Different Types of Speakers

Ⅰ. Types of speakers

There are various types of speakers, and we can classify them in five ways: sound frequency, usage, driving method, shape of diaphragm, and principle of sound generation.

1. According to the sound frequency

It can be mainly divided into four types: woofer, mid-range speaker, tweeter and full-range speaker.

(1) Woofer

The woofer is a speaker with good low-range performance designed for reproduction in the low frequency range. These speakers are almost always cone speakers. The lower limit of the playback frequency band should be as low as possible, and the allowable value of the vibration plate amplitude should be as large as possible. Therefore, each item of the vibrating plate opening should be as large as possible. In order to increase the amplitude of the vibrating plate, we need to use soft and relatively wide side supports.

A good woofer needs to have the following conditions:

① The diameter of the vibrating plate should be large;

② The vibrating system should not be too thin, the elasticity should be good, and the vibration will not be fatigued for a long time;

③ There must be a strong and powerful magnetic circuit;

④ The baffle and the flange of the vibration should be soft and maintain good linearity at large amplitudes.

(2) Mid-range speaker

In a multi-frequency speaker system with more than three frequency divisions, the unit used to replay the mid-range is called a mid-range speaker. The most important performance requirement for a midrange speaker is that the sound pressure frequency characteristic curve should be flat, with little distortion, good directivity, and high frequency. All the shapes of this unit, in addition to the conical speaker, are also commonly used in the shape of a dome and a horn.

(3) Tweeter

The unit that withstands high-frequency playback is called a tweeter. The general working frequency range of the tweeter is above 1~5KHz. The main performance requirements of this unit, in addition to the same as the mid-range unit, also require a higher playback frequency band and a larger input capacity. Tweeters come in various forms such as conical, flat-top, dome-shaped, horn-shaped, ribbon-shaped and sheet-shaped.

A good tweeter should have the following conditions:

① Large input capacity;

② Small voice coil diameter and thin wire diameter;

③ The high-frequency characteristics are flat and wide;

④ Small high-frequency distortion and good directivity;

⑤ The diameter of the vibration plate should be small and light.

(4) Full-range speaker

Speakers that can cover the system, high and low frequencies at the same time are called full-band speakers. The speaker's diaphragm vibrates to produce a full-range sound from bass to treble. Among the full-range speakers, there are single-diaphragm full-range speakers, double-diaphragm-type and coaxial-type speakers. The double-diaphragm speaker is the same as the single-diaphragm speaker, and it is an integral structure, so it is very convenient to use. But the coaxial speaker is actually a combination of two speakers, which is a multi-channel device.

2. According to the purpose

(1) Coaxial speaker

It is to place the mid-range speakers on the coaxial or same chassis. The advantage of coaxial speakers is that they are easy to install and have a consistent sound source, that is, a point source. The disadvantage is that the treble often "covers" the midrange; the sound is hard and the sound field is uneven, so it is generally recommended to be used as a rear sound field speaker.

(2) Kit speaker

The set speaker is composed of tweeter, midrange speaker, frequency divider and so on. Commonly used set speakers include two-way frequency and three-way frequency. The advantage is that it is beneficial to the positioning of the sound field. Different speakers are responsible for different frequencies, the crossover is accurate and the frequency range is wide. Because the set speaker has excellent sound field positioning ability, it is generally used in the front sound field. Because the tweeter determines the position of the entire sound field, its installation position is very important.

(3) Subwoofer

It is generally installed in a specially made subwoofer. The smaller the size of the woofer, the harder and crisper the sound effect. the larger the size, the deeper the sound effect and the heavier the reverberation. Bass can greatly improve the listening experience in the car, especially in high-speed driving, the bass will be greatly attenuated. Therefore, it is necessary to add a bass system.

(4) Unit speaker

The original speakers on many cars are single-unit speakers, which have a simple structure and can only express the mid-frequency range. It is mainly manifested in that the treble is not bright, the bass is not thick, and the effect is not good enough.

3. According to the driving method

It only adds electrical signals to the vibrating plate to transform it into mechanical force and then generate vibration.

(1) Electromagnetic type: The vibrating part magnetized by the sound source signal and the magnetism of the magnet attract and repel each other to generate a driving force. Under the action of this force, the vibrating plate vibrates and emits sound.

(2) Electrostatic type: Match the conductive diaphragm and the fixed electrode according to the reverse polarity to form a capacitor. At the same time, we add an electrical signal to the two poles of the capacitor, and the change of the electric field between the poles produces an attractive force, which makes the diaphragm vibrate and produce sound.

