The relationship between sound structure materials and sound reproduction
A pair of ideal speakers should not vibrate with sound waves except for the diaphragm of the speaker when working. On the contrary, it is mainly caused by insufficient thickness and weight of the box board. Therefore, the speaker should consider that the larger the volume and power of the speaker, the greater the air pressure in the chamber, the harder and thicker the board of the cabinet wall, especially the front and rear panels, which are prone to vibration, and the thickness of the board should be appropriately thicker than Side panels.
The panel of a closed speaker is thicker than that of an inverted speaker. If it is a low speaker, its cabinet board is much heavier than the HI-FI speaker cabinet board. Since the natural resonance of a thick plate is smaller than that of a thin plate, a box plate with a hard texture, heavier weight, and a certain thickness should be used as much as possible.
The airtight speaker does not have any air leakage, so the box plate is too thin and more likely to cause resonance. If a certain frequency excites the vibration of the box board, a large amount of energy at this frequency will be consumed in the vibration damping of the board, which is enough to produce a deep valley, which seriously affects the sound quality. Only by thickening the box can the resonance of the box wall be significantly suppressed and the generation of standing waves can be reduced.
From the empirical data of making speakers, it can be known that the relationship between the size of the speaker diameter and the thickness of the panel is as follows:
Speaker diameter <12.70cm (5in),
The panel thickness of the sound box should be 16~18mm;
The speaker diameter is 15~20cm (6~8in),
The panel thickness of the sound box should be 18~20mm;
The speaker diameter is 25~30cm (10~12in),
The thickness of the speaker should be 20~25mm;
The speaker diameter is 35.6~45.7 (14~18in),
The panel thickness of the sound box 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%~15%.
1. The choice of speaker structure
No matter which cabinet you choose, it is hoped not to be made into an equilateral square, at least to avoid the same length, width, and depth dimensions. The cabinet 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 floor-standing speakers can be used to place HI-FI speakers in such a hall, their height should not exceed 1M, and the power should not be too large. If the rated power of the audio system is 100W, the effective power provided to the speakers is insufficient. It is also impossible for the speakers to play the sound effect as they should. Only by giving the speaker more than 70% of the power can the performance of the speaker be truly reflected.
If it is a small narrow hall, it is advisable to use small HI-FI speakers or bookshelf speakers. The volume is moderate, the tone is beautiful, and the appearance is also elegant. The production of car speakers is mostly designed according to the space at the rear of the car, which is difficult.
2. Selection of box material
Some small speakers are made of plastic, but generally large and medium-sized speaker cabinets are made of wood. In the 1950s, the domestic speaker cabinets were mainly made of original wood or plywood. The form was monotonous and the quality of the system was not high. Since the fiberboard in the mechanism was put on the market, it has basically replaced the original wood board, and the quality of the cabinet made from it has also been continuously improved.
⑴The choice of speaker panel
There are many types of wood and the quality is very different. The board used to make the sound box should have a good fiber density, so that it has a strong ability to suppress vibration. At the same time, the board should have the characteristics of moisture-proof and not easy to deform. At present, the widely used boards are mainly medium fiberboard and particle board; followed by raw boards, such as ash, riverwood, rosewood, birch, walnut, maple, and rosewood. For high-end speakers, fine wood like sandalwood can be used. Choosing hard, fine-grained miscellaneous wood is also an excellent wood for making speakers.
High-grade raw wood 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 prevented from deforming and cracking. The use of high-grade wood to make speakers is costly, and the use of narrow-faced original boards requires splicing, which will increase the difficulty of production, so it is rare to use log boards.
The splint is a large-area flat plate of the machine-made plate. The panel is large, easy to cut, easy to process, suitable for large and small speakers. However, since the board is laminated into a plate with adhesive, it is easy to be damp, degummed, deformed, and even eaten by insects.
