In the early days of concert sound, the 1950s and '60s, there were few choices for professional sound-reinforcement speaker systems. JBL, Electro-Voice and Altec-Lansing were the first companies to develop industry-standard live-concert speakers, and remained the only choices until the mid-1970s. As concerts became larger, other speaker manufacturers came on the scene. Eastern Acoustic Works (EAW), Cerwin Vega, Turbosound, McCauley, Community and a host of other companies joined in. While the number of concert speaker manufacturers is still plentiful, most companies follow industry standards in the basic components necessary for concert-sound reinforcement, adding their individual engineering ideas in speaker and cabinet design.
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Speaker Size Standards
Industry-standard speaker sizes are still followed by most every manufacturer, developed and tested over many years of research and development. But it was the acceptance of professional sound engineers in the field that ultimately determined which sizes and designs worked best. The chart below shows the industry standard size for the frequency application:
• Sub-bass: 18-inch speaker • Bass: 15-inch speaker • Midrange: 12- or 10-inch speaker • High midrange: 10-inch speaker or 2-inch horn driver • High: 1-inch or 2-inch horn driver
The construction of speaker cabinets is as important as the speaker itself, and can add favourable frequency and performance attributes. While marine-grade plywood is widely used, new composites that resist damage during transport, and provide necessary sonic capabilities, are now used in designs by several manufacturers.
Cabinet design dictates a speaker's "throw," which is the ability of sound to travel. Short-throw cabinets are designed to project sound over short distances, such as in a nightclub. Long-throw cabinets are used when sound needs to travel a greater distance, such as in a concert hall. Long-throw cabinets incorporate a horn design, in which the speakers are recessed, and a curved horn port helps sound project and spread. Short-throw cabinets feature front-surface speaker mounting to help control sound travel. Large concert venues will use a combination of short and long-throw cabinets.
Folded Horn Cabinets
Folded horn cabinets are used to enhance sub-bass frequencies. Speakers are mounted internally in a sealed chamber, and emit sound through a series of baffles that enhance the low end. Folded horn cabinets usually have mid- to long-throw attributes, although short-throw designs are also available. Manufacturers use proprietary designs in baffle arrangements, making the choice of cabinet a matter of preference.
Bass-reflex cabinets make use of ports, or openings, to take advantage of sound emitting from the rear of the speaker. Many proprietary designs exist, but all provide enhanced speaker sound. Simple ports allow rear speaker sound to add to the overall audio performance by increasing bass, while special tuned-ports are used to filter certain low-end frequencies by dampening some and enhancing others.
Full-Range Speaker Cabinets
Full-range cabinets include two or more speaker combinations to provide full-spectrum sound. Typical full-range cabinets in live concert settings include one or more 10-inch or 12-inch midrange speakers, and a high-frequency horn. Since sub-bass and bass cabinets are usually placed at ground level, full-range cabinets are placed on the stage, or flown overhead with wire rigging. Full-range cabinets are short- to medium-throw in design.
High frequencies are produced by a type of speaker called a "driver". Horn drivers are 1 inch to 2 inches in diameter, and use only a voice coil to produce sound, which limits air movement and resulting bass frequencies. To project sound, drivers are fitted to directional horns, designed to increase and direct sound to concert volume levels. Like speaker cabinets, horns come in many styles and proprietary designs. Horns are made of aluminium, fibreglass and other composite materials, mounted in a wood or rugged composite enclosure. Since the horn itself is designed to produce a particular sound, the enclosure simply acts as a protective case, offering no sound-enhancing design features. Depending on horn design, short-, medium- and long-throw models are available.
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