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Voice coil (Voice Coil) is directly defined as the coil that passes the audio current. It is an important part of the vibration system of the electrodynamic speaker, and it can be said to be the heart of the speaker. The performance of the voice coil will affect the sound pressure frequency characteristics of the speaker, sound pressure level, impedance curve, distortion, transient characteristics, speaker parameters, sound quality, etc., especially the bearing power and life of the speaker. Like the fatal factor of heart disease, speaker damage often starts from the voice coil.
Basic Information
Chinese name
voice coil
foreign language name
Voice Coil
use
Cutting magnetic lines of force produces mechanical vibrations
Main material
BOBBIN, enameled wire, reinforced paper, brocade wire
equipment
speaker
Fold and edit the structure and function of this paragraph
The most commonly used voice coil is the voice coil with a skeleton, as shown in the reference picture, it consists of the following parts
1. Voice coil skeleton ( BOBBIN ). It is the skeleton that supports the coil, usually composed of kraft paper, asbestos paper, Nomex, polyimide, aluminum foil, copper foil, glass fiber, etc.
2, enameled wire. It is usually composed of self-melting enameled wire such as enameled oxygen-free copper wire, copper-clad aluminum wire, pure aluminum wire, etc.
3. Reinforcing paper. It is used to fix the leads and enhance the rigidity of the voice coil frame, usually composed of kraft paper, Xuanhua paper, Spunlace, Nomex and some special composite materials.
4, brocade thread. It is made of one or more copper alloy or silver alloy flakes, and then twisted or braided with this multi-strand, and can be added with wax, waterproof, anti-static treatment, etc. as required.
The position of the voice coil in the horn loudspeaker The position of the 
voice coil in the horn loudspeaker (1) When the voice coil in the magnetic gap of the loudspeaker magnetic field strength is B, the voice coil will be subjected to an electromotive force F=BLI (L is the length of the voice coil), and the force direction follows the left-hand rule.
(2) After the force occurs, when the vibration system including the voice coil vibrates at the speed V, an induced voltage BLV will be generated inside the voice coil, the direction of which conforms to the right-hand rule and is related to the original current direction. At this time, the voice coil is the initial effector of damping, and it is also the bearer of damping.
Fold and edit the voice coil material of this section
The skeleton of the voice coil is the backbone of the entire voice coil. It is responsible for transmitting the sound source driving force generated by the voice coil to the diaphragm for radiation diffusion. The voice coil skeleton is required to be light and rigid, and the inner surface of the skeleton should be flat and smooth. , After the coating treatment, but also high temperature.
Kraft paper
Kraft paper is a tougher paper. The voice coils of early speakers are made of kraft paper. It can be made of a rectangular paper or spiral paper circle into a column shape. The outer surface is coated with lock high temperature resistant insulating glue. The paper skeleton is suitable for small-diameter, low-power speakers, and the kraft paper voice coil skeleton has the following advantages:
⑴ low cost.
⑵ flat, no burrs.
Low cost: In the production of small-diameter speakers, the batch is large, and the cost of components has an impact on the profit of speaker manufacturers
Large, paper voice coil has the advantage of low cost, which can help you reduce the cost of small-diameter speakers.
Flat, no burr: The burr of the skeleton is a common fault of the paper voice coil. It affects the movement of the voice coil in the magnetic gap, making the speaker produce abnormal sound and increasing the waste.
Aluminum
Aluminum is a light metal with high rigidity, light weight, and is not easy to oxidize. Aluminum is commonly used as a voice coil frame in Hi-Fi and Hi-end speakers.
⑴ light weight, good rigidity.
(2) The inner surface is flat and smooth.
Light weight and good rigidity: The electromagnetic force generated by the voice coil drives the voice coil and the cone to vibrate together when the speaker emits sound. . The light weight can effectively improve the efficiency and sound quality of your speaker. The speaker relies on the voice coil frame to push the diaphragm (cone) to vibrate and produce sound, so the voice coil frame is required to have sufficient rigidity to ensure that your speaker is in Hi-Fi sound is still emitted under high power and large kinetic energy range .
The inner surface is flat and smooth: the magnetic gap space of the speaker is very small, and the voice coil is placed in it, and the small deformation or burr of the voice coil skeleton will touch the magnetic circuit components, resulting in abnormal sound. The aluminum voice coil bobbin is very finely cut, smooth, and free of burrs, making your speaker sound the most pure.
Nomex (asbestos paper)
Asbestos is a heat-resistant material, non-conductive, non-magnetic, and low-cost. It is a good material for the voice coil frame of sirens, small-bore (3.5 inches or 5 inches) or woofers. It has the following characteristics:
⑴Smooth and smooth surface.
(2) It is a non-conductor, and there will be no magnetic field electric current (votex) inside.