(3) Piezoelectric type: We put piezoelectric components in an electric field, and displacement (deformation) occurs. A speaker made of this principle is called a piezoelectric speaker.

(4) Electric type: The signal of the sound source is generated by the magnetic field generated by the current flowing through the voice coil, which interacts with the magnetic field of the magnet to form an electromagnetic force. The diaphragm vibrates under this force to produce sound.

4. According to the shape of the diaphragm

(1) Flat diaphragm speaker

The radiating surface of the flat diaphragm speaker is concave, so in practical applications, there will be a phenomenon of frequency characteristic fluctuation attenuation. This phenomenon is called "front cavity effect", which greatly reduces the piston movement range of the speaker. To overcome this shortcoming, we can use the diaphragm as a flat plate shape. In order to further provide the range of motion of the piston, we have to choose its structure and shape and the materials used.

(2) Ribbon-shaped speaker

The diaphragm of this loudspeaker is made of very light aluminum foil strips in the shape of short strips. The diaphragm itself is a conductive material. We put it in a magnetic field, and it can vibrate and sound if it is passed a signal current. The diaphragm of this structure has very small impedance. When connecting with amplifiers and frequency division networks, matching transformers must be used.

(3) Cone speaker

Cone speakers are one of the most widely used speakers today. Cone speakers are divided into circular speakers and oval speakers according to the shape of the cone. Oval speakers are mainly designed and manufactured for the needs of installation space such as TVs and radios. Due to its structural limitations, it is rarely used in high-fidelity audio. The nominal size of the cone speaker is expressed according to its largest diameter, while the oval speaker is expressed by its major and minor axes. Conical speakers can be divided into four types according to different frequency ranges: low-frequency speakers, mid-frequency speakers, high-frequency speakers, and full-range speakers. According to the difference of quasi-cone materials, cone speakers can be divided into paper cone speakers, wool cone speakers, polypropylene speakers, metal cone speakers, composite cone speakers and so on. Among high-fidelity speakers, polypropylene speakers (we usually call it PP pots) are the most widely used. Because the cone of the polypropylene speaker is used, it is easy to process, the price of raw materials is low, the consistency is good, and the sound is not bad. It can be processed into various cone shapes according to preferences. It can be seen from the above points that the cone speaker is widely used in high-fidelity audio systems due to its simple structure and low price.

Cone speakers are direct radiating speakers and consist of 11 segments. Because the effective vibration area of the cone speaker can be made larger and the amplitude is larger, it still dominates many speakers with good low-frequency response under the condition that various new speakers continue to emerge today.

(4) Sheet speaker

The diaphragm of this speaker is made of high temperature resistant molecular film. The voice coil is installed or printed on the polymer diaphragm. If the polymer diaphragm printed with a voice coil is placed in a magnetic field formed by a magnet with a special shape, it can be made into a sheet-shaped speaker.

The voice coil wire resistance of this speaker can be designed to several ohms, and no matching transformer is needed. In addition, it also has the advantage of large input capacity. In terms of sound quality, it is the same as a ribbon speaker, with a sense of natural sound without distortion extending to the ultra-high frequency range.

(5) Dome-shaped speaker

A dome speaker has a spherical diaphragm. From the driving method, it belongs to the dynamic speaker. Compared with cone speakers, dome speakers are slightly less efficient, but the lack of directivity is just one of its advantages. The materials used range from soft materials to hard materials. However, according to the soft and hard texture of the vibrating plate material, there are soft ball tops and hard ball tops.

It is one of the most widely used dynamic speakers in the cabinet. Its biggest advantage is its excellent medium and high frequency response and wide directivity. In addition, it also has the advantages of good transient characteristics, small distortion and good sound quality. The dome-shaped speaker is suitable for all home theater series speakers currently on the market.

(6) Horn speaker

The horn speaker is composed of two parts: the drive unit (sound head) and the horn. The drive unit of the horn speaker is similar to the structure of the electric cone speaker, but it usually does not use a paper cone but a rigid dome-shaped diaphragm.

The reason why the efficiency of the paper cone speaker is not high is that the radiated energy of the paper cone propagates along a spherical surface that increases in proportion to the square of the distance from the radiated sound source, and the sound pressure amplitude decreases rapidly as it moves away from the sound source. To improve the radiation efficiency of loudspeakers, we must delay the phenomenon of rapid sound attenuation. The radiator of the horn speaker vibrates in a horn whose cross-sectional area gradually increases, and expands slowly near the beginning of the horn, and the sound is reflected in the horn, mixing the original sound with the echo, and strengthening the original sound . And the opening at the end of the horn is sufficiently large to avoid reflection of sound waves back into the horn, resulting in loss of sound energy.

