The mystery inside the speaker

The speaker is the terminal equipment in the audio playback system, which is roughly composed of a speaker unit, a cabinet and a frequency divider. Its working principle is to divide the sound signal into frequency bands through a frequency divider to divide the sound signal into frequency bands, and then allocate these frequency bands to the corresponding driving units to produce sound. Therefore, under the influence of the unit's craftsmanship, the adjustment of the frequency divider, the production of the cabinet, and the designer's aesthetic ability to the sound, the speakers have different sound performance. And this article will introduce the structure of the speaker and the various components of the speaker, in order to help readers understand all aspects of the speaker.

Types of speakers
For the speakers that are currently available on the market, most of them are composed of the above three components. These speakers need an external amplifier to drive them. Therefore, they are also called passive speakers. Speakers are also one of the most common and most used speakers on the market.
In addition to passive speakers, there is also an active active speaker with its own built-in electronic crossover and amplifier. This type of speaker is relatively easy to use. Users only need to give its signal from the CD player or preamplifier to work.

▲Active active speaker with built-in electronic crossover and amplifier
Therefore, active speakers are now widely used in professional recording studios and multimedia computers.
In addition, for home theater systems, there are two special-purpose speakers, dipole surround speakers and subwoofer speakers. The former’s sounding method usually uses double-sided sounding, which mainly creates surround sound by reflecting sound waves. Sound effect. The subwoofer speaker is used to increase the low frequency energy to enhance the shocking movie sound effect, and at the same time can compensate for the lack of the low frequency limit of the main speaker, so it can be regarded as a very important part of the speaker.

Drive unit
Drive unit, also known as "speaker unit". It is one of the important components in the speaker, mainly responsible for the reproduction of different frequencies. Its working principle is to use electric energy to drive the horn diaphragm to push the air, so that people can hear the sound. The driving unit is divided according to the sound frequency that it is responsible for, and can be roughly divided into three types: high pitch unit, midrange unit and woofer unit.
Why on earth is the unit divided into high, medium, and low units to be responsible for the sound reproduction? This is because the sound is divided into several frequency bands and multiple units are responsible for each, so that each unit is only responsible for a part of the sound signal , Which can broaden the effective frequency of the speaker, while increasing the output sound pressure and reducing distortion, so as to achieve high-fidelity sound reproduction.

▲Speaker
In addition, the drive unit can be divided into dome unit, cone unit and horn unit according to the type (take common types on the market as an example). Next, we will give a specific introduction to these types of speaker units:
1. Dome unit: The dome unit is one of the most common tweeter units on the market. The diaphragm area of the dome unit is relatively small, so the mass is light and the vibration speed is fast, and the diffusion angle is also relatively large, so usually Used for high frequency replay. However, there are also a few speaker manufacturers using it to reproduce mid-range sound. The most enthusiasts are familiar with the "steamed bun" midrange from the British company ATC, which is a more "alternative" dome unit.

▲The dome type is mostly used to make tweeters
2. Cone unit: Compared with the dome unit, the cone unit is more suitable for mid-frequency or low-frequency playback due to the better rigidity, high strength, and strong directivity of the diaphragm. Therefore, we usually see that the diaphragm area of the cone unit is made larger, so that a larger amount of air can be pushed, and thus more low-frequency energy can be obtained.

▲The cone is a common form of mid-woofer
3. Horn unit: The horn unit is composed of a vibration system and a horn. Its purpose is to make the sound spread farther and cover a wider range. At the same time, this design can effectively improve the conversion efficiency. Therefore, the sensitivity of the horn unit is very high. The higher the sensitivity, it means that the speaker only needs to input a small amount of power to output a larger sound pressure, so that all sound details can be hidden. At the same time, because the amplifier is working under low power, the distortion rate will also be maintained at a low level.

