Tips for making fever speakers
In the Hi-Fi audio equipment, the electro-acoustic conversion device that serves as the man-machine interface-the speaker is known as the mouthpiece of the audio system. The final re-interpretation 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 yuan, and hundreds of thousands of yuan are not uncommon, and domestic hot spots in recent years have also concentrated on this.
In addition to the use of high-quality drive units (speakers) for making high-quality fever speakers, the proper cabinet structure and processing and processing techniques are also of great significance. Since the speaker units have been manufactured and finalized by the factory, the cabinet design and manufacture have become The decision stage that affects the expressiveness of a particular unit. This article only summarizes the following points based on the production materials and processes, based on the introduction of newspapers and literature and my production practice.
The main function of the speaker is to eliminate the acoustic short circuit, improve the bass sound pressure and uniformity, thereby improving the acoustic characteristics of the speaker's low frequency band, but its intervention will also bring some negative effects, such as enhanced formant, mid-high frequency reflection and diffraction, etc. , Leads to bass sound staining and treble sound staining. Try to eliminate negative effects and play a role in improving bass, which is the root of production.
Speaker material
1. High-quality wood such as mahogany, rosewood, peach, sandalwood and other precious hardwoods, preferably the whole board without seams, the top material for the speaker, but the material is difficult to find, the price is expensive, the processing is not easy, and it is often used in top-grade speakers Medium. The next is flower willow, jujube, catalpa, etc., with a large specific gravity, even wood is better. The new material is easy to deform and needs to be dried before being applied.
2. Medium density fiberboard is the most widely used, low cost, easy to buy materials, and easy to process. However, in actual production, it is found to have poor strength, easy to produce sound staining, coaxing, 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 loosened under high sound pressure, and the rigidity is also poor, which is not conducive to the robustness of the cabinet.
3. Medium-density particle board is also known as a pressing template, which has high strength, low cost, and inconvenient processing.Many commercial speakers, including many Japanese matching machine speakers, use this material, but some people report that the pressure is not solid, including There are many air gaps and poor sound insulation performance. It is best to do special treatment to improve the sound insulation capacity.
4. High-density fiberboard, particle board and plywood have high strength, good sound insulation performance, and easy to find materials. It is the first choice for amateur high-quality fever speakers, but the cost is slightly higher, and the processing is not easy. Special tools are needed. Especially high-density particle board The hardness is very high and it is not easy to nail. I often break the screw tip and make a fuss in my production.I use a hand drill to pre-drill a small hole and then tighten the screw.
5. Inorganic materials, such as concrete casting, are formed with stone plates (marble, concrete slab, granite slab, gypsum board, etc.) by a special process, or simply use a thick and large pottery jar as the box body. The sound field stability and other advantages are often used by fever experts, but it is too heavy, and it is very inconvenient to move the tuning. And the box wall must be specially treated.
6. Engineering plastics, polypropylene, reinforced modified epoxy resin, thick plexiglass plates and other high-density polymers (polymers) uphold modern advanced technological material technology, and many European and American professional speaker manufacturers use this technology to create High-end, high-quality speakers, such as the JBL MM series speakers are made of high-density plastics, and the famous JBLPROJECT K2 actually manufactures high-frequency throats with plexiglass up to several inches thick. 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 .... Amateurs are not easy to stain due to the high resonance frequency of their metal cabinets. Processing is rarely used.
8. The paper materials are mostly used by the burners who first enter the burning channel and have economic constraints. There are also many experts who use this as a cabinet and use special processes to enhance the treatment, such as epoxy resin impregnation. If it is made properly, the effect is also good.
Production Method
1. The combination of plates is the method adopted by most speakers, including some of the best speakers. The process is mature, simple, and suitable for factory production.
2. Casting molding This method is most suitable for coagulation (Hong Kong is called seamless concrete) and polymers.
3. Cavity method 1. Top-grade fever speakers, the whole piece of precious hardwood or solid stone is taken out of the cavity as a box. It can be imagined that this method is very difficult and costly. Occasionally seen in European and American commemorative products. The ground speakers of the gun family. The ground will be hollowed out, done a dry and moisture-proof treatment, and then installed the panel and the speaker unit. The cost is low, the sound quality is also very good, and the subwoofer playback is just right, but it can not be moved, and it can meet all conditions. At this point, the high fever is really "home".
