Live Sound 501

Front 1

Microphone cables

Back 1

can run for several meters without booster amplifiers (ifbalanced twisted pairs).

Front 2

Line level cables

Back 2

be balanced to reject EM noise.

Front 3

Speaker cables

Back 3

Carry currents that are high enough to not need balancing & should be as thick / short as possible

Front 4

Stereo system cables

Back 4

should be of equal length

Front 5

Capacitance:

Back 5

long lengths of parallel cable act as plates in a capacitor

Front 6

Inductance:

Back 6

improperly coiled cables can induce current into each other,causing noise.

Front 7

Cable Laying:

Back 7

end and return cables shielded / separate from each other (capacitance/inductance between send and return = feedback).

Do not place HT (high tension power or lighting) cables near audio leads as thiscauses noise.

Front 8

Stage Box

Back 8

containing XLR connections for ‘mic’ and DI signals

Collects ‘mic’ / DI signals and feeds them into a multicore cable .

Many stage boxes may be used at once on stage (one specifically for drummicrophones, etc.)

Front 9

Microphone Splitter Box

Back 9

Splits stage mic/DI signals into two or more copies (FOH / monitor consoles)

Active - FOH console must not be fed via transformer (phantom power wouldbe blocked).

Active – May derive power from console (for self-operation). May be passive (simple parallel split) or active (transformers used preventingdirect electrical connections from causing earth loops).

Front 10

Multicore / Snake

Back 10

Many cables (signals) housed within one larger cable.

EDAC connections are the most common (allowing for easy connection).

Front 11

Live Sound Graphic EQ

Back 11

Used to tune/condition the signal being sent to speakers (usually 31bands typeused). Graphic Equalisers allow maximisation of level before feedback. FOH - Used to ‘tune’ the room slightly by attenuating room modes, etc.Foldback speakers - Used to prevent feedback / tune speakers to a musician’srequirements

Front 12

Live Sound Feedback Buster

Back 12

An automatic, dynamic graphic EQ.• Feedback has a very distinctive envelope that is recognised and attenuated by the feedback buster

Front 13

Limiters

Back 13

Used to protect the crossover, amps and speakers from extreme transients thatmight occur.

Front 14

Crossover

Back 14

A set of filters splitting the frequency range into separate bands destined forspecific types of speaker drivers.

Front 15

Amplifiers

Back 15

should be placed as close to speakers as possible i.e. long speakercables affect efficiency / increase impedance.

Front 16

Bridging Stereo Amplifiers

Back 16

Most amps have a mono/stereo or bridge/normal switch.One O/P (usually right) is polarity reversed (when amp is set on ‘bridged’ mode)O/P is taken from the positive terminals of the two channelsThe RMS voltage is effectively doubled which would relate to a 4X increase inpower. The electrical components usually cannot deal with this increase inpower so the impedance of the amp is doubled which relates to only a‘controlled’ power increase to double the normal power.

Front 17

Power Rating

Back 17

Continuous power (long term average)Tested with pink noise typical program material

Peak powerMaximum, instantaneous, short-term power handling

RMS powerAverage sine-wave producing power that can be handled over long periodsTested / measured using a sine inpute.g. A 300 Watt ‘RMS’ amplifier would be able to produce a 100 Watt sine-wave on the load.

Front 18

Power Matching

Back 18

As a rule of thumb, amplifiers should have power rating equal to at least twice theIEC continuous power rating of the speakers.

Front 19

Damping Factor

Back 19

The damping factor describes the ability of the amplifier to control the movementof the driver’s cone. It is calculated as a ratio of load impedance over outputimpedance.The higher the damping factor the higher the fidelity.

Front 20

Slew Rate

Back 20

Measure of an amp’s ability to track an input transient and reproduce it at theoutput.Measured in ‘volts per microsecond’ V/μsImportant during high amplification levels when it is harder for the amp toreproduce the transients accurately.

Good Slew Rates: • amps up to 100W (continuous) = 10V/μs• amps over 200W (continuous) = 30V/μs

V= max peak voltage

Front 21

Clipping

Back 21

Occurs when an amplifier attempts to reproduce levels over those for which it isdesigned.When a sine wave is driven through an amp and its level is increased to clipping itwill resemble a square wave. This is due to the fact that harmonics were added(harmonic distortion) which results in a higher voltage resulting in a 3dB boost inlevel over a sine wave at max level.

Front 22

Amplifier Protection Mechanisms

Back 22

Protect the amp from short circuits at its outputs (from very low Z or incorrectconnections)• Protect the amp from overheating (e.g. it will automatically switch off or a fusewill blow) • Protect the speaker from on/off transients.

