Ⅰ. What is a speaker?
Ⅱ. The development of the speaker
Ⅲ. Construction of the speaker
Ⅳ. How speakers work？
Ⅴ. The main technical parameters of the speaker
Ⅵ. Speaker damage and protection
Ⅶ. What are the new technologies for piezoelectric speakers?
Speaker, also known as horns and loudspeakers, are electronic components that convert electronic signals into sound. It can be composed of one or more speakers to form a sound group. Speakers are the weakest component in audio equipment. And for the sound effect, it is one of the most important components. There are many types of speakers, and their prices vary widely. Audio electricity produces sound by vibrating its cone or diaphragm through electromagnetic, piezoelectric or electrostatic effects and resonating with the surrounding air.
Ⅱ. The development of the speaker
On February 14, 1876, Alexander Graham Bell filed the most important patent in history, the "telephone." This invention allows the human voice to travel farther than shouting. Since then, humans have realized the conversion relationship between sound and electricity.
On December 14, 1877, Ernst Werner VonSiemens, the founder of Siemens AG, applied for the German patent N0.2355 related to loudspeakers. It can be seen that his technical solution is a great improvement over the telephone invented by Bell. He canceled the electromagnet part, and placed a circular active coil in the radial magnetic field to form an electric voice coil structure, so that the diaphragm can obtain more free vibration space and better linear support. The simple structure creates conditions for the speaker to obtain better sound quality.
On February 16, 1901, John Stroh applied for the British Patent No. 3393. In his patent, he described the technique of making a conical diaphragm using paper as raw material. The diaphragms of previous loudspeakers are mostly planar, and it is difficult to maintain a relatively fixed overall shape under the action of the driving force of the voice coil. Another outstanding technical feature of this patent is that in order to provide more flexible and linear support for the diaphragm, the diaphragm is generally conical in shape. He also specially made the shape of the paper cone at the edge of the diaphragm into a wavy structure that is easy to deform, so as to avoid large deformation of the entire paper cone.
In 1910, S.G. Brown separated the driving force from the diaphragm and invented the 'armature' earphone. The armature earphone is a movable iron plate (armature) set in the middle of a U-shaped magnet. When current flows through the coil, the armature is magnetized, and the magnet generates attraction and repulsion, driving the diaphragm to move at the same time. This design is low cost and is mostly used in telephone tubes and small earphones. Although the effect of this technology is not good, it is also an epoch-making invention.
In 1917, Wente and Thuras designed the condenser microphone.
On January 8, 1918, Henry Egerton applied for a patent for the US No. 1365898 Balanced-Armature speaker. It can be seen that the structure of the balanced armature speaker is mainly composed of a diaphragm, a transmission rod, an armature (reed), an electromagnetic coil, a magnetic pole, and a permanent magnet. Balanced armature speakers generally have high electro-acoustic conversion sensitivity, but narrow frequency response and large distortion.
In 1924, C.W.Rice and E.W.Kollogg of the United States invented the electric speaker.
In 1930, the electrostatic loudspeaker was introduced, based on the principle of the condenser microphone. In early 1950, C.V.bocciarelli proposed the law of constant charge. P. Walker independently developed the same theory during the same period and applied it to the design of the famous quad electrostatic loudspeaker.
Our most common type is the electric cone speaker. Electric cone speakers are what we used to call paper cone speakers in the past. Although the diaphragm is still dominated by paper cones, many polymer material diaphragms and metal diaphragms have appeared at the same time, so the name of the cone speaker is worthy of the name. The cone-shaped paper cone speaker is generally composed of three major components: the magnetic circuit system (permanent magnet, core column, magnetic plate), the vibration system (paper cone, voice coil) and the supporting auxiliary system (centering piece, basin frame, edge pad).
1. Paper cone: There are many types of materials used for the cone-shaped diaphragm of a cone-shaped paper cone speaker, and there are generally two types of natural fibers and man-made fibers. Cotton, wood, wool, spun silk, etc. are often used as natural fibers, and rayon, nylon, glass fiber, etc. are just used as artificial fibers. Since the paper cone is the sound radiation device of the speaker, it determines the sound reproduction performance of the speaker to a considerable extent. Therefore, no matter what kind of paper cone, we require it to be both light in weight and good in rigidity, and it cannot be deformed due to changes in ambient temperature and humidity.
2. Voice coil: The voice coil is the drive unit of the cone speaker. It is wound on the paper tube in two layers with very thin copper wires, generally dozens of turns, and placed in the magnetic gap formed by the magnetic core column and the magnetic plate. The voice coil and the paper cone are fixed together. When the sound current signal is passed into the voice coil, the vibration of the voice coil drives the paper cone to vibrate.
3. Centering support: The centering support is used to support the joint between the voice coil and the paper cone to ensure that it is vertical and not skewed. There are many concentric rings on the centering strut, so that the voice coil can move up and down freely in the magnetic gap without moving laterally, so as to ensure that the voice coil does not collide with the magnetic plate. The dust cover on the centering strut is to prevent external dust from falling into the magnetic gap, and to avoid friction between the dust and the voice coil, which will cause the speaker to produce abnormal sound.
