Sound ReinforcementSound Reinforcement

Hal HarrisonHal Harrison

hlh@clemson.eduhlh@clemson.edu

What is a Sound System?What is a Sound System?

A sound REINFORCEMENT system, not a A sound REINFORCEMENT system, not a sound system.sound system.

Reasons for having a reinforcement system:Reasons for having a reinforcement system:Help people hear something better.Help people hear something better.To make sound louder for artistic reasons.To make sound louder for artistic reasons.To enable people to hear sound in remote To enable people to hear sound in remote

locations.locations.

Conceptual Model of a Sound SystemConceptual Model of a Sound System

Sound Waves and PropagationSound Waves and Propagation What we hear as sound is a class of kinetic energy called What we hear as sound is a class of kinetic energy called acoustical acoustical

energyenergy.. Acoustical energy consists of fluctuating waves of pressure in air.Acoustical energy consists of fluctuating waves of pressure in air. Waves have peaks and valleys.Waves have peaks and valleys. The start and end of a wave (either peak to peak or valley to valley) The start and end of a wave (either peak to peak or valley to valley)

is known as a is known as a cyclecycle.. To be classified as sound, waves must fluctuate at a rate between To be classified as sound, waves must fluctuate at a rate between

20 and 20,000 cycles per second (cps).20 and 20,000 cycles per second (cps). The amount of cycles waves fluctuate per second is known as The amount of cycles waves fluctuate per second is known as

frequencyfrequency.. Hertz (Hz) is used to indicate frequency in cycles per second.Hertz (Hz) is used to indicate frequency in cycles per second. 20 Hz = 20 cps20 Hz = 20 cps Generally speaking, the higher the frequency, the higher the Generally speaking, the higher the frequency, the higher the

perceived pitch of a sound.perceived pitch of a sound.

Representation of a Sound WaveRepresentation of a Sound Wave

The Electrical Representation of SoundThe Electrical Representation of Sound

An audio signal is an electrical An audio signal is an electrical representation of sound.representation of sound.

In analog audio electronics, the signal In analog audio electronics, the signal voltage fluctuates the same way as the voltage fluctuates the same way as the acoustical energy it represents.acoustical energy it represents.

The amplitude (or strength) of an audio The amplitude (or strength) of an audio signal is called the signal level.signal is called the signal level.

Sound level is specified in decibels (dB).Sound level is specified in decibels (dB).

Input TransducersInput Transducers Air pressure or velocity microphonesAir pressure or velocity microphones Contact pickupsContact pickups

acoustic guitar, mandolin, violinacoustic guitar, mandolin, violin Magnetic pickupMagnetic pickup

electric stringed instrumentselectric stringed instruments Tape headsTape heads

cassette tapescassette tapes Phonograph pickupsPhonograph pickups

record playersrecord players Laser pickupsLaser pickups

CD, MDCD, MD

Output TransducersOutput Transducers

Woofer loudspeakersWoofer loudspeakers low frequency reproduction >500Hzlow frequency reproduction >500Hz

Midrange loudspeakersMidrange loudspeakers mid-range frequency reproduction mid-range frequency reproduction 500Hz-4kHz range500Hz-4kHz range

Tweeter loudspeakersTweeter loudspeakers high frequency reproduction <4kHzhigh frequency reproduction <4kHz

Full-range loudspeakersFull-range loudspeakers Integration of 2 or more of the other loudspeaker Integration of 2 or more of the other loudspeaker

systems.systems.

Output Transducers Output Transducers continuedcontinued

Subwoofer loudspeakersSubwoofer loudspeakersextended low frequency extended low frequency 30Hz-150Hz range30Hz-150Hz range

Monitor (foldback) loudspeakersMonitor (foldback) loudspeakers full range loudspeakers designed for the full range loudspeakers designed for the

performer on stage to hear themselves.performer on stage to hear themselves.HeadphonesHeadphones

Practical Model of a Sound SystemPractical Model of a Sound System

Frequency ResponseFrequency ResponseThe Frequency Response (FR) of a device The Frequency Response (FR) of a device

describes the relationship between the describes the relationship between the devicedevice’’s input and output with regard to s input and output with regard to signal frequency and amplitude.signal frequency and amplitude.

