Basic knowledge of speakers

1. Speaker
There are many types of loudspeakers: according to their energy conversion methods, they can be divided into electric, electromagnetic, piezoelectric, digital, etc.; according to the diaphragm structure, they can be divided into single cones, composite cones, composite horns, and the same There are many kinds of shafts; according to the beginning of the diaphragm, it can be divided into cone type, dome type, flat type, belt type, etc.; according to the replay frequency, it can be divided into high frequency, intermediate frequency, low frequency and full band speakers; according to the magnetic circuit The form can be divided into external magnetic type, internal magnetic type, dual magnetic circuit type and shielded type; according to the nature of the magnetic circuit, it can be divided into ferrite magnets, neodymium boron magnets, and alnico magnet speakers; according to the material of the diaphragm Divided into paper and non-cone speakers, etc.
A. The electrodynamic speaker is the most widely used. It uses the interaction force between the voice coil and the constant magnetic field to make the diaphragm vibrate and produce sound. Electric woofers are mostly cone type, midrange speakers are mostly cone type or dome type, and tweeters are usually dome type, ribbon type and horn type.
B. The cone speaker has a simple structure and high energy conversion efficiency. The diaphragm material used is mainly pulp material, or mixed with wool, silk, carbon fiber and other materials to increase its rigidity, internal damping and waterproof properties. The new generation of electric cone loudspeakers uses non-paper diaphragm materials, such as polypropylene, mica carbonized polypropylene, carbon fiber textiles, bulletproof cloth, hard aluminum foil, CD corrugated, glass fiber and other composite materials, and its performance is improved.
C. Dome speakers are divided into soft dome and hard dome. The diaphragm of soft dome speakers, colored silk, silk, cotton cloth impregnated with phenolic resin, chemical fiber and composite materials, is characterized by soft playback sound quality; the diaphragm of hard dome speakers is made of aluminum alloy, titanium alloy and beryllium alloy, etc. Its characteristic is that the playback sound quality is clear and crisp.
D. The radiation mode of the horn speaker is different from that of the cone speaker. After the diaphragm vibrates, the sound is diffused through the horn. Its characteristics are high electro-acoustic conversion and radiation efficiency, long distance, low distortion, but narrow playback frequency band and directivity.

E. The voice coil of the ribbon speaker is directly made on the entire diaphragm (aluminum alloy polyimide film, etc.), and the voice coil and the diaphragm are directly coupled. The alternating magnetic field produced by the voice coil interacts with the constant magnetic field, causing the belt diaphragm to vibrate and radiate sound waves. It is characterized by fast response speed, low distortion, fine playback sound quality and good layering.

2. Cabinet
The cabinet is used to eliminate the acoustic short circuit of the speaker unit, suppress its acoustic resonance, broaden its frequency response range, and reduce distortion. The cabinet shape structure of the speaker is divided into bookshelf type and floor type, as well as vertical type and horizontal type. The internal structure of the box has various forms such as closed type, phase inverted type, band pass type, empty paper cone type, labyrinth type, symmetric drive type and horn type. The most used are closed type, phase inverted type and band pass type. .
Floor-standing speakers are large speakers, the cabinet height is above 750MM, the cabinet height of bookshelf speakers is below 750MM, those between 450MM and 750MM are medium bookshelf speakers, and those below 450MM are small bookshelf speakers.

The front main speaker of the home theater system is a vertical speaker, either a bookshelf type or a floor type. This depends on the size of the audio-visual room, the power amplifier power, and personal preferences. Generally, for the audio-visual room below 15 square meters, medium bookshelf speakers should be used; for rooms less than 10 square meters, small bookshelf boxes should be used; for rooms larger than 15 square meters, medium bookshelf speakers or floor boxes should be selected. The front main speakers, center speakers and surround speakers are mostly designed with inverted phases, followed by airtight and 1/4-wavelength loading, labyrinth, etc. Subwoofer speakers are mostly band-pass and double-cavity double-opening, followed by inverted and closed.

3. Frequency divider
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 divider is also called passive post divider, which divides the frequency after the power amplifier. It is mainly composed of passive components such as inductors, resistors, capacitors and other passive components to form a filter network, and send the audio signals of each frequency band to the speakers of the corresponding frequency band for reproduction. Its characteristics are low production cost, simple structure, suitable for amateur production, but large insertion loss, low efficiency, and poor transient characteristics.
Electronic frequency divider, also known as active front-stage frequency divider, is composed of various resistance-capacitance components and active devices such as transistors or integrated circuits. It is a kind of analog that is placed in the signal line of preamplifier and power amplifier. 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 amplifying processing. Its characteristic is that the frequency spectrum of each frequency band is balanced, mutual interference is small, the output dynamic range is large, it has a certain amplification ability, and the insertion loss is small. But the circuit composition is relatively complicated.
The frequency divider can be divided into two frequency divisions, three frequency divisions and four frequency divisions according to the frequency division frequency band. Two-way frequency divides the entire frequency band of the audio signal into two frequency bands, high-frequency and low-frequency; three-way frequency divides the entire frequency band into three frequency bands, high-frequency, intermediate frequency, and low-frequency; four-way frequency divides the three-way frequency into one more Ultra low frequency band.
The crossover point and the crossover slope directly affect the crossover quality and the crossover frequency.
The crossover point refers to the intersection of the frequency response curves of two adjacent speakers (such as the treble and bass in the two-way frequency, the treble and the midrange in the three-way frequency, the midrange and the bass) at a certain frequency, usually It is the frequency at half of the power output of the two speakers (that is, the -3dB point), which should be determined according to the speaker and the frequency characteristics and distortion of each speaker. Usually the frequency divider of the two-way frequency divider is between 1KHZ~3KHZ, and the three-way frequency is 250HZ~1KHZ and 5KHZ.
The frequency division slope (also called the attenuation slope of the filter) is used to reflect the falling slope of the frequency response curve below the frequency division point, expressed in decibels/octave (dB/oct). It is divided into first-order (6 dB/oct), second-order (12 dB/oct), third-order (18 dB/oct) and fourth-order (24 dB/oct). The higher the order, the frequency after the crossover point The slope of the curve is greater. The more commonly used is the second-order crossover slope. The high-order frequency divider can increase the slope, but the phase shift is large; the low-order frequency divider can produce a smoother slope and good transient response, but the amplitude-frequency characteristics are poor. Deciding the order of high and low frequency filtering should mainly consider the good connection of the phase of the loudspeaker itself at the crossover point.
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