The development history of speakers

As early as 1877, the speaker manufacturer, Erenst Verner of Siemens, Germany, obtained the patent for the moving coil horn speaker based on Fleming's left-hand law. In 1898, Sir Oliver Lodge of the United Kingdom further created a cone speaker based on the principle of a telephone microphone, which is very similar to the modern speakers we are familiar with. Sir Lodge called it "the roaring phone." However, this creation cannot be used, because it was not until 1906 that Lee De Forest created the triode vacuum tube, and it was several years later to make a usable amplifier, so cone speakers did not gradually become popular until the 1930s.

Another reason is that a new record that was recorded electrically in 1921 came out. It has a better dynamic range (up to 30dB) than the traditional mechanically engraved record, forcing people to try to improve the horn characteristics to match. In 1923, Bell Labs decided to develop a perfect music reproduction system, including new phonographs and speakers, stereo recording and MC cartridges, stereo recording methods, etc., which were created in this wave of behavior. The heavy responsibility for developing speakers falls on C. W. Rice and E. W. Kellogg two engineers. The equipment they used was unprecedented at that time, including a 200-watt vacuum tube amplifier, many Bell Labs’ own recordings, and various speakers developed by Bell Labs over the years-such as Lodge’s The prototype of the cone horn, the compressed air horn that uses the diaphragm to control the compressed air flow, the corona discharge horn (called the ion driver today), and the electrostatic horn.　　

It didn't take long for Rice and Kellogg to select two designs from a large number of styles-cone type and electrostatic type. This decision made the development direction of the speaker divided into two: traditional and innovative. Moving coil horn The moving coil horn is basically evolved from the reed horn. There is a cylindrical coil in the middle of the ring magnet. The front end of the coil is directly fixed on the cone or diaphragm, but the audio current and magnetic field pass through the coil. Subject to changes, the coil will move back and forth to cause the paper cone to make sound. At the beginning of the advent of the moving coil speaker, because the strength of the permanent magnet was difficult to match, the electromagnetic design was often used, and another coil was wound in the magnet to generate the magnetic field. This design has been popular for 20 years. However, electromagnetic horns have their own problems. For example, the direct current pulse passing through the electromagnetic coil easily produces 60Hz and 120Hz exchange sound interference; and the current intensity of the electromagnetic coil changes with the audio signal, causing new unstable factors.　　

During the Great Depression in the 1930s, Edison's phonograph company was opened, and others were not much better. Speakers that needed amplifiers were not popularized. The old Victorla phonographs were still popular until the Second World War. After the Second World War, the economy took off, and various new audio accessories became popular products, and the cone-shaped speakers were once again seriously tested. During this period of time, because of the successful development of powerful alloy magnets, all moving coil speakers changed from electromagnetic to permanent magnets. The shortcomings of the past were wiped out. (In addition to natural cobalt magnets, there are Alnico and Ferrite magnets, except for magnetic flux. In addition to the density, the various characteristics of natural magnets are superior. In recent years, high-end speakers have adopted neodymium magnets).

In order to cope with the advent of LP and the pause of the Hi-Fi system, cone speakers sought innovation in the paper cone materials. The common ones are as the woofer made of thicker materials, and the light and hard diaphragm is used as the bass; perhaps the speakers of different sizes are assembled into coaxial monomers; there are also horns added in front of the bass to become a compressed horn woofer; There is a design to hide the bass horn behind the bass cone. In 1965, British Harbeth created a vacuum formed (Bextrene) plastic diaphragm, which is a major advancement in materials. This soft but high damping coefficient product can still be seen on KEF and some British speakers. Later, Harbeth also created a polypropylene plastic diaphragm. This new material has a higher internal damping coefficient and is lighter. It is still used by many speakers. When engineers design speakers, they have two thinking directions: the woofer seeks a breakthrough in the structure of the speaker; the woofer is improved by the monomer. So some of the new designs that appeared at this time were almost all woofers. The more successful design is an electrostatic horn.

