The earphone is an audio product that converts the electrical signal output by the sound source into a sound that can be heard by the human ear through the principle of electroacoustic conversion. From the development history of headphones, the earliest is the application of electric transducer technology to the small head-mounted speaker by German scientist Eugen Beyer in 1924. After the continuous development and maturity of the technology, the earphones of today are formed.
In 1924, the development team of Eugen Beyer, the father of dynamic headphones
In the history of nearly a hundred years of development, there are many classic headphones, the first of which achieves high fidelity standards is the Beyerdynamic DT48 headset, which was born in 1937, with a frequency response range of 16Hz-20kHz. The DT48S is the world's first stereo headset, representing the era of high-fidelity headphones. After years of development and advancement, consumer-grade headphones have undergone numerous changes in performance and performance.
Classic Dynamic Headphones Beyerdynamic DT48
There are many types of earphones. The most basic ones can be divided into head-mounted, ear-mounted, over-the-ear and in-ear according to the wearing method and volume. If they are distinguished according to the working characteristics, they can be divided into moving coils. , electrostatic type, plane diaphragm type, etc., if it is divided according to the degree of openness, it is open, semi-open and closed. In recent years, with the in-depth development of the earphone technology, active noise canceling headphones and wireless headphones have emerged, which greatly enhances the adaptability of the headphones in an outdoor environment.
This topic is mainly divided into the wearing method and volume, and then subdivided each type of headphones, including dynamic coil, static electricity, plane diaphragm and moving iron headphones, and will also discuss active noise canceling headphones and wireless headphones.
Analysis of working principle of moving coil, static electricity and plane diaphragm
At present, most of the headsets use the moving coil type electroacoustic conversion working principle. The dynamic coil type is the earliest electroacoustic conversion method used in earphones. Its principle is similar to that of the conventional speaker system. The diaphragm on the structure is connected with the cylindrical coil in the permanent magnetic field. The coil drives the diaphragm under the current of the signal. Sounds. The dynamic performance of the dynamic earphone is high. In theory, the larger the size of the diaphragm, that is, the larger the driving unit, the better the performance.
Drive unit design and diaphragm material for moving coil headphones are the key factors affecting sound quality
The moving coil type earphone and the ordinary sound box have certain differences in the diaphragm structure. The diaphragm edge of the speaker speaker is generally fixed on the elastic medium, and the shape is mostly conical, and the elastic medium provides vibration power. For moving coil headphones, the edge of the diaphragm is directly fixed to the frame of the drive unit, and the source of vibration is completely provided by the expansion and contraction of the material of the diaphragm itself. Therefore, the material selection and shape design of the diaphragm of the moving coil type driver unit There is a direct relationship to the performance of sound. Many brands, such as Sennheiser, SONY, and SHURE, have unique drive unit designs and diaphragm materials to ensure excellent sound output. In addition, the development of higher magnetic flux permanent magnets is another effective method. For example, the BEYERDYNAMIC Tesla series has a high magnetic flux of 1 Tesla.
The electrostatic earphone diaphragm is very thin and light, resulting in faster, more transient response and more detailed sound
As for the electrostatic type, due to the high content and cost of manufacturing technology, the price of electrostatic headphones is often more than 10,000 yuan. The working principle of the electrostatic earphone is different from that of the dynamic earphone. The diaphragm is mainly polarized by a high DC voltage and is in an electrostatic field formed by the change of two fixed metal plates. The diaphragm is driven by the electric field force to sound. Because electrostatic headphones need to convert audio signals into hundreds of volts, special amplifiers must be used to drive them.
The structure of the electrostatic earphone has an innate advantage over the dynamic earphone. The most critical one is that the diaphragm is very thin and light, only about 1/10 of the dynamic earphone diaphragm. This lighter and thinner diaphragm delivers faster, more transient response and more detailed sound. In addition, due to the structural limitations of the diaphragm of the moving coil earphone, there is always a problem of splitting vibration, which affects the uniformity of the three frequencies. The diaphragm of the electrostatic earphone is fixed between the parallel fixed plates, and the electric field is completely uniform, which can realize linear driving.
Both flat diaphragm headphones and electrostatic headphones can achieve linear diaphragm motion, while the low frequency performance is more outstanding
The flat diaphragm earphone can also be called the equal-magnetic earphone. The working principle is different from the moving coil and the electrostatic earphone. It is very similar to the flat diaphragm speaker, mainly embedding the planar voice coil into the thin diaphragm. The magnet is concentrated on one or both sides of the diaphragm, and the diaphragm vibrates in the magnetic field it forms. Both the flat diaphragm earphone and the electrostatic earphone can realize linear diaphragm motion without the problem of split vibration. Planar diaphragm headphones can also withstand greater input power, lower distortion under loud pressure, but also lower efficiency and sensitivity, often requiring high-power and high-current output amps to match. In addition, the volume and weight are large, which is not conducive to long-term wear.
