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The Origin of the Audio Revolution: Do you know the historical story behind the phase plug?
In the development of audio technology, speaker design plays a pivotal role, and phase plugs are one of the keys to the evolution of this technology. A phase plug, or audio transformer, serves as a mechanical interface between the speaker driver and the listener. It can effectively improve high-frequency response, guide sound waves outward, and reduce sound quality loss caused by interference near the driver.
Phase plugs are often found in high-power horn loudspeakers, especially in filters in the mid- to high-frequency range, between the diaphragm of the compression driver and the acoustic horn. These ever-evolving designs aim to balance the path length of sound waves from the driver to the listener, thereby preventing sound cancellation and frequency response issues. It can be said that the phase plug is a further reduction of the throat of the horn and becomes an extension of the diaphragm surface.
"During the sound playback process, the phase plug greatly improves the high-frequency performance and transmits the sound in a unified wavefront manner."
Historical overview
The history of phase plugs can be traced back to the 19th century. In 1877, German industrialist Werner von Siemens invented a motor driver similar to the one later used in loudspeakers, but it was not until 1921 that a real practical amplifier was developed, allowing the speaker technology to develop.
In the 1920s, as technology evolved, various speaker designs gradually emerged. Especially in 1925, General Electric engineers Chester W. Rice and Edward W. Kellogg successfully combined an acoustic horn with a speaker driver. In 1926, Bell System engineers Albert L. Thuras and Edward C. Wente inserted the first phase plug into a horn loudspeaker. Through this new design , improving the transmission characteristics of the speaker in the high frequency range.
Phase plugs in compression drivers
In a horn loudspeaker, the function of the phase plug is to transport sound waves from various areas of the compression driver to the horn throat so that each sound pulse arrives with a uniform wavefront. This design not only improves the high-frequency response, but also makes the sound quality clearer. In compression drivers, the phase plug is a complex and expensive component whose manufacture requires very precise tolerances.
"Through continuous optimization of the phase plug, the high-frequency performance of the speaker can be further improved."
Phase plugs of different shapes and materials
There are many variations in phase plug designs today, but they can be divided into two main categories to match the main diaphragm types: domes and donuts. Dome-based diaphragm designs are still common, while ring-shaped diaphragm designs were developed to minimize problems associated with wave propagation. These phase plugs are typically machined from metals such as aluminum, or cast from hard plastic or phenolic resin. Most high-end audio companies such as Meyer Sound Laboratories choose lightweight plastic because of its resistance to temperature and humidity.
Phase plug in woofer
Phase plugs can also be used in front of the speaker cone of a woofer, especially in horn-loaded speaker designs. This design is intended to reduce high-frequency wave interference near the driver. In loudspeakers, a phase plug is usually a solid plug placed in the center of the woofer, often covering or replacing a central dust cap. The purpose of this is to steadily disperse the sound source outward to improve the overall sound quality.
"In the actual process, only the best half of the wave can play a role directly from the diaphragm through the phase plug, and the other half may be interfered by space."
With the increasing advancement of audio technology, phase plugs will continue to play an important role in the future audio revolution. With more innovation, the acoustic performance of sound systems is expected to reach higher levels, so what are your thoughts on this process?
