As a key component of a loudspeaker, the design and selection of the voice coil directly affect the performance and rated power of the loudspeaker, and there is a close relationship between the two.

According to the national standard GB/T 12060.5-2011 "Methods for Testing the Main Performance of Loudspeakers", the power bearing capacity of a loudspeaker refers to the rated noise power. According to this standard, the rated noise power is equal to Un ²/R, where Un is the rated noise voltage and R is the rated impedance. Rated noise voltage refers to the analog program signal and signal voltage that is fed back to the speaker within the rated frequency range to produce a specified analog program signal without generating thermal or mechanical damage.

It is worth noting that the experimental signal is an analog program signal, not a pink noise signal. The simulated program signal is obtained from pink noise signal through a suitable weighting network, which is closer to the actual usage of the speaker.

According to this standard, the power test time is 100 hours.

For speakers, all technical specifications of the speaker system are important, but there is no doubt that the reliability and lifespan of the speaker come first. If the speaker breaks down as soon as it is used, users who die before they succeed will certainly not be satisfied.

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Sudden death and heart attack are one of the main causes of human death. The voice coil is known as the heart of a speaker, but it also limits the lifespan of the speaker. The damage to the voice coil can occur in the following situations: the lead out part is broken; The voice coil overheats and scatters; The voice coil line is detached from the skeleton; Partial burning of voice coil lines; The cause of voice coil damage is usually due to overheating and vibration of the voice coil.

The power that the voice coil can withstand is certain, and the setting of the rated noise power of the voice coil should be scientific, reasonable, and practical.

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The voice coil should have a considerable thermal strength, which means that although it generates heat due to current passing through it during operation, it will not deform, the adhesive will not peel off, and the paint film will remain intact. The voice coil will dissipate heat through the air (magnetic fluid) in the magnetic gap through the magnetic circuit during operation. Maintain a dynamic balance with good design and craftsmanship.

One of the methods for designing voice coil parameters is introduced below. The thermal power of the voice coil is

Pe= J² Pe SL (W)

In the formula, J is the current density (A/m ²);

Pe is the electrical resistivity of the wire (Ω· m);

S is the coil side area (m ²);

L is the length of the voice coil wire (m).

The ratio of Pe/S is called the heat transfer rate Pt.

J is the current density, which is the current intensity allowed to pass through the voice coil, generally ranging from 30A/mm ² to 90A/mm ².

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Figure 2 shows the relationship curve between the magnetic gap width L3 and the maximum amplitude X1, which can be used as a reference.

It can be understood that when the maximum amplitude is relatively large, the required magnetic gap width should also be larger. However, due to the limitation that the magnetic gap width cannot be too large, the widths of the two are not linearly related. An increase in magnetic gap width is beneficial for heat dissipation and process reliability, but it can lead to a decrease in magnetic flux density.

Of course, the width of the magnetic gap also depends on our experience, such as the overall thickness of the voice coil and the amount of gap left in front and behind the voice coil. It is possible to achieve the highest pass rate under the current assembly process conditions.

The magnetic gap width of the speaker can also be determined based on the aperture of the speaker. Generally speaking, the larger the aperture of the speaker, the larger the magnetic gap width.

Another experience for reference is that increasing the magnetic gap width will reduce sensitivity, but in the end, the playback sound of the speaker will be cleaner.

After the magnetic gap width is determined, the heat transfer rate Pe/S can be calculated according to Figure 1. If the thermal power Pe of the voice coil is known, the voice coil area S can be calculated.

There is a certain correlation between the diameter and height of the voice coil. If the height ratio is K, then

K= d/h

In the formula, d is the diameter of the voice coil;

H is the height of the voice coil.

For heat dissipation, the higher the power of the speaker, the greater the ratio K. For high-power speakers, the K value is 4-6; For low-power speakers, the K value is 3-4.

From this, the diameter d and height h of the voice coil can be calculated, that is

d=√（SKIπ)

h=d/k