Technical testing of speakers and subjective sound quality evaluation

6. Advantages and disadvantages of NdFeB

For speaker units, magnetic materials are their skeleton and the basis of their power. Selecting materials with high magnetic energy product to manufacture speaker units is a good way to improve the sensitivity of speakers, but it is not the only way.

For the magnetic materials of speakers, especially the magnetic materials of high-power bass speakers, one very important standard is that the thermal stability must be good. The magnetic energy product of NdFeB magnetic materials is very large. But it also has fatal flaws. One is that it is easy to oxidize; the other is that its thermal stability is poor. The Curie temperature of NdFeB magnetic materials is very low. At 80℃, its performance will drop to 80% of the reference temperature (reference temperature is 24℃). This explains the following problem: if it is a NdFeB woofer unit that has not undergone special heat dissipation treatment, when working at high power, the bass will be insufficient due to the influence of the temperature increase. This change in timbre can be clearly perceived by most music lovers.

Therefore, most foreign speaker manufacturers currently use NdFeB materials as the magnetic material for tweeters and take more effective heat dissipation measures, but rarely use NdFeB magnetic materials in the manufacturing process of woofers.

After years of HiFi practice, most people can basically clearly distinguish the slight differences in the playback sound caused by different audio signal cables. However, it is a great pity that the frequency response variation of the bass unit is higher than 10% due to the poor thermal stability of NdFeB magnetic materials.

7. It is not advisable to use demagnetization to improve sound quality

A while ago, there was a popular saying that the demagnetization method can improve the sound quality. The so-called demagnetization method refers to adsorbing some large iron nails on the magnet of the speaker unit of the finished speaker. The magnetism of the unit itself is dispersed to a certain extent, reducing the sensitivity of the speaker unit and changing the original Q value. The demagnetization method can be used to adjust the playback effect of the speaker, which will play a certain role. However, the demagnetization method is only suitable for speakers that originally sound dry and tight. It is impossible to apply it to most occasions. For speakers that can improve the playback by demagnetization, the method of adjusting the sound-absorbing material in the speaker and adjusting the speaker reflex tube can also achieve the purpose, and the sensitivity of the speaker will not be lost.

8. Frequency response curve of an ideal small speaker

Since the bass reproduction ability of small speakers is most restricted by the speaker cabinet, the gap between the frequency response test curve and subjective listening is also the largest, which puts forward a compromise and new requirement for the frequency response test curve of small speakers. This requirement is: the low end of the frequency response should not pursue a lower digital effect, and the extension of the low frequency end should not be deliberately pursued below 35Hz or more, because for small bookshelf speakers using small-caliber woofers (less than 6.5 inches), its test frequency response below 40Hz is of little significance in practical applications. However, if the low-end frequency of the frequency response test is changed to 50Hz, and the curve is changed to a curve with a small peak at the low end and a slight decline at the high end, the sound effect during playback will be greatly improved without exceeding the test standard.

There are actually many misunderstandings about speakers. It is impossible to explain this issue clearly in one article. At the same time, with the development and progress of science and technology, we will get rid of old misunderstandings and encounter new ones. Therefore, if we want to avoid detours on the road of speakers, we must truly keep pace with the international standards and constantly learn advanced international cutting-edge technologies.