Sound: Signal Flow and Equipment

Signal Flow: The Basic Sound System

• Source - the origin of the sound at the moment of reinforcement
  • Computer Playback/Programs
  • Microphones
  • Electronic devices (cell phone, ipods, cd player, guitars, electric keyboards, etc.)
• Mixer - also called the sound board or sound console; allows for the mixing of multiple sound elements and allows for the manipulation of their sound quality
• Amplifier -  increases the power of the electrical signal going out of the mixer into a speaker in order to get the speaker to generate sound waves
• Speaker - device that converts electrical signal into sound waves that are then broadcast to the audience or listener

Sources

Playback

These are sources like computers, cd players, and ipods that output a digital signal to the mixer. For most theatres, this is the main source for things like soundscapes and sound effects. Playback software on a computer is the most common type of playback source because it allows for a whole variety of adjustments like arranging a cue list, playing back multiple files at once, adding fade ins or outs, adjusting volumes, adding effects (like echoes or distortion), and playing various audio formats (like .mp3 or .wav).

Microphones

Take the sound waves of the singer, instrument, or other thing to be reinforced and converts those sound waves into an electrical signal through something called a diaphragm and a magnet. A diaphragm is small piece of thin metal that vibrates whenever it is hit by sound waves. The diaphragm is attached to a magnet inside of an internal coil and the movement of these generates electricity which then goes down the cable as a signal that the sound mixer can manipulate.

There are many types of microphones that each have their best uses. One of the more popular types that you will see for musical theatre shows is the body mic. These are wireless microphones consisting of a small mic connected to a wire, a belt pack transmitter, and a receiver either backstage or next to the mixer. This kind of microphone is extremely popular because it can attached to the actor's head or face to provide constant, consistent reinforcement no matter where they are on-stage. The single wire is often run down the actor's back to the mic pack, which is approximately the size of a deck of cards and can be hidden in a variety of places under the actor's costume.

Making the Custom Microphones for Hamilton! Links to an external site.

(Length 16:38) from Adam Savage's Tested on YouTube

Mixer

This is the main control interface for the sound system. Consists of a whole bunch of input channel strips which each represent a single input (and therefore signal) into the mixer. Each input has a fader that can be raised and lowered to adjust its volume, as well as other features like an equalizer, mute button, and routing controls.

Most mixers are digital now and have useful features like grouping, pages, recallable settings and scenes, faders that are motorized to move on their own, and on-board effects (like reverb, delay, and distortion). They also allow the sound engineer nearly endless options for how to program and mix the show.

Adam Savage Explores the Sound Mixing of Hamilton! Links to an external site.

(Length 11:25) from Adam Savage's Tested on YouTube

Amplifiers

Amps are essentially sound boosters. Some amplifiers come built into speakers while others are a separate, stand-alone piece of gear in the signal flow. Either way, their job is to take the electrical signal from the mixer and make it so powerful that it can cause the speaker to output sound and for the audience to be able to hear that sound from anywhere in the theatre.

Speakers

We've all seen them, both big and small. Speakers are the devices that output the final sound for the audience to hear. They are directional and must be placed in a position to point to the area of the audience that they need to output towards. The signal from the amplifier causes a flexible cone in the speaker to move and vibrate, which produces the sound.

As mentioned above, speakers come in two different versions: active and passive. Active speakers have a built in amplifier while passive speakers need a separate, external amplifier in order to work. Most theatres use passive speakers due to their higher power/output potential and the ability to place all the amplifiers in a central location that can be easily accessed (as opposed to needing to get a technician up to the speaker itself in order to adjust the amp settings).

Speakers are also separated by their output frequency. Higher pitched sounds are routed to speakers called tweeters while lower pitched sounds go to special speakers called subwoofers. The reason for this is that low-frequency sounds have larger sound waves and require bigger cones in order to create the appropriate vibrations. The reverse is true for tweeters and higher frequencies.

CYMATICS: Science Vs. Music - Nigel Stanford Links to an external site.

(Length 5:52) from Nigel John Stanford on YouTube