The sound efficiency of the horn speaker can reach about 10% to 40%, the working frequency is narrow, and the frequency distortion at the low frequency end is large. The horn loudspeaker has poor high-frequency response, and it has a shell suitable for outdoor installation, which is suitable for language sound reinforcement and outdoor sound reinforcement with low requirements. The high-frequency response of the tweeter is good, but it is not suitable for low-frequency sounds below 800Hz. When a low-frequency signal is input, it will damage the speaker due to excessive amplitude. Therefore, the high-frequency speaker cannot be used alone, and must be used in conjunction with the low-frequency speaker through a frequency divider.

5. According to the principle of sound

(1) Piezoelectric speaker

Speakers that use the inverse piezoelectric effect of piezoelectric materials are called piezoelectric speakers. The dielectric (such as quartz, potassium sodium tartrate and other crystals) is polarized under pressure, so that a potential difference appears between the two ends of the surface, which we call "piezoelectric effect". Its inverse effect, that is, the dielectric medium placed in the electric field will undergo elastic deformation, which is called "inverse piezoelectric effect" or "electrostriction".

Piezoelectric speakers do not require a magnetic circuit compared to dynamic speakers, and do not require bias voltages compared to electrostatic speakers. The structure is simple and cheap, but the disadvantages are large distortion and unstable operation. Currently on the market, piezoelectric speakers are mostly piezoelectric ceramic speakers.

(2) Ultrasonic speaker

Ultrasonic speaker is an ultrasonic sound reproduction technology that has just been successfully developed in recent years and is entering the practical stage. The principle of this ultrasonic sound reproduction technology: it does not use any traditional speaker unit, but uses an ultrasonic generator to generate two specially processed ultrasonic beams. When these two beams act on the tympanic membrane of the human ear at the same time, hearing can be produced due to the interaction.

Usually, when only one beam hits the eardrum, we don't hear anything. Due to the strong and controllable directivity of the supersonic wave, the intersection of the two beams can form a small sound reproduction area. When the human ear is in this area, the sound can be heard, but once the human ear leaves the area, it cannot be heard.

Taking advantage of this feature, some top luxury cars are now equipped with multiple sets of this ultrasonic sound reproduction system, forming a listening area on each seat. In this way, each passenger can choose the content he or she likes without interfering with each other or affecting the conversation between passengers.

(3) Ion speaker

In a normal state, the molecules of air are neutral and uncharged. However, after high-voltage discharge, it becomes charged particles. This phenomenon is called ionization. Vibrating the ionized air with an audio voltage generates sound waves, which is the principle of an ion speaker.

In order to ionize, we need to add a 20MHz high-frequency voltage, and superimpose the audio signal voltage on it. The ion speaker is composed of a high-frequency oscillation part, an audio signal modulation part, a discharge cavity and a horn. The discharge chamber adopts a quartz rod with a diameter of 8 mm to open a hole in the center to form a quartz tube, insert one electrode into it, and the other electrode is sleeved outside the quartz tube in a cylindrical shape. Due to the silent discharge form, only the needle electrode in the center wears out, and we can replace the center electrode regularly. The ion speaker is different from other speakers in that there is no diaphragm, so the transient characteristics and high-frequency characteristics are very good, but the structure is very complicated.

(4) Capacitive speaker

An electrostatic speaker is a speaker that works by using the electrostatic force applied to the plates of a capacitor. In terms of its structure, because the positive and negative poles face each other to form a capacitor shape, it is also called a capacitor speaker. It has two thick and hard materials as fixed plates, which can transmit sound on the plates, and the middle plate uses thin and light materials as diaphragms (such as aluminum films). We fix and tighten around the diaphragm and keep a considerable distance from the fixed pole. Even on a large diaphragm, it will not collide with the fixed pole.

There is a DC voltage (called bias voltage) between the two electrodes of the electrostatic speaker. If the audio voltage output by the amplifier is added between the two electrodes, it will overlap with the original output voltage to form an alternating pulsating voltage. This pulsating voltage is generated by the change in the strength of the attractive force between the two poles, and the diaphragm vibrates to produce sound.

The advantage of the electrostatic speaker is that the entire diaphragm vibrates in phase, the diaphragm is light, the distortion is small, and it can reproduce extremely crisp sound, with good resolution, clear details, and realistic sound. Its disadvantages are low efficiency, high-voltage DC power supply, easy to vacuum, and distortion will increase when the diaphragm is enlarged. It is not suitable for listening to rock and heavy metal music, and the price is relatively expensive.