FR and Acoustical FactorsFR and Acoustical Factors

The FR of any sound system is affected by the The FR of any sound system is affected by the environment in which it works.environment in which it works.

Outdoor factors:Outdoor factors: wind – deflects sound as it travelswind – deflects sound as it travels temperature – deflects sound as it travelstemperature – deflects sound as it travels air absorption – sound (higher frequencies) are air absorption – sound (higher frequencies) are

absorbed over distanceabsorbed over distance

Indoor factors:Indoor factors: room reflections – walls, ceilings, floor surfacesroom reflections – walls, ceilings, floor surfaces room resonancesroom resonances

The DecibelThe Decibel Decibel (dB)Decibel (dB) Decibels describe a ratio of two quantities often Decibels describe a ratio of two quantities often

related to power.related to power. PROBLEM: What is the ratio, in dB of 2 watts to PROBLEM: What is the ratio, in dB of 2 watts to

1 watt?1 watt?dBdB = 10 log (P= 10 log (P11 / P / P00))

= 10 log ( 2 / 1)= 10 log ( 2 / 1)

= 10 log 2= 10 log 2

= 10 X .301= 10 X .301

= 3.01 or = 3.01 or 3dB3dB WHICH MEANS - Whenever one power is twice WHICH MEANS - Whenever one power is twice

another, it is 3dB greater!another, it is 3dB greater!

Relating the Decibel to Acoustic LevelsRelating the Decibel to Acoustic Levels

Volume, Level, and GainVolume, Level, and Gain

Volume – defined as a power level Volume – defined as a power level in audio, it means turn up the volume!in audio, it means turn up the volume!bad term as it relates to a cubic dimension.bad term as it relates to a cubic dimension.

Level – magnitude of a quantity in relation Level – magnitude of a quantity in relation to a arbitrary reference value.to a arbitrary reference value.Sound Pressure Level (SPL)Sound Pressure Level (SPL)

Gain – assume to be transmission gain, Gain – assume to be transmission gain, which is the power increase of a signal which is the power increase of a signal expressed in dB.expressed in dB.

Dynamic Range and HeadroomDynamic Range and Headroom

Dynamic Range - the difference in dB Dynamic Range - the difference in dB between the loudest and the quietest between the loudest and the quietest portion of a program.portion of a program.

Headroom – the difference between the Headroom – the difference between the normal operating level and the highest normal operating level and the highest (peak) level of program material.(peak) level of program material.

Headroom IllustrationHeadroom Illustration

Break Time!Break Time!

Balanced CablesBalanced Cables

Used to connect line level and mic level Used to connect line level and mic level sources such as microphones (XLR) and sources such as microphones (XLR) and input/output connections (console to amp)input/output connections (console to amp)

Unbalanced CablesUnbalanced CablesUsed to connect line-level signals such as Used to connect line-level signals such as

guitars, keyboards, bass, etc. (1/4guitars, keyboards, bass, etc. (1/4””))

Insert CablesInsert CablesUsed to connect channel or group specific Used to connect channel or group specific

devices such as:devices such as:CompressorsCompressorsLimitersLimitersGatesGates

Microphones: SelectionMicrophones: Selection

Dynamic (3.1)Dynamic (3.1)Condenser (3.2)Condenser (3.2)

Phantom power +48v needed for operationPhantom power +48v needed for operation

Microphones: Pickup PatternMicrophones: Pickup PatternA pick-up pattern refers to the area(s) from A pick-up pattern refers to the area(s) from

which a microphone which a microphone ““picks uppicks up”” its sound. its sound.Types:Types:

Omni (3.3)Omni (3.3)Cardioid (3.4)Cardioid (3.4)Super-cardioid (3.5)Super-cardioid (3.5)