4. Ring: The ring is set to ensure the axial movement of the paper cone along the speaker and limit the lateral movement. The material of the ring is not only the material of the commonly used paper cone, but also plastic, natural rubber, etc., which are bonded to the paper cone by hot pressing.
Firstly, we apply AC current to the sound coil of the speaker. The voice coil generates an alternating magnetic field under the action of input current, and the voice coil is placed in a permanent magnet. The voice coil moves perpendicular to the current direction of the voice coil under the action of these two magnetic fields, so that the voice coil moves back and forth under the action of the current.
Because the voice coil and the paper cone are connected together, the movement of the voice coil drives the front and rear vibrations of the paper cone, and the vibration of the paper cone pushes the vibration of the air, and the human ear can feel the vibration of the air and produce sound. In this way, the current input to the speaker is converted into sound by the action of the speaker.
When the AC current input to the speaker is larger, the AC current flowing through the voice coil is also larger, and the magnetic field is stronger. The greater the vibration amplitude of the cone of the speaker, the louder the corresponding sound. Conversely, when the AC current input to the speaker is smaller, the sound from the speaker is smaller.
1. Impedance
Impedance is the measured impedance at the speaker input, which varies with the frequency of the input signal. Generally, the measured impedance at 400 Hz is printed on the speaker. This value is 1.05 to 1.1 times the DC resistance of the voice coil for small diameter speakers, and 1.1 to 1.5 times for large diameter speakers.
The impedance of the paper cone speaker is generally: 4Ω, 8Ω, 16Ω, 25Ω, etc.
The impedance of the horn speaker is generally: 4Ω, 8Ω, 16Ω, etc.
2. Sensitivity
It indicates how responsive a speaker is to input level, usually expressed in decibel sound pressure level (dB SPL). The higher the sensitivity, the louder the speaker will produce sound for the same input power.
3. Directivity
Radiation directivity refers to the relationship between the sound pressure level of each point in space and the sound radiation direction when the speaker emits sound. Pointing characteristics are marked by the size of the radiation angle. The radiation angle refers to the angle at which the sound pressure level is 6dB lower than the main axis in the directivity curve pattern, that is, the so-called 6dB radiation angle.
The directivity characteristics of paper cone speakers have a great relationship with frequency. The higher the frequency, the smaller the radiation angle, that is, the stronger the directivity. Generally less than 250 ~ 300Hz directivity is not obvious. For horn speakers, generally the larger the aperture, the sharper the directivity. The directivity shift of horn speakers is not as pronounced as that of paper cone speakers. In a fairly wide frequency range, the directivity of the horn is roughly elliptical.
4. Nominal Power
The nominal power is the power when the speaker can work for a long time, and the unit is W or VA. The short-term overload capacity of the speaker is 1.5 to 2 times the nominal power. The rated power of common paper cone speakers are: 50mW, 100mW, 250mW, 400mW, 500mW, 1W, 2W, 3W, 5W, 10W, 20W, etc. The rated power of common horn speakers are: 5W, 10W, 12.5W, 15W, 25W, etc.
Some manufacturers give the maximum allowable power of a speaker, which refers to the maximum power that the speaker can withstand in a short period of time without damage. The other is the maximum instantaneous power of the speaker, which refers to the electric power allowed to be input under the condition that the harmonic distortion of the speaker is less than a certain value. At present, many manufacturers at home and abroad tend to give this power.
5. Voice Coil DC Resistance
The DC resistance of the voice coil is smaller than the rated impedance, generally about 0.85 times the rated impedance.
6. Distortion
Speaker distortion refers to the nonlinear harmonic distortion, intermodulation distortion, and transient distortion generated when the speaker reproduces the sound. When a sinusoidal signal of a certain frequency is input, due to the nonlinearity of the speaker, in addition to the original input signal, an acoustic signal whose frequency is an integer multiple of the fundamental frequency appears in the output sound signal of the speaker. The labeled distortion of speakers generally refers to the maximum nonlinear harmonic distortion at rated power, as the distortion level of speakers varies at different power levels.
Generally, the distortion of carton speakers above φ100mm ≤7%
Horn speaker distortion ≤ 15%
High-fidelity paper cone speaker distortion ≤ 0.8%
7. Effective Vibration Diameter
Its value is the sum of the diameter of the speaker diaphragm and 1/2 the width of the surround (unit: mm). This value is not only related to the volume of the box, but also determines the maximum sound power that the speaker can output in the low frequency range (20-100Hz).
8. Equivalent Vibration Mass
The equivalent vibration mass of the speaker refers to the sum of the vibration system of the speaker and the additional mass attached to both sides of the cone due to the reaction force of the air when the speaker vibrates.
9. Resonant Frequency
The resonant frequency refers to the value of the corresponding frequency when the low-frequency impedance value of the speaker reaches the maximum value in the free sound field, which is related to the caliber of the speaker. When the caliber is large, the resonance frequency is generally relatively low. The resonant frequency of the woofer is generally in the range of 18-80Hz.
