Connect the PA speakers to the amplifier(s). Multiple amplifiers are used for larger sound systems. Speakers typically include at least one speaker on either side of the stage (left and right), plus at least one subwoofer. Larger sound systems include equal amount of multiple speakers on both sides, and multiple subwoofers.
Connect the mixing board (aka "sound board") to the amplifier. Sometimes you will run the mixing board first through an equalizer, then connect the equalizer to the speaker amplifier(s). Power the sound system on once it is connected.
Connect microphones and instruments into your mixing board. Typically, you use XLR cables (three-pronged cables) for these connections, though you can use quarter-inch cables as well if your mixing board has quarter-inch input jacks. Keep the volume of the sound system muted as you connect each instrument. Each microphone or instrument gets its own channel in the mixing board; you are limited as to how many microphones and instruments you can send through the sound system based on the number of channels on your mixing board. If the performance includes a drum set, set up microphones around the drum set to include the drums in the sound-system mix. Guitar amps should also have a microphone in front of the speaker on the amp, unless the guitar amp has an output jack you can plug into your mixing board.
Turn on all electric instruments. Un-mute the sound system. One by one, test each channel to make sure it is working properly. Have a vocalist sing into each microphone, and instruct instrumentalists to play their instruments one by one, until you have verified that all channels are working properly and that the sound being played on stage is being projected from the sound-system speakers. If a channel is not working properly, double check the connection from the microphone or instrument to the sound mixing board.
Conduct a full sound check, in which the entire band or performance group plays together. Usually, they play a song or piece from the upcoming performance. As they play, mix each microphone or instrument accordingly, so nothing is too loud or too quiet. Different musical styles call for different mixes; electronic music is heavy on the bass and low frequency tones, while rock-and-roll often has guitars, drums and vocals in the forefront. Sound checks typically take at least thirty minutes, sometimes much more, for large rooms or groups with several performers. Do not rush the sound check; if the performance sounds bad, people will complain and possibly leave. Get the sound dialed in just right. When you are done, keep the levels exactly as they are.
Adjust the levels of each microphone or instrument accordingly throughout the performance. Many musicians play louder during the live performance than in a sound check, to compensate for crowd noise and excitement. If an instrument sounds too loud or a microphone is giving off the high-pitched whining feedback noise, turn that channel down to a more tolerable level. You can also control the volume of the overall mix with the system's master volume control on your mixing board.