Particleboard: Particleboard is a board made by processing the planed wood chips into particles of varying thickness, using an adhesive and mechanically hot pressing. There are two types of particle board: single-layer and multi-layer. The sawdust particles inside the single-layer board are evenly distributed, the hardness is high, and the surface is smooth; the inside of the multi-layer board is arranged in layers according to the size of the sawdust particles, the surface particles are small, the density is large, the middle particles are large, and the density is small (or layered according to the size of the density) Made in a cross arrangement). Due to the large particles of particleboard, the pressed sheet is looser, has low strength, is afraid of moisture, and is easy to break. Its cross-section is rough and difficult to be processed and flattened. It is only suitable for the production of less demanding speakers, and it is a small speaker.
Fiberboard: MDF is a new high-tech product that has emerged in recent years. It uses the roots, branches and stems of trees as materials, which are processed into fine fibers, and then filled with a binder, which is mechanically hot pressed into density boards (MDF) of various specifications. The internal material structure of the fiberboard is uniform and fine, with good toughness, moderate strength, moisture resistance, not easy to deform, smooth surface, strong damping characteristics, thin cross-section, and suitable for finishing. It is the fastest growing new type of wood-based panel 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 relatively expensive and generally less used. The medium-density board is moderately priced and has excellent performance. It is the best choice for the production of medium and high-end speakers.
⑵The box body plate cutting
The cabinet of the sound box is mainly made of plates, most of which are rectangular, but also have a barrel shape or other special shapes. According to the structure of the box and its requirements, it is also possible to add compartments or stiffener slats in the inner cavity of the box.
Before cutting the material, draw the line to be cut on the pre-selected plate according to the design size. If you use raw wood or veneer to make speakers, you should pay attention to the color and texture of the wood, and pay attention to the symmetry (for each pair of speakers). If the wood texture of the front panel of the box board is horizontal, then the side panel texture should be in the same direction as the upper panel, so that it looks similar to the original wood texture and is also very elegant. If the fiberboard is used, it has no wood grain, and the cabinet should be pasted with veneer. The cutting material should be based on the principle of reasonableness and no waste.
⑶The position and shape of the opening of the inverted tube hole
The opening of the inverter tube holes should be carried out according to a certain procedure, that is, the arrangement of the speaker mounting holes and the inverter tube holes on the panel and the position of the orifices are set first.
The position of the inverted tube hole
Most of the inverting tube holes are opened under the front barrier, and some are opened on the back plate.
Usually empty speakers are used as phase-inverted radiation, which is used in large speakers. Because the speaker has a large caliber and high power, it is rarely installed on the front panel, otherwise the height of the speaker needs to be increased.
The shape of the inverter tube
Inverted tubes are in round hole, rectangular, flat and other shapes, but most of them are round. This is because for the same inverted 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 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 fails the adjustment, it cannot be changed at will, otherwise it will affect the superposition of the inverted sound pressure and cause the frequency change.
⑷ Opening of speaker installation holes
In fact, there are no strict regulations on the positions of the installation holes on the front baffle of each speaker unit in the sound box. However, the woofer unit is generally located under the front baffle, the mid-range speaker unit is located in the middle, and the tweeter unit is located above it. Of course, under the premise of not affecting the playback tone, reducing distortion, and maintaining beauty, you can also devise their own features and design their own features. The following designs are for reference:
This arrangement is easy to obtain a flatter response. The tweeter is arranged on the upper part of the speaker, which can prevent the sound sources from interfering with each other due to frequency changes 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 sound source has a more consistent trapezoid shape. The most ideal is of course the coaxial configuration, but this will produce distortion. Because of this, generally for large speakers, each unit can be properly opened when listening at a longer distance; for small speakers, each unit can be slightly closer for close listening.
The speakers are arranged in mirror symmetry on both sides of a pair of speakers. The advantage is that the high and woofer speaker units are not on the same axis, which is conducive to the balance and spread of the tweeter, and the sound image positioning is more accurate. However, the phase frequency and radial frequency characteristics of the low-frequency speaker unit will show a linear shift.
