How to make your own speakers

How to make your own speakers

If you want to sit at home and enjoy beautiful music, you need to have the most basic audio equipment. For example, if you have a cassette recorder or CD player as a signal source, an audio power amplifier and a pair of speakers, as well as audio signal cables and speaker cables, you can form the most basic audio equipment. Among audio equipment, there are CD players and amplifiers with complex structures, and there are speakers with simple structures. But among audio equipment, the most individual and the most influential in replaying music are the seemingly simple speakers. Therefore, in terms of the sound quality of the speaker replay, there are so-called "British sound", "American sound", "German sound" and "Japanese sound", and there are speakers that cost thousands, tens of thousands, or even millions of yuan a pair.

For music lovers who are not well-off and audio enthusiasts who want to gain fun and knowledge from DIY, the easiest audio equipment to make is the speaker. As long as you know some of the rules in speaker design and production, you can make a pair of speakers that satisfy you. In the process of speaker production and debugging, there are the following issues that need to be paid attention to.

1. Choose the right speaker unit

The speaker unit, commonly known as the speaker, is the key part of the speaker box to produce sound. Only with the help of the speaker unit can people convert the audio electrical signals transmitted by the CD player and the power amplifier into audible sound signals.

Speaker units are generally divided into three categories: tweeters, midranges, and basses. Basically, each unit has its own scope of work. For well-made small-caliber bass units (generally referring to bass units with a speaker diameter less than 6.5 inches), they can generally take into account the role of midrange speakers; and a tweeter unit with excellent design and sufficient power can also take into account part of the role of midrange speakers. Therefore, it is very common to use only two speaker units, one high and two low, in small bookshelf or floor-standing speakers. Let's talk specifically about the issue of selecting speaker units.

1. How to choose a tweeter

As the name implies, the tweeter is a speaker unit that is used to reproduce high-frequency sounds. The structural forms of tweeters mainly include horn type, cone type, dome type and aluminum ribbon type.

Due to the strong directivity of the horn tweeter, powerful treble can be heard from the front of the horn. It is mostly used in high-power sound reinforcement, conference speakers and a small number of monitor speakers.

Cone tweeters are often found in old speakers and have been gradually phased out in recent years because their diaphragm area is too large and too heavy, and their high-frequency characteristics are not as good as other types of tweeters.

The dome tweeter is currently the most commonly used tweeter in home speakers and small monitor speakers.

Dome tweeters can be divided into positive dome units and negative dome units based on the dome structure.

Dome tweeters are divided into two categories based on the dome material: hard dome and soft dome.

The diaphragm materials of hard dome tweeters include aluminum alloy, titanium alloy, titanium alloy composite membrane, glass membrane, diamond membrane, etc. The treble reproduced by the hard dome tweeter has a bright tone and a metallic feel. It is suitable for playing pop music, movie music and effect music. The aluminum alloy membrane and titanium alloy composite membrane dome tweeters with excellent processing and production can also better express classical music and vocals.

The diaphragm materials of soft dome tweeters include silk membrane, silk membrane, rubber membrane and bulletproof cloth membrane. The high notes of soft dome tweeters are flexible and relaxed when reproducing music, and have good natural expression. It is particularly handy when expressing classical music, vocals and other music with standard listening concepts. It is an ideal choice for manufacturing mid- and high-end home speakers and small monitoring speakers. In particular, the upper limit frequency of silk dome tweeters in recent years can reach 40,000Hz. Theoretically, the upper limit frequency of tweeters should be at least 20,000Hz, the higher the better. However, the price of units with excellent high-frequency upper limit is also more expensive.

When the positive dome tweeter plays music, its horizontal diffusion angle is larger; when the reverse dome tweeter plays music, its horizontal radiation angle is smaller, but the sound is purer and the power it can withstand is also larger. The aluminum ribbon tweeter is a tweeter that was invented very early and has a long history. However, due to its structural factors, it is not easy to make its high-frequency upper limit high enough and its power large enough, so it is not easy to popularize it.

The upper limit frequency of the top grade aluminum ribbon tweeter is above 30000Hz, and the power handling capacity is more than 150W. If you are a classical music lover and have strict requirements on the sound quality during playback, you may choose a soft dome tweeter such as a silk membrane.

If you want to use your speakers for karaoke and movie playback, it is better to choose a hard dome unit. Of course, this is not absolute, because the sound quality of the speaker is not only related to the unit selected, but also to many factors such as the design of the crossover and the production of the cabinet.

2. The structure of the midrange unit

There are generally only two types of midrange units: cone and dome. It's just that its size and power handling are larger than tweeters and it is more suitable for playing mid-range frequencies. The diaphragm of the midrange unit is mainly made of soft materials such as paper cone and silk membrane, and occasionally there are a small number of alloy dome diaphragms.

3. How to choose a bass unit

The structure of the woofer is mostly cone type, but a small number are flat-panel type.

