Tips for making audiophile speakers
In Hi-Fi audio equipment, the electro-acoustic conversion device that serves as the human-machine interface-the speaker is known as the mouthpiece of the audio system. The final reinterpretation of the audio source depends on this, which shows its important position in the audio. No wonder many foreign countries High-end speakers cost tens of thousands of dollars, and hundreds of thousands of them are not uncommon, and the domestic fever hotspots in recent years are mostly concentrated here.
To make high-quality audiophile speakers, in addition to the use of high-quality drive units (speakers), the appropriate cabinet structure and processing and processing techniques are also of great significance. Since the speaker units have been manufactured and shaped by the factory, the cabinet design and production have become The decision stage that affects the expressiveness of a specific unit. This article only summarizes the following points on the relevant production materials and craftsmanship, based on the introduction of newspapers and periodicals and my own production practice.
The main function of the speaker is to eliminate the sound short circuit, improve the bass sound pressure and uniformity, thereby improving the sound characteristics of the low frequency range of the speaker, but its intervention will also bring some negative effects, such as strengthening the formant, mid-to-high frequency reflection and diffraction, etc. , Leading to the dyeing of bass sound and treble sound. Try to eliminate negative effects and play the role of improving the bass, which is the foundation of production.
Sound box material
1. High-quality wood such as mahogany, rosewood, peach, sandalwood and other precious hardwoods, preferably seamless whole boards, top materials for speakers, but materials are difficult to find, expensive, and difficult to process. They are often used in top-quality speakers. Medium. The second is flower willow wood, jujube wood, catalpa wood, etc., preferably with high specificity and uniform wood. New materials are damp and easy to deform, and can be applied after drying.
2. Medium-density fiberboard is the most widely used board, low cost, easy to buy, and easy to process. However, in actual production, it is found that its strength is poor, it is easy to produce sound dyeing, humming, and the material is fine and soft, and cannot be combined with wood screws. It can only be nailed with iron nails, which may be shaken loose under high sound pressure, and the rigidity is also poor, which is not conducive to the robustness of the box.
3. Medium-density particleboard is also known as a pressing template. It has high strength, low cost, and inconvenient processing. Many commercial speakers, including many Japanese packaged machine supporting speakers, use this material, but some people report that its compression is not strong, including There are more air gaps and poor sound insulation performance. It is best to make special treatment to improve the sound insulation ability.
4. High-density fiberboard, particleboard and plywood have high strength, good sound insulation performance, and easy to find materials. They are the preferred materials for amateur production of high-quality fever speakers, but the cost is slightly higher and the processing is not easy, requiring special tools. Especially high-density particleboard , The hardness is very high, and it is not easy to be nailed. In my production, I often break the tip of the screw and call it no matter.
5. If the inorganic matter is formed by concrete casting, use stone slabs (marble, concrete slab, granite slab, gypsum board, etc.) to be formed by a special process, or simply use a heavy large clay pot as the box. It has small sound and color, The sound field is stable and other advantages are often used by masters with fever, but it is too heavy and mobile tuning is very inconvenient. And the wall of the box must be specially treated.
Six. Engineering plastics, polypropylene, reinforced modified epoxy resins, thick plexiglass panels and other high-density polymers (high molecular polymers) adhering to modern advanced technology material technology, many European and American professional speaker manufacturers have used this technology to create High-end, high-quality speakers, such as the JBL MM series speakers are made of high-density plastic, and the famous JBLPROJECT K2 is actually made of plexiglass with a thickness of several inches. It is difficult to achieve under amateur conditions.
7. Metal materials are mainly used for professional speakers and special occasions, such as stage speakers, mobile speakers, all-weather speakers for sports, all-weather mobile speakers for military use... Amateurs are not easy to dye due to the high resonance frequency of their metal cabinets Treat and rarely use.
8. Paper materials are mostly used by enthusiasts who are new to the burning path and are financially struggling. There are also experts who use this as a box and use special techniques to enhance it, such as impregnating with epoxy resin. If made properly, the effect is also good.
1. Panel combination This is the method used by most speakers, including some top-quality speakers. The process is mature, simple, and suitable for factory production.
2. Casting molding This method is most suitable for coagulation (the port is called seamless concrete) and high polymers.
3. The cavity method 1. The top fever speaker, the whole piece of precious hardwood or solid stone is taken out of the cavity and used as the cabinet. It can be imagined that this method is very difficult and costly. It is occasionally seen in European and American commemorative products. 2. Soil The ground speaker of the gun family. The ground is hollowed out, dried and moisture-proof, and then the panel and speaker unit are installed. The cost is low, the sound quality is also very good, and the subwoofer playback is just right, but it cannot be moved, which restricts all conditions. So far, the fever is really "home".
