Speaker box production
The relationship between the sound structure material and the sound reproduction. A pair of ideal speakers, except for the speaker diaphragm, the surroundings should not vibrate with sound waves during operation. On the contrary, it is mainly caused by the insufficient thickness and weight of the box board. Therefore, when making speakers, you should consider that the larger the volume and power of the speaker, the greater the air pressure in the box cavity, and the harder and thicker the wooden board wall, especially the front and back panels are prone to vibration. Side panel.
Enclosed speakers are thicker than inverted speakers. If it is a subwoofer, its box board is much heavier than the HI-FI speaker box board. Because the natural resonance of the thick board is smaller than that of the thin board, the hard board with a certain thickness and a certain thickness should be selected as much as possible.
The sealed speaker does not have any air leakage, so the box is too thin to cause resonance. If a certain frequency excites the vibration of the box board, the energy at this frequency will be largely consumed in the vibration damping of the wooden board, which is enough to produce a deep valley and seriously affect the sound quality. Only by thickening the box plate can the effect of the box wall resonance be significantly suppressed and the generation of standing waves be reduced.
From the experience data of making speakers, we can know that the relationship between the size of the speaker caliber and the thickness of the box plate is as follows:
The caliber of the speaker is <12.70cm (5in),
The thickness of the speaker board should be 16 ~ 18mm;
The caliber of the speaker is 15 ~ 20cm (6 ~ 8in),
Speaker board thickness should be 18 ~ 20mm;
The caliber of the speaker is 25 ~ 30cm (10 ~ 12in),
The thickness of the speaker should be 20 ~ 25mm;
The caliber of the speaker is 35.6 ~ 45.7 (14 ~ 18in),
The thickness of the speaker board should be 25 ~ 30mm.
If the original wood board is used and its texture is hard, the thickness of the box board can be reduced by 10% to 15%.
1. The choice of speaker structure
No matter which cabinet you choose, you want to avoid making equilateral squares, at least to avoid the same length, width and depth. The box is preferably rectangular to avoid standing waves at a certain frequency in the cavity.
High-fidelity HI-FI sound systems are generally placed in the living room. The area of ​​the living room is mostly about 15 square meters. Although HI-FI speakers can be placed in such halls, although the floor-standing type can be used, the height should not exceed 1M, and the power should not be too large. If the rated power of the sound system is 100W, the effective power provided to the speaker is insufficient. It is also impossible for the speakers to exert their due playback effects. Only by giving the speaker more than 70% of the power can the true performance of the speaker be truly reflected.
If it is a narrow small hall, you should use small HI-FI speakers or bookshelf speakers. The volume is moderate, the sound is beautiful, and the appearance is elegant. The production of car speakers is mostly designed according to the space at the rear of the car, which is more difficult.
2. Selection of cabinet material
Some small speakers are made of plastic. Generally, large and medium-sized speakers are made of wood. In the 1950s, the domestic speaker box was mainly made of original wooden boards or plywood, and its form was monotonous, and the system quality was not high. Since the fiberboard has been put on the market in the mechanism, it has basically replaced the original wood board, and the quality of the cabinets made therefrom has been continuously improved.
â‘´Selection of speaker plate
The variety of wood is of great quality. The board used to make the speaker should have a better fiber density, so that it has a stronger ability to suppress vibration. At the same time, the board must be moisture-proof and not easily deformed. At present, the widely used boards are mainly medium fiber board and particle board; followed by original wood boards, such as ash, river wood, rosewood, birch, walnut, maple and rosewood. High-end speakers can be made of sandalwood wood. Choosing hard wood with fine texture is also an excellent wood for making speakers.
High-grade raw boards generally have high fiber density, high hardness and low shrinkage. The wood needs to be evaporated and dried or naturally dried and aged for more than 1 to 2 years before it can be used to make speakers. Only in this way can the speaker be easily deformed and cracked. The use of high-quality wood to make speakers is expensive, and the use of narrow-faced original wood boards requires splicing, which will increase the difficulty of production, so it is not uncommon for those who use original wood boards.
A splint is a large-area flat plate of machine-made plates. Its large surface is easy to cut and easy to process, suitable for large and small speakers. However, because the board is laminated with glue, it is easy to get wet and degummed, deformed, or even moth-eaten.
