Sound Systems - An Introduction
(Written By Derek Rowell, Last updated 27/09/2000)

Sound Systems – An Introduction

This manual aims to provide an introduction to sound engineering. It is tailored for those who have little or no previous experience of sound systems. It may also serve as a useful reference for anyone involved with USSU Stage Crew.

An advanced manual is currently under development with the intention of covering concepts and techniques in more detail.

A glossary has been included at the end of this manual, along with some useful desk charts.

Whether you are about to make the first steps in sound engineering or have already gained some experience, good luck – and remember, enjoy yourself!

System Components

The flow diagram below is a simplified illustration of a system suitable for bands:

This may appear a little complicated. Please do not worry, all will become clear!

At most events, there are 2 separate groups of people requiring a sound system. For this reason, we use 2 separate sound systems. These systems are known as FOH (Front of House) and Monitors.

One group of people is the audience – normally located on a dance floor or in an auditorium in front of the stage. These people listen to the FOH system.

The other group of people are the performers – normally located on the stage. These people use the Monitors system to allow clear monitoring of parts of the signal source relevant to them.

The various components of a sound system will now be explained:

FOH Desk
This is the mixing console used to combine all the signal sources for the FOH system. It is typically located in the auditorium.

Each signal appears on a separate desk channel and is normally mixed down to a 2 channel (stereo) output. The individual desk channels allow adjustment of characteristics such as tone.

USSU own a number of mixing consoles of varying size and specification to cater for a wide range of events.

Monitors Desk
Whereas the FOH system normally consists of only 1 stereo mix, the Monitors system may contain many different mixes – often 1 or more mix for each performer. Each person on stage may need to hear a completely different combination of signal sources.

The monitors desk is the mixing console used to create these mixes and is similar to the FOH desk. It is normally located at the side of stage.

Stage Box
All the signal sources are split here and sent off to the FOH and Monitors systems. The FOH desk is connected to the stage box via a multicore. This is a long link containing many cables.

Graphic Equaliser
This unit takes the audible frequency range and divides it into around 30 parts (bands). A fader is assigned to each frequency band to allow precise control of the sound. It is possible to have analogue or digital units.

A graphic equaliser is used in the FOH system primarily to make the rig sound good and also to avoid feedback. Every venue has a different acoustic profile and will therefore require a different set of adjustments to be made with the graphic equaliser. The acoustic properties of a room will be affected by factors such as temperature, humidity, the size and position of audience, draping etc.

A graphic equaliser is used in the Monitors system primarily to reduce the dangers of feedback due to the close proximity of speakers and microphones. Each mix has its own graphic equaliser.

Limiter
This unit simply governs the amount of signal passing through it to protect equipment and/or for environmental reasons.

Active Crossover
Please refer to the “Active/Passive Systems” section for an explanation of this unit.

Drive Rack
This is the name given to a flight case containing equipment such as a graphic equaliser, active crossover or limiter. Playback/record modules (CD player, mini-disk deck etc) may also be found in a drive rack.

The main FOH system currently used by USSU includes 2 separate drive racks. This allows more precise control for each zone of the system. Alternatively, the system can be split across several venues.

Effects Rack
This is the name given to a flight case containing equipment such as effects units or modules for more precise control and manipulation of sound. Most of the equipment in an effects rack is not discussed until the Advanced Manual. Typically, the signal from each channel of a mixing console can be sent to an effects rack. An effect such as reverberation, delay or pitch change can then be applied to the signal before it is returned to the mixing console and added to the overall mix.

Amplifier
This unit increases the power of an incoming signal before it is fed to a speaker cabinet.

USSU owns a wide range of amplifiers. Characteristics such as maximum power output available for a given input signal level and handling capabilities should influence choice of a suitable amplifier.

Speaker Cabinet
There are many different designs of speaker cabinet available. Designs cater for various applications, power output requirements and budgets.

The main FOH system currently used by USSU includes Renkus Heinz speaker cabinets. There are 2 types of cabinet:

• Trapezoidal cabinet – handling all frequencies above sub-bass. These cabinets were chosen for their ability to array and quality of sound reproduction.
• Cuboid-shaped cabinet – handling sub-bass frequencies. These cabinets were chosen for their short-throw abilities and quality of sound reproduction.

• Apply power to all control equipment (mixing console, graphic equaliser, active crossover etc)
  
• Apply power to amplifiers – starting with the low-frequency end and finishing with the high-frequency end
  
• Ensuring all crossovers are muted, turn all amplifier volume controls to full
  
• Send through a small amount of highest frequency range signal. Check that it is coming out of the correct drivers and that all drivers are working properly
  
• Only when you are satisfied that this is the case, repeat the above step with the next highest frequency range and continue until the complete system has been checked

• Microphone (picks up sound created by voice, instrument etc)
  
• Musical instrument connected via cable and DI (Direct Inject) box
  
• Recorded media (e.g. CD, mini-disc, DAT, vinyl, DVD or cassette)

• Dynamic – a robust design that requires no electrical power to operate. They are ideal for all-round high sound pressure levels (SPL). However, they are not as sensitive to high frequencies as condenser types
• Condenser – need power to operate. Condenser mics are very sensitive to distant sounds and high frequencies.

• Cardioid – a “heart-shaped” polar response, meaning that most of the sound is picked up from the front. Dynamic cardioid mics help reduce unwanted spill from other instruments, thus reducing the risk of feedback.
  
• Hyper-cardioid – similar to a cardioid pattern but with greater directionality. This provides even greater protection from unwanted spill and feedback.
  

• XLR – same connector as used on mic leads
• Speakon – round plastic connector – normally black, often with a blue ring or metal release tab. USSU currently use 2 different sizes of speakon connector – the Speakon 4 which can accommodate 4 wires (up to 2 way applications) and the Speakon 8 that can accommodate 8 wires (up to 4 way applications).
• Socapex – these are large round metal connectors that contain 19 pins. They are used on the back of racks of amplifiers. USSU have a number of looms for interfacing with these connectors.

• 13 Amp – the standard plug and socket found in any home or office. Providing the fuse is rated, maximum current rating is 13 amps
• IEC – a mains connector that you have probably seen before on the back of a PC. This connector is available in 2 types with a maximum current rating of either 6 or 10 amps.
• C-Form (16A, 32A, 63A) – a blue plastic connector available in a range of sizes and current ratings.