High-fidelity speaker cabinets are often exposed to rapidly changing high sound pressures, which can easily induce noise, resonance, cause sound staining, and affect the pure beauty of replayed music. Therefore, the production process is very important. "Reinforce vibration reduction, avoid sound staining" for production The eight-character "guideline" of craftsmanship.
1. Extensive and reasonable use of reinforcing ribs for the weak links in the speaker. At the joint corners formed by each surface in the box, use a sufficient amount of glue, rather than less, and stick a thick hard triangular wood or square wood stick, and then add The wood screws are fastened, and the sound pressure level on the back of the woofer is the highest, which is easy to induce box sound. A round hardwood board is glued to the back panel to strengthen it. The material can use the remaining material under the panel opening. The box body, due to the large aspect ratio of the sheet, the strength and rigidity become worse, the resonance point becomes lower, and the resonance frequency of the speaker or the box body is approaching, and the sound staining is extremely dangerous. Please glue a few hard square wood sticks asymmetrically. The purpose is to eliminate air leakage in the gap, strengthen the rigidity of the box, destroy the resonance, and avoid inducing noise and arousing box vibration.
2. Add appropriate amount of sound-absorbing materials in the box, such as ultra-fine glass wool, slag cotton, fiber spray cotton, vacuum cotton, and the second such as foam sponge, cotton wool, cotton paper, and soft toilet paper to absorb sound energy and control the Q value of the speaker At the same time, the vibration of the box is reduced. For a closed box, the entire box needs to be filled. For an inverted box, three-finger wide sound-absorbing materials are applied on the front, rear, left, and right, and the upper and lower walls are increased and decreased in an appropriate amount during monitoring to suppress the resonance peak. Standard. For transmission line type (i.e. labyrinth type), lay at the inflection point of the channel that is prone to standing waves. For horn type (mainly refers to the rear-loaded horn type) speaker structure, standing waves are easily generated behind the woofer and in the horn Place a small amount of sound-absorbing material in the place where it is located. The amount should be determined based on the actual listening evaluation.
Three. A simpler way to increase the sound damping performance of the box wall is to pour a layer of 1-2cm of asphalt inside each box, and apply multiple layers of high sound damping materials (oil felt, rubber, etc.). The more complicated but better method is to make The double wall is filled with dry dust-removing fine sand in the middle, or the box body is infiltrated with high-sound damping materials. This action blocks the transmission path of sound energy to the box body and greatly reduces the Q value of the box wall, which can reduce even It is very effective to eliminate sound dyeing. Boxes made of inorganic materials must undergo this treatment.
Four. Box body support reinforcement. This refers to the use of hard square wood, porous wood planks or round steel rods to firmly support the front and rear walls and/or side walls, so that the box wall will not be excited by high sound pressure and produce annoying box. Acoustic dyeing, perforated plate also has the function of Q adjustment. The steel rod can be made of steel cars above 40, Φ45mm or more, and the two ends are tapped with Φ8mm fixing screw holes. If necessary (if the box body is larger), welding flanges can be added. , Use screws to fasten between the two walls that need to be supported.According to some predecessors, this method is particularly effective in eliminating the box sound caused by the poor strength of the plate, so it is listed separately.
5. The speaker unit should be fixed from the outside to the inside to reduce the front cavity effect. The installation hole is best to be counterbored to prevent the basin frame from protruding and causing diffraction. The distance between the basin frame and the box is 5-10mm The rubber gasket is sealed and isolated to avoid acoustic short-circuit, and to prevent the vibration of the basin frame from being transmitted to the panel radiation, which interferes with the direct radiation sound.