There are many types of diaphragms for bass units, including aluminum alloy diaphragms, aluminum-magnesium alloy diaphragms, ceramic diaphragms, carbon fiber diaphragms, bulletproof cloth diaphragms, glass fiber diaphragms, acrylic diaphragms, paper diaphragms and so on.

Paper diaphragms are also called speaker cones. There are many types of paper diaphragms, such as paper cones, compressed paper cones, paper-based wool cones, and reinforced paper cones. Bass units that use aluminum alloy and aluminum-magnesium alloy diaphragms generally have smaller calibers and withstand greater power, while bass units that use reinforced paper cones and glass fiber diaphragms have more accurate timbre when reproducing music and have good overall flatness.

When choosing a speaker unit, the power handling capacity of the tweeter is generally not less than one tenth of that of the woofer. If the speaker is made of a two-way, two-unit system, the power handling capacity of the tweeter will be even higher.

When making a three-way speaker, it is sufficient for the midrange unit to handle power that is one-third of that of the woofer.

When choosing a speaker unit, it is best to choose the same impedance. Common low impedance speaker units are generally divided into 4Ω and 8Ω. When choosing a speaker unit, you should also pay attention to choosing the same sensitivity level. Generally, 86dBW·m is the medium sensitivity. Those below 84d B are called low-sensitivity speakers, and those above 90dB are called high-sensitivity speakers.

If the impedance and sensitivity differ too much when selecting the speaker unit, problems will arise when making the speaker, such as poor crossover design and unbalanced sound pressure in each frequency band.

Of course, when making a two-way speaker, the lower limit frequency of the tweeter is lower than 2kHz and the upper limit frequency of the woofer is higher than 4kHz, which will bring a lot of convenience when adjusting the speaker.

2. Selection and production of crossover

After you have selected the speaker unit, the next step is to choose and make the crossover. The crossover is divided into two categories: ordinary crossover and electronic crossover.

The electronic crossover is to directly send the tiny audio signal transmitted from the signal source into the electronic crossover. The electronic crossover divides the full-band (from bass to treble) signal into treble and bass signals, which are respectively transmitted to the corresponding power amplifier for amplification, and then the corresponding speaker unit is driven to make sound (see Figure 1). Electronic crossover is a relatively complex music playback system with good playback effect. In addition to the crossover, the electronic two-way frequency division system also requires a 4-channel audio power amplifier. The electronic three-way frequency division system requires a 6-channel power amplifier, while the electronic four-way frequency division requires an 8-channel power amplifier. The advantages of electronic crossover are good playback sound quality and easy balance adjustment between frequency bands, but the production cost is relatively high.

For homemade speakers, it is relatively simple to use a traditional power divider, as shown in Figure 2. As can be seen from the figure, the traditional power divider can be composed of only five components, including L1, C1, L2, C2, and the tweeter attenuation resistor R. L1 and C1 form a low-pass filter, through 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, which only retains the high-frequency part of the audio signal to drive the tweeter unit. Ordinary two-way dividers can also use a frequency division method with one inductor and one capacitor, and a frequency division method that is more complex than Figure 2. These different frequency division methods have their own advantages and disadvantages. However, the starting point of this article is still based on the most common Figure 2.

We have listed the values ​​of inductance and capacitance at different speaker impedances and different crossover frequencies in the attached table.

Why do we list so many values? There is a reason for this. As long as your speaker unit is good enough, the design and processing of the speaker are reasonable, and the debugging is accurate, no matter the crossover frequency is 2000Hz, 3000Hz or 4000Hz, you can get a flat and qualified test curve; but when listening subjectively, the playback sound and music performance of speakers with different crossover points are very different. Speakers with higher crossover frequencies have brighter high frequencies, but the overall sound is thinner; speakers with lower crossover frequencies have thicker and more natural playback sounds. Of course, all this is done within a certain range. If the crossover point is offset too much, the high and low frequencies will be poorly connected due to the bandwidth limitation of the speaker unit itself.

There is a rule that the lower the crossover frequency is, the larger the inductance and capacitance used in the crossover will be, and the higher the production cost will be. Therefore, some irresponsible manufacturers choose a very high crossover frequency for their products, which cannot guarantee the sound performance of the speakers when they are replayed.

Although the ordinary crossover has a simple structure, it also has its own characteristics in production.

1. How to choose an inductor

The inductor coils used in the crossover are divided into two categories: air-core coils and iron-core coils; and iron-core coils are further divided into two categories: true iron core and ferrite core.

In the crossover, the air-core coil has the best effect, but it is also relatively the largest and the most expensive to produce. The advantage of the air-core coil is that it has low loss and is less affected by the magnetic field of the speaker. When choosing an air-core inductor, you should pay attention to the selection of the inductor wire diameter. The enameled wire selected must be able to carry the corresponding power current. If the wire diameter used is too thin, the inductor is prone to overheating and burning when working at high power. The selected wire diameter can be calculated as long as it is sufficient or has some margin. Blindly increasing the wire diameter will not only cost too much, but also be difficult to process.

