A complete loudspeaker will consist of several parts: the speaker unit, the crossover network, and the speakers. We will discuss them in different categories. The first is the speaker unit. Basically, the working principle of the microphone is reversed, and the electrical signal is input to the coil on the voice coil in the magnetic system. The coil will produce magnetic changes with the signal, and drive the voice coil in the magnetic system. Waveform movement of sound. The voice coil then pushes the diaphragm or cone of the speaker unit to push the air to generate sound waves, and the sound is just like this.
It is really not difficult to say, but it is another matter to make the electrical signal sound as low as possible with the original waveform and response. The audio frequency range from low frequency (20Hz) to high frequency (18kHz) exceeds ten octaves. If a single speaker can cover this audio range, it will be limited by the structure in terms of volume. However, now the full-range monomer technology is mature and developed, and there are already many full-range monomers with good performance available for sale on the market.
Of course, in order to build a loudspeaker system that can emit large volume and high bandwidth, it is necessary to allocate different sound ranges to monomers with different characteristics, such as the low frequency range (below 300Hz) for the woofer, and the middle frequency range (300Hz-2500Hz) for the midrange. Monomer, high-frequency domain (above 2500Hz) pronounces separately for treble monomer, and integrates into a complete range. Because the low frequency needs to push a lot of air, it needs the largest diaphragm/sound cone; the middle range needs to push less air, so the diameter of the cone and the size of the monomer are also smaller and lighter; while the high range only needs to push the least Air, so the tweeter is also the lightest and smallest diaphragm.
Basically, the larger the diameter of the single cone/diaphragm, the heavier the mass and the more air it can push, but it also has greater inertia, so the reaction speed will be reduced, so it is suitable for lower frequencies; on the contrary, the single The smaller the diameter of the diaphragm and the lighter the mass, the faster the response speed and can emit higher frequencies, but the relative amount of air that can be pushed is limited. This is why speakers with a small size on the market are equipped with multi-channel and multiple monomers for integrated pronunciation.
Of course, if this is the case, the electrical signal of the amplifier must be separated into the high-bass path or even the mid-range path, which is the so-called “frequency division”. Generally speaking, there are two ways to divide the frequency of the speaker system. The most mainstream way is to use the passive frequency division network to divide the signal of the amplifier into sound channels with different frequency ranges. To put it bluntly, the passive crossover network is a “filter” composed of passive inductors, capacitors, and resistors, which filter out the frequency bands outside the sound range of the audio circuit, and only the required frequency bands can pass through. Therefore, there are several sound channels in the speaker system, and there will be several sets of filter networks to form a frequency division network to drive the monomers responsible for different sound ranges.
Another method is “electronic crossover”, which is to send the signal to the electronic crossover when it is still output from the pre-stage, and divide the required frequency band into each range, but it uses an active electronic crossover circuit. , generally speaking, the frequency division effect will be better than the passive frequency division network. However, the different audio channels from the frequency division require individual amplifiers to drive the monomers of each audio channel, which will greatly increase the cost of the speaker system; usually, electronic sound division is used by relatively large speaker systems ( There are also professional listening speakers that will be introduced in another article).
In the end, of course, these monomers with different sound paths must be installed to form a complete set of speaker systems, but further consideration is required. The reciprocating vibration of the monomers pushes the air to produce sound, and the front and rear sounds are “inverted”. If there is no further processing, the effect of canceling each other will be produced in the listening space, so “boxing” is required to further process the “back wave” emitted from the rear of the monomer. Generally speaking, each monomer will have an independent space to deal with the back wave. If the volume of the mid-range and high-pitched monomer is small, a sealed back cavity will be built for pre-treatment when the monomer leaves the factory.
Therefore, the speaker box is mainly designed for certain midrange and woofer units with larger calibers. At present, there are two mainstream ways of loudspeaker cabinet design: closed type and open type. The mainstream of open type is bass reflex type, that is, the bass chamber capacity of the speaker box and the diameter and length of the reflection duct are calculated, and the low frequency characteristics of the monomer are calculated. Tuned to produce a greater amount (just the right amount) of low frequency presence. However, the volume of the closed speaker still has to be calculated by considering the characteristics of the monomer, so that the low frequency can be extended to the lowest frequency.
However, open speakers do not only have bass reflex design methods, but also have many methods such as the Isobarik form of dual monomers and multiple air chambers or transmission lines (the form of separating the inside of the speaker into a long tube to extend the low-frequency frequency). There are also many designs on the material and structure of the speaker to strengthen its structure to avoid resonance and affect the sound quality. The most mainstream material is the so-called “medium density fiberboard” (MDF). This material is cheap, easy to process and has many ideal effects. characteristic. Of course, some speaker manufacturers use metal or special materials to design/construct speakers to achieve better characteristics and effects.
The above are the components of a typical loudspeaker. Of course, there are other technically different designs that deviate from the above categories. For example, the “plasma/ion tweeter” uses discharge to drive the air; the “electrostatic speaker” uses electrode/electric field drive The membrane is used to push the air to speak, and there is no speaker structure at all. There are indeed many other ways to convert electrical energy into sound energy, but the most mature and mainstream approach is still the traditional speaker based on the electromagnetic system and integrated with the speaker structure.