As early as 1877, Erenst Verner of Siemens in Germany obtained the patent for the moving coil horn based on Fleming's left-hand law. In 1898, British Sir Oliver Lodge further invented a cone speaker based on the principle of a telephone microphone. It was very similar to the modern speakers we are familiar with. Sir Oliver called it the "roaring telephone". However, this invention could not be used, because it was not until 1906 that Lee De Forest invented the triode vacuum tube, and it was several years before a usable amplifier was made, so the cone speaker did not become popular until the 1930s. Another reason is that the new electrically recorded records came out in 1921. They have a better dynamic range (up to 30dB) than traditional mechanically recorded records, forcing people to try to improve the speaker characteristics to match. In 1923, Bell Labs decided to develop a complete music reproduction system, including new record players and speakers, stereo recording and MC cartridges, stereo recording methods, etc., which were invented during this wave of actions. The important responsibility of developing speakers fell on two engineers, C.W. Rice and E.W. Kellogg. The equipment they used was unprecedented at the time, including a 200-watt vacuum tube amplifier, many recordings completed by Bell Labs itself, and various speakers developed by Bell Labs over the years - such as Lodge's The prototype of a cone speaker, a compressed air speaker that uses diaphragm flaps to control compressed air flow, a corona discharge speaker (called an ion driver today), and an electrostatic speaker.
It didn’t take long for Rice and Kellogg to select two designs from many styles - cone type and electrostatic type. This decision separated the development direction of the speaker into two: traditional type and innovative type. Dynamic speaker The dynamic speaker evolved from the reed speaker. There is a cylindrical coil in the middle of the ring magnet. The front end of the coil is directly fixed on the paper cone or diaphragm, but the audio current and magnetic field pass through the coil. When subjected to changes, the coil will move back and forth and affect the paper cone to produce sound. When dynamic speakers first came out, it was difficult to match the strength of the permanent magnets, so electromagnetic designs were often used. A coil was wound around the magnet to generate a magnetic field. This design was popular for 20 years. However, electromagnetic speakers have their own problems. For example, the DC pulse passing through the electromagnetic coil can easily produce 60Hz and 120Hz hum interference; and the current intensity of the electromagnetic coil changes with the audio signal, causing new instability factors.
During the Great Depression of the 1930s, the Edison Phonograph Company went bankrupt, and others were not much better off. Speakers that needed to be driven by amplifiers were not widely promoted. The old Victorla phonograph was still in use until World War II. Very popular. After the Second World War, the economy took off, and various new audio accessories became hot commodities. Cone speakers were once again severely tested. During this period, due to the successful development of powerful alloy magnets, all moving coil speakers were changed from electromagnetic to permanent magnets, and the past shortcomings were wiped out (in addition to the commonly used natural magnets cobalt, there are also Alnico and Ferrite magnets. In addition to magnetic flux In addition to density, natural magnets have superior characteristics. In recent years, high-end speakers use neodymium magnets). In order to cope with the advent of LP and the development of Hi-Fi systems, cone speakers sought reforms in paper cone materials. Common ones include using thicker materials to make the woofer unit and a light and hard diaphragm as the tweeter; or assembling speakers of different sizes into coaxial units; there are also cases where a horn is added in front of the tweeter to become a compression horn tweeter; or even There are designs that hide the treble horn behind the bass cone. In 1965, the British Harbeth invented the vacuum-formed (Bextrene) plastic diaphragm, which was 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 invented the polypropylene plastic diaphragm. This new material has a higher internal damping coefficient and is lighter. It is still used by many speakers. Engineers have two thinking directions when designing speakers: the woofer seeks a breakthrough in speaker structure; the tweeter seeks to improve the monomer.
So some of the new designs that appeared at this time were almost all tweeters. The more successful design is the electrostatic speaker. Electrostatic speakers mentioned earlier were Bell Labs' Rice and Kellogg experimental speakers. The electrostatic speakers they manufactured were as big as door panels, and their diaphragms were made of gold foil wrapped in pig intestines (plastics were not yet available on the market). When the light of the vacuum tube shines, the shiny golden behemoth has a hypnotic effect, and the air in the laboratory is filled with the rotten smell of pig intestines and ozone. The two scientists may think of "Frankenstein" and Bell made of dead people's ears. Recorder". But after it started to sound, its dazzling voice and realistic timbre simply stunned everyone, and they understood that a new era had arrived. However, Rice and Kellogg encountered insurmountable problems when designing electrostatic speakers: a huge diaphragm was required to reproduce a complete bass. When the technology was difficult to break through, Bell Labs had to turn to the development of cone speakers. This stagnation made The electrostatic horn lay dormant for thirty years. In 1947, a young naval officer, Arthur Janszen, was assigned to develop a new sonar detection device, which required a very accurate horn. Janszen discovered that the cone speaker was not linear, so he tried to make an electrostatic speaker by coating a plastic sheet with conductive paint as a diaphragm. It later proved that both the phase and amplitude performance were extraordinary. Janszen continued his research and discovered that insulating the stator could prevent the destructive arcing effect. In 1952, Janszen completed commercial production of the electrostatic tweeter, which, when paired with AR's woofer, was the best combination that audio fans at the time dreamed of. In 1955, Peter Walker published several articles on the design of electrostatic speakers in the British "Radio World". He believed that electrostatic speakers inherently have a wide and flat response, as well as extremely low distortion, and the distortion is higher than that of the time. The amplifier is much lower. In 1956, Peter Walker's ideal was realized on the Quad ESL speaker (Quad is named after the abbreviation of one of his early amplifiers, Quality Unit Amplifier-Domestic). Its accuracy was hailed as a new standard for listening, but there are still There are some issues to overcome: insufficient volume, impedance loading that prohibits some amplifiers, insufficient dispersion, and limited power handling. In the early 1960s, Janszen joined KLH and worked hard to launch the KLH-9. Due to the large size of the KLH-9, the problem of Quad ESL was solved. Until the establishment of Infinity in 1968, the KLH-9 electrostatic speaker was the most popular. Hi-End products. Janszen's achievements don't stop there. With his help, electrostatic speakers such as Koss, Acoustech, and Dennesen came out one after another. Roger West, the chief designer of Janszen Company, also founded the Sound Lab company.