Smooth and smooth surface: The smoothness and smoothness of the surface are important indicators for evaluating the quality of the voice coil.
It is a non-conductor, and there will be no magnetic field electrical flow inside: the metal voice coil skeleton will produce flow, which consumes part of the energy, reduces the efficiency of the speaker, and affects the magnetic field in the magnetic gap to make the speaker effective. The frequency range becomes smaller, and asbestos is not a conductor, preventing the adverse effects of sloshing.
Polyimide
Polyimide is one of the organic polymer materials with the best comprehensive performance , high temperature resistance up to 400℃, long-term use temperature range -200~300℃, no obvious melting point, high insulation performance, dielectric constant 4.0 at 103 Hz , the dielectric loss is only 0.004~0.007, which belongs to F to H class insulating material.
Glass Fiber, also known as TIL
Glass fiber is a non-conductive material with strong rigidity and good heat resistance. High-quality glass fiber is selected as the voice coil frame, and the surface is coated with high-temperature resistant SV glue. It is an excellent material for the manufacture of Hi-Fi and Hi-end speakers. The advantages of fiberglass are:
⑴ non-conductor, no adverse effects of electrical current
⑵ good heat resistance.
⑶ good rigidity.
It is non-conductor and has no adverse effects of electrical current: the disadvantage of the conductor voice coil skeleton is that when the voice coil has an AC signal passing through, a magnetic field electrical current (votex) will be generated in the metal skeleton, resulting in energy loss, and it will Affect the magnetic circuit system. Glass fiber is not a conductor and will not be affected by the electrical votex of magnetic fields, which can broaden the effective frequency range of the speaker.
Good heat resistance: glass fiber is a heat-resistant material, and the surface of the glass fiber voice coil frame is coated with high-temperature resistant SV glue, which will not burn the glue under high power conditions, nor will it be deformed by heat, and the heat resistance is very high. outstanding.
High rigidity: The rigidity of the glass fiber voice coil frame is very large, and the surface is not easy to produce scars and creases, and it will not cause burrs, so that the voice coil can always be kept flat and clean. The use of glass fiber voice coils can make speaker assembly more convenient and more efficient. High, the quality of the speakers is excellent.
Duralumin (dura aluminum)
Duralumin is an aluminum alloy material with light weight and great rigidity. It is a good material for making high-frequency speaker voice coils. It has the following advantages:
⑴ light weight, strong rigidity.
(2) The appearance is smooth and the inner surface is smooth.
⑶ high temperature resistance.
Light weight and strong rigidity: In order to effectively radiate high-frequency sound waves, the tweeter diaphragm is required to be very light, and the voice coil is also required to be light. The specific gravity of duralumin is very light, and the voice coil made of You widen the range of the high frequency band.
The appearance is smooth and the inner surface is smooth: the magnetic gap of the speaker is very small, and the voice coil is required to be neat and burr-free.
High temperature resistance: After the signal is applied, the voice coil of the speaker will heat up. The greater the loading power, the more heat it will generate. Modern speakers pursue high power and require sound performance to withstand high temperatures.
Anodized Aluminal
Anodized aluminum is made of a protective layer on the aluminum substrate. It has the advantages of light weight and high rigidity. In addition, due to the protective layer, it is not easy to oxidize. It is a good material for making Hi-end speakers. Available in black and silver-white, black helps absorb surrounding thermal radiation. Its advantages are:
⑴ light weight, strong rigidity.
⑵ high temperature resistance, not easy to oxidize.
(3) The surface is smooth and free of burrs, which can absorb heat radiation.
Light weight and strong rigidity: In order to improve and widen the frequency band, in the vibration system of the speaker, the voice coil is required to be as light as the cone, and the rigidity is strong. Anodized aluminum has this advantage. Choose our anodized aluminum. The voice coil can improve the efficiency of your speakers and widen the effective frequency range of your speakers.
High temperature resistance, not easy to oxidize: High power is one of the important indicators of Hi-Fi speakers, and the voice coil temperature of the speaker is relatively high when it is subjected to high power. The outer surface of the anodized aluminum voice coil frame is coated with high temperature insulating material (SV) glue, which can withstand high temperature of 250 degrees, and the aluminum substrate is coated with a protective layer to resist oxidation, so that the sound quality of your Hi-end speakers can be maintained for a long time. Change.
Flat surface, no burrs: The anodized aluminum voice coil skeleton is cut with advanced technology to ensure that the surface is flat, not deformed, and free of burrs.
Generally, the enameled wire used in the voice coil is self-melting enameled wire, and the self-melting enameled wire is a double-layer paint film, which is covered with a polyurethane or polyester or other insulating paint film, and is covered with a thermoplastic or thermosetting resin melting paint film, which is baked on the conductor. surface. Various insulating paint films and melting paint films are matched with each other to form different types of self-melting enameled wires.
