear to a channel - soft patching is digital

What is "Local I/O"?

Local I/O is connected directly to the processor elements of the DSP

What is bit depth, sample rate, and clock? What must we do to these things to connect multiple digital devices together?

Bit depth is a measure of the available dynamic range in audio- sample rate measures the available bandwidth of frequency - clocking is the process by which an A-D convertor collects audio samples - sample rates and bit depth must match between devices

What is Occlusion and how does it affect my musicians?

Occlusion is when the outer ear canal is fully covered, often by in ear monitors - this makes people's voices louder in their heads and noticeably boosts low frequency perception

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

full range speakers on side of stage - provides additional coverage across stage, allows musicians to move around and still hear what's necessary - only use when needed

What are the different types of monitor setups?

Wedges, side fills, IEM (In Ear Monitors)

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

Amps(current)*Voltage

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

Drains excess electricity to earth, protection from EMI/RMI

What happens when we have a ground loop and how can I safely remove it from my system?

EMI/RMI travels back to original source instead of the ground because another source is hooked up to ground at different voltage - break connection to shield for one of them, ground lift switch, cable adapters with ground connected on only one side to break loops, connect both sources to same power outlet

Standard voltage for US

120 volts

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

high voltage system with 5 wires - use 3 wires that carry 120 volts each - neutral and ground connections - all running together

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

Line level is the level of an audio signal used to transmit sound between two devices - voltage depends on the reference

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

Consumer - -10 dbV

Professional - +4dbu

What is dBSPL?

Sound Pressure Levels

Do you know the differences between dB(A), dB(B), and dB(C)?

Different frequency weightings

Additional knowledge

- Study mics and cables

- icons on a system diagram

- calculating impedance load for amps and wattage being delivered to speakers. - Know and identify the parts of a dynamic and compression driver (loudspeakers)