Public address system
Typical applications include sports stadiums, public transportation vehicles and facilities, and live or recorded music venues and events.
PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations—such as schools, stadiums, and passenger vessels and aircraft.
[4] A short time later, the Automatic Enunciator Company formed in Chicago order to market the new device, and a series of promotional installations followed.
[5] In August 1912 a large outdoor installation was made at a water carnival held in Chicago by the Associated Yacht and Power Boat Clubs of America.
The company also set up an experimental service, called the Musolaphone, that was used to transmitted news and entertainment programming to home and business subscribers in south-side Chicago,[8] but this effort was short-lived.
When the 12 V battery was connected to the system, they experienced one of the first examples of acoustic feedback,[9] a typically unwanted effect often characterized by high-pitched sounds.
[9] Jensen and Pridham refined the system and connected a phonograph to the loudspeaker so it could broadcast recorded music.
[10] They did this on a number of occasions, including once at the Napa laboratory, at the Panama–Pacific International Exposition,[9] and on December 24, 1915, at San Francisco City Hall alongside Mayor James Rolph.
[10] This demonstration was official presentation of the working system, and approximately 100,000 people gathered to hear Christmas music and speeches "with absolute distinctness".
[9] By the early 1920s, Marconi had established a department dedicated to public address and began producing loudspeakers and amplifiers to match a growing demand.
The 1925 Royal Air Force Pageant at Hendon Aerodrome used a Marconi system to allow the announcer to address the crowds, as well as amplify the band.
[9] In 1929, the Schneider Trophy race at Calshot Spit used a public address system that had 200 horns, weighing a total of 20 tons.
During the late 1920s to mid-1930s, small portable PA systems and guitar combo amplifiers were fairly similar.
Small handheld, battery-powered electric megaphones are used by fire and rescue personnel, police, protesters, and people addressing outdoor audiences.
With many small handheld models, the microphone is mounted at the back end of the device, and the user holds the megaphone in front of her/his mouth to use it, and presses a trigger to turn on the amplifier and loudspeaker.
Larger electric megaphones may have a microphone attached by a cable, which enables a person to speak without having their face obscured by the flared horn.
PA systems of this type, often providing 50 to 200 watts of power, are often used in small venues such as school auditoriums, churches, and coffeehouse stages.
Public address systems consist of input sources (microphones, sound playback devices, etc.
), amplifiers, control and monitoring equipment (e.g., LED indicator lights, VU meters, headphones), and loudspeakers.
In non-performance applications, there may be a system that operators or automated equipment uses to select from a number of standard prerecorded messages.
This was pioneered by Stephen Robert Pearson of Lancashire, England who was granted patents for the systems, which also incorporate control functionality.
A UK company called Remvox Ltd (Remote Voice experience) has been appointed under license to develop and manufacture products based on the technology.
Systems of this type are commonly found in the rail, light rail, and metro industries, and let announcements be triggered from one or several locations to the rest of the network over low bandwidth legacy copper, normally PSTN lines using DSL modems, or media such as optical fiber, or GSM-R, or IP-based networks.
These are linked to train describers, which state the location of rolling stock on the network from sensors on trackside signaling equipment.
[citation needed] Small clubs, bars and coffeehouses use a fairly simple set-up, with front of house speaker cabinets (and subwoofers, in some cases) aimed at the audience, and monitor speaker cabinets aimed back at the performers so they can hear their vocals and instruments.
For popular music concerts, a more powerful and more complicated PA System is used to provide live sound reproduction.
Touring productions travel with relocatable large line-array PA systems, sometimes rented from an audio equipment hire company.
It often sounds like a loud high-pitched squeal or screech, and can occur when the volume of the system is turned up too high.
Sound engineers take several steps to maximize gain before feedback, including keeping microphones at a distance from speakers, ensuring that directional microphones are not pointed towards speakers, keeping the onstage volume levels down, and lowering gain levels at frequencies where the feedback is occurring, using a graphic equalizer, a parametric equalizer, or a notch filter.