Electrostatic horns The Rice and Kellogg experimental horns of Bell Labs mentioned earlier. The electrostatic horns they make are as big as a door panel, and the diaphragm is made of pig intestine out of gold foil (plastic is not yet on the market). When the vacuum tube shines brilliantly, the shiny golden behemoth has hypnotic effects, and the laboratory air is filled with the smell of pig intestines and ozone. The two scientists may think of "Frankenstein" and Bell made from dead human ears. Recorder". But after it started to vocalize, its glorious sound and lifelike timbre almost shocked everyone. They knew that a new era had arrived. However, Rice and Kellogg ran into an invincible problem when designing electrostatic speakers: a large diaphragm was needed to regenerate complete bass. Under the condition that the technology was difficult to break through, Bell Labs had to turn to the development of cone speakers. This suspension made The electrostatic horn has been silent for thirty years. In 1947, a young naval officer, Arthur Janszen, was assigned to develop a new sonar detection equipment, and this equipment required the right speakers. Janszen found that the cone speaker is not linear, so he tried to make an electrostatic speaker, and coated a plastic sheet with conductive paint as the diaphragm. It was confirmed in advance that both the phase and amplitude expressions are different. Janszen continued to study and found that insulating the Stator plate can avoid the arcing effect of destruction. In 1952, Janszen realized the commercial production of electrostatic woofer, which was matched with AR woofer, which was the best combination for audio fans at that time.

In 1955, Peter Walker announced several articles on the design of electrostatic horns in the "Radio World" in the United Kingdom. He felt that electrostatic horns were born with a broad and straight response, and extremely low distortion. The amplifier is much lower.

In 1956, Peter Walker's ideals were realized on Quad ESL speakers (Quad was named after his early amplifier, Quality Unit Amplifier-Domestic). Its correctness is hailed as the new standard for listening and listening, but there are still Some problems need to be overcome: lack of volume, impedance load makes some amplifiers daunting, lack of dispersion, and limited carrying power. In the early 1960s, Janszen participated in the KLH company and worked hard for the listing of KLH-9. Because of the large size of KLH-9, the problem of Quad ESL was solved. Until Infinity was established in 1968, KLH-9 electrostatic horns were the best. Hi-End products. Janszen's accomplishments are not limited to this. With his help, electrostatic speakers such as Koss, Acoustech, and Dennesen have come out one after another. Roger West, the chief designer of Janszen, also founded Sound Lab on his own.　　

When the Janszen company launched, RTR bought the production equipment and launched the Servostatic electrostatic board. Infinity's first pair of speakers used RTR products. Janszen has changed hands several times, but it has never disappeared. One of today's loudspeaker kings-Dave Wilson's WAMM giant system, uses some electrostatic plates designed by Janszen. The design of electrostatic speakers has attracted investment from many manufacturers. The more well-known ones include Acoustat, Audio Static, Beverage, Dayton Wright, Sound Lab, Stax and Martin Logan. Acoustat X itself is equipped with a vacuum tube amplifier, which can output high-voltage signals without using a booster; Beverage 2SW is equipped with a high-voltage amplifier and controller, as well as a pair of subwoofers. Because the two-meter-high diaphragm of Beverage 2SW is installed in an elliptical speaker, the sound is transmitted evenly from the front opening by the sound guide plate, which can create a very three-dimensional audio and video. It is recommended to place it on both sides of the wall. And the opposite is played back.

The design of Dayton Wright is also very special. The diaphragm is installed in a plastic bag sealed with sulfur hexafluoride inert gas to increase the efficiency of the speaker and the output sound pressure. The most expensive electrostatic speaker is Mark Levinson's HQD. Each channel uses two Quad electrostatic speakers, plus an improved band bass and a 24-inch bass boost frequency extension, with three Mark Levinson ML-2 post stage and electronic crossover, asking price 15 ，000 US dollars, it was really sky-high at the time. In order to deal with the problem of bass produced by large diaphragms, Martin Logan has achieved great success in recent years with a series of designs that blend cone bass. Coupled with the introduction of new technologies such as delay lines, acoustic lenses, and wave-shaped diaphragms, electrostatic speakers have become more The more amiable, I trust that it will continue to exist.