Six. Adopt a special cabinet shape and shape. This is not to discuss the acoustic method of the speaker, but to effectively prevent standing waves. The generation of standing waves will seriously affect the performance of the acoustic system. In order to eliminate standing waves, damage the cabinet The parallelism in the body is the key. For example, the TANNOY SIX series uses a hexagonal body design. Many professional speakers use a fan-shaped design (JBL MM-SERIES, AC, etc.). The shape of the cabinet also has a greater impact on the radiation characteristics. Too many sharp edges and corners will cause diffraction and interference, and a blunt surface transition angle can be used. The shape of the front panel will affect the service angle and phase characteristics. Specially designed panels can be improved, including curved design, stepped design and Other special shapes. The front panel of JBL 4208 has undergone computer-aided analysis and design. It uses curved surfaces instead of the traditional plane, which effectively improves the phase characteristics of the near sound field. BOSE301 is introduced after the research of direct and reflected sound technology. Hi-Fi masterpiece, it adopts a unique shape design, a bevel is cut on the top of the bass speaker, and two tweeters are installed for radiation in different directions before and after, effectively creating a uniform sound field, and it is said to listen to stereo It is no longer just the "selfish" enjoyment that only comes when you sit in the emperor's seat. It is reported that a new type of speaker that looks like a big snail will soon be available as the new flagship of British B&W. Therefore, when designing speakers, you should also liberate your mind. Break the tradition, be bold in fantasy, be diligent in hands-on, and be good at thinking.
7. The strong sound absorption and strong sound damping material on the panel will transmit the residual vibration of the basin frame to the panel, and the direct sound radiation will be reflected on the panel. The vibration generated by the air stiffness in the box will also be reflected on the front panel. Panel radiation, superimposed and interfered with direct sound, causes more peaks and troughs on the frequency characteristic curve, and the phase characteristics are degraded, especially at high frequencies. The panel is pasted with "heavy sound damping" material is an effective way to improve. Damping materials include high-density foamed plastics, special felts, and factory-made sound-absorbing felts.
8. After completion, the speakers should be supported and "isolated" from the ground to avoid puffiness, unstable sound field, and poor transparency. Support methods include support frames, metal feet, hardwood feet, etc. Different types can be widely used The hard material test determines that the cone tip with a 45°～60° taper is in contact with the ground.
Frequency divider production
The frequency divider occupies a very important position in the speaker system. It is necessary to ensure that the high and bass signals are accurately and accurately transmitted to the respective units without interference, distortion, and intermodulation, and the frequency response curve will not cause large peaks and valleys. There is no large phase distortion. At present, LC power frequency division is mostly used. As for electronic frequency division, it is not discussed in this article.
1. Under amateur conditions, it is difficult to find a magnetic core that meets the requirements, let alone testing its linearity, magnetic flux and other properties. Even under professional conditions, it is difficult to find the ideal magnetic core, so the magnetic core structure is difficult to care about. Too harsh enthusiasts. In order to reduce the additional resistance, you should try to use thicker high-quality enameled wire (oxygen-free copper wire, large crystal copper wire, single crystal copper wire is better), Φ1.0 ~ 1.2mm is better, Computer-aided optimization design is used to minimize the resistance under the condition of a certain inductance, and the resistance value should generally be less than one-tenth of the horn impedance. Because paramagnetic substances will affect the inductance, the inductor coil should be as far away as possible from the horn head, Paramagnetic materials such as fixing screws and supporting steel rods, and each frequency dividing element are fixed with epoxy glue to avoid increasing magnetic saturation distortion and causing crossover point drift. Inductance coils will be caused by spatial coupling Mutual electromagnetic interference should be kept as far away as possible, and they should be placed perpendicular to each other on the magnetic axis.The high and low frequency crossover networks are separately placed on a circuit board and kept away from each other. It is an excellent fever method.
2. The capacitors are preferred for non-inductive polypropylene, polystyrene and other non-inductive film electrodeless capacitors that have a fixed rating. Avoid using electrodeless electrolytic capacitors, and it is not suitable to use electrodeless electrolytic reverse series instead. Multiple small-capacity capacitors are used in parallel, rather than alone A large capacitor has a much smaller winding inductance and a much faster speed, which has better high-frequency performance and sound quality. The way to save without compromising the fever is to use only the signal path of the high and woofer speakers. For the above components, bypass inductors and bypass capacitors slightly reduce the requirements, use ordinary non-polar capacitors, and inductors with smaller wire diameters.
3. Wiring There are a variety of high-quality speaker wires on the market, which can be used as appropriate. The core wire is thicker, the number of strands is more, the copper content is higher, and the copper crystal is longer and larger, the better sound, such as silver wire is the best Beware of fakes and counterfeit products. The method is preferably bi-wire or tre-wire. Many magazines have introduced it. Be careful not to affect the airtightness of the box.
Speaker production is a more complex system engineering. It is an edge science and technology between mechanical engineering, acoustics, psychology, and ergonomics. It is both technology and art. The above measures complement each other and should be implemented in practice. In the production process, according to the specific situation, symptomatic prescription, comprehensive application, we will be able to make a more satisfactory work.