How to select suitable speaker magnets? When you press the play button, whether you are enjoying your favorite music or answering an important call, you cannot do without a crucial component —— the speaker.

As an indispensable part in our lives, speakers are widely used in various electronic products, such as home audio systems, mobile phones, computers, and car audio systems. This small yet vital device is composed of multiple delicate parts, including the voice coil responsible for energy conversion, the magnet that provides the necessary magnetic field, the diaphragm that converts vibration into clear sound, and the cabinet structure used to optimize sound output.

Ⅰ.The working principle of a speaker

The working principle of a speaker is based on the principle of electromagnetic induction. When an electric current passes through the voice coil, a magnetic field that changes with the current will be generated. This dynamic magnetic field interacts with the constant magnetic field generated by the magnet inside the speaker, causing the voice coil to drive the connected diaphragm to vibrate. This series of actions finally realizes the conversion from electrical energy to mechanical energy and then generates the sound we hear.

During this process, the speaker magnet plays a central role. It not only provides a stable magnetic field environment but also ensures that the voice coil can accurately perform the reciprocating motion in this magnetic field. The quality of the magnet directly affects the performance of the speaker. High – quality magnet materials can improve the sensitivity and response speed of the speaker, thus significantly improving the quality of the output sound and bringing a richer and more delicate auditory experience to the listeners.

Ⅱ.What influence does the performance of magnets have on speakers?

On the premise of keeping the volume of the magnet and the voice coil unchanged, the performance of the magnet has a direct impact on the sound quality of the speaker.

① When the magnetic flux density (magnetic induction intensity) of the magnet increases, the driving force exerted on the diaphragm will also be enhanced accordingly. This phenomenon is based on Ampere’s force law, that is, the force (F) exerted on a current – carrying conductor in a magnetic field is directly proportional to the magnetic field intensity (B), the current (I), and the length of the conductor (L).

F = BILsin(θ)

Where θ is the angle between the direction of the magnetic field and the direction of the current.

A stronger driving force can enable the diaphragm to reproduce audio signals more accurately, especially maintaining good clarity and low distortion even in a large dynamic range.

② A higher magnetic flux density implies greater power – handling capacity, thereby enhancing the sensitivity of the speaker. Here, the sensitivity refers to the sound pressure level (in dB) that the speaker can generate when a 1 mW power is input into the speaker and the frequency is a sine – wave signal of 1 kHz.

A higher sound pressure means a louder volume. Therefore, the higher the sensitivity and the lower the impedance of the speaker, the easier it is to produce sound. A magnet with stronger magnetism can make the speaker more efficient and produce greater loudness under the same power input.

③Increasing the magnetic flux density can also improve the transient response of the speaker, which means that the speaker can respond to signal changes more quickly. A speaker with good transient response can react rapidly when the signal starts and stop making sound immediately when the signal stops. This characteristic is especially important when presenting elements such as drumbeats or the transition from the solo part to the ensemble part in a symphony.

④When the magnetic flux density increases, the overall quality factor of the speaker will decrease. The quality factor is a dimensionless parameter that describes the relationship between the stored energy and the dissipated energy of the speaker system at a specific frequency, and is used to measure the proportion of energy storage and loss of the speaker at resonance.

As the magnetic flux density increases, the electromagnetic damping on the voice coil of the speaker when it moves in the magnetic field will also increase. This means that more energy will be converted into heat and consumed, thus reducing the quality factor of the system. In addition, the resistance and inductive reactance of the voice coil will also change under a strong magnetic field, further increasing the electrical damping and reducing the quality factor.

This reduction is usually beneficial because it helps to suppress the resonance peak of the voice coil, reduce the distortion during resonance, improve the stability of the speaker, and enhance the sound quality. However, an overly low quality factor is also not conducive to the performance of the speaker, because excessive damping will cause the system response to become sluggish, affecting the transient response and detail reproduction. Therefore, when designing a speaker, engineers need to find an optimal balance between the magnetic flux density and the quality factor to ensure that the speaker has good stability and can also provide excellent sound quality performance.

⑤Coercivity refers to the reverse magnetic – field strength required to demagnetize a magnet from a saturated state until the net remanence is zero. The higher the coercivity of the magnet, the less the speaker is affected by the reverse magnetic field and high temperature. If the coercivity is too low, the magnet will experience a decrease in magnetism under the influence of these external factors, and this performance loss may even be permanent.

The resonance frequency of a speaker is closely related to factors such as structure, material and magnetic field. In a well – designed speaker, these factors work together to enable the speaker to accurately reproduce sounds of different frequencies and ensure pitch accuracy.