Typical Console Typical Console Signal FlowSignal Flow

Mono InputMono Input A – XLR microphone level inputA – XLR microphone level input

balancedbalanced B – ¼B – ¼”” line level input line level input

balanced/unbalancedbalanced/unbalanced C – ¼C – ¼”” line level insert (1.1) line level insert (1.1)

Inserts are both sends and returnsInserts are both sends and returns UnbalancedUnbalanced

D – ¼D – ¼”” line level direct output line level direct output balanced/unbalancedbalanced/unbalanced

Mono InputMono Input

E – Gain / trim controlE – Gain / trim controlF – High Pass Filter (HPF)F – High Pass Filter (HPF)

aka Low-cut filteraka Low-cut filterG – Equalization sectionG – Equalization section

Mono InputMono Input

H – Auxiliary send sectionH – Auxiliary send section I – Pan controlI – Pan controlJ – Pre-Fade Listen (PFL) switchJ – Pre-Fade Listen (PFL) switchK – Channel K – Channel ““OnOn”” switch switch

aka mute buttonaka mute buttonL - FaderL - FaderM – Assignment switchM – Assignment switch

aka routing buttonaka routing button

SubgroupsSubgroups

Allow logical Allow logical assignment of groups of assignment of groups of instruments or vocalists instruments or vocalists so that they may be so that they may be controlled by just one controlled by just one pair of faders, or even a pair of faders, or even a single fader.single fader.

Console Master SectionConsole Master Section N – line level master outputs N – line level master outputs

(¼(¼”” or XLR) or XLR) O – line level control O – line level control

room/monitor output room/monitor output P – line level 2-track tape return P – line level 2-track tape return

(RCA)(RCA) S – metersS – meters U – 48v global Phantom power U – 48v global Phantom power

switchswitch V – headphone output (1/4V – headphone output (1/4””) )

headphone levelheadphone level

Console Master SectionConsole Master Section

Q – auxiliary send master Q – auxiliary send master sectionsection

R – After-fade listen (AFL)R – After-fade listen (AFL)

Typical Console Input/Output SetupTypical Console Input/Output Setup

Input GainInput Gain

Input gain controls are designed to take a Input gain controls are designed to take a signal and adjust it till it is usable by the signal and adjust it till it is usable by the mixing console.mixing console.

Setting Gain StructureSetting Gain Structure

1.1. Press the PFL/Solo switch on the Press the PFL/Solo switch on the relevant input. relevant input.

2.2. Adjust gain/input sensitivity until meters Adjust gain/input sensitivity until meters read within the yellow (read within the yellow (‘‘33’’ to to ‘‘66’’ on meter on meter scale). This allows for the extra 10dB of scale). This allows for the extra 10dB of gain that is available on Soundcraft input gain that is available on Soundcraft input faders. faders.

3.3. Release PFL/Solo. Release PFL/Solo. 4.4. Repeat for all other inputs. Repeat for all other inputs.

FadersFadersFaders allow for fine adjustments to your Faders allow for fine adjustments to your

inputs.inputs.Normal operating levels for faders should Normal operating levels for faders should

be at be at ““00”” or unity. or unity.Faders are logarithmic.Faders are logarithmic.

EqualizationEqualization Used to make corrective and creative sound Used to make corrective and creative sound

changes.changes. BASIC RULE OF EQ:BASIC RULE OF EQ:

If it sounds good, it is good!If it sounds good, it is good!

Console EQ types:Console EQ types: fixed band, semi-parametric, fully parametricfixed band, semi-parametric, fully parametric

Center position has no effect on sound.Center position has no effect on sound. Counterclockwise – decrease in EQ frequency Counterclockwise – decrease in EQ frequency

level.level. Clockwise – increase in EQ frequency level.Clockwise – increase in EQ frequency level.

Fixed EqualizationFixed Equalization

Same as treble/bass controls on home Same as treble/bass controls on home stereo systems.stereo systems.

Semi-parametric EqualizationSemi-parametric EqualizationSimilar to fixed EQ, but has more control as Similar to fixed EQ, but has more control as

the midrange EQ is usually the midrange EQ is usually sweepablesweepable..Sweep – console EQ knob which is Sweep – console EQ knob which is

selectable between a range of frequencies.selectable between a range of frequencies.

