The source of headphones
1924 The R&D team of Eugen Bayer, the father of dynamic headphones, has many classic headphones with a history of nearly 100 years. Among them, Beyerdynamic DT48 headphones, born in 1937, have a frequency response range of 16Hz-20kHz, and the upgraded DT48S is the first in the world. After years of development and promotion, consumer headphones have undergone many changes in performance and expression.
Types of headphones
Classic dynamic headset Beyerdynamic DT48
There are many kinds of headphones, and the most basic ones can be divided into head-mounted, ear-attached, ear-hung and in-ear according to the way of wearing and the volume. According to the working characteristics, it can be divided into moving coil type, electrostatic type and planar diaphragm type. According to the degree of openness, there are open, semi-open and closed. In recent years, with the in-depth development of earphone technology, active noise-reducing headphones and wireless headphones have appeared, which greatly enhance the adaptability of headphones in outdoor environment.
This topic mainly discusses the way and size of wearing, and then subdivides each kind of earphone, including moving coil earphone, electrostatic earphone, flat diaphragm earphone and moving iron earphone. Active noise reduction headphones and wireless headphones will also be discussed.
Working principle analysis of moving coil, static electricity and plane diaphragm
At present, most headphones adopt the working principle of moving coil electroacoustic conversion. As the earliest electroacoustic conversion method for headphones, the moving coil type is similar to the conventional speaker system in principle. Structurally, the diaphragm is connected with a cylindrical coil in a permanent magnetic field, and the coil drives the diaphragm to sound under the current drive of the signal. Moving-coil headphones have high working efficiency. Theoretically, the larger the size of the diaphragm, that is, the driving unit, the better the performance.
The design of the driving unit and the material of the diaphragm are the key factors affecting the sound quality.
However, dynamic headphones are different from ordinary speakers in membrane structure. The edge of the diaphragm of the loudspeaker is generally fixed on the elastic medium, and its shape is mostly conical, and the elastic medium provides the vibration power. For dynamic headphones, the edge of the diaphragm is directly fixed on the frame of the driving unit, and the vibration source 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 dynamic earphone driving unit are directly related to the sound performance. Many brands, such as Sennheiser, Sony and Shure, have unique drive unit design and diaphragm materials to ensure excellent sound output. In addition, developing permanent magnets with higher magnetic flux is another effective method. For example, Beye Power Tesla series has a magnetic flux as high as 1 Tesla.
The diaphragm of electrostatic earphone is very thin, which can bring faster sound, better transient response and more prominent sense of detail.
As for the electrostatic type, due to the high manufacturing technology and cost, the price of electrostatic headphones is often more than 10 thousand yuan. The working principle of electrostatic headphones is different from that of dynamic headphones, mainly because the diaphragm is polarized by high DC voltage, and it is in an electrostatic field formed by the change of two fixed metal plates, which is driven by electric field force to make the diaphragm sound. Because electrostatic headphones need to convert audio signals into voltage signals of several hundred volts, special amplifiers must be used to drive them.
The structure of electrostatic headphones has inherent advantages over dynamic headphones. The most important thing is that the diaphragm is very thin, which is only about110 of the diaphragm of dynamic headphones. This lighter and thinner diaphragm can bring faster speed, better transient response and finer sound. In addition, due to the structural limitation, the diaphragm of dynamic earphone always has the problem of vibration separation, which affects the uniformity of three frequencies. The diaphragm of the electrostatic earphone is fixed between parallel fixing plates, and the electric field is completely uniform, so that linear driving can be realized.
Both planar diaphragm headphones and electrostatic headphones can realize linear diaphragm movement, and the low frequency performance is more prominent.
Planar diaphragm earphone, also called isoelectric earphone, is different from moving coil and electrostatic earphone in principle, and is very similar to planar diaphragm speaker, mainly by embedding planar voice coil in thin diaphragm. Magnets are concentrated on one side or both sides of the diaphragm, and the diaphragm vibrates in the magnetic field it forms. Both planar diaphragm headphones and electrostatic headphones can realize linear diaphragm movement without splitting vibration. Planar diaphragm headphones can also bear more input power, and the distortion is lower when pressed loudly, but the working efficiency and sensitivity are also lower, so they often need the cooperation of high-power and high-current output amplifiers. In addition, it is bulky and heavy, which is not conducive to wearing for a long time.
Characteristics of open, semi-open and closed headphones
According to the different ways of turning on the sound, the sound performance of headphones will have different characteristics. For open headphones, the sound will spread to the outside world, the sound field is wide, the high, medium and low frequency balance is high, and the timbre is neutral and natural. However, the noise reduction performance is poor and the low frequency loss is also large.
