The Role Of Magnets In Speakers

- Dec 18, 2020-

The magnet generates a magnetic field, and the voice coil of the speaker is placed in the magnetic field. When the audio current passes through the voice coil, this current will be subjected to the force of the magnetic field, causing the voice coil to vibrate and drive the paper cone adhered to the voice coil to vibrate. sound.

The magnets on the speakers mainly include ordinary ferrite magnets and neodymium iron boron magnets.

Ordinary ferrite magnets are generally mainly used for low-end earphones, 2-3 pieces of one-way goods, needless to say, the sound quality is very rubbish, and it is not suitable for earphone materials. Neodymium iron boron magnets are used in high-end headphones, with first-class sound quality, good flexibility, good performance in details, good vocal performance, and accurate sound field positioning.

At present, most of the speakers still use the traditional cone-type single-body front and rear motion sound. In a more academic way, these speakers are called Electrokinetic Dynamic or Moving Coil. As early as 1877, Ernest Vemer of Siemens, Germany, obtained a patent for a moving coil speaker, but the vacuum tube was not officially used until 1907, and Edison’s earliest record player was a stylus directly driving the diaphragm and then amplified by the horn. Sounds, so Siemens’ patent has never been used. In 1920, Chester Rice, Edward Kerrog, and Edison Bell PGHokuto of the American singular company developed practical moving coil speakers for the first time. For more than 70 years, in addition to the continuous improvement of materials, you are regarded as the true technology of speakers. Is there any progress? The following are several common ways of sounding speakers:


1. Moving coil type. The basic principle comes from Fleming’s left-hand law. Put a line of electric current perpendicular to the magnetic field line between the north and south poles of the magnet. The line will be moved by the interaction between the magnetic field line and the current, and a piece of the diaphragm is attached to it. On this track, the diaphragm will move back and forth as the current changes. At present, more than 90% of cones are of moving coil design.

2. Electromagnetic type. A movable iron chopping piece (armature) is installed in the middle of a U-shaped magnet. When the current flows through the coil, the armature will be magnetized and repelled by the magnet, and at the same time drive the diaphragm to move. This kind of design is low cost but not effective, so it is mostly used in telephone receivers and small earphones.

3. Inductive. Similar to the electromagnetic principle, but the armature is doubled, and the two voice coils on the magnet are not symmetrical. When the signal current passes through, the two armatures will push each other for different magnetic fluxes and move. The difference from electromagnetic is that inductance can regenerate lower frequencies, but the efficiency is very low.

4. electrostatic type. The basic principle is Coulomb's law, which is usually based on the vacuum vaporization of a plastic diaphragm with inductive materials such as aluminum. The two diaphragms are placed face-to-face. When one of them is applied with a positive current and high voltage, the other will sense With a small current, the air can be driven by mutual attraction and repulsion to produce sound. Due to its lightweight and low vibration dispersion, the electrostatic monomer is easy to get a clear and transparent mid-to high-frequency sound, and it is not able to grasp the bass power, and its efficiency is not high, and it is easy to collect dust when using a direct current generator. At present, manufacturers such as Martin-Logan have successfully developed static and dynamic hybrid speakers, which solves the problem of insufficient bass of the static body. The static type is also widely used in headphones.

5. Flat style. The first design developed by SONY of Japan, the voice coil design is still the theme of the moving coil, but the cone diaphragm is changed to a honeycomb structure flat diaphragm, because of the fewer people and the hollow effect, the characteristics are better, but the efficiency is also low.

6. ribbon type. There is no traditional voice coil design, the diaphragm is made of very thin metal, and the current flows directly into the channel body to make it vibrate. Because its diaphragm is a voice coil, it has very lightweight, excellent transient response, and high-frequency response. However, the efficiency and low impedance of the ribbon speaker have always been a big challenge to the amplifier, and Apogee can be a representative. Another way is to have a voice coil, but the voice coil is printed directly on the plastic sheet, which can solve some of the problems of low impedance. Magnepang is the leader of such designs.

7. horn style. The diaphragm pushes the air at the bottom of the horn to work. Because the sound is not diffused during transmission, the efficiency is very high. However, because the shape and length of the horn will affect the tone, it is not easy to replay low frequencies. Now it is mostly used in giant PA systems or In terms of the tweeter, Klipsch is a long-established manufacturer of horn speakers.

8. There is also a ribbon-like improved design developed by Dr. Haier in 1973, called the Haier horn, which is excellent in theory, but Taiwanese users are very rare. Piezoelectric is a design that uses piezoelectric materials such as titanic acid to expand or contract by applying voltage. Pioneer has improved the piezoelectric design with high polymers and used them on their tweeters. Ion horn (Ion) uses high-voltage discharge to make air become a charged substance.