Speakers used in live concerts come in a variety of types and sizes. While there is no real universal standard speaker, there are standard configurations, chosen for the type of music and concert venue. The primary function of concert speakers, also called drivers or loudspeakers, is to allow the audience to enjoy high-quality sound wherever they are situated in the venue. Performers also need to hear themselves and other band members and require monitor speakers to be accurately placed.
Sound Frequency and Reproduction
Sound frequencies produced in a concert environment are identified as: sub-low, low, midrange, mid-high, and high frequencies. In order to provide balanced sound, each frequency must be isolated using an electronic crossover device, set by the sound engineer. Crossovers filter and separate overall frequencies, and the signals are routed to dedicated amplifiers. The amplified filtered signal is sent to loudspeakers, designed to reproduce the particular frequencies efficiently.
Lower frequencies require more amplifier power and larger speakers to reproduce. As frequencies go from low to high, power and speaker sizes are reduced proportionately. It is not unusual to find four and five-way crossover systems in place at large concerts, with separate amplifiers and speakers for each frequency. Smaller venues use simpler two or three-way crossover speaker systems, when critical reproduction of all frequencies is not necessary or warranted.
Sub-bass, or sub-woofer speakers, are usually 18 inches in diameter. Since very low frequencies are more often felt than heard, sub-bass cabinets are placed on the floor for maximum effect, and the speakers are often mounted facing the back of the speaker cabinet, which is tuned to produce enhanced sub-bass tones. Smaller concert venues may use one or two sub-bass enclosures, while large concert arenas will use 12 or more. Low frequencies are not overly directional, making speaker placement in relationship to audience members not as critical. Sub-bass frequencies are generated by bass guitars, bass drums and lower range synthesizer keyboard notes.
Speakers used to reproduce bass frequencies are normally 15 inches in diameter, and are ideally placed at chest level of the audience. Bass frequencies are in the audible range, but are placed physically lower than higher frequency speakers in an effort to separate the sound in the most efficient and pleasing manner to the listener. Bass speaker frequencies also are generated by bass guitars, drums, lower range synthesizer and other keyboard notes, but in a higher frequency register than sub-bass.
Midrange concert speakers are typically 12 or 10 inches in diameter, and reproduce sounds in the middle of the frequency spectrum. Speakers are placed above bass speakers and below high-frequency drivers. Midrange frequencies are produced by vocals, guitars, keyboards, drums and other instruments. The dominant sound we hear is in the midrange, since these frequencies are audible and easily understandable.
High frequency reproduction requires small speakers with tight diaphragms to limit bass-inducing air movement. Since these speakers, called drivers, use diaphragms of 1 to 2 inches in diameter, they will not handle high-wattage amplifiers. Their inherent design also causes sound levels to be low and must use an attachment called a "horn" to project sound to audible concert levels. Horns produce high-midrange and high-frequency sound and are usually directed at audience head level. Cymbals, guitars, keyboards, vocals and other instruments produce sound in the high-frequency domain.
Concert Speaker Cabinets
Most of the cabinets used in large concert venues are full-range cabinets, containing bass speakers, midrange speakers and high frequency horns. These cabinets are usually suspended by wire rigging, at different angles and placement arrays. Separate bass and sub-bass cabinets are placed on the floor, and other full-range cabinets may be placed on the stage, depending on the venue setup and performance type.
Monitor speakers are placed in front, and sometimes to the side, of performers to allow them to hear themselves and other band members. Monitors are connected to separate mixers and amplifiers and allow custom sound mixes for each performer. Monitors are usually two-way systems, containing a 12- or 15-inch speaker and high-frequency horn.