Sound system speakers come in a variety of shapes, sizes and types. FOH (front-of- house or "main") speakers are the speakers that emit sound to the audience. Monitor speakers are aimed at performers, allowing them to hear themselves. The most common sound system speakers consist of the full-range type. Full-range speakers contain two or more speakers of differing sizes in a single enclosure, with each speaker reproducing different frequencies such as low, mid-range and high frequency sounds. In large systems, multiple full-range speakers are used for wider sound dispersion, and separate sub-woofers may also be employed to handle very low bass frequencies. Speakers are either non-powered, requiring a separate amplifier, or powered versions with built-in amplifiers. Both types are used in both small and large systems.
Power amplifiers provide the power to non-powered speakers. In smaller systems, one amplifier is used to power speakers, but it is common for large systems to use more than one amplifier for each full-range speaker cabinet. This arrangement is called "bi-amping" or "tri-amping". More powerful amplifiers are used for the bass speakers, less-powerful amplifiers for mid-range and lower power amplifiers are used for high frequencies. The arrangement allows more efficient power distribution to the speakers.
Mixers strengthen the input signals from microphones and musical instruments, add equalization and sound enhancements and send the overall signal to the power amplifiers. Mixers allow the operator to adjust the sound quality and output level of each input signal, resulting in a "mix" of sounds. Each input is assigned a separate mixer channel, numbering from two to 48 channels or more depending on need and are combined in a master section which controls the sum of all channels. Smaller systems use combination mixer/amplifiers called powered mixers, while larger systems use non-powered mixers, relying on the power amplifiers to drive the speakers.
Effects are added to individual channels or to the combined mix. These include sound enhancing devices such as echo and reverb, or sound controlling effects such as equalizers, compressors and limiters. Equalizers adjust individual sound frequencies to enhance or correct the sound of the room or individual instruments. Compressors and limiters even out the sound by adjusting loud or soft signals. Some smaller non-powered and powered mixers, integrate effects and equalization with the mixer, allowing for a compact all-in-one system.
Cables are used to patch the whole sound system together, and come in three basic varieties (excluding AC power cables.) Low-impedance (also called low-z or balanced) cables are shielded three-conductor cables to connect mics and most sound system components, except for speakers. High-impedance (also called high-z or unbalanced) cables are shielded two-conductor cables used for the connection of sound system components in smaller systems. Speaker cables are unshielded two-conductor cables used to connect the speakers to the power amplifiers.
An input device can be a microphone, musical instrument, or musical instrument direct box (called a DI.) A DI box is used to directly connect musical instruments to the mixer, but electrically modifies the electrical signal to eliminate RF (radio frequency) interference and voltage hum. Hums and RF problems often occur when long cable lengths are required to reach to mixer.