For music lovers who are not well-off in the economy and audio enthusiasts who want to have fun and knowledge from their own hands, the most convenient audio equipment is the speaker. As long as you know the regularity of some speaker design, you can still make a pair of speakers that you are satisfied with. In the process of speaker production and debugging, there are the following problems to be aware of.
First, select the speaker unit
The speaker unit, commonly known as the speaker, is a key part of the speaker's ability to make a sound. Only by means of the speaker unit can the audio signal transmitted from the CD player and the power amplifier be converted into an audible sound signal.
The speaker unit is generally divided into three categories: treble, midrange and bass. Basically, it belongs to the scope of work of each division. For making small, small-diameter woofers (generally referred to as woofer speakers with a caliber of less than 6.5 inches), they generally have the effect of a mid-range speaker; and a tweeter that is designed to withstand enough power It is also possible to take care of the role of some midrange speakers. Therefore, in a small bookshelf or floor-standing speaker, it is quite common to use only one high-two low-two speaker unit. Let's talk specifically about the problem of choosing a speaker unit.
1 . How to choose a tweeter
The tweeter is the name of the speaker unit for replaying high frequency sounds. The structure of the tweeter is mainly horn type, cone type, dome type and aluminum belt type.
The horn tweeter can hear powerful treble on the front of the horn due to its strong directivity. It is used for high-power sound reinforcement, conference speakers and a small number of monitor speakers.
Because the diaphragm area is too large and too heavy, the high-frequency characteristics of the cone-type tweeter are not as good as other types of tweeters. Therefore, it is more common in old-fashioned speakers and has been gradually eliminated in recent years.
The dome tweeter is the most commonly used tweeter in home speakers and small monitors.
The dome type tweeter is divided from the dome structure and can be divided into a positive dome unit and an anti-ball item unit.
The dome-type tweeter is divided into two categories: the hard dome and the soft dome.
The diaphragm material of the hard dome treble is aluminum alloy, titanium alloy, titanium alloy composite film, glass film, diamond film and the like. The high-pitched sound of the hard dome tweeter is bright and has a metallic feel. Suitable for playing popular music, movie music and effect music. It is also good at expressing classical music and vocals by processing excellent aluminum alloy film and titanium alloy composite film dome.
The diaphragm material of the soft dome top has several types such as enamel film, silk film, rubber film and bulletproof cloth film. The soft dome tweeter reproduces the music with high dexterity and slack, and has a good natural expression. It is especially handy when expressing music with standard listening concepts such as classical music and vocals. It is an ideal choice for making medium and high-end home speakers and small monitor speakers. In particular, in recent years, the upper limit frequency of the resurfacing of the enamel film and the silk dome treble has reached 40000 Hz. In theory, the upper limit frequency of the tweeter should be at least 20,000 Hz, the higher the better. However, the unit with excellent high-frequency ceiling is also more expensive.
The dome tweeter is playing music. The horizontal diffusion angle is larger; when the anti-ball top tweeter plays music, the horizontal radiation angle is smaller, but the tone is purer and the power is also greater. The aluminum belt tweeter is a tweeter that has a very early history and a long history. Just because of its structural factors, it is not an easy task to really make its high-frequency upper limit frequency high enough and the power is large enough, so it is not easy to popularize it.
The upper part of the aluminum belt tweeter has an upper limit frequency of more than 30,000 Hz, and the current withstand power is more than 150W. If you are a classical music lover and have strict requirements on the sound of the replay, you may wish to choose a soft dome tweeter such as a enamel film.
If your speakers are also karaoke and playing movies, it is better to choose a hard dome unit. Of course, this is not absolute, because the replay tone of the speaker, in addition to the selected unit, is also related to the design of the crossover, the production of the cabinet and many other factors.
2 . The structure of the midrange unit
The midrange unit generally has only two cones and a dome. It is only larger in size and power than the tweeter and more suitable for playing mid-range audio. The diaphragm of the midrange unit is mainly composed of soft materials such as paper cones and enamel membranes, and occasionally a small amount of alloy dome diaphragms.
3 . How to choose a woofer
The structure of the woofer is mostly a cone type, and a small amount is a flat type.
There are many types of diaphragms in the woofer, such as aluminum alloy diaphragm, aluminum-magnesium alloy diaphragm, ceramic diaphragm, carbon fiber diaphragm, bulletproof cloth diaphragm, glass fiber diaphragm, acrylic diaphragm, paper diaphragm and so on.
The paper diaphragm is also known as the speaker cone. The paper diaphragm is divided into paper cones, pressed paper cones, paper-based wool basins, and strengthened paper cones. The woofer with aluminum alloy and aluminum-magnesium alloy diaphragm generally has a relatively small caliber and a relatively large power consumption, while the woofer with the enhanced paper cone and the glass fiber diaphragm reproduces the sound more accurately, and the overall flat density is good.