Features of open, semi-open and closed headphones
Depending on how the sound is opened, the sound performance of the headphones will have different characteristics. For open-type headphones, the sound will be transmitted to the outside world, the sound field will behave wide, the balance of high, medium and low tri-band is high, and the tone is neutral and natural. However, the noise reduction performance is poor, and the loss to the low frequency is also large.
The closed type can completely cover the entire auricle, and the earmuffs are completely free of voids, which can prevent the leakage of sound and prevent the influence of external sounds. The closed earphones have rich sound details but a narrow sound field.
The advantages and disadvantages of the semi-open type are between the closed and open headphones. With a certain ability to reduce noise, it can also bring a good sound field and detailed performance.
Open and closed headphones are the current mainstream, and the sound characteristics of the two structures are different.
Main related parameters of earphones<br> With the development of earphone technology, more and more earphones can meet the standards of the International Electrotechnical Commission IEC581-10 high-fidelity earphones. The specific criteria are: the frequency response of the earphone is not narrower than 50Hz to 12.5kHz, and the allowable error of the typical frequency response is ±3dB; the frequency response curve of the two sounding bodies of the stereo earphone corresponds to the average sound pressure of each octave bandwidth. The difference between the stages shall not be greater than 2 dB; in the range of 100-5000 Hz, the harmonic distortion shall not exceed 1% when the sound pressure level is 94 dB, and shall not exceed 3% at 10 0 dB. Therefore, the biggest advantage of headphones compared to speakers is that the reproduction of details is better.
Impedance and sensitivity are two important parameters. Headphones with high impedance and low sensitivity need to be matched with headphone amplifiers.
The frequency response range determines the level of detail of the sound reproduction. The range of the headphone frequency response is not only wide but also flat.
The main relevant parameters that affect headphone performance include impedance, sensitivity, and frequency response range. The so-called impedance is the abbreviation of the headphone AC impedance, and the unit is Ω (ohm). The impedance of professional headphones is often above 200Ω, and personal headphones can reach up to 600Ω, 16-300Ω is a common value. Headphones with high drive impedance require a large amount of power, so the latest generation of headphone impedance is often only 16-32 ohms for use with low output power sources.
Sensitivity refers to the sound pressure level that the earphone can emit when inputting 1mW of power. The higher the sensitivity and the lower the impedance, the easier the headphone is to drive. The unit of sensitivity is dB/mW, and the sensitivity of moving coil headphones is generally above 90dB/mW.
The frequency response range is the width of the sound band that the headphones can output. The human hearing range is 20 Hz-20 kHz, and the frequency band that the earphone can reproduce is quite wide, even up to 5-45000 Hz or wider. It is worth noting that the unevenness of the frequency response is also worth noting. Most of the brands have this parameter of ±3dB. The excellent range of headphone frequency response is not only wide but also flat. In addition to these three parameters, total harmonic distortion is also worth noting. The smaller the distortion, the better the sound quality.
Analysis of working principle of moving iron
In the previous analysis of the working principle of moving coils, static electricity and planar diaphragm headphones , it was mentioned that most of the headphones are based on the moving coil type. For the in-ear headphones that need to enter the ear canal, the two technologies are mainly micro-coil and moving iron (also called balanced armature), and most of the high-end headphones adopt multi-unit moving iron structure, the main one. Brands include SHURE, ETYMOTIC, LOGITECHUE and more. Of course, with the maturity of the micro-coil technology, the high-end dynamic in-ear headphones brought by Sennheiser are also very good.
In addition, many brands, such as WESTON E and JHAUDIO, will also provide users with customized personalization services for moving iron in-ear headphones. According to the shape of the user's ear and ear canal, they can be fully fitted with in-ear headphones to provide higher resolution. Sound performance with better sound insulation.
Moving iron earphone structure
Dynamic iron unit structure diagram
The structure and working mode of the moving iron earphones are completely different from the conventional moving coil headphones. The musical electrical signal of the moving iron earphone firstly changes the magnetic field of the electromagnet through the electromagnet, and finally drives the iron piece wound around the center of the electromagnet to vibrate. Why is the moving iron unit also called the balance armature? The main reason is that in general, the iron piece is often at the center of the magnetic field, and when there is no magnetic force acting on it, it is in a balanced state. According to such a structure, it is known that only a slight electrical signal can cause the moving iron unit to emit a sound. Therefore, the moving iron headphones have excellent electroacoustic conversion capability.
Advantages of moving iron headphones
Based on the mechanical characteristics of the moving iron unit, the moving iron in-ear headphones are generally small in size.
Due to the characteristics of the working principle, the moving coil unit requires more operating space and driving air, and is often bulky. However, in recent years, with the in-depth development of the micro-coil unit, adding a new generation of manufacturing technology, the volume has gradually approached the moving iron unit. The moving iron unit is very compact, allowing the moving iron headphones to be placed deeper into the ear canal to improve the sense of hearing. And because the moving iron unit will greatly increase the weight as the unit diameter increases, this is the main reason why the moving iron technology is not applied to the headphones.