The closed type can completely cover the whole auricle, and the earmuffs have no holes at all, which can prevent the sound from leaking out and the influence of external sound. Closed headphones have rich sound details, but the sound stage is narrow.
The advantages and disadvantages of semi-open headphones are between closed headphones and open headphones, which can not only reduce noise, but also bring good sound field and detail performance.
Open and closed headphones are the mainstream at present, and the sound characteristics of the two structures are more different.
Main related parameters of headphones
With the development of earphone technology, more and more earphones can meet the standard of IEC58 1- 10 high fidelity earphones. The specific standards are: the frequency response of headphones is not narrower than 50Hz to 12.5kHz, and the allowable error of typical frequency response is? The difference between the frequency response curves of the average sound pressure level corresponding to each octave bandwidth between the two speakers of a 3dB stereo headset should not be greater than 2dB, and the harmonic distortion should be less than 100-5000Hz, less than 1% at 94dB and less than 3% at 10 0 dB. Therefore, the biggest advantage of headphones over speakers lies in the better reproduction of details.
Impedance and sensitivity are two important parameters. Headphones with high impedance and low sensitivity need to be driven by headphone amplifiers.
The frequency response range determines the details of sound reproduction. Excellent earphone frequency response range is not only wide, but also flat.
The main related parameters that affect the performance of headphones include impedance, sensitivity and frequency response range. The so-called impedance is the abbreviation of earphone AC impedance. What unit is used? (Ohms). The impedance of professional headphones is often in 200? Above, personal headphones can reach up to 600? , 16-300? Is a universal value. Driving headphones with high impedance requires more power. Therefore, in order to match the mobile audio source with low output power, the impedance of the latest generation headphones is often only 16-32? .
Sensitivity refers to the sound pressure level that the earphone can emit when the power of 1mW is input. The higher the sensitivity, the smaller the impedance, and the easier it is to drive headphones. The unit of sensitivity is dB/mW, and the sensitivity of dynamic headphones is generally above 90dB/mW.
Frequency response range refers to the sound frequency band width that headphones can output. People's hearing range is 20 Hz-20 Hz, and the frequency band that headphones can play back is quite wide, even reaching 5-45000Hz or wider. It is worth noting that the non-uniformity of frequency response is also worth noting. What is this parameter for most brands? 3dB. Excellent earphone frequency response range should be not only wide, but also flat. In addition to these three parameters, total harmonic distortion is also worthy of attention. The smaller the distortion, the better the sound quality.
Analysis of working principle of moving iron
When analyzing the working principles of dynamic, electrostatic and planar diaphragm headphones, it is mentioned that most headphones are based on dynamic working mode. For in-ear headphones that need to enter the ear canal, two technologies are mainly micro-motion ring and moving iron (also known as balanced armature), among which high-end headphones mostly adopt multi-unit moving iron structure, and the main brands are Shure, ETYMOTIC, LOGITECHUE and so on. Of course, with the maturity of micro-dynamic technology, the high-end dynamic in-ear headphones brought by Sennheiser are also excellent.
In addition, many brands, such as WESTON E and JHAUDIO, will also provide users with personalized customization services for moving iron in-ear headphones, and create perfect-fitting in-ear headphones according to the shapes of users' auricles and ear canals to provide sound performance with higher resolution and better sound insulation efficiency.
Structure of earphone
Schematic diagram of moving iron unit structure
The structure and working mode of moving iron headphones are completely different from those of conventional moving coil headphones. The music electric signal of the moving iron earphone first causes the change of the magnetic field of the electromagnet through the electromagnet, and finally drives the iron plate around the center of the electromagnet to vibrate and make sound. Why is the moving iron unit also called the balanced armature? The main reason is that under normal circumstances, the iron sheet is often in the center of the magnetic field, and it is in equilibrium when there is no magnetic field force. According to this structure, it can be known that only a slight electrical signal can make the moving iron unit sound. Therefore, the moving iron earphone has excellent electroacoustic conversion ability.
Advantages of headphones
Based on the mechanical characteristics of moving iron unit, moving iron in-ear headphones are generally small in size.
Because of the characteristics of working principle, moving coil units need more operating space and driving air, and are often large in size. However, in recent years, with the in-depth development of micro moving coil unit and the addition of new generation manufacturing technology, the volume has gradually approached the moving iron unit. The movable iron unit is very small, so that the movable iron earphone can be placed deeper in the ear canal to improve hearing. Because the weight of the moving iron unit will increase greatly with the increase of the diameter of the unit, this is also the main reason why the moving iron technology has not been applied to headphones.