When the speaker unit is selected, the power consumption of the tweeter is generally not less than one tenth of that of the woofer; if the speaker is made of two-way and two-unit, the power of the tweeter is higher.
When making a three-way speaker, the midrange unit can withstand as much as one-third of the woofer.
When selecting a speaker unit, it is best to choose the same impedance. Common low-impedance speaker units are generally divided into 4Ω and 8Ω. When selecting the speaker unit, it is also necessary to select the same sensitivity level, generally with a sensitivity of 86dBW·m. Below 84d B is called a low-sensitivity speaker, and above 90dB is called a high-sensitivity speaker.
If the impedance and sensitivity are too different when the speaker unit is selected, when the speaker is made, the crossover is not well designed and the sound pressure imbalance in each frequency band is encountered.
Of course, when making a two-way speaker, the lower limit frequency of the tweeter is lower than 2 kHz, and the upper limit frequency of the woofer is higher than 4 kHz, which will bring a lot of convenience for adjusting the speaker.
Second, the choice and production of the divider
When you select the speaker unit, it is followed by the selection and production of the divider. The frequency divider is divided into two types: a common type of frequency divider and an electronic frequency divider.
The electronic crossover directly feeds the tiny audio signal from the signal source into the electronic crossover. The signal of the full frequency band (from bass to treble) is divided into high-pitched and low-pitched signals by electronic cross-over, which are respectively transmitted to the corresponding power amplifier for amplification, and then the corresponding speaker unit is driven to emit sound as shown in Fig. 1. Electronic crossover is a relatively complex, but replayed music replay system. In addition to the crossover, the electronic two-way system requires a 4-channel audio power amplifier. The electronic three-way system requires a 6-channel amplifier, while the electronic four-way requires eight independent channels. The advantage of electronic crossover is that the replay sound is good, and the balance adjustment between the frequency bands is simple and easy, but the production cost is high.
For homemade speakers, the traditional power divider is relatively simple, see Figure 2. As can be seen from the figure, the conventional power divider can be composed of only five components such as L1, C1, L2, C2 and treble attenuating resistor R. L1 and C1 form a low-pass filter, by which only the low-frequency part of the audio signal is retained to drive the woofer unit. L2 and C2 form a high-pass filter that only keeps the high-frequency part of the audio signal to drive the tweeter. Ordinary two-way dividers can also use an inductor, a capacitor divider and a more complex divide than Figure 2. These different frequency division methods have their own advantages and disadvantages. But the starting point of this article is based on the most common Figure 2.
We list the values ​​of inductance and capacitance at different speaker impedances and different crossover frequencies in the attached table.
Why list such a large number of values? This has its own reason. As long as your speaker unit is good enough, the speaker design and processing are reasonable, the debugging is accurate, regardless of the frequency division frequency of 2000Hz, 3000Hz or 4000Hz, you can get a flat, qualified test curve; but in subjective listening, different The replay tone of the crossover point speaker is quite different from the music performance. Speakers with high crossover frequency, high frequency is brighter, but the overall tone is thin; speakers with lower crossover frequency, replay sound is more kind and natural. Of course, all of this is done within a certain range. If the crossover point is too large, the connection between the high and low frequencies will be poor due to the limitation of the speaker unit's own bandwidth.
There is such a rule, that is, the lower the crossover point is selected, the larger the inductance and capacitance values ​​used by the frequency divider, and the higher the manufacturing cost. Therefore, some less responsible manufacturers choose the crossover point of the product very high, which can not guarantee the sound performance when the speaker is replayed.
Although the ordinary frequency divider has a simple structure, it has its characteristics in terms of production.
1 . How to choose an inductor
The inductors used in the frequency divider are divided into two types: air core coil and iron core coil; and iron core coil is divided into two types: true iron core and ferrite core.
In the crossover, the effect of the air-core coil is the best, but it is also the largest and the most expensive. The advantage of the air core coil is that it is low and is less affected by the magnetic field of the speaker. When selecting an air core inductor, the main choice should be the choice of the wire diameter of the inductor. The enameled wire selected must be able to carry the corresponding power current. If the wire diameter used is too small, the inductor coil is easily overheated and burned when operating at high power. The selected wire diameter can be calculated by using as long as it is sufficient or some margin. Blindly increasing the wire diameter, the cost is too high, and the second is more difficult to process.
The core coil and the core coil (ferrite coil) can reduce the volume of the coil and reduce the manufacturing cost. However, due to the intervention of the magnetizer, distortion due to magnetic saturation is introduced. It is also due to the influence of the magnetic field of the speaker unit. Causes the offset of the crossover point.
