Magnetic Materials in Loudspeakers (Horns)

The core component responsible for producing sound in audio equipment is the loudspeaker, commonly known as the horn, whether it is a stereo or a headset, this key component is indispensable. The loudspeaker is a transducer device that converts electrical signals into acoustic signals. The performance of the loudspeaker has a great influence on the sound quality, and the magnet in the loudspeaker determines its performance to a large extent.

The principle of loudspeaker sound

The speaker is composed of several key components such as T iron, magnet, voice coil and diaphragm. When the AC current passes through the coil of the speaker (that is, the voice coil), a corresponding magnetic field is generated in the voice coil, and this magnetic field interacts with the magnetic field generated by the magnet on the speaker. The permanent magnet magnetic field of the belt vibrates with the audio current. The diaphragm and the voice coil are connected together. When the voice coil and the speaker diaphragm vibrate together, the surrounding air is pushed to vibrate, and the speaker produces sound. As shown above, this is the principle of the horn sounding.

Influence of magnet properties on sound output quality of loudspeaker

In the case of the same magnet volume and the same voice coil, the performance of the magnet has a direct impact on the sound quality of the speaker:

The greater the magnetic flux density (magnetic induction) B of the magnet, the stronger the thrust acting on the sound membrane.
The greater the magnetic flux density (magnetic induction) B, the greater the power and the higher the sensitivity of the speaker. Headphone sensitivity is the sound pressure level that the headphone can emit when a 1mw, 1khz sine wave is input to the headphone. The unit of sound pressure is dB (decibel). The greater the sound pressure, the greater the volume, so the higher the sensitivity, the smaller the impedance, and the easier it is for the earphone to make sound.
The larger the magnetic flux density (magnetic induction) B is, the lower the overall quality factor Q of the speaker is. Q value (quality factor) refers to a set of parameters of the horn damping coefficient,
The larger the magnetic flux density (magnetic induction) B, the better the transient. Transient can be understood as “fast response” to the signal. Headphones with good transient response should respond immediately as soon as the signal comes, and stop abruptly as soon as the signal stops. The transition part of the ensemble is most obvious.

Magnetic Materials in Loudspeakers (Horns)

Magnetic Materials in Loudspeakers (Horns)

How to choose the horn magnet

There are three types of speaker magnets on the market: AlNiCo, ferrite and NdFeB:

Alnico is the earliest magnet used in horns, such as horn horns (known as tweeters) in the 1960s. It is generally made into an internal magnetic horn (external magnetic type is also available). Its disadvantages are low power, narrow frequency range, hard and brittle, and inconvenient processing. In addition, cobalt is a scarce resource, and the price of AlNiCo is relatively high. From the perspective of cost performance, AlNiCo is rarely used as speaker magnet.

Ferrite is generally made of external magnetic speakers. The magnetic performance of ferrite is relatively low, and it needs a certain volume to meet the driving force of the speaker. Therefore, it is generally used in larger audio speakers. The advantage of ferrite is that it is cheap and cost-effective; the disadvantage is that it is large in size, low in power, and narrow in frequency range.

The magnetic properties of NdFeB are far superior to those of AlNiCo and ferrite, and are currently the most used magnets on speakers, especially high-end speakers. Its advantages are small size, high power, and wide frequency range under the same magnetic flux. At present, HiFi headphones basically use this type of magnet. Its disadvantage is that because it contains rare earth elements, the material price is relatively high.
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Preparation process of sintered NdFeB magnets (3) – orientation forming

Preparation process of sintered NdFeB magnets (4) – Sintering, heat treatment and machining

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