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PA System
A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound source or recorded sound or music. PA systems are used in any public venue that requires that an announcer, performer, etc. be sufficiently audible at a distance or over a large area. Typical applications include sports stadiums, public transportation vehicles and facilities, and live or recorded music venues and events. A PA system may include multiple microphones or other sound sources, a mixing console to combine and modify multiple sources, and multiple amplifiers and loudspeakers for louder volume or wider distribution. Simple PA systems are often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Napa, California
Napa is the largest city and county seat of Napa County and a principal city of Wine Country in Northern California. Located in the North Bay region of the Bay Area, the city had a population of 77,480 as of the end of 2021. Napa is a major tourist destination in California, known for its wineries, restaurants, and arts culture. History The name "Napa" was probably derived from the name given to a southern Nappan village whose native people shared the area with elk, deer, grizzlies and cougars for many centuries, according to Napa historian Kami Santiago. Mexican era At the time of the first recorded exploration into Napa Valley in 1823, the majority of the inhabitants consisted of Native American Indians. Padre José Altimira, founder of Mission San Francisco Solano in Sonoma, led the expedition. Spanish priests converted some natives; the rest were attacked and dispersed by Mexican soldiers. The first now American immigrants began arriving in area in the 1830s. Post ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Rolph
James "Sunny Jim" Rolph Jr. (August 23, 1869 – June 2, 1934) was an American politician. A member of the Republican Party, he was elected to a single term as the 27th governor of California from January 6, 1931, until his death on June 2, 1934, at the height of the Great Depression. Previously, Rolph had been the 30th mayor of San Francisco from January 8, 1912, until his resignation to become governor. Rolph remains the longest-serving mayor in San Francisco history. Life and career Rolph was born in San Francisco, the son of Margaret (Nicol) and James Rolph. He had four brothers and two sisters. After attending school in the Mission District, he went to work as an office boy in a commission house. He married Annie Marshall Reid (1872–1956) and had at least one son: James Rolph, III (1904-1980). Rolph entered the shipping business in 1900, by forming a partnership with George Hind. Over the next decade, he served as president of two banks, one of which he helped ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mayor Of San Francisco
The mayor of the City and County of San Francisco is the head of the executive branch of the San Francisco city and county government. The officeholder has the duty to enforce city laws, and the power to either approve or veto bills passed by the San Francisco Board of Supervisors, the legislative branch. The mayor serves a four-year term and is limited to two successive terms. Because of San Francisco's status as a consolidated city-county, the mayor also serves as the head of government of the county; both entities have been governed together by a combined set of governing bodies since 1856. There have been 45 individuals who have served as mayor in San Francisco since 1850, when California became a state following the American Conquest of California. Prior to the conquest, Californios served as Mayor of San Francisco during the Spanish and Mexican eras since 1779. The current mayor is former District 5 supervisor and president of the Board of Supervisors London Breed, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
San Francisco City Hall
San Francisco City Hall is the seat of government for the City and County of San Francisco, California. Re-opened in 1915 in its open space area in the city's Civic Center, it is a Beaux-Arts monument to the City Beautiful movement that epitomized the high-minded American Renaissance of the 1880s to 1917. The structure's dome is taller than that of the United States Capitol by . The present building replaced an earlier City Hall that was destroyed during the 1906 earthquake, which was two blocks from the present one. The principal architect was Arthur Brown, Jr., of Bakewell & Brown, whose attention to the finishing details extended to the doorknobs and the typeface to be used in signage. Brown also designed the San Francisco War Memorial Opera House, Veterans Building, Temple Emanuel, Coit Tower and the Federal office building at 50 United Nations Plaza. __TOC__ Architecture The building's vast open space is more than and occupies two full city blocks. It is between V ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Panama–Pacific International Exposition