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, making the sound image positioning more accurate. Due to the same frequency when playing, and the two woofer units are far apart, the pronunciation positions are different, and the sound interference has a greater influence, so there will be some differences in the frequency curve, and there are fluctuations in the phase, which narrows the directivity of the mid-frequency band. In order to reduce this effect, the two woofer units should be as close as possible.
The subwoofer has low resonant frequency, high power, and large amplitude, so its cabinet structure is special. The speaker installation location is usually quite different from HI-FI speakers. In order to obtain a sufficiently low sound, the speaker is always installed in the inner cavity of the speaker.
This method is mainly matched with a cabinet with a special structure, which is designed to obtain different frequency responses and appearances. Because the cabinet is of irregular structure, it plays a certain role in reducing standing waves and distortion.
This installation method is mainly used in large dance halls. The stage is large, there are many rows, and the sound field spreads wide, which can enhance the horizontal pointing characteristics and enable the audience to obtain a more uniform sound pressure. Horizontal speakers are not suitable for small halls and homes because they are placed in a low position.
⑸The opening process of the speaker hole
At present, the speakers placed on the front of the speaker are installed on the front inward plane. When opening the hole, it is sufficient to cut the inner part of the speaker frame. It should be noted that the aperture cannot be too large or too small. If the hole diameter is too large, the fixing screw will be smaller, and it is easy to cause collapse when the screw is tightened; if the hole diameter is too small, the speaker cannot be smoothly placed on the surface, exposing the gap and causing air leakage. Therefore, the cutting size is required to be accurate.
In professional speaker manufacturers, there are special tools to cut speaker mounting holes. Amateurs should choose the position on the panel, draw the production line to be cut, first drill a small hole, pass the wire saw through the small hole, and cut a circular hole according to the drawn line, and then use a curved plane and a wooden file. Fix.
⑹The opening of the junction box hole
Junction box a is a monophonic combination, and junction box b is a dual-sound combination. Single-sound combinations are mostly used for small sounds, and dual-sound combinations are mostly used for medium and large speakers. It can connect different speakers in the speaker box separately. Its shapes are round, square and rectangular. The requirements are not too strict. The cutting method is the same as that of opening the speaker mounting hole. It is better to just fit into the junction box and fix it with screws.
⑺The opening of speaker pin mounting holes
Foot nails are a kind of accessory of speakers, but not every speaker needs to be equipped with foot nails. If you need to install foot nails, there are many options to choose from. The simplest is to nail a curved or small round bezel at the appropriate positions on the four corners of the bottom of the box, which is economical and practical. But generally, special speaker foot nails made of metal are selected, and a hole of the appropriate depth and size of the foot nail size is drilled at the appropriate position of the 4 corners of the bottom plate, and the foot nail nut can be tightened, and the nut is pre-coated with viscose cloth. , Use a hammer to drive into the hole so that the nail can be screwed in at any time.
⑻The opening of the button hole of the net cover
The speaker grille can cover the entire front baffle (or part of the cover. The grille frame should be thin but not high, and the grille should be movable so that it can be easily disassembled and assembled at any time. In this way, you must choose the snap button method, as shown in the figure:
To install it, the key is the key. It can be done as follows:
(1) Measure the positions to be punched at the 4 corners or sides of the net cover frame, and drill through the frame with a 1mm drill bit vertically, and install the mother and child holes of the net cover at the 4 corners and sides of the frame.
(2) Put the frame on the panel, use nails to align the pre-drilled holes on the frame, and vertically nail them on the panel to make a reaming mark. After all nails are completed, the small nails will be removed after inspection.
(3) On the nail hole of the panel, use a suitably large drill bit to drill out the snap button (subject to the size that can only be tightened), and then use the same method to drill the snap hole of the frame. When inserting the snap button, apply glue and hammer it into the drilled hole.