Understanding these few basic tips will let your sound be heard, with minimal hassle and feedback.

Public address (PA) systems have

This portable PA system includes a combined mixer/amp and two loudspeakers that connect together into a single unit. Image courtesy of Fender Musical Instruments Corp.

three main components:

1. SOUND SOURCE: Can be a microphone or a playback device such as a CD/DVD player or videoconference system. (For more information about using microphones, see our February 2009 AVMO.)

2. SIGNAL PROCESSING: Electronics that in some way modify the signal from the sound source before delivering it to the loudspeakers. Includes microphone mixers, equalizers (tone controls), sound effects, and amplifiers. A self-contained system may include all of this in a single unit.

3. LOUDSPEAKERS: The amplifier’s output is connected to the loudspeaker. Loudspeakers may be permanently installed in rooms or in temporary portable systems, allowing them to be moved from room to room as needed. microphones, CD players, DVD players, MP3 players, and other devices can all be controlled by a mixer. Each incoming signal has its own input on the mixer. Each input is called a “channel.” Each channel has its own processing controls. A basic mixer only has gain (volume) knobs for each channel while an advanced mixer may have controls for equalizing, muting, panning, and much more. Every mixer also has what is called a “master” control. This control sets the baseline audio output for all channels to the room.

Mixers are often defined by the maximum number of inputs it can handle. An 8-channel mixer can take 8 separate inputs, a 16-channel mixer can handle 16 inputs, and so on.

The channel strip on most mixers is organized vertically, as in a column. From the bottom of each channel reading up to the top are the following controls:

1. Fader slider (gain)
2. Mute (push button)
3. Pan (Left-Right)
4. Equalizer section
5. Auxiliary sends
6. Pre-amp control


WHY USE A MIXER?
Assume you are using an audio system with two microphones that are connected to a mixer. During an event, one presenter is speaking very softly into her microphone on channel 1, and the other presenter is speaking very loudly into his microphone on channel 2. You can adjust the individual audio levels on each channel so the audience can hear both presenters comfortably. The outputs of each channel are combined and sent to the mixer’s output. This process, called “mixing,” is the process of combining different audio sources or tracks and blending them for the best sound quality and balance.

COMMON MIXER FUNCTIONS
MUTE: A button that allows you to silence that channel only, without moving the volume knob.

PHANTOM POWER: A push button or switch that sends power to condenser-type microphones through an XLR connection.

PAN: A knob that allows you to

Simplified signal flow block diagram.

move a sound source from left through right output channels.

EQUALIZATION: Often simplistically described as a sophisticated “tone control,” an equalizer allow you to manage given frequency ranges for a specific channel.

AUDIO SIGNAL TYPES
When working with audio equipment, you are likely to see labels referring to mic, line, or speaker signal levels:

These labels refer to the three different voltage levels of an audio signal — microphone level, line level, and loudspeaker level. These three signal inputs are incompatible with one another. Because of these differences, you must use the proper connectors and adapters that are designed to carry that specific type of signal level.

Source: “AV Setup Guide for Events, Meetings, Conferences, and Classrooms: Best Practices & Procedures,” InfoComm International.