Craftsmanship
High-fidelity speaker cabinets are often exposed to rapid changes in high sound pressure, which is very easy to induce noise and resonance, causing sound staining and affecting the purity of the replayed music. Therefore, the production process is very important. The "character" of craftsmanship.
1. Extensive and reasonable use of reinforcing ribs for the weak links in the speaker. Use sufficient amount of glue at the joint angle formed by each face of the box body, rather than stick it, stick it with a thick hard triangular wood or square wood stick, and then add Fastened with wood screws, the sound pressure level on the back of the woofer is the highest, and it is easy to induce box sounds. A round hard wood board is glued on the back panel to reinforce it. The material can be used for the narrow and long holes in the panel. For the cabinet, due to the large aspect ratio of the sheet material, the strength and rigidity become worse, the resonance point becomes lower, and the resonance frequency of the horn or the cabinet is approaching. The risk of sound staining is extremely great. Please glue a few hard wooden sticks asymmetrically. It is to eliminate gap leakage, strengthen the rigidity of the box, destroy the resonance, and avoid inducing noise and exciting box vibration.
2. Add appropriate amount of sound-absorbing materials such as ultra-fine glass wool, slag cotton, fiber-sprayed cotton, vacuum cotton, and the second such as foam sponge, cotton wool, cotton paper, soft toilet paper to absorb sound energy and control the Q value of the speaker At the same time, reduce the vibration of the box. For the closed box, it is necessary to fill the entire box. For the inverted box, apply three-finger thick and thick sound-absorbing materials to the front, back, left, right and left and right walls, and increase or decrease the amount during monitoring to suppress the resonance peak. For transmission line type (that is, labyrinth type), it is laid at the inflection point of the channel that is easy to produce standing waves. For the horn type (mainly referring to the rear loading 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. The amount should be based on the actual listening evaluation.
3. A simpler way to increase the sound damping performance of the box wall is to pour a layer of 1-2CM of asphalt inside the box body and apply multiple layers of high-sound damping materials (oil felt, rubber, etc.). The complicated but better effect method is to make Double wall, filled with dry dust and fine sand in the middle, or infiltrating the box with high-acoustic damping material. This action blocks the transmission of sound energy to the box and greatly reduces the Q value of the box wall. The elimination of acoustic staining is very effective. Cabinets made of inorganic materials must undergo this treatment.
Four. Box support and reinforcement here refers to the use of hard square wood, perforated wooden boards 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 to produce a nasty box Acoustic dyeing, perforated plate also has the function of Q adjustment. The steel rod can be made of a steel car of size 40 or more, Φ45mm or more, and Φ8mm fixing screw holes are tapped at both ends. If necessary (if the box is large), welding flanges can be added It is fastened with screws between the two walls that need to be supported.This method is particularly effective for eliminating the box sound caused by the poor strength of the plate according to some predecessors, so it is listed separately.
5. The fixing of the speaker unit should adopt the method of fixing from the outside to the inside to reduce the effect of the front cavity. The mounting holes are preferably treated as countersinks to avoid the protrusion of the basin frame and causing diffraction. 5-10mm between the basin frame and the box body The rubber pads are sealed and isolated to avoid short-circuiting of sound, and to prevent the vibration of the basin rack from being transmitted to the panel to radiate and interfere with the direct radiation of sound.
6. Adopt a special shape and shape of the box. This is not to discuss the acoustic method of the speaker, but to effectively prevent the standing wave. The generation of the standing wave will seriously affect the performance of the acoustic system. To eliminate the standing wave, destroy the box The parallelism in the body is the key. For example, the TANNOY SIX series uses a hexagonal design. Many professional speakers use a fan design (JBL MM-SERIES, AC, etc.). The shape of the cabinet also has a greater impact on the radiation characteristics. Excessively sharp corners will produce diffraction and interference, and a relatively dull surface transition angle can be used. The shape of the front panel will affect the service angle and phase characteristics. The specially designed panel can be improved, including curved surface design, stepped design and Other special shapes. The front panel of JBL 4208 has undergone computer-aided analysis and design. The anti-planar tradition uses curved surfaces, which effectively improves the phase characteristics of the near sound field. BOSE301 was introduced after lapping direct and reflected sound technology. Hi-Fi masterpiece, which adopts a unique shape design, cuts a slope on the top of the subwoofer, and installs two tweeters to radiate in different directions before and after, effectively creating a uniform sound field. It is said that listening to stereo sound is no longer just a "selfish" enjoyment when sitting in the emperor's seat. It is said that a new type of speaker that looks like a big snail is about to be released as the new flagship of the British B & W company. So when designing the speaker, it should also be Emancipate the mind, break the tradition, boldly fantasize, be diligent, and good at thinking.
