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Sound Equipment

Sources
Signal Processing
Amplification and Speakers

Sources

A source is anything that generates a electrical sound signal, and will always be at the beginning of the sound chain. These can be anything from a single microphone, which converts sound vibrations in the air to an electrical signal, to a CD player or a computer.

Playback

Within theatre, you will most likely be dealing with sound effects, so a minidisc or CD player will almost certainly feature somewhere in your design. For basic sound effect playback, I will almost always use minidiscs, due to the fact that they are digital, you can record to them very easily and they are cheap. You can also name your tracks and it is very easy to re-order tracks, combine or delete things at a moments notice. CD's, or playback from a computer are also good options, but these are more prone to problems. You can't change track order on a CD, so you may end up having to skip backwards and forwards, or even change CD's over in the middle or a performance. I always build up my sound effects on computer, and then transfer them onto minidisc, so you might ask why I don't just stick to using computers during a show. One simple reason - The Blue Screen Of Death. Computers will crash mid-show, so are best avoided. That said, computers are getting better and more robust software is becoming available, so in the future things may be very different.

Microphones

Microphones fall into two broad categories; spot microphones for dealing with individual people or instruments, and ambient microphones for capturing sound over a wider area. All microphones work through a diaphragm within them being vibrated by sound waves in the air. These vibrations are converting into an electrical signal which can them be carried away further down the sound chain.

Microphones are either dynamic (moving coil) or condenser microphones. Dynamic microphones, such as the industry standard Shure SM58, are very robust and have a good frequency response in the higher range such as the human voice. They are widely used in theatre (and also the music industry) as vocal microphones and for applications where the poor low-end response is not a problem or in risky situations as they are reasonably robust and cheap. Condenser microphones are more expensive, and have a much flatter frequency response than dynamic microphones, but are more expensive and easier to damage. They will tend to be used in less risky situations or as instrument microphones for bands and orchestras. Condenser microphones also require phantom power (a 48V supply provided by the mixing desk, or internal batteries).

There are two common microphones that are widely used to pick ambient sound onstage. These are shotgun microphones and boundary microphones, or "floats". Shotguns are highly directional, and are designed to pick up sound directly in front of the microphone over a greater distance than other microphones, but not much to the sides. This makes them very useful when placed at the sides of the stage to amplify a chorus in a musical for example. Float microphones contain a ribbon which is used to pick-up the sound, and as such are quite fragile. The small ribbon pick-up is mounted on a flat plate to enable them to pick up sounds in front of the microphone, and they can be placed across the front of the stage to provide coverage right across the width.

Radio Microphones use a radio transmitter and receiver rather than a cable to connect to the sound system, making them portable and enables them to be worn by performers. The microphones either be hand-held, or a small omni-directional capsule connected to the transmitter by a wire. These small capsules can be worn by performers to amplify speech or more often the singing in musicals, either in the hair, behind the ear or within clothing. Care must be taken when selecting the frequency for a radio microphone, as certain frequencies require licenses, and others may be in use by other people. Taxi firms are normally the worst culprits for this. Care should also be taken to ensure that radio microphones are turned down when the performer exits, they will almost certainly not want the audience to hear what goes on backstage!

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Signal Processing

Mixing Desks

The centre of any sound set-up will be the mixing desk, and from this the sound engineer has full control of everything that goes on with the sound for the show. Mixing desks do exactly what it says on the tin. They takes the source(s) and combine them to produce the final mix which the audience hears. Effects and equalisation are also added at this stage by outboard equipment. Mixers can range in size from a tiny little desktop mixer to something which takes up an entire room, however essentially they all do the same thing, albeit in more and more elaborate ways.

Each source signal will be allocated a separate channel within the mixer, giving the sound designer full control over each part of the system. A typical single channel will normally consist of the following components:-

• Input Section - All the connectors on the back!
• Gain or Trim - Amplifies the incoming signal to a level that is useable.
• Equalisation - Tone controls for boosting/cutting bass, treble etc.
• Auxiliaries - Sends part of the signal to external processors such as effects units or to onstage monitors.
• Pan - Controls if the signal is going left, right or centrally in the final mix.
• Fader - Controls the overall volume of the signal in the overall mix.

After passing through the channels, the signals can then be routed to various different outputs in the master section, ranging from a simple stereo pair of speakers to a much more elaborate set-up. Other common features of mixing desks include prefade listen and sub-grouping. Prefade allows the sound engineer to listen to a single channel through their headphones, subgrouping allows the overall level of several channels to be controlled by a single fader (very useful for drums),

Outboard Equipment

Outboard equipment is used to process the raw sound and change it, normally for the better! Outboard can be connected to the mixer channel either as an insert or an auxiliary. Inserts take the entire signal through the outboard gear and back again, whereas with an auxiliary the sound designer can choose how much of the signal to send. Different types of outboard gear can include:-

• Graphic Equalisers - Provides a boost/cut control of very parts of the sound frequency spectrum, usually 1/3rd of an octave. Used for shaping the sound or cutting troublesome frequencies.
• Delays - Delays do exactly that, delay the incoming signal for a period of time before letting it through. Can be used to provide a "clean" echo, or to counteract problems with the sound from various speakers arriving at the same point at different times.
• Compressors - Compression is used to reduce the level between the loudest and quietest parts of the signal. Used mainly for vocals and bass guitars, they reduce the gain of the signal above a certain decibel threshold, and also smooth the sound and help vocals and others sit better in the mix.
• Noise Gates and Expanders - Noise gates act as a switch, and mute a signal when it falls below a certain decibel threshold. This has the effect of cutting out background noise when an instrument is not playing for example.
• Effects / Reverberation - These can be used to enhance the signal or to produce a noticeable difference in the sound. Common effects include reverbs and echoes, which can make vocals sound smoother or as if they are in a cathedral, but there also any many effects units out there that can produce anything from a flanger to the sound of an old radio.

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Amplification and Speakers

Amplifiers

Amplifiers take the relatively low level signal output from a mixing desk and increase it to a level which can be used to drive a speaker. Amplifier power is measured in Watts, with the average power amplifier being in the range of hundreds of Watts. The best power amps for theatre use generally consist of simply a power switch and a volume control - there is nothing which can impair the quality of the mixed signal. It is important that the power output of the amplifier is matched to the speakers. If it is too large then you may damage your speakers, too low and you will have to drive the amp very hard and run the risk of distorting the signal. Ideally, each speaker you use would have it's own separate amplifier, connected to a single output from the mixing desk.

Loudspeakers

Finally, at the end of the sound chain is the loudspeaker. These take the electrical signal from the amplifier and convert it, by means of a cone moved by an electromagnet, into the vibrations in the air that the audience hear as sound. It is very difficult to produce a single speaker cone that can cope with all the frequencies that we hear, so often speaker systems will be built up from several speakers which handle different regions of the spectrum. You can either choose to use "Full Range" speaker cabinets which have several cones in them to handle all the frequencies required, or have separate speakers. When using a system of several speakers (typically a sub for bass, a midrange speaker and a horn for the top end) you will often need to include a crossover as well. This splits the signal into the different frequency ranges to drive the various speakers, trying to run bass through a horn would almost certainly damage it! See also the section on Speaker Positioning on the Production Process page.

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