In addition to the size advantage, moving iron headphones generally have very high sensitivity, but it should be noted that this does not mean that moving iron headphones must be easy to open. Moving iron headphones with 3 units or more often need high-power output sound source or matching power amplifier to drive them. However, when using the amplifier, we must pay attention to the impedance matching problem in order to obtain the best performance. High sensitivity means that the moving iron earphone has better sound resolution than the moving coil earphone, especially in the middle and high frequency details.
High-end moving iron headphones often adopt multi-unit structure, which requires stronger driving force.
Moving iron headphones were born in the early 20th century, mainly used for professional and military purposes. At that time, due to the narrow frequency band of the unit, it could not be further promoted in the civil field. With the continuous development of technology, the moving iron unit has made great progress. At present, there are high frequency, intermediate frequency, low frequency and full frequency moving iron units. The moving iron unit is mainly made of metal, and its stability is much higher than that of the moving earphone.
Knowles Electronics brings a variety of high-performance balanced armature units.
Different from the dynamic headphones, the research and development of this unit is basically developed by the manufacturers themselves. Because the moving iron unit requires extremely fine manufacturing technology, except for a few manufacturers such as SON Y, most brands use third-party units. Among them, the most popular are all kinds of high-performance moving iron units brought by Knowles Electronics (Lou's), and the full-frequency moving iron unit has been able to reach the level of 20 Hz-20 Hz. Sony's latest moving iron unit includes full frequency, treble, bass and heavy low frequency units. For high-end multi-cell moving iron headphones, in addition to the performance of the unit, the design of frequency division circuit is also the key to determine the sound quality. Different manufacturers often have different adjustment methods, which is also the main reason for their different sound characteristics.
Instructions for use of in-ear headphones
Importance and different types of earmuffs
Earmuff is a very important part of in-ear headphones, and it is a bridge between the driving unit and the ear canal. High-quality earmuffs can not only improve the sound quality, but also improve the comfort of wearing. High-end in-ear headphones often prepare multiple sets of earmuffs with different materials for users, while low-end popular products only have earmuffs with the same material and different sizes. So in fact, you can choose a third-party brand earmuffs.
Common soft rubber earmuffs
ETYMOTIC classic three-stage rubber sleeve
At present, the earmuffs used by non-customized in-ear headphones are divided into two categories: soft rubber and sponge. Soft rubber can be divided into single rubber sleeve and multi-rubber sleeve according to different shapes. Single rubber sleeve is comfortable to wear, but it is not adjustable. ET YMOTIC and other multi-section rubber sleeves are classic three-section rubber sleeves. The design prototype comes from medical hearing aid products. Users can choose whether to increase the insertion depth according to their own ear canal depth, and at the same time enhance the sound insulation effect. The inconvenience of this kind of rubber sleeve is that the comfort is not as good as that of a single rubber sleeve, which is not acceptable to every user.
Sponge sleeve from Comply
Sponge cover is the most comfortable type of earmuffs at present, among which Comply's series of sponge covers are the most famous. Compared with the soft rubber sleeve, it is closer to the ear canal to form a more closed space and has better sound insulation performance. From the auditory point of view, the details and levels of sound will be richer and more natural, and the analytical power will be stronger.
But compared with soft rubber sleeve, sponge sleeve is a big problem in cleaning. Generally speaking, it can't be cleaned, and it needs to be replaced after a period of use, so the use cost is high. Different from the soft rubber sleeve, the diameter of the catheter connected with the sponge sleeve is fixed, so it cannot be used on headphones with different catheter sizes.
In terms of customized in-ear headphones, due to the large volume of headphones, there is no earmuff when passing through, but the whole earphone is directly inserted into the ear. Therefore, users do not need to consider replacing the earmuffs, which is also a big advantage in the use of customized headphones. In terms of use, in-ear headphones are not suitable for long-term use, and they need to be matched with appropriate earmuffs, which is the biggest problem compared with headphones. Excellent portability, low driving requirements, and sound performance comparable to headphones make in-ear headphones recognized by more and more users.
Characteristics of headphones
In the development of headphones, in addition to the above-mentioned types, active noise reduction and wireless headphones are becoming more and more popular. Active noise reduction headphones use microphones and active noise reduction circuits to reduce external noise interference, thus improving the performance of headphones in outdoor noisy environment. Many active noise canceling headphones usually include amplifier circuits. For example, PSB M4U 2 is a multifunctional earphone, which can switch between active noise reduction, active amplification and passive mode, and users do not need to consider driving problems. Wireless headphones usually use Bluetooth, Wi-Fi or other wireless signal transmission technologies in the 2.4GHz band to improve the wearing comfort.