In addition to the advantages of volume, moving iron headphones generally have very high sensitivity, but need to pay attention, this does not mean that the moving iron headphones must be easy to drive, in the face of 3 or more moving iron headphones, often need high power output The source or drive with the amp. However, when using the amp, you must pay attention to the problem of impedance matching in order to get the best performance. The high sensitivity means that the moving iron earphone has better sound resolution than the dynamic earphone, especially in the middle and high frequency detail level.
High-end moving iron headphones tend to adopt multiple unit structures and require stronger driving force.
The moving iron headphones were born in the early 20th century, and were mainly used for professional and military purposes in the early days. At that time, due to the narrow frequency band of the unit, it was not able to be further popularized in the civilian sector. With the continuous development of technology, the moving iron unit has made great progress. At present, there are high-frequency, medium-frequency, low-frequency and full-frequency moving iron units. The moving iron unit is mainly made of metal material, and the stability is much higher than that of the dynamic ring earphone.
Various high performance balanced armature units from Knowles Electronics
Unlike dynamic coil headphones, the development of the unit is basically developed by the manufacturers themselves. Due to the extremely fine manufacturing process required by the moving iron unit, most brands except the few manufacturers such as SON Y use third-party units. Among them, the most popular is the high-performance moving iron unit brought by Knowles Electronics, and the full-range moving iron unit can reach the level of 20Hz-20kHz. SONY's newly developed moving iron unit includes full-range, treble, bass and heavy-frequency units. For high-end multi-unit moving iron headphones, the quality of the sound is determined. In addition to the performance of the unit, the design of the frequency dividing circuit is also the key. Different manufacturers often have different adjustment methods, which is the main reason for their different sound characteristics.
In-ear headphones
The importance and different types of earmuffs
The earmuff is a very important part of the in-ear earphone, which is the bridge between the drive unit and the ear canal. High-quality earmuffs enhance the sound quality while enhancing the comfort of wearing. Mid-to-high-end in-ear headphones often have more sets of earmuffs of different materials for users, while low-end popular products only have earmuffs of the same material size. Therefore, you can actually choose a third-party brand of earmuffs.
Commonly used soft rubber earmuffs
ETYMOTIC classic three-section rubber sleeve
At present, the earmuff materials used in non-customized earphones are divided into two categories: soft rubber and sponge. Soft rubber can be divided into two types: single-piece rubber sleeve and multi-section rubber sleeve according to the shape. The single-section rubber sleeve is comfortable to wear, but it is not adjustable. The multi-section rubber sleeve, such as ET YMOTIC, is a classic three-section rubber sleeve. The prototype is from medical hearing aids. It allows users to choose whether to increase the insertion depth according to the depth of their ear canal, and also enhance the sound insulation effect. The inconvenience of this kind of rubber sleeve is that the comfort is not as good as the single-section rubber sleeve, which is not acceptable to every user.
Sponge cover from Comply
The sponge cover is currently the most comfortable type of earmuff, and Comply's range of sponge covers is best known. Compared with the soft rubber sleeve, it is closer to the ear canal to form a more sealed space, and the sound insulation performance is also better. From the sense of hearing, the details and levels of the sound will be richer and more natural, and the resolution will be stronger.
However, the sponge sleeve is a big problem compared to the soft rubber sleeve. Under normal circumstances, it cannot be cleaned, and it needs to be replaced after a short period of use, and the use cost is high. Unlike soft rubber sleeves, the diameter of the catheter sleeve connected to the earphone is fixed and cannot be used on headphones with different catheter sizes.
In terms of customized in-ear headphones, because the size of the earphone is large, there is no earmuff in the case of passing, but the entire earphone is directly inserted into the ear. Therefore, the user does not need to consider the problem of changing the earmuffs, which is also a great advantage in the use of customized headphones. In terms of use, in-ear headphones are not suitable for long-term use, but also need to match the appropriate earmuffs, which is the biggest problem compared with headphones. The excellent portability and low drive requirements, coupled with the sound performance of the headphones, make the in-ear headphones more and more users.
Other types of headphones features
In the development of the headset, in addition to the many types mentioned above, active noise reduction and wireless headphones are also becoming more and more popular. Active noise canceling headphones use microphones and active noise reduction circuits to reduce external noise interference to improve the performance of headphones in noisy outdoor environments. Many active noise canceling headphones often incorporate amplifying circuits. For example, the PSB M4U 2 is a multi-function earphone that can switch between active noise reduction, active amplification and passive mode. Users do not need to consider the driver problem. Wireless headsets are usually powered by Bluetooth, Wi-Fi or other 2.4 GHz band wireless signal transmission technology to improve wearing comfort.
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