Balanced Earphones

In 1910, Baldwin also invented the 'balanced armature' earphone. An armature earphone is a movable iron plate (armature) placed in the middle of a U-shaped magnet. When current flows through the coil, the armature will be magnetized and the magnet will generate attraction and repulsion, and at the same time drive the diaphragm to move. This design was low-cost and, although not effective, it was also a groundbreaking invention at the time. This technology was often used on telephone receivers and small headphones.
In terms of recording sound technology, in 1917, Wente and Thuras designed a capacitive microphone.
In the mid-1930s, electrostatic speakers were introduced based on the principle of capacitive microphones. In the early 1950s, C V. Bocciarelli proposed the 'constant charge' law of constant charge. P. Walker independently developed the same theory during the same period and applied it to the famous Quad electrostatic speaker design.
The basic principle of electrostatic boomers is Coulomb's law, which usually involves vacuum vaporization of plastic film and aluminum or other inductive materials. The two films are placed face to face, and when one of them is subjected to a positive current and high voltage, the other will induce a small current. By mutual attraction and repulsion, the air can be pushed to produce sound. Due to its lightweight and low vibration dispersion, electrostatic speakers operate in the mid to high frequency range, with cool and ethereal sound quality and distinctive features, making it easy to obtain cool and ethereal high pitched sound. However, its low efficiency, low sound pressure output, small dynamics, and high cost are also its weaknesses.