Front 23

Speakers

Back 23

Speakers may contain different drivers for different frequencies:2 Way (HF and LF drivers)3 Way (HF, MF and LF drivers)

Front 24

Bi-amping

Back 24

Different speakers / drivers are powered by different amplifiers through the use ofan active crossover network.

Front 25

Speaker Placement

Back 25

Spaced speaker systems may cause comb filtering (mainly at LF).‘Cluster’ of speakers radiate the sound outwards with less interference and combfiltering (better clarity/definition)

Front 26

= HF speakers:

Back 26

Very directional

Must be aimed at audience

Coverage angles to determine placement

Placed high up above the stage

If the audience is very large then ‘long throw’ speakers can project HF (andsometimes MF) to the rear audience using directional horns

Front 27

LF speakers:

Back 27

Less directional

Do not need to be placed high up / may be placed under or along-side thestage (adequate LF radiation)

If placed in a corner then the 3, 6 or 9 dB SPL increases can be used

Front 28

Delay Towers

Back 28

If the audience is too large and the sound levels at the back are too low, extraspeakers may be used for reinforcement (delay distribution system).‘Delay towers’ provide delayed sound O/P to the audience in order to preservelocalisation and maintain visual and audible sync.

Front 29

Amount of delay:

Back 29

Time taken for sound to travel from FOH to Delay tower + Haasamount.Haas delay added so that the audience will still perceive the sound as comingfrom the FOH (this allows the delay tower’s level to be up to 10dB louder withoutaffecting localisation).

Front 30

Other factors will affect the sound’s movement:

Back 30

Live Sound Air temperature: Lower temperatures will slow the sound down (use longerdelay times)

Wind

Front 31

Impedance matching

Back 31

The amount of power drawn from an amp by a driver is proportional to itsimpedance.

Front 32

Impedance matching series

Back 32

Series: ZT =Z1 +Z2 +Z3 +...

Voltage is split but current is the same for all speakers

Disadvantage of series speaker configuration:

If one speaker is faulty, all the other speakers are affected

More interaction between speakers could cause distortion

The damping factor as seen by each individual speaker is degraded - eachspeaker ‘sees’ more source Z)

Front 33

Impedance matching Parallel

Back 33

Parallel: 1/ZT = 1/Z1 + 1/Z2 + 1/Z3....

Current is split but voltage is the same across all speakers

Advantages of parallel array: If one speaker breaks down the others are not affectedDamping factor is not adversely affected

Front 34

FOH Console

Back 34

Any type of console may be usedMain speakers fed by stereo bus (not a separate monitor section)High voltage lines may be needed to feed FOH (voltage stepped up /transmitted / stepped down)

Required Features: Channels have on/off switches (prevent unwanted signals from feedingFOH speakers)

Many fader / mute groups (VCA groups)

Many auxiliaries

Gates (gate as much as possible)

PFL soloing

L-C-R pan assign

Front 35

Front/Back Placement of FOH Console

Back 35

- Between1/3 and1/2 the length of hall from stage

- Not closer than the distance between the speakers and not further thantwice the distance between the speakers.

Front 36

Left/Right placement of the FOH Console

Back 36

On the middle line to prevent comb-filtering (may only benefit peoplestanding on the middle line)

Front 37

Monitor Console

Back 37

Matrix consoles are preferred (multiple mixes)Auxiliar feeds may be used on all types of consoles to create different mixes

Front 38

Powered Mixers

Back 38

A mixer with built-in power ampOutputs must be at speaker levelsGood for small venues (pubs) but can be limiting in size, power andfacilities

Front 39

Digital Consoles

Back 39

Digital consoles are extremely efficient as they offer ‘recall’ functions‘Recall’ combined with IEM makes monitor mixing extremely easy

Front 40

Tips for Mixing FOH

Back 40

Live Sound Do FOH mix before monitor mix (specially in small venues)Set vocal levels higher than in a ‘studio mix’ (treat songs like you’ve neverheard them)Don’t be afraid of using ‘drastic’ EQFilters (cut mids) may be used to create space on pre-recorded (pre-mixed /samples / etc.) material

Front 41

Tips for Monitor Mixing

Back 41

Remember always to use pre-fader ‘auxes’Take advantage of rear rejection by pointing a cardioid ‘mic’ to the singer’smouth (perpendicular to wedge)Avoid putting low end through to the wedgesWhen using IEM: Have a pre-made mix ready Small changes are effective!