What are the factors that affect the in-ear headphones sound quality?

Short circuit

This is the most common common problem with some in-ear headphones products. Many inexpensive in-ear earphone products, when assembled in the factory, directly mount the speaker into the speaker cavity of the front cover of the earphone without any sealing measures. This forms an acoustic short circuit that has the greatest impact on the overall sound quality. In popular terms, it is the “leakage” state between the outer edge of the speaker and the earphone shell. Sound waves before and after the diaphragm of the speaker pass through the outer edge of the speaker, causing an acoustic short circuit. As a result, the low-frequency sound wave amplitudes are offset before and after, are greatly attenuated, and the amplitude is distorted. The sounds reproduced from the headphones are almost entirely intermediate and high-frequency, and there is no fullness and elasticity of the low-frequency sound waves, and the sense of fullness and sensation of shock, the overall sense of sound Fine impetuosity, similar to the vocal term used in the narrow range of the sound field.

Acoustic short circuit also brings a serious loss of sound pressure, so that the overall sound pressure sensitivity of the headset is greatly reduced, and the volume on hearing is obviously insufficient. The smaller the diameter of the bell mouth used by the headset, the more pronounced the effect of the acoustic short circuit.

2. Silence effect

The design structure or manufacturing process of the earphone is unreasonable, so that the acoustic wave encounters a silencing effect when it is conducted from the speaker to the human ear. For example, some products simply stick a self-adhesive foam ring on the front of the speaker. Use this foam ring to attach the speaker to the front case. On the surface, this foam ring acts as a seal to prevent the formation of acoustic short circuits, but the flexibility of the foam ring just happens to dampen the sound. This silencing effect seems to be minimal, but for the in-ear headphones with extremely stringent sound pressure requirements, its negative effects must not be underestimated.

For another example, for the sound tube at the front of the in-ear earphone case, many products only use it as a supporting part of the cover rubber sleeve, and do not notice that this part also has a significant influence on the sound quality on the acoustic principle. In some products, the sound tube is designed to be very short. After the rubber sleeve is put on, a large part of the inner tube is the inner tube of the rubber sleeve. The inner front end of the inner tube of the rubber sleeve is flexible and will play a role in silencer.

This silencing effect mainly affects both the low frequency and the high frequency. The overall performance is that the low frequency sound pressure is greatly reduced and there is no elasticity. It is a kind of “false low”; the high frequency details are excessively attenuated, and many harmonic components in the natural sound are Eliminated, the overall tone becomes dry and emaciated, lacks beauty, and sometimes becomes harsh. In this case, the smaller the diameter of the speaker is, the more serious it will be.

3. Reverberation interference and inter-frequency modulation distortion

If natural sound contains moderate reverberation, it will help to fully express the differences between various harmonic components in the details and space-time, resulting in a timbre of beauty. However, if the headphones themselves have a reverberation effect, or can form a strong inter-frequency modulation distortion, it will destroy the original color when the sound is restored, so that the overall sound effect becomes a level of confusion, chaos unclear, with some enthusiasts say It is "not clean" or "not clear." Reverberation interference and inter-frequency modulation distortion may be generated in the sound tube cavity, or may be generated in the cavity formed by the back cover of the earphone, which is mainly caused by the reflection formed by the smooth inner surface of the cavity. In these cavities, sound waves of different frequencies form various interferences and modulations in the reflection process, changing the original waveform and amplitude ratio, and forming inter-frequency modulation distortion. These are similar to the "standing wave interference" involved in speaker production technology. The method to eliminate the standing wave interference in the production of the speaker is usually to add a sound-absorbing material in the box to prevent sound waves of various frequencies from regularly reflecting and modulating each other in the box. The acoustical principle of the in-ear earphone housing is different from that of a speaker, and the volume of the cavity is also very narrow, and it is impossible to solve this problem by simply filling the sound-absorbing material. In particular, if sound-absorbing materials are added to the sound tube cavity, on the one hand, the process is very difficult, and on the other hand, it will cause large attenuation of the high-frequency sound waves, which will degrade the frequency response characteristics of the entire machine.

From a technical point of view, the earphone itself should not have its own reverberation effect, but it should be able to truly and accurately restore the original reverberation effect contained in the sound signal.

4. Acoustic cavity shape and volume

Ordinary speakers usually have only one acoustic cavity. In ear headphones, there are two acoustic cavities. One is the front cavity formed by the space in front of the speaker diaphragm and the inner cavity of the sound tube, and the other is formed by the back cover of the earphone. Rear cavity. Both of these cavities have a very significant effect on the sound quality of the headphones. As mentioned earlier, if the inner surfaces of these two cavities are too smooth, they can cause reverberation interference. In addition, the volume and shape of these two cavities will also have a significant impact on sound quality. If the volume of the front cavity is too large, especially when the shape of the guide tube is too slender, the high-frequency and intermediate-frequency sound wave transmission paths will become longer, the amplitude will be weakened, the sound pressure will be reduced, and the sound field will be moved backward. The result is a complete machine. The effect is boring and not beautiful. It makes people feel that vocals and musical instruments are too far from the ear, and they are prone to hearing fatigue.

At the same time, low-frequency sound waves will become less elastic, loose and lacking fullness and shock. Some people with a keen sense of hearing will also feel that there is a delay in the sound information at low frequencies. If the guide tube is too thick and short, the distance between the treble and the treble will be too close to the ear, the bass will not be full, and the middle and high pitch will be harsh. Moreover, if the aperture is too large, reverberation interference may also form. The inner volume of the sound guide tube is too large, which means that the inner diameter is large and the length is too long. This will make the loudspeaker diaphragm push the air insufficiently and cause delay, so that the overall sound effect will have a clear sense of space, the sound is not solid, and the sound is not solid. There is a sense of distance, and sometimes there is a clear reverberation disturbance. The smaller the diameter of the bell, the more obvious this effect will be.

The article comes from China Headphone Exchange:/