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What are speaker magnets?

What are speaker magnets?

Speaker magnets refer to the magnet used in the horn, that is, the magnet used in the horn.

Sound principle of horn

The horn is generally composed of T iron, magnet, voice coil and diaphragm.

How do speakers make sound? We all know that a magnetic field will be generated in an electrified wire. The strength of the current affects the strength of the magnetic field (the direction of the magnetic field follows the right-hand rule). When the AC audio current passes through the coil of the horn (i.e., the voice coil), according to the above principle, the corresponding magnetic field is generated in the voice coil. This magnetic field interacts with the magnetic field generated by the speaker magnet on the horn, which makes the voice coil in the The horn magnetic field vibrates with the strength of the audio current. The diaphragm and voice coil of the loudspeaker are connected together. When the voice coil and the horn diaphragm vibrate together, the surrounding air vibrates, and the loudspeaker generates sound. This is how the horn works.

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The influence of speaker magnet performance on the sound output quality of speakers

In the case of the same magnet volume and the same voice coil, the performance of the magnet has a direct effect 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 film.
  • The greater the magnetic flux density (magnetic induction) B, the greater the relative power, and the higher the SPL sound pressure level (sensitivity).
  • Headphone sensitivity refers to the sound pressure level that the headphones can emit when a 1mw, 1khz sine wave is input to the headphones. The unit of sound pressure is dB (decibel). The greater the sound pressure, the greater the volume, so the higher the sensitivity, the lower the impedance, and the easier it is for headphones to produce sound.
  • The greater the magnetic flux density (magnetic induction) B, the lower the total quality factor Q of the speaker.
  • Q value (qualityfactor) refers to a set of parameters of the damping coefficient of the horn. Qms is the damping of the mechanical system, which reflects the energy absorption and consumption of the various parts of the horn. Qes is the damping of the power system, which is mainly reflected in the consumption of electric energy by the DC resistance of the voice coil; Qts is the total damping, which is related to the above two as Qts=Qms*Qes/(Qms+Qes).
  • The greater the magnetic flux density (magnetic induction) B, the better the transient.
  • Transient state can be understood as “fast response” to the signal, and the Qms is relatively high. Headphones with good transient response should respond as soon as the signal comes, and stop abruptly as soon as the signal stops. For example, the transition from the lead to the ensemble is the most obvious in drums and symphonies with larger scenes.

How to choose a speaker magnet?

The speaker magnets on the market mainly include AlNiCo, ferrite and neodymium iron boron:

  • Alnico is the earliest magnet used in speakers, such as horn speakers (known as tweeters) in the 50s and 60s. Generally made of internal magnetic horn (external magnetic type is also available). The disadvantage is that the power is small, the frequency range is narrow, hard and brittle, and processing is very inconvenient. In addition, cobalt is a scarce resource, and the price of AlNiCo is relatively high. From the perspective of cost performance, horn magnets choose AlNiCo.
  • Ferrites are generally made of external magnetic speakers. Ferrites have relatively low magnetic properties and require a certain volume to meet the driving force of the speakers. Therefore, they are generally used in larger audio speakers. The advantage of ferrite is that it is cheap and cost-effective; the disadvantage is that it is larger in size, smaller in power, and narrow in frequency range.
  • The magnetic properties of NdFeB are much better than that of alnico and ferrite, and NdFeB is the most used magnet in loudspeaker, especially in high-end loudspeaker. It has the advantages of small size, large power and wide frequency range under the same magnetic flux. At present, hifi earphone basically uses this kind of magnet. Its disadvantage is that it contains rare earth elements, so the material price is high.

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Several factors should be considered when selecting speaker magnet

  • First of all, it is necessary to determine the ambient temperature in which the horn works, and which magnet should be selected according to the temperature. Different magnets have different temperature resistance characteristics and can support different maximum operating temperature. When the working environment temperature of the magnet exceeds the maximum working temperature, magnetic attenuation and demagnetization may occur, which will directly affect the sound production effect of the horn.
  • Secondly, the horn magnet should be selected by considering the magnetic flux demand and the magnet volume. The louder the speaker is, the better the sound is? In fact, the bigger the magnet, the better. From the influence of the magnet performance on the sound output quality of the loudspeaker, we can find that the magnetic flux of the magnet has a great influence on the sound quality of the horn. Under the same volume, the magnet performance is: NdFeB > alnico > ferrite; under the same magnetic flux requirement, the volume of NdFeB magnet is the smallest and the ferrite is the largest. For the same magnetic material (the same material and same performance), the larger the diameter and the greater the magnetic induction, the greater the power of the horn is, the higher the sensitivity of the horn is, and the better the transient response is. Therefore, it is necessary to determine which kind of magnetic material to choose by considering the limitation of horn volume to magnet volume and the requirements of magnetic flux performance.

Add: some people ask how many cores and how much magnetism does the horn mean?
When we say how much magnetism the horn has, we mean the diameter of the magnet in the horn. For example, 100 magnetism means that the diameter of the magnet is 100 mm. The number of cores refers to the diameter of the voice coil. For example, 100 cores means that the diameter of the voice coil is 100 mm.

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