Frequency divider, cabinet and its structure type

Divider
The frequency divider is also another important component in the speaker. Its main responsibility is to divide the sound signal into several signals of different frequency bands and then distribute them to each corresponding speaker unit. At the same time, it can also correct the phase difference and sensitivity inconsistency between the unit and the unit. Therefore, the design of the crossover directly affects the sound reproduction quality of the speakers.

For now, power frequency division (LC frequency division network) and electronic frequency division are the most commonly used frequency division methods. The former uses capacitors and inductors to form a filter network, which is characterized by relatively simple wiring and convenient use. Therefore, most civilian speakers now use this method for frequency division. However, this frequency division method is prone to audio valleys and cross-distortion, and when the number of "orders" involved in the frequency divider is more, the circuit is more complicated and the power consumed will be greater. In addition, the amplifier needs to work at full frequency, so distortion will naturally increase.

▲Active speakers with power division
Electronic crossover is mainly used in professional sound reinforcement systems and active speakers. It is located between the pre-amplifier and the post-amplifier. Its working method is to divide the weak signal first, and then use each independent The power amplifier amplifies, and then drives the speaker unit.

▲Active speakers with electronic crossover
The advantage of this frequency division method is that it can greatly reduce the power loss and make the attenuation slope very steep, making the connection between the unit and the unit more perfect. In addition, since the power amplifier does not work in a full-frequency amplification state, the output power requirements for the power amplifier are correspondingly reduced, and the distortion rate will also be greatly reduced. However, the circuit structure of the electronic frequency divider is more complicated than that of the power frequency divider, and the cost is correspondingly increased.

Box and its structure type
Different cabinet structures and materials used will have a direct impact on the sound. Among our common speaker brands, speakers with closed, phase-inverted, and labyrinth structures account for the largest proportion. The following is an introduction to these common speaker structures:
Closed enclosure (Closed Enclosure) is the simplest speaker system. It was proposed by Frederick in 1923. It consists of a speaker unit installed in a fully sealed cabinet. It can completely isolate the forward and backward radiated sound waves of the speaker. Due to the existence of the closed box, the rigidity of the resonance of the motion mass of the speaker is increased, and the minimum resonance frequency of the speaker is increased. The sound and color of the airtight speaker is a bit deep, but the bass analysis is good. When using ordinary hard folding ring speakers, in order to obtain satisfactory bass reproduction, a large volume cabinet is required. The new airtight speaker uses a closed box The elastic effect of the compressed air quality, although the speakers are installed in a smaller box, the air cushion behind the cone will exert a counter-driving force on the cone, so this small airtight speaker is also called an air-cushioned speaker.

▲2.1 Satellite boxes of multimedia speakers are mostly sealed

Bass-Reflex Enclosure (Bass-Reflex Enclosure) is also called Acoustical Phase Inverter, invented by Thuras in 1930. In its load, there is a sound outlet opening on a panel of the cabinet. The opening position and There are many shapes, but most of them also have acoustic tubes in the holes. According to the Helmholtz resonance principle, the relationship between the internal volume of the box and the sound duct hole produces resonance at a certain frequency, which is called the anti-resonance frequency. The sound waves radiated from the back of the loudspeaker are inverted through the tube, and then radiated from the sound outlet to the front, and superimposed in phase with the sound waves radiated from the front of the loudspeaker. It can provide a wider bandwidth than a closed sound box, with higher sensitivity and smaller Under ideal conditions, the lower limit of the low-frequency playback frequency can be as much as 20% lower than the speaker resonance frequency. This type of speaker can reproduce rich bass with a smaller cabinet, and is currently the most widely used type.