Particleboard: Particleboard is a board made of wood chips that have been shaved and processed into granules of varying thickness with adhesive and mechanically hot pressed. There are single-layer and multi-layer particleboard. Sawdust particles inside the single-layer board are evenly distributed, with high hardness and smooth surface; the inside of the multi-layer board is layered according to the size of the wood chip particles, with small surface particles and high density, large intermediate particles and low density (or layered according to the size of density) Made by cross arrangement). Due to the large particle size, the particle board is loose, low strength, afraid of moisture, easy to break. Its cross-section is rough, it is difficult to process flat, it is only suitable for making less demanding speakers, and it is a small speaker.
Fiberboard: MDF is a new high-tech product that has risen in recent years. It is based on the roots, branches, stems, etc. of the trees, processed into fine fibers, and then filled with a binder, and mechanically pressed into various density boards (MDF). The internal structure of the fiberboard is uniform and fine, with good toughness, moderate strength, moisture resistance, easy deformation, smooth surface, strong damping characteristics, thin cross-section, and suitable for finishing. It is the fastest-growing new type of artificial board in the world today. , Is the best material for making speakers.
Fiberboard is divided into medium density board (600kg / m3) and high density board (up to 90kg / m3). High-density boards are more expensive and generally less used. The medium-density board is moderately priced and excellent in performance, making it the best choice for making medium and high-end speakers.
⑵The material of the box body is cut out. The box body of the speaker is mainly made of sheet metal, most of which are rectangular, and also have a barrel shape or other special shapes. According to the structure of the box and its requirements, the compartments in the box or stiffeners can also be added.
Before cutting, according to the design size, draw the lines to be cut on the pre-selected plates. If the speakers are made of original wood or veneer, pay attention to the direction of the wood color and texture, and pay attention to the selection of symmetry (each pair of speakers). If the wooden texture of the panel on the box board is horizontal grain, then the grain of the side panel should be in the same direction as the upper panel, so that it looks similar to the texture of the original wood, and it is also very elegant. If the fiberboard is used, it has no wood grain, and the cabinet should be covered with wood veneer. Cutting is based on the principle of reasonableness and no waste.
(3) The position and shape of the opening of the inverter tube hole The opening of the inverter tube hole should be carried out according to a certain procedure, that is, the arrangement of the speaker installation hole and the inverter tube hole on the panel and the position of the orifice are first set.
Inverter tube hole location Most of the inverter tube holes are opened below the front barrier, and some are also opened in the rear plate.
Usually empty speakers are used for reverse radiation and are used in large speakers. Due to the large diameter and high power of the speaker, it is rarely installed on the front panel, otherwise the height of the speaker needs to be increased.
Inverted tube shape Inverted tube is in the shape of round hole, rectangle, flat, etc., but most of them are round. This is because for the same inversion orifice position, the circumference of the circular hole is the smallest, so the radiation damping in the tube is the smallest, that is, the resonance frequency f0 is in obtaining the maximum sound pressure.
The size of the inverter tube The size of the inverter tube should be according to the original design value. If it has not been adjusted, it cannot be changed randomly, otherwise it will affect the superposition of the inverter sound pressure and cause frequency changes.
â‘·Opening of speaker mounting holes In fact, there are no strict regulations on the location of the mounting holes of each speaker unit in the speaker on the front baffle. However, the woofer speaker unit is generally located below the front baffle, the middle audio speaker unit is located in the middle, and the high frequency speaker unit is located above it. Of course, on the premise of not affecting the sound quality of the playback, reducing distortion, and maintaining beauty, they can also make their own designs and design their own characteristics. The following designs are for reference:
This arrangement is easy to get a flatter response. The tweeters are arranged in the upper part of the speaker, which can prevent the sound sources from interfering with each other during normal operation. For this reason, the radiation angle of the high-frequency speaker unit should be as large as possible, and the installation positions of the inverter tube and the woofer should be as close as possible, so that the fixed trapezoid of the sound source is more consistent. Of course, the most ideal is the coaxial configuration, but this will produce distortion. For these reasons, generally speaking, for large speakers, the units can be properly pulled apart when listening at a longer distance; for small speakers, the units can be slightly closer when listening at close distances.
