Pembesar suara

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Pembesar suara fideliti rendah murah 3.5 inci, biasanya ditemui dalam radio kecil
Sistem pembesar suara fideliti tinggi 4-hala mahal

Pembesar suara merupakan transduser elektroakustik yang menukar isyarat elektrik kepada bunyi. Pembesar suara menolak satu perantaraan menurut denyutan isyarat elektrik, dengan itu menyebabkan gelombang bunyi terhasil dari mana ia boleh diterima oleh telinga. Pembesar suara (dan transduser elektroakustik yang lain) ialah unsur paling banyak kepelbagaian dalam sistem audio moden dan biasanya bertanggungjawab bagi kebanyakan perbezaan bunyi apabila membanding sistem-sistem berlainan.

Istilah 'pembesar bunyi' boleh merujuk kepada transduser individu (dikenali sebagai 'pemacu'), atau kepada sistem lengkap yang terdiri daripada kotak pembesar suara yang mengandungi satu atau lebih pemacu. Untuk menghasilkan julat frekuensi yang luas dengan memuaskan, kebanyakan sistem pembesar suara memerlukan lebih dari satu pemacu, terutamanya bagi aras tekanan bunyi atau kejituan tinggi. Pemacu individu digunakan bagi menghasilkan kembali julat frekuensi berlainan. Pemacu-pemacu tersebut dinamakan subwufer (frekuensi amat rendah), wufer (frekuensi rendah), pembesar suara julat sederhana (frekuensi serdahana), twiter (frekuensi tinggi) dan kadang kala supertwiter, optimum bagi frekuensi bunyi tertinggi boleh dengar. Istilah bagi pemacu pembesar suara berbeza bergantung kepada aplikasi. Dalam pembesar suara dua hala, tidak terdapat pemacu "julat-pertengahan", dengan itu tugas menghasilkan kembali bunyi julat pertengahan jatuh kepada wufer dan twiter. Stereo rumah menggunakan julukan "twiter" untuk frekuensi tinggi manakala sistem audio profesional untuk konsert mungkin menggelar pemacu frekuensi tinggi sebagai "HF" atau "high". Apabila pemacu berganda digunakan dalam satu sistem, satu "rangkai penapis", dipanggil lintasan, memisahkan isyarat mendatang kepada julat frekuensi berbeza, dan melencongkan isyarat tersebut ke pemacu yang sewajarnya. Sistem pembesar suara dengan n jalur frekuensi berlainan disebut sebai "pembesar suara n-hala": sistem 2-hala akan mempunyai pembesar suara wufer dan twiter; sistem 3-hala terdiri dari gabungan wufer, julat sederhana dan twiter atau subwufer, wufer dan twiter.[perlu rujukan]

Sejarah[sunting | sunting sumber]

Johann Philipp Reis memasang pembesar suara eletrik pada telefonnya pada 1861; ia tidak mampu membunyikan suara, tetapi mampu menghasilkan nada sempurna. Alexander Graham Bell menfile paten pembesar suara eletrik pertamanya (yang mampu mengeluarkan pertuturan boleh difahami) sebagai sebahagian dari telefonnya pada 1876, yang dikuti pada 1877 dengan versi lebih baik dari Ernst Siemens. Nikola Tesla dilaporkan menghasilkan peranti serupa pada 1881, tetapi tidak diberikan paten.[1] Semasa masanya, Thomas Edison diberikan paten British bagi sistem yang menggunakan udara mampat sebagai mekanisma penguat bagi phonograf silinder awalnya, tetapi dia akhirnya menggunakan tetuang logam yang biasa dipancu oleh selaput yang disambung kepada stylus. Pada 1898, Horace Short patented a design for a loudspeaker driven by compressed air and then sold the rights to Charles Parsons, who was issued several additional British patents before 1910. A few companies, including Victor Talking Machine Company and Pathe, produced record players using compressed-air loudspeakers. However, these designs were significantly limited by their poor sound quality and their inability to reproduce sound at low volume. Variants of the system were used for public address applications, and more recently other variations have been used to test space equipment resistance to the very loud sound and vibration levels that launching rockets produce.

The modern design of moving-coil drivers was established by Oliver Lodge in (1898).[2] The first practical application of moving coil loudspeakers was established by Peter L. Jensen and Edwin Pridham, at Napa, California.[3] Jensen was denied patents. Being unsuccessful in selling their product to the phone companies, 1915, they changed strategy to public address, and named their product Magnavox. Jensen was for years after the invention of the loudspeaker a part owner of "The Magnavox Company.".[4]

The moving coil principle as commonly used today in direct radiators was patented in 1924 by Chester W. Rice and Edward W. Kellogg. The key difference between previous attempts and the patent by Rice and Kellogg was the adjustment of mechanical parameters so that the fundamental resonance of the moving system took place at a lower frequency than that at which the cone's radiation impedance had become uniform. See the original patent for details.[perlu rujukan]

About this same period, Dr. Walter H. Schottky invented the first ribbon loudspeaker.[5]

These first loudspeakers used electromagnets because large, powerful permanent magnets were generally not available at a reasonable price. The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil filtering the power supply of the amplifier to which the loudspeaker was connected. AC ripple in the current was attenuated by the action of passing through the choke coil; however, AC line frequencies tended to modulate the audio signal being sent to the voice coil and added to the audible hum of a powered-up sound reproduction device.[perlu rujukan]

In the 1930s, loudspeaker manufacturers began to combine two and three bandpasses worth of drivers in order to increase frequency response and sound pressure level.[6] In 1937, the first film industry standard loudspeaker system, "The Shearer Horn System for Theatres"[7] (a two-way system) was introduced by Metro-Goldwyn-Mayer. It used four 15" low frequency drivers, a crossover network set for 375 Hz and a single sectoral horn with two compression drivers providing the high frequencies. John Kenneth Hilliard, James Bullough Lansing and Douglas Shearer all played roles in creating the system. At the 1939 New York World's Fair, a very large two-way public address system was mounted on a tower at Flushing Meadows. The eight 27" low-frequency drivers were designed by Rudy Bozak in his role as chief engineer for Cinaudagraph. High frequency drivers were likely made by Western Electric.[8]

Altec introduced their coaxial Duplex driver in 1943, incorporating a high frequency horn sending sound through the middle of a 12-inch woofer for near-point-source performance.[9] Altec's "Voice of the Theatre" loudspeaker system arrived in the marketplace in 1945, offering better coherence and clarity at the high power levels necessary in movie theaters.[10] The Academy of Motion Picture Arts and Sciences immediately began testing its sonic characteristics; they made it the film house industry standard in 1955.[11] Subsequently, continuous developments in enclosure design and materials led to significant audible improvements.[perlu rujukan] The most notable improvements in modern speakers are improvements in cone materials, the introduction of higher temperature adhesives, improved permanent magnet materials, improved measurement techniques, computer aided design and finite element analysis.[perlu rujukan]

Reka bentuk pemacu[sunting | sunting sumber]

Cutaway view of a dynamic loudspeaker
A traditional stamped loudspeaker frame is clearly visible.

Rujukan[sunting | sunting sumber]

Pautan luar[sunting | sunting sumber]