▲Front inverted speaker
Acoustic resistance enclosure (Acoustic resistance Enclosure) is essentially a deformation of an inverted enclosure. It is filled with sound-absorbing material or structure in the sound outlet duct, which acts as a semi-closed box to control the phase inversion and buffer it. Reduce the anti-resonance frequency to broaden the bass reproduction frequency band.
The transmission line speaker (Labyrinth Enclosure) is named after the transmission line of classical electrical theory. There is a sound tube made of sound-absorbing wall panels on the back of the speaker, and its length is a quarter or eighth of the wavelength of the low-frequency sound that needs to be increased. one. In theory, it attenuates the sound wave coming from behind the cone, preventing it from being reflected to the open end and affecting the sound radiation of the woofer. But in fact, the transmission line speaker has a slight damping and tuning effect, which increases the sound output of the speaker near or below the resonance frequency, and reduces the amount of stroke while enhancing the bass output. Usually the sound ducts of this kind of sound box are mostly folded in a labyrinth shape, so they are also called labyrinth or tortuous.
Passive radiating speaker (Drone Cone Enclosure) is a branch of bass reflex speaker, also known as empty cone speaker. It was published by Olson and Preston in the United States in 1954. Its opening sound outlet was replaced by an empty paper cone (passive cone) without a magnetic circuit and voice coil. The radiated sound produced by the vibration of the passive cone and the forward radiated sound of the speaker In the in-phase working state, the composite sound and passive cone quality formed by the air in the box and the passive cone support elements form resonance to enhance the bass. The main advantage of this kind of speaker is that it avoids the unstable sound produced by the reflected sound hole, and it can obtain good sound radiation effect even if the volume is not large. Therefore, the sensitivity is high, which can effectively reduce the working range of the speaker, and the standing wave influence is small. Clear and transparent.


▲Passive radiating subwoofer (passive radiator on the side)
The coupled cavity speaker is a cabinet structure between the closed type and the bass reflex type. It was published by Henry Lang in the United States in 1953. Its output is output by the sound hole driven by one side of the cone, and the other side of the cone is connected with a Closed box coupling. The advantage of this kind of speaker is that the amount of air pushed by the speaker at low frequencies is greatly increased. Because the coupling cavity is a tuning system, when the cone movement is restricted, the output of the sound outlet does not exceed the sound output of a single cone, which broadens the low frequency weight. Amplify the range, so the distortion is reduced and the withstand power increases. In 1969, the A·S·W (Acoustic Super Woofer) speaker published by Yukihiko Kawashima of Lo-D in Japan is a coupled cavity speaker, suitable for reproducing bass without distortion with small-diameter long-stroke speakers.
Horn type enclosure (Horn type Enclosure) for household type, mostly adopt the form of folded horn (Folded Horn), its horn mouth is coupled with a larger air load at the mouth, and the diameter of the driving end is very small. It is fully sealed, and the pressure in the chamber is as much as the back of the speaker cone. In order to keep the pressure balance between the front and rear of the cone, an inverted horn is installed in front of the speaker. The folding horn speaker is a derivative of the phase-inverted speaker, and its sound effect is better than the closed speaker and the general bass reflex speaker.
In addition to the effect of the structure of the speaker on the sound, the material of the cabinet is also very important. Because in the eyes of the speaker designer, an ideal cabinet cannot be affected by the vibration of the unit, so the sound pollution caused by the vibration of the cabinet can be eliminated. But in fact, this kind of box does not exist, so we can only suppress the box vibration as much as possible. The designers also tried every means to achieve this goal. The simplest and cheapest method is to use MDF board or wood to make the box, and then use reinforcing ribs in the box to strengthen the strength of the box to appropriately reduce the sound dyeing. For some high-end speaker manufacturers (such as Wilson Audio, YG Acoustics), metal is used as the box material, while other more "abnormal" manufacturers also use marble clips to make the box.

▲Box of metal material (cast aluminum)
However, the craftsmanship and cost of the cabinet made of metal or marble are much higher than that of MDF board and wood. At the same time, the vast majority of people are always unaccustomed to listening to bass-dyed sounds, because they all believe that the right amount of sound-coloring will make the sound sound better and more humane. After the above introduction, I believe that readers should have a certain understanding of the mainstream speakers on the market. But in fact, there are many types of speakers, and it is impossible to introduce a complete description with a few short narratives. Therefore, in this issue of the magazine, we only briefly introduce the structure and related components of the speaker.
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