When the performance of the magnet deteriorates, it will affect the resonance characteristics of the speaker. Changes in the magnetic field may cause the resonance frequency of the speaker to shift, and the situation where the speaker should accurately emit a sound at a certain frequency may change. For example, a speaker that could originally accurately emit a certain sound at 440Hz may emit this sound at 435Hz or 445Hz due to the decline in magnet performance, thus resulting in a deviation in pitch accuracy.

Common types of speaker magnets

The mainstream magnets used in speakers have mainly gone through three stages in the past: alnico, ferrite, and neodymium – iron – boron.

1.Alnico magnet

Alnico magnets first emerged in the 1920s. It has good temperature stability and a strong magnetic field, and is able to provide high – fidelity sound reproduction capabilities. Since cobalt, as a raw material for this type of magnet, is too expensive, and alnico magnets are very brittle with a relatively low yield rate after processing, the price has always been high.

With the development of new permanent magnet materials, ferrite, which is cheaper, and neodymium magnets with stronger magnetic properties have emerged, and the usage amount of alnico magnets in the speaker field has been decreasing.

Although we rarely see it in modern audio equipment nowadays, it is still used in some special audio equipment thanks to its unique properties. This material was first used in high – frequency speakers in the 1950s – 1960s, especially in high – frequency horn speakers. Some high – frequency speakers still use alnico magnets today because it can provide clear and delicate high – frequency sounds, with a frequency range of approximately 2 kHz—20 kHz or even higher. Alnico magnets are sometimes the top choice for guitar speakers because, compared with ferrite magnets, musicians like the warmer sound and natural compression brought by these magnets.

2.Ferrite magnet

Since the 1950s, ferrite magnets have been widely used in speakers. Compared with other permanent magnets, ferrite magnets have lower magnetic performance, which means they require a larger volume to provide the same driving force.

Therefore, these magnets are more often used in large – scale audio equipment. Due to their relatively weak magnetic force, ferrite magnets will cause the frequency response range of the speakers to be limited, and usually it is difficult to meet the frequency requirements for high – end audio equipment.

Nevertheless, ferrite magnets still have significant advantages. They have good resistance to demagnetization and corrosion resistance, which means that complex surface treatment steps such as electroplating can be omitted during the production process, thus simplifying the manufacturing process and effectively controlling the cost. This feature is particularly important for audio equipment used outdoors, because these devices are often exposed to the natural environment, and corrosion resistance becomes a key consideration factor when choosing magnet materials.

Neodymium magnets far exceed ferrite magnets in performance. However, since the price of neodymium magnets of the same weight is about dozens of times that of ferrite magnets, the low price enables ferrite magnets to still maintain a relatively high market share in application scenarios where there are no excessive requirements for sound quality or where the equipment volume is not very sensitive.

3.Neodymium – Iron – Boron Magnet

As the third – generation rare – earth permanent magnet product, neodymium – iron – boron (Nd – Fe – B) magnets have excellent characteristics such as high magnetic energy product, small size and light weight. Compared with traditional ferrite or alnico magnets, the use of Nd – Fe – B magnets can significantly improve the sensitivity and frequency response range of speakers. At the same time, it can greatly reduce the volume and weight of the required magnets. When designing headphones, a more compact and lighter magnetic circuit system can be created, which is especially suitable for portable audio devices such as headphones. Currently, neodymium magnets have become a standard configuration for Hi – Fi headphones and high – end speakers.

The main drawback of Nd – Fe – B magnets lies in their relatively high cost, because neodymium magnets contain rare and expensive rare – earth elements such as neodymium, dysprosium, and terbium. But it is also these elements that endow neodymium magnets with excellent magnetic properties. Neodymium magnets are relatively sensitive to the working temperature. In a high – temperature environment, their magnetic field strength will decrease, which in turn will affect the sound performance of speakers. However, generally speaking, as long as the working temperature does not exceed the standard value, this short – term magnetic loss will be recovered after the neodymium magnets cool down.

Lower – grade N – series neodymium magnets will experience permanent demagnetization when exposed to temperatures above 176°F (80°C). The highest – grade AH – series neodymium magnets can maintain their magnetization intensity at temperatures as high as 446°F (230°C).

When the size of the magnet is reduced, its main cost does not come from the material itself but is determined by the processing cost during the manufacturing process. Although sintered Nd – Fe – B is relatively fragile, ferrite magnets are more brittle and more difficult to process. Therefore, in some speakers that require a fine and complex magnetic circuit design, the actual processing cost of ferrite components is sometimes even higher than that of neodymium magnets of the same size.

If you don’t have extremely high requirements for the sound quality of the speaker, or need a magnet material with higher toughness and easier processing, then bonded neodymium magnets are a choice worth considering. This kind of magnet is not only superior to alnico and ferrite magnets in terms of toughness and magnetic force, but also can be directly molded during the manufacturing process without complex subsequent processing steps.

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