How Does The Speaker Make Sound?

- Jul 29, 2020-

"Speaker" is also commonly known as "speaker". At present, human technology needs to convert electrical energy into sound waves. The most mainstream technology is still the "electromagnetic" method. At present, the speakers on the market are mainly designed and manufactured using electromagnetic principles.

The complete speaker will consist of several parts: speaker unit, crossover network, and speakers. We will discuss them in different categories. The first is the single speaker. Basically, the working principle of the microphone is reversed. The electrical signal is input to the coil on the voice coil in the magnetic system. The coil will change magnetically with the signal, and drive the voice coil to change in the magnetic system. Wave motion 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 emitted.


It is really not difficult to say, but it is another matter to make electrical signals as low as possible in terms of waveform and response as they should be. The audio range from low frequency (20Hz) to high frequency (18kHz) exceeds ten octaves. If a single speaker unit can cover this audio range, the volume will be limited by structure. But now the technology of full-range monomers is mature and developed, and there are already many full-range monomers with good performance on the market.


Of course, to build a loudspeaker system that can emit high volume and high bandwidth, you need to configure different sound ranges to different characteristics of the monomer, such as low frequency domain (below 300Hz) configured to the bass unit, mid frequency domain (300Hz-2500Hz) to the midrange Monomer, high-frequency range (above 2500Hz) separately pronounces the high-pitched monomers and integrates them into a complete range. The low frequency needs to push a lot of air, so it needs the largest diaphragm/cone; the mid-range requires less air, so the cone diameter and unit size are also smaller and lighter; while the high-range only needs to push the least Air, so the tweeter is also the lightest diaphragm and the smallest body.


Basically, the larger the diameter of the single cone/diaphragm, the heavier the mass can push more air, but it also has greater inertia so the speed of reaction will be reduced, so it is suitable for lower frequencies; on the contrary The smaller the diameter of the diaphragm, the lighter the mass, the faster the response speed and the higher the frequency, but the relatively limited amount of air that can be pushed. This is why the speakers with a little volume on the market will be equipped with multi-channels and multiple monomers for integrated pronunciation.



Of course, in this case, the electrical signal of the amplifier must be separated into the high and low frequency path or even the midrange path, which is the so-called "frequency division." Generally speaking, there are two ways to divide the frequency of the loudspeaker system. The most mainstream way is to use a passive frequency division network to separate the signal of the amplifier out of the sound channels with different frequency ranges. The passive crossover network is simply a "filter" composed of passive inductors, capacitors, and resistors, which filter out the frequency bands outside the range of the sound path, leaving only the required frequency bands to pass. Therefore, the speakers are equipped with several sound paths, and there will be several groups of filter networks to form a crossover network, respectively driving the monomers responsible for different sound ranges.


Another method is "electronic crossover". The signal is sent to the electronic crossover when the signal is still in the pre-output stage, and each range of the required frequency band is separated. However, an active electronic crossover circuit is used. , Generally speaking, the crossover effect will be better than the passive crossover network. However, the different sound paths derived from the frequency division require separate amplifiers to drive the individual sound paths, which will greatly increase the cost of the speaker system; usually electronic crossovers are used by relatively large speaker systems.

Finally, these units with different sound paths must of course be installed to become a complete speaker system, but further consideration is needed. The unit reciprocates back and forth to push the air to produce sound, and the sound before and after is "inverted". If it is not processed further, it will have an effect that cancels each other out in the listening space, so it is necessary to "box" the "back wave" emitted from the rear of the monomer for further processing. Generally speaking, each monomer will have an independent space to deal with the back wave. If the volume of the middle and high pitch is small, a sealed back cavity will be built before the monomer leaves the factory.


Therefore, the speaker cabinet is mainly designed for some large-caliber midrange and bass monomers. At present, there are two mainstream ways of speaker cabinet design: closed type and open type. The mainstream of open type is the bass reflex type, which means that the volume of the bass chamber of the speaker and the diameter and length of the reflection duct are calculated, and the low frequency characteristics of the monomer Tune to produce a larger amount (appropriate amount) of low frequency performance. However, the volume of the closed speaker still has to be calculated considering the characteristics of the individual, so that the low frequency can be extended to the lowest frequency.

However, open speakers are not only designed for bass reflex, there are also many methods such as the Isobarik form of two-unit multi-air chambers or transmission lines (the form of a long duct that separates the inside of the speaker to extend low-frequency frequencies). 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), which has many kinds of materials that are affordable, easy to process, and have ideal effects. characteristic. Of course, there are also speaker manufacturers that use metal or special materials to design/build their speakers to achieve better characteristics and effects.


The above are the components of a typical speaker. Of course, there are other technically different designs that will deviate from the above categories. For example, the "plasma/ion tweeter" type uses electric discharge to drive the air; the "electrostatic speaker" uses electrode/electric field drive There is no sound box structure at all because the film is used to promote air pronunciation. There are indeed many other ways to convert electrical energy into sound energy, but the most mature and mainstream approach at present is still a traditional single unit based on the electromagnetic system and a traditional speaker integrated with the speaker structure.