Iron core coils and magnetic core coils (ferrite coils) can reduce the size of the coil and reduce the production cost. However, due to the involvement of the magnetic conductor, distortion caused by magnetic saturation will be introduced. At the same time, due to the influence of the magnetic field of the speaker unit, the crossover point will be offset.

When choosing an iron core coil, the power of the iron core itself is a key factor. A large number of experiments have confirmed that the iron core coil power can only work normally with low distortion when it reaches or exceeds 50% of the maximum power of the woofer.

The iron core coil has a sweeter playback tone due to the hysteresis of the iron core material, but the transient characteristics are also reduced.

In recent years, the better power dividers basically use air-core coils.

The cost of winding an air-core coil with round enameled wire is the lowest. Using stranded wire, hexagonal wire, or strip wire will be much more expensive. There are many varieties of oxygen-free copper enameled wires, and the playback sound quality will be improved after using them.

2. How to choose the frequency division capacitor

There are many types of capacitors to choose from in the crossover, from the most common electrolytic capacitors, non-inductive capacitors, audio-specific through-core capacitors, polyester, polystyrene, and polypropylene capacitors. But the prices of these capacitors are higher than one another, and some individual brand-name capacitors are sold at sky-high prices.

Using brand-name capacitors certainly has advantages such as accurate capacitance, stable performance, and good playback sound quality, but for mid-range homemade speakers, choosing capacitors that cost only a hundred yuan each is a bit expensive.

When choosing the frequency division capacitor, the low frequency channel can use high precision and good quality electrolytic capacitors in reverse series connection, or connect a small polyphenylene or polypropylene capacitor at both ends (see Figure 3). This has a good effect and is very economical. As for high frequency capacitors, due to their small capacity and relatively low price, it is okay to choose a better one.

When choosing a high-frequency attenuation resistor, you should pay attention to the power of the resistor itself. When used in a high-power speaker, the power of the attenuation resistor should be relatively large; when used in a low-power speaker, the power of the resistor can be reduced. Otherwise, it will cause a mismatch between a large head and a small body or a small head and a large body.

In short, when choosing the components of the crossover, it is most economical and reasonable to have a clear purpose and tailor them to your needs.

3. Box Processing

In the process of speaker production, the processing of the speaker cabinet is a crucial link.

In the cabinet processing, there are only two most important points. One is that the cabinet processing size accuracy should be high; the other is that the cabinet material selection should be accurate. Among the materials used to make the speaker cabinet, there are high-grade logs; high-strength multi-layer boards; synthetic materials; organic glass and stone, etc. The so-called high-grade logs do not only refer to the high-grade and precious wood itself, but the most important thing is that the wood itself must have been dried and aged for many years. Only in this way can the cabinet be guaranteed not to crack or deform.

After years of practice, the materials for making speaker cabinets are multi-layer boards with sufficient thickness and high-grade logs, which have the best sound quality, but are also the most expensive. The overall feeling of the plexiglass cabinet is also good; medium-density fiberboard is the most affordable material for making speaker cabinets.

There are several methods for processing the speaker box:

1. Bending method See Figure 4. This method is to make a V-shaped groove on a long strip of medium density board with PVC fabric, and then bend and glue it to form a speaker box. This method is often used in large-scale speaker production.

2. The strip reinforcement method is shown in Figure 5. In the homemade speaker, the board material is cut according to the drawing, and then the glue-coated wood strips are added to the interface of the board material for reinforcement. This method is suitable for handmade speakers.

3. The assembly method is shown in Figure 6. This is a new process for making speakers. Precision machining machines are used to cut 45° + 90° bevels and notches around the speaker board. When making the speaker box by hand, the self-positioning effect of the 90° notch of the speaker board and the 45° long bevel can be used. As long as enough adhesive is applied to the interface and tied with ropes after assembly, and the glue is dried, a speaker box with high processing precision, firmness and beauty can be obtained.

After the speaker cabinet is completed, all you need to do is paint the surface, apply veneer, and other decorative treatments, and you're done.

4. Assembly and debugging of homemade speakers

When assembling and debugging a homemade speaker, there are several issues that need attention:

First, the + and - poles of the crossover and the speaker unit must not be connected incorrectly. If they are connected incorrectly, the sound of the speaker will not be adjusted well.

Second, when installing the speaker unit, the tightness of each fixing screw should be consistent, otherwise the speaker will easily produce unexpected resonance when working.

Third, the length of the bass reflex tube and the amount of sound-absorbing material in the box must be appropriate, otherwise it will affect the performance of the replayed music. In particular, the length of the bass reflex tube will have a direct impact on the low end of the test frequency response of the speaker.

The above parts need to be adjusted carefully and repeatedly. Making a speaker by yourself is a process of practice and knowledge.

Through your hard work, you can not only get speakers, but also increase your talent in speaker making. You can also save some of the money you would have spent on buying finished speakers and use it for other purposes. So it is a great thing with multiple benefits. The production process is also simple and everyone can learn to make it.