10. Equivalent Volume
Equivalent volume is an extremely important parameter in loudspeaker design. It means that the sound compliance of the air in this volume is equal to that of the speaker (unit: L). It is a quantity proportional to the volume of the tank. The Vas of different speakers varies greatly, the small one is only 2 liters, and the large one can reach more than 300 liters.
11. Rated Maximum Sinusoidal Power
This parameter refers to the maximum sinusoidal power that feeds a continuous sinusoidal signal without thermal damage and mechanical damage within the rated frequency band of the loudspeaker. This power can also be regarded as the maximum power that the speaker unit can work normally continuously.
12. Characteristic Sensitivity
The sound pressure level (unit: db) at a distance of 1 meter from the reference point on the front axis of the speaker when the speaker is installed on the standard baffle and input a pink noise signal of one watt within the effective frequency band. It reflects the ease of pushing the speaker unit.
13. Linear Displacement
It refers to the unidirectional maximum linear amplitude of the speaker cone (unit: mm). The linear displacement of modern new high-power woofers can reach 3-12 mm. It effectively improves the low-frequency reproduction capability of modern small-diameter speakers, so that small-diameter units can also emit low-frequency energy similar to large-diameter units.
14. Rated Harmonic Distortion
The harmonic distortion of the speaker is mainly caused by the nonlinearity of the magnetic circuit system and support system. The smaller this value, the better. The rated harmonic distortion of modern high fidelity speakers is mostly below 3%.
15. Power Handling Capacity
It refers to the maximum power input that the loudspeaker can handle safely. It is a parameter to measure the durability and reliability of the loudspeaker.
16. Frequency Response
It describes the output capability of a speaker in different frequency ranges. It shows how the speaker responds to and delivers sound at various frequencies and determines the sound quality of the speaker and its ability to accurately reproduce audio content.
17. Effective Frequency Range
On the frequency response curve, the frequency response width between 15dB unevenness is called the effective frequency range. It is the main frequency range in which speaker reproduction works. In order to make the frequency distortion of the reproduced sound small, the effective frequency range should be wide, and the smoother the curve is, the closer the tone and timbre of the reproduced sound are to the tone and timbre of the original sound.
For paper cone speakers above 0.5W, the frequency range starts from 100-180Hz to 4000-6000Hz.
Horn speaker range from 200~450Hz to 6000Hz.
The frequency range of the high-power low-frequency paper cone speaker is about 80-1200Hz.
The frequency range of the tweeter is about 800~10000Hz.
The frequency range of high-fidelity speakers can be as wide as 36-9000Hz.
It is very difficult to reproduce the entire frequency range with a single speaker. Therefore, we usually divide the retransmission frequency range into 2 to 3 frequency bands, and use a combination of bass, midrange and tweeter speakers to reproduce the sound of a wide frequency range.
18. Bandwidth
It refers to the frequency range in which a speaker can effectively operate. It means that the speaker can produce normal, clear sound output in the range of low frequency to high frequency.
19. Maximum Sound Pressure Level
It represents the maximum sound intensity a speaker can achieve at maximum output power. It is a parameter that measures the volume output capability of a speaker.
1. The reasons for the damage of the speaker are:
(1) The microphone produces strong acoustic feedback and howling, the power amplifier is strongly overloaded, and the speaker system is damaged.
(2) Improper operation, the output power of the power amplifier is too large.
(3) When the performance reaches its climax, the atmosphere in the venue is warm and the sound pressure needs to be increased. When the signal is increased, the input signal of the microphone is too large, which will cause the power amplifier to overload and clip, and the distorted waveform will generate a large number of harmonics, which will damage the tweeter.
2. To this end, modern new speaker systems have adopted a variety of protective measures, which can be divided into two categories:
(1) To improve the heat dissipation of the speaker unit so that it will not be damaged by overheating when it is overloaded.
(2) To install a limiter protection device in the speaker box. When the driving power and peak level exceed the rated value of the speaker, the limiter uses a non-linear resistor (bulb) to stop the voice coil from the excess power level.
Ⅶ. What are the new technologies for piezoelectric speakers?
1. Acoustic optimization technology: By optimizing the design of the speaker's acoustic system, we can further improve the quality and clarity of the sound. For example, by changing the distance between the diaphragm and the air, the shape and material of the diaphragm, the size and layout of the sound hole and other parameters, the acoustic performance of the speaker can be optimized to make the output sound more pure and natural.
2. Adaptive diaphragm technology: The traditional piezoelectric speaker diaphragm is fixed and cannot adapt to different audio signals and sound frequencies. Adaptive diaphragm technology uses a special structure and material, which can adaptively adjust the shape and motion state of the diaphragm according to the frequency and amplitude of the input signal, so as to achieve more accurate and clearer sound output.
3. Intelligent control technology: The new piezoelectric speaker can also be equipped with an intelligent control system. Through real-time monitoring and processing of input signals and environmental noise, the speaker's sound output and gain can be automatically adjusted to better adapt to different usage scenarios and environments.
4. Fine processing technology: The precision and reliability of piezoelectric speakers have a great influence on the quality and stability of sound. The new fine processing technology can make the structure and shape of the piezoelectric material more uniform and stable, thereby improving the response speed and frequency response range of the speaker.