The conductor parts generally include oxygen-free copper, copper-clad aluminum, and pure aluminum:
1. The direct solderability and corrosion resistance of copper wire conductors are better, but the disadvantage is that the density is high and the quality after winding into a voice coil is relatively large.
2. The conductor of copper-clad aluminum wire is a composite material with aluminum as the main body and copper cladding on the outside. It has the light weight of aluminum and the direct weldability and corrosion resistance of copper.
3. The weight of the pure aluminum wire conductor is only about 30% of that of the copper wire, which effectively reduces the weight of the coil. The conductivity is more than 61% of copper, and its weight is about half of copper under the same conductor resistance. Therefore, the working efficiency of the speaker can be improved, and the high frequency can also be extended to a certain extent.
Insulating paint film
Enameled wire name | Insulating paint film | Heat resistance class | UL recognized | direct solderability | Features |
1LOCK | UE | B(130℃) | MW75C | Y | Solder temperature: 360~380℃ Widely used for polyurethane enameled copper wire |
1 SFBSVW | SFB | F(155℃) | MW26C | Y | Solder temperature: 380~400℃ Class F solderable enameled copper wire |
1 PESVW | ON | F(155℃) | MW5C | N | General purpose polyester enameled copper wire Excellent solvent resistance |
1 SFFSVW | SFF | F(155℃) | MW79C | Y | Solder temperature: 390~410℃ F grade solderable polyurethane enameled copper wire |
1 EISVW | NO | 200℃ | MW74C | N | UL recognized TI(200℃) Widely used in heat-resistant electronic equipment |
1 EIAISVW | EIAI | 200℃ | MW35C MW73C | N | Double insulating paint film, plus AI on the outer layer of EI Good refrigerant resistance and wear resistance |
1AISVW | AI | (220℃) | MW81C | N | The heat resistance level is increased to 220℃ Wear resistance, heat resistance and refrigerant resistance are higher than EIW |
1APISV2W | AIPI | (220~240℃) | - | N | Heat resistance class 220~240℃ Wear resistance, heat resistance and refrigerant resistance are higher than EIW |
1 PISV2W | PI | (240℃) | - | N | The heat resistance level is increased to above 240℃ The wire with the highest heat resistance among organic materials |
There are two types of wires: round wire and flat wire according to the shape. The round wire is the most widely used, and the flat wire is difficult to manufacture and expensive. However, the copper wire occupancy rate is high, so the efficiency is high, and the high-frequency characteristics of the speaker are extended.
As an advanced technology, flat wire voice coil was first used in woofers, and later tweeters were also widely used, both aluminum and copper wires. The flat wire has a high space factor and a high utilization rate of the magnetic void, designed to improve sensitivity. According to the test, in the same magnetic circuit, the flat wire voice coil can improve the sensitivity by about 1dB than the round wire voice coil.
Folded reinforcement paper
Commonly used reinforcing paper is composed of kraft paper, Xuanhua paper, Spunlace, Nomex, etc.
The brocade wire is also called the wire. Its function is to connect the voice coil and the terminal, so that the current is introduced into the voice coil. The conductor material of the brocade wire is generally made of copper, pure copper, tin copper, cadmium copper, silver copper alloy, etc. There are also differences in performance between silver plating and tin plating:
a. Silver plating: It is less prone to oxidation, easy to solder, and has a beautiful appearance, but it is expensive and is a high-end product.
b, Tin plating: easier to oxidize, more difficult to solder, but very cheap.
There are generally three types of brocade wire in terms of structure:
a, Covered wire: there are 1.2.4.6 layers, its outer diameter is small, it is used for SPK with small diameter;
b, Stranded wire: poor shape, easy to bifurcate, and poor workability;
c, braided wire: good shape, hard, not easy to split, good workability
lead wire voice coil
pre-process
Set skeleton ( BOBBIN ) operation => winding line operation => whole line operation => sticking reinforcement paper operation => gluing operation => intermediate inspection operation => heat treatment (baking) operation
post-processing
Stripping operation 1 => stripping operation 2 => brocade wire positioning operation => brocade wire welding operation => blue glue application => mold removal operation => punching operation => enlargement inspection => DCR and polarity detection operation
Fold and edit the calculation formula of this paragraph
1. Number of voice coil turns = ( DC resistance (DCR)*1000000)/(pi() * inner diameter of voice coil)/wire resistance/km (OKM)
2. Voice coil winding width = (number of turns/number of voice coil layers) * outer diameter of enameled wire * product of winding width (different products according to different winding methods)
3. *** outer diameter of voice coil = *** outer diameter of wire diameter * 2 * number of layers of voice coil + 2 * BOBBIN thickness + inner diameter of voice coil + coefficient