Removing Unwanted Sound with EQRemoving Unwanted Sound with EQ

1.1. Increase sweep-EQ gain. Increase sweep-EQ gain. 2.2. Sweep the frequency pot until the aspect of the sound Sweep the frequency pot until the aspect of the sound

you wish to modify becomes as pronounced as you wish to modify becomes as pronounced as possible. This should only take a few seconds. possible. This should only take a few seconds.

3.3. The cut/boost control is now changed from its full The cut/boost control is now changed from its full boost position to cut. The exact amount of cut required boost position to cut. The exact amount of cut required can be decided by listening to the sound while making can be decided by listening to the sound while making adjustments. adjustments.

4.4. Even a small amount of cut at the right frequency will Even a small amount of cut at the right frequency will clean up the sound to a surprising degree. clean up the sound to a surprising degree.

Other sounds may benefit from a little boost, one example being the electric guitar which often Other sounds may benefit from a little boost, one example being the electric guitar which often needs a little extra bite to help it cut through the mix. Again, turn to full boost and use the needs a little extra bite to help it cut through the mix. Again, turn to full boost and use the frequency control to pick out the area where the sound needs help. Then itfrequency control to pick out the area where the sound needs help. Then it ’’s a simple matter s a simple matter of turning the boost down to a more modest level and assessing the results by ear.of turning the boost down to a more modest level and assessing the results by ear.

Caution: when adjusting EQ, there is a danger of feedback which can cause damage to your Caution: when adjusting EQ, there is a danger of feedback which can cause damage to your speakers. You may need to reduce your levels to compensate.speakers. You may need to reduce your levels to compensate.

Fully Parametric EqualizationFully Parametric Equalization

Similar to a semi-parametric EQ, but has Similar to a semi-parametric EQ, but has more control.more control.

Fully parametric EQs have sweeps on all Fully parametric EQs have sweeps on all bands of EQ and most have bands of EQ and most have bandwidthbandwidth control as well.control as well.

Bandwidth aka (Q) – the broadness or the Bandwidth aka (Q) – the broadness or the steepness of a frequency curve.steepness of a frequency curve.

The higher the bandwidth, the steeper the The higher the bandwidth, the steeper the curve.curve.

Fully Parametric Equalization CurveFully Parametric Equalization Curve

Auxiliary SendsAuxiliary Sends Two types:Two types:

Pre-fade auxes – monitorsPre-fade auxes – monitors Post-fade auxes – reverbs, delays, recording feeds, etcPost-fade auxes – reverbs, delays, recording feeds, etc

Pre-fade auxiliaries are independent of the fader so that Pre-fade auxiliaries are independent of the fader so that the amount of effect will not change with new fader the amount of effect will not change with new fader levels. This means you will still hear the effect even levels. This means you will still hear the effect even when the fader is at the bottom of its travel when the fader is at the bottom of its travel

It is important to use post fade auxiliary sends for effects It is important to use post fade auxiliary sends for effects units. This is because post fade auxiliaries units. This is because post fade auxiliaries ‘‘followfollow’’ the the input fader so that when input level changes the amount input fader so that when input level changes the amount of effect remains proportional to the new input level. of effect remains proportional to the new input level.

GatesGates

A gate is designed to shut down the audio A gate is designed to shut down the audio signal path when the input signal falls signal path when the input signal falls below a threshold set by the user. It may below a threshold set by the user. It may be used to clean-up any signal that has be used to clean-up any signal that has pauses in it. pauses in it.

CompressorsCompressors A compressor reduces the difference between the A compressor reduces the difference between the

loudest and quietest parts of a performance.loudest and quietest parts of a performance. It works on a threshold system where signals It works on a threshold system where signals

exceeding the threshold are processed and those exceeding the threshold are processed and those falling below it pass through unchanged. When a falling below it pass through unchanged. When a signal exceeds the threshold the compressor signal exceeds the threshold the compressor automatically reduces the gain. automatically reduces the gain.