1. Classification of speakers
There are many types of speakers:
According to its energy conversion method, it can be divided into electric, electromagnetic, piezoelectric, digital, etc .;
According to the diaphragm structure, it can be divided into single paper cones, composite paper cones, composite horns, coaxial, etc .;
According to the beginning of the diaphragm, it can be divided into cone cone type, ball top type, flat type, and belt type;
According to the playback frequency, it can be divided into high frequency, intermediate frequency, low frequency and full band speakers;
According to the form of magnetic circuit, it can be divided into external magnetic type, internal magnetic type, double magnetic circuit type, and shield type.
According to the nature of the magnetic circuit, it can be divided into ferrite magnets, neodymium boron magnets, and aluminum nickel cobalt magnet speakers;
According to the diaphragm material, it can be divided into paper and non-paper speakers.
The cabinet is used to eliminate the acoustic short circuit of the speaker unit, suppress its acoustic resonance, widen its frequency response range, and reduce distortion. There are two types of speakers: bookshelf and floor, as well as vertical and horizontal. The internal structure of the box has various forms such as closed type, inverted phase, belt type, empty paper basin type, labyrinth type, symmetrical drive type and horn type. .
Floor speakers are large speakers. The height of the cabinet is above 750MM. The height of the bookshelf speakers is below 750MM. Between 450MM ~ 750MM are medium-sized bookshelf speakers, and below 450MM are small bookshelf speakers.
The frequency divider is divided into power frequency divider and electronic frequency divider. The main functions are frequency band division, amplitude-frequency characteristic and phase-frequency characteristic correction, impedance compensation and attenuation.
The power frequency divider is also called a passive rear stage frequency divider, which divides the frequency after the power amplifier. It mainly consists of passive components such as inductors, resistors, capacitors, etc. to form a filter network, which sends the audio signals of each frequency band to the corresponding frequency band speakers for playback. Its characteristics are low production cost, simple structure, suitable for amateur production, but large insertion loss, low efficiency, and poor transient characteristics.
The electronic frequency divider is also called active front stage frequency divider, which is composed of various resistance-capacitance components and active devices such as transistors or integrated circuits. It is an analog in the preamp and power amplifier signal lines. The electronic filter can divide the audio signal output by the preamplifier into different frequency bands, and then send it to the power amplifier for amplification. Its characteristics are spectrum balance in each frequency band, small mutual interference, large output dynamic range, a certain degree of amplification itself, and small insertion loss. But the circuit configuration is relatively complicated.
4. The main performance indicators of the speaker are: sensitivity, frequency response, rated power, rated impedance, directivity and distortion.
①. Rated power
Speaker power is divided into nominal power and maximum power. Nominal power is rated power and undistorted power. It refers to the maximum allowable input power of the speaker within the rated undistortion range. The power marked on the speaker's trademark and technical specifications is the power value. Maximum power refers to the peak power that the speaker can withstand at a certain moment. In order to ensure the reliability of the speaker operation, the maximum power of the speaker is required to be 2 to 3 times the nominal power.
②. Rated impedance
Speaker impedance is generally frequency dependent. The rated impedance refers to the impedance measured from the speaker input when the audio frequency is 400Hz. It is generally 1.2 to 1.5 times the DC resistance of the voice coil. Common dynamic coil speakers have 4Ω, 8Ω, 16Ω, 32Ω and so on.
③. Frequency response
When an audio signal with the same voltage and different frequencies is applied to a speaker, the sound pressure produced by the speaker will change. Generally speaking, the sound pressure generated during middle audio is relatively high, while the sound pressure generated during low audio and high audio is small. The high and low frequency range when the sound pressure drops to a certain value of mid-range audio is called the frequency response characteristic of the speaker.
The ideal speaker frequency characteristic should be 20 ~ 20KHz, so that the entire audio can be reproduced evenly, but this is not possible. Each speaker can only play back a good portion of the audio.
The phenomenon that the speaker cannot reproduce the original sound realistically is called distortion. There are two types of distortion: frequency distortion and non-linear distortion. Frequency distortion is caused by strong playback of signals of some frequencies and weak playback of signals of other frequencies. Distortion destroys the original ratio of high and low sound and changes the original sound color. The non-linear distortion is caused by the vibration of the speaker vibration system and the signal fluctuation not being completely consistent. A new frequency component is added to the output sound wave.
⑤. Pointing characteristics
It is used to characterize the sound pressure distribution characteristics of speakers radiating in various directions in space. The higher the frequency, the narrower the directivity, and the larger the paper cone, the stronger the directivity.