7. The strong vibration absorption and strong sound damping material applied on the panel can transfer the residual vibration to the panel, direct sound radiation will be reflected on the panel, and the vibration caused by the air stiffness in the box will also be reflected on the front panel. Panel radiation, superimposed with direct sound, and interference cause more peaks and troughs on the frequency characteristic curve, and the phase characteristics are degraded, especially in high-frequency audio. The panel is attached with "acoustic damping" material is an effective method of improvement. Damping materials include high-density foamed plastic foam, special felt, and factory-specific sound-absorbing sound felt.
8. After the completion of the speaker, support should be added to "isolate" from the ground to avoid puffy sound, unstable sound field, and poor transparency. The methods of support are support frame, metal foot nails, hardwood foot nails, etc. Different types can be widely used The hard material test decided to contact the ground with a cone tip of 45 ° ~ 60 ° taper.
Crossover production
The frequency divider occupies a very important position in the speaker system.It is necessary to ensure that the high and low frequency signals are accurately transmitted to the respective units without interference, distortion, and intermodulation.The frequency response curve does not cause large peaks and valleys. 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. It is difficult to find a magnetic core that meets the requirements under amateur conditions, let alone test its linearity, magnetic flux and other properties. Even under professional conditions, it is not easy to find the ideal magnetic core, so the structure of the magnetic core is difficult to worry about. Too harsh for enthusiasts. In order to reduce the additional resistance, thicker high-quality enameled wires (oxygen-free copper wire, large-crystal copper wire, and single-crystal copper wire are better) should be used as much as possible, with Φ1.0 ～ 1.2mm being preferred. And adopt computer-aided optimization design, so that under a certain inductance, the resistance is the smallest, and the resistance value should generally be less than one-tenth of the horn impedance. Because paramagnetic substances will affect the inductance, the inductance coil should be as far away as possible from the horn head, Paramagnetic materials such as screws for fixing and steel rods for support are used, and each frequency dividing element is fixed by epoxy glue to avoid increasing magnetic saturation distortion and causing frequency division drift. Inductance coils will be caused by spatial coupling Mutual electromagnetic interference should be as far away as possible, placed perpendicular to each other with the magnetic axis, and the high and bass crossover networks are placed on a circuit board separately and away from each other is an excellent fever method.
2. Capacitors are preferred to have non-inductive film electrodeless capacitors such as non-inductive polypropylene, polystyrene, etc. Avoid using electrodeless electrolytic capacitors, and it is not suitable to use polar electrolytic reverse series substitution. Multiple small-capacity capacitors are used in parallel, which is more separate A large capacitor has a much smaller winding inductance and a much faster speed. It has better high-frequency performance and sound quality. The way to save without losing fever is to use it only in the signal path of high and low speakers. The above components, while the bypass inductance and bypass capacitance slightly reduce the requirements, use ordinary stepless capacitors and thinner wire diameter inductors.
3. There are a variety of high-quality speaker wires on the market, which can be used as appropriate. The thicker core wire, more strands, higher copper content, longer copper crystals are more beautiful, such as silver wire .Beware of counterfeit goods and inferior products. The method is preferably bi-wire or tre-wire. Many magazines have introduced it. Pay attention to the lead wire not to affect the tightness of the box.
Ending language
Loudspeaker production is a more complicated system engineering. It is a marginal science and technology between mechanical engineering, acoustics, psychology, and ergonomics. It is both technology and art. The above measures should complement each other and should be practical. During the production process, according to the specific situation, symptomatic prescriptions and comprehensive application will definitely make more satisfactory works.
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