The speakers are arranged on both sides of a pair of speakers to form a mirror symmetry. The advantage is that the high and low speaker units are not on the same axis, which is conducive to the balanced diffusion of the tweeter unit, and the sound image localization is more accurate. However, the phase and radial characteristics of the low-frequency speaker unit will be linearly displaced.
The tweeter unit is arranged between the two woofer units, and the sound image positioning falls exactly in the middle of the two woofer units, and coincides with the sound image position of the tweeter unit, so that the sound image positioning is more accurate. Because the same frequency is used for playback, and the two woofer units are far away, the pronunciation positions are different, and the sound interference is greater, so there will be some differences in the frequency curve, and there will be fluctuations in the phase, which narrows the directivity of the mid-band. To mitigate this effect, the two woofer units should be as close as possible.
The subwoofer has low resonance frequency, high power and large amplitude, so its cabinet structure is special. The installation location of the speakers is usually quite different from the HI-FI speakers. In order to obtain a sufficiently low sound, the installation of the speaker is always placed in the inner cavity of the speaker.
This method is mainly equipped with a special structure of the cabinet, which is designed to obtain different frequency responses and its appearance. Because the cabinet is an irregular structure, it plays a certain role in reducing standing wave and distortion.
This installation method is mainly used in large-scale dance halls. The stage is large, there are many positions, and the sound field is wide, which can enhance the horizontal pointing characteristics and make the listener get a more uniform sound pressure. Horizontal speakers are not suitable for small halls and homes because they are placed in a low position.
⑸The process of opening the speaker hole At present, the speakers placed on the front of the speaker are all installed inwardly and inwardly. When opening the hole, you can saw the inner part of the speaker frame. It should be noted that the pore size cannot be too large or too small. If the aperture is too large, the position of the fixing screw will be small, and it is easy to cause sags when tightening the screw; if the aperture is too small, the speaker cannot be placed flat against the surface, exposing the gap, causing air leakage. Therefore, the cutting size is required to be accurate.
In professional speaker production plants, there are special tools to cut the speaker installation holes. Amateurs should choose a good location on the panel, draw the production line to be cut, first drill a small hole, pass the wire saw through the small hole, cut a circular hole according to the drawn line, and then use a curved planer and a wooden file Fix.
⑹ The opening of the junction box hole commonly used junction box specifications are as follows:
Junction box a is a monophonic combination, and junction box b is a two-tone combination. For small sounds, use mono combination, and for medium and large speakers, use double combination. It can connect different speakers in the speaker separately. Its shape is round, square and rectangular. The requirements are not too strict. The cutting method is the same as the method of opening the speaker installation hole. It is appropriate to just fit into the junction box and fix it with screws.
⑺ Opening of the mounting holes for the speaker spikes The spikes are a kind of ornament for the speakers, but not every speaker needs to be equipped with spikes. If you need to install the spikes, there are many options. The easiest is to nail the square-shaped or small round key plates at the appropriate positions at the four corners of the bottom of the box, which is both economical and practical. However, it is common to choose special speaker feet made of metal, drill a hole with a suitable depth and size at the four corners of the bottom plate, and fit the hole of the foot nut, install the pre-coated adhesive nut , Use a hammer to drive into the hole, so that you can screw in the nail at any time. 
â‘» The opening of the speaker and mother button holes of the net cover can cover the entire front baffle (or cover part. The frame of the net cover should be thin and not high, and the net cover should be movable, so that it can be easily disassembled at any time. The way of female buckle, as shown:
To install well, the son-mother buckle is the key. It can be done as follows:
(1) Measure the positions to be drilled at the four corners or sides of the grille frame. A 1mm drill bit is drilled vertically through the frame, and the mother and son holes of the grille are installed at the four corners and the frame side.
(2) Place the frame on the panel, align the small holes pre-drilled on the frame with nails, and make a hole-reaming mark on the panel vertically. After all the nails are fixed, pull out the small nails after inspection.
(3) On the nail hole of the panel, use a suitably large drill bit to drill out the child and mother buckle (based on the size that can only be tightly closed), and then drill the mother and child holes of the frame in the same way. When installing the buckle, apply viscose and hammer it into the drilled hole.
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