What parts are headphones made of?

An earphone mainly consists of four parts: headband, left and right sound generating units, earmuffs and leads.

The role of the headband is to fix the left and right vocal units and place them on both sides of the head. Its structure and connection mode with the unit determine the pressure of the headband and earmuffs on the head, and affect the comfort of wearing headphones.

Earmuff is the part of the head that contacts with the sound generating unit. It is very important for dynamic headphones. Its function is to reflect the low frequency back and ensure the low frequency playback. There are generally two styles of earmuffs, one is pressed on the ear, which is called over-the-ear type, and the other is cup-shaped and surrounds the ear, which is called hoop earmuffs. Earmuffs should be as soft and comfortable as possible, generally filled with sponge and covered with leather or flannel. The material used in the earmuffs can absorb medium and high frequencies, so that the ear and the diaphragm form a distance and a cavity is formed between the earphone and the head. The inner space of the earmuffs is large, and the sound can act on the auricle, forming a good sense of space. A well-designed earphone has fully considered the role of earmuffs, so the earmuffs of middle and high-end headphones cannot be damaged or replaced at will.

The lead wire of the earphone is the connecting wire between the output end of the earphone amplifier circuit and the earphone voice coil. High-quality earphone cables often use oxygen-free copper (OFC) wires with multi-branch cores, which are strictly insulated and shielded to prevent the influence of impurities in copper on signal transmission and the interference of external clutter. At the end of the earphone cable is a plug, which has two specifications, 6.35mm and 3.5mm, and is usually called a large and small plug. 6.35mm plug is used for professional audio and civil audio equipment, and 3.5mm plug is used for portable equipment. General high-fidelity headphones will provide plug converters to ensure the use of headphones on various devices. The plug of high-end headphones is gold-plated, not for beauty, but mainly to prevent the oxidation of the plug from affecting the sound. Because gold is smooth and soft, it can also provide as large a contact area as possible. Low-grade headphones often use nickel-plated plugs, which can prevent oxidation, but have a certain negative impact on sound.

The sound generating unit of earphone is the most complicated and technical part in earphone design. The working principle of dynamic earphone is the same as that of dynamic loudspeaker. After the audio signal is input into the voice coil, the electromagnetic field generated by the voice coil changes with the signal. The changing electromagnetic field interacts with the magnetic circuit to push the voice coil and diaphragm to move, and the diaphragm pushes the air to make sound. The sound generating unit of dynamic earphone is mainly composed of three parts: magnetic circuit system, vibration system, cavity and hole.

The magnetic circuit system is composed of permanent magnets, polar plates and polar shoes, which has a direct impact on the performance and reliability of headphones. One side of the permanent magnet is a flat plate, and the other side is a T-shaped pole shoe. A small annular magnetic gap is formed between the pole plate and the pole shoe, and the voice coil of the vibration system is suspended in this magnetic gap. Usually, the permanent magnets used in high-fidelity headphones are neodymium ferromagnets with excellent performance. Early earphone models used expensive samarium cobalt magnets, while low-end headphones generally used ferromagnetic magnets. The design of magnetic circuit system is complicated. The magnetic circuits of high-end headphones such as Sennheiser HD580 and HD600 are all designed by computer. The production technology of magnetic circuit is also an aspect that affects its performance. The design and manufacture of excellent magnetic circuit system can effectively control the vibration system and obtain higher sensitivity, less distortion, good transient and low frequency.

The vibration system consists of voice coil and diaphragm. The diaphragm is an acoustic radiation element, which pushes the air to vibrate to produce sound, which directly affects the frequency response and sensitivity. Its performance mainly depends on the manufacturing material, shape and manufacturing process. The materials used to make the diaphragm need as little mass per unit area as possible, high mechanical strength and large internal damping. The higher the mechanical strength, the lighter the mass, the wider the effective frequency range and the higher the output sound pressure level. Large internal damping, small distortion under large signal. At present, polyester film with easy thermoforming, light weight and good rigidity is mostly used for diaphragm, and some companies have developed new diaphragm materials. For example, Sony's advanced headphones and earplugs use a "biological diaphragm" made of cellulose separated from Acetobacter, which has excellent high frequency. The diaphragm is usually circular, with a convex arc at the center and reinforcing ribs around it, which can strengthen the rigidity of the diaphragm and increase the effective area of the diaphragm. Sometimes, for the need of air pressure balance, a small hole is machined in the non-vibrating part of the diaphragm. The manufacturing technology of diaphragm requires high requirements, and the control of various differences in processing is extremely strict.

Voice coil is the vibration source of dynamic earphone, and most parameters of earphone, such as impedance, sensitivity and rated power, are related to it. The performance of voice coil mainly depends on the material used and the number of turns of voice coil, that is, the length of voice coil wire. The material of voice coil is generally copper enameled wire. Advanced headphones commonly use oxygen-free copper enameled wire and copper-clad aluminum enameled wire. The latter has the advantages of copper enameled wire, but it is lighter in weight, and some use silver as voice coil material. The enameled wire section of voice coil is mostly round, and there are also triangular and regular hexagonal sections, which makes the wires more closely combined, reduces the capacitance between wires and further reduces the quality of voice coil. The size of voice coil also has a certain influence on the performance of headphones. The voice coil vibrates in the magnetic gap, and its diameter should ensure that the voice coil is located in the center of the magnetic gap and will not collide with the pole plate and pole shoe during vibration. On the other hand, because the magnetic field of the magnetic gap on the surface of the polar plate is uneven, the movement of the coil in the uneven magnetic field will reduce the conversion efficiency of electroacoustic energy and cause earphone distortion, so the height of the voice coil should be properly selected.

Acoustic structures such as cavities and holes are important parts that affect the performance of headphones. The magnetic circuit system and the vibration system are fixed by a plastic frame called a table top, and the edge of the diaphragm is bonded to this frame. The frame should be rigid enough not to be deformed by the fixed magnetic circuit and the vibration part, and the transmitted vibration should be as small as possible. Behind the magnetic circuit and the vibration system is the shell of the earphone, and a cavity is formed between the shell and the desktop. The size and shape of the cavity, the location, type and quantity of damping material filled in it affect the frequency response of the earphone. Generally speaking, the larger the cavity, the easier it is to obtain high quality and deep dive low frequency.