The Panama–Pacific International Exposition was a world's fair held in San Francisco, California, United States, from February 20 to December 4, 1915. Its stated purpose was to celebrate the completion of the Panama Canal, but it was widely seen in the city as an opportunity to showcase its recovery from the 1906 earthquake. The fair was constructed on a site along the northern shore, between the Presidio and Fort Mason, now known as the Marina District. Exhibits and themes Among the exhibits at the Exposition was the '' C. P. Huntington'', the first steam locomotive purchased by Southern Pacific Railroad; the locomotive is now on static display at the California State Railroad Museum in Sacramento. A telephone line was also established to New York City so people across the continent could hear the Pacific Ocean. The Liberty Bell traveled by train on a nationwide tour from Philadelphia, Pennsylvania, to attend the exposition. The 1915 American Grand Prize and Vanderbilt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phonograph
A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogue recording and reproduction of sound. The sound vibration waveforms are recorded as corresponding physical deviations of a spiral groove engraved, etched, incised, or impressed into the surface of a rotating cylinder or disc, called a "record". To recreate the sound, the surface is similarly rotated while a playback stylus traces the groove and is therefore vibrated by it, very faintly reproducing the recorded sound. In early acoustic phonographs, the stylus vibrated a diaphragm which produced sound waves which were coupled to the open air through a flaring horn, or directly to the listener's ears through stethoscope-type earphones. The phonograph was invented in 1877 by Thomas Edison. Alexander Graham Bell's Volta Laboratory made sev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acoustic Feedback
Audio feedback (also known as acoustic feedback, simply as feedback) is a positive feedback situation which may occur when an acoustic path exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a loudspeaker). In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting howl is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen, hence it is also known as the Larsen effect. Feedback is almost always considered undesirable when it occurs with a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Microphone
The carbon microphone, also known as carbon button microphone, button microphone, or carbon transmitter, is a type of microphone, a transducer that converts sound to an electrical audio signal. It consists of two metal plates separated by granules of carbon. One plate is very thin and faces toward the speaking person, acting as a diaphragm. Sound waves striking the diaphragm cause it to vibrate, exerting a varying pressure on the granules, which in turn changes the electrical resistance between the plates. Higher pressure lowers the resistance as the granules are pushed closer together. A steady direct current is passed between the plates through the granules. The varying resistance results in a modulation of the current, creating a varying electric current that reproduces the varying pressure of the sound wave. In telephony, this undulating current is directly passed through the telephone wires to the central office. In public address systems it is amplified by an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gauss (unit)
The gauss, symbol (sometimes Gs), is a unit of measurement of magnetic induction, also known as '' magnetic flux density''. The unit is part of the Gaussian system of units, which inherited it from the older CGS-EMU system. It was named after the German mathematician and physicist Carl Friedrich Gauss in 1936. One gauss is defined as one maxwell per square centimetre. As the cgs system has been superseded by the International System of Units (SI), the use of the gauss has been deprecated by the standards bodies, but is still regularly used in various subfields of science. The SI unit for magnetic flux density is the tesla (symbol T), which corresponds to . Name, symbol, and metric prefixes Albeit not a component of the International System of Units, the usage of the gauss generally follows the rules for SI units. Since the name is derived from a person's name, its symbol is the uppercase letter ''G''. When the unit is spelled out, it is written in lowercase ("gauss"), unless ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horn (acoustic)
An acoustic horn or waveguide is a tapered sound guide designed to provide an acoustic impedance match between a sound source and free air. This has the effect of maximizing the efficiency with which sound waves from the particular source are transferred to the air. Conversely, a horn can be used at the receiving end to optimize the transfer of sound from the air to a receiver. Acoustic horns are found in nature in the form of the burrows constructed by male mole crickets to amplify their song. The earliest appearance of the horn in connection to sound in The Times was published in 1786: Applications Acoustic horns are used in: * horn loudspeakers * brass and woodwind musical instruments * vehicle horns such as those used on cars, trucks, trains, boats, and bicycles * megaphones, often used by lifeguards at public swimming pools. * foghorns, used to warn ships * ear horns, used by people who are hard of hearing (the human ear itself having the form of a horn) * pickup horns ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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