When selecting a core coil, the power of the core itself is a key. It has been proved by a large number of experiments that the core coil power can only work normally with low distortion when it reaches or exceeds 50% of the maximum power of the woofer.
The core coil is sweetened by the hysteresis of the core material, but the transient characteristics are also reduced.
In recent years, power dividers, a little better, basically use air-core coils.
Air core coils are wound at the lowest cost with a round enameled wire. The cost of using stranded wires, hexagonal wires, and strip wires is much more expensive. At present, there are many varieties of oxygen-free copper enameled wires. After use, the replay tone will be improved.
2 . How to choose a frequency dividing capacitor
In the frequency divider, there are many types of capacitors to choose from. From the most common electrolytic capacitors, non-inductive capacitors, audio dedicated core capacitors, polyester, polystyrene, polypropylene capacitors. But the price of these capacitors is also higher than a kind, and some individual brand-name capacitors are sold at a high price.
The use of brand-name capacitors, of course, has the advantages of accurate capacitance, stable performance, and good playback sound. However, for a self-made speaker with a mid-range or so, if you choose a capacitor of one hundred yuan, there will be some high cost.
When selecting the frequency dividing capacitor, the low frequency channel can be reversely connected in series with high precision and good quality electrolytic capacitor, or a small polystyrene and polypropylene capacitor at both ends thereof is shown in Fig. 3. This works well and the price is very economical. As for the high-frequency capacitors, due to the small capacity, the price is relatively low, and it is fine to choose properly.
For the selection of high frequency attenuation resistors, it is mainly to pay attention to the power of the resistor itself. Used in high-powered speakers, the power of the attenuation resistor is relatively large; in low-power speakers, the power of the resistor can also be reduced. Otherwise, it will cause a mismatch between the big head and the small body.
In short, when selecting the components of the frequency divider, it is the most economical and reasonable to be clear and tailored.
Third, the box processing
In the production process of the speaker, the processing of the speaker cabinet is a crucial part.
In the processing of the box, the most important thing is only two points. First, the dimensional accuracy of the box processing is high; second, the box material selection is accurate. Among the materials used to make the speaker cabinet are high-grade logs; high-strength multi-layer boards; synthetic materials; and plexiglass and stone. The so-called high-grade logs not only refer to the high-grade and precious wood itself, but the most important thing is that the wood itself has to be dried and aged for many years. Only in this way can we ensure that the box is not cracked or deformed.
After many years of practice, the material of the speaker box is made, and the sound quality of the multi-layer board and the high-grade wood with sufficient thickness is the best, but the price is also the most expensive. The overall feel of the plexiglass cabinet is also good; the MDF is the most affordable material for making the speaker cabinet.
In the processing of the speaker cabinet, there are several methods as follows:
1 . The bending method is shown in Figure 4. This method is a speaker cabinet that is formed by inserting a V-shaped groove on a long strip of medium density board with a PVC fabric and then bending and gluing. This method is used in the production of large-volume speakers.
2 . The reinforcement method is shown in Figure 5. In the homemade speaker, the sheet is cut according to the drawing, and then the glued wood strip is used for reinforcement and bonding at the interface of the sheet. This method is suitable for hand-made speakers.
3 . The assembly method is shown in Figure 6. This is a new process for speaker production. Around the speaker board, precision machining machines have 45° + 90 ° bevels and notches. In the hand-made speaker cabinet, you can pass the self-positioning of the 90° notch of the speaker board and the long bevel of 45°. As long as enough adhesive is applied at the interface, tie it with a rope and assemble it. A speaker cabinet with high processing precision and firm appearance can be obtained.
After the speaker cabinet is completed, as long as the surface of the cabinet is painted, and the veneer is decorated, it is done.
Fourth, the assembly and debugging of homemade speakers
When debugging the final assembly of the homemade speaker, there are several issues to be aware of:
First, the connection between the crossover and the speaker unit +, - must not be connected. If you make a mistake, the sound of the speaker can't be adjusted well.
Second, when installing the speaker unit, the tension of each fixing screw should be the same. Otherwise, the speaker is prone to unexpected resonance when it is working.
Third, the length of the inverted tube and the amount of sound absorbing material in the box should be appropriate, otherwise it will affect the performance of the replayed music. In particular, the length of the inverted tube has a direct impact on the low end of the speaker's test frequency response.
The above parts must be adjusted carefully and carefully. Making a speaker by yourself is a process of practice and long knowledge.
Through my hard work, I harvested the speakers and increased the talents in the speaker production. I also saved a part of the money to buy the finished speaker and changed it to use it. So it is a good thing for many benefits, and the production process is also simple. You can learn to make.
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