(5) Magnetic speaker

Magnetic speakers are also known as "reed speakers". In the magnetic loudspeaker structure, there is an electromagnet with a movable iron core between the poles of the permanent magnet. When there is no current in the coil of the electromagnet, the movable iron core is attracted by the phase-level attraction of the two magnetic poles of the permanent magnet, and remains stationary in the center. When current flows through the coil, the movable iron core is magnetized and becomes a bar magnet.

As the direction of the current changes, the polarity of the bar magnet also changes accordingly, making the movable iron core rotate around the fulcrum. The vibration of the movable iron core is transmitted to the diaphragm by the cantilever to push the air to vibrate thermally.

Ⅱ. The difference between speakers and home appliance speakers

The environment in which speakers are located is different from that of home audio, which is manifested in the following aspects:

1. Dust: Home appliance speakers are used in rooms with less dust, but there is a lot of dust in the car, so a dust cover is required to prevent noise from friction of the voice coil.

2. Vibration: The car speaker is subject to the vibration and impact of the car movement anytime and anywhere, so the design should be firm and not loose.

3. Temperature: The temperature difference in the car is much larger than that in the room, especially in summer, so the speaker needs to be resistant to high temperature and aging.

4. Noise: The vibration sound, brake sound and engine sound when the car is running will have a negative impact on the listening effect of the audio system, thereby deteriorating the sound quality effect. This requires the sound reproduction performance of the speaker to be better.

5. Humidity: Cars will be threatened by moisture when it rains or walks on watery roads. Therefore, car speakers must be moisture-proof. Nowadays, cones made of chemically synthesized materials are mostly used.

Ⅲ. The use of speakers

We need to choose the speaker according to the field inversion used and the sound requirements, combined with the characteristics of the speaker. For example, for outdoor voice-based broadcasting, we can choose electric tube speakers. If higher sound quality is required, we should use electric speaker boxes or sound columns. For indoor general broadcasting, a small speaker box made of a single electric cone speaker can be selected. But for listening to music or for high-quality loudspeaker amplification, we should choose a speaker box with a combination of tweeters and woofers.

Pay attention to the following points when using speakers:

1. Note that the impedance of the speaker should match the output line.

2. Electric horn speakers must be used after the sound head is set on the horn, otherwise the sound head will be easily damaged.

3. The power received by the speaker should not exceed its rated power. Otherwise, it will burn the voice coil, or vibrate the voice coil apart. The operating voltage of electromagnetic and piezoelectric ceramic speakers should not exceed 30V.

4. Select the model of the speaker correctly. If it is used in a square, we should choose tweeters. For indoor use, we should choose paper cone speakers and choose a good auxiliary speaker. We can also make the tweeter and woofer into a successful speaker group to expand the frequency response range.

5. When setting up the speakers, the speakers should be even and have a sufficient volume level. If a single speaker is not enough, we can use multiple speakers, so that everyone can hear about the same volume, thereby increasing the clarity of the sound. Also the speaker should have a good sense of direction. The speaker should be more than three meters above the ground so that the listener can "see" it. And in the horizontal direction, the sound source and the speaker are as consistent as possible. The distance between the two speakers should not be too far.

6. When two people use the speakers together, they must pay attention to the phase problem. If it is out of phase, the sound will be significantly weakened. The easiest way to measure the phase of the speaker is to use the high-sensitivity meter or the 50~250μA current block of the multimeter, connect the test meter to the speaker terminal, hold the paper cone with both hands, and push it hard. At this time, their phase can be determined from the swing direction of the hands. If the phases are the same, the hands will swing in one direction. At this time, the lead-out head of the voice coil connected to the positive meter pen can be regarded as the "ten" level.

Ⅳ. The detection of the speaker

1. Judgment of polarity

The speakers must be connected with the correct polarity, otherwise the sound quality will be affected due to phase distortion. Most of the speakers mark the positive and negative polarities of the two lead wires with the symbols "+" and "−" on the wiring bracket on the back, while some speakers do not. For this we need to discriminate the polarity of such speakers. The discrimination methods we adopt mainly include battery detection method and multimeter detection method.

2. Estimation of impedance

There is usually a nameplate printed or affixed directly on the back of the speaker core, and the nameplate is usually marked with the impedance. If the nameplate falls off and its impedance cannot be identified, we need to use a multimeter to identify it. We put the multimeter in the "R × 1" block. After zeroing, we measure the resistance of the coil, the resistance is 6.1Ω, and the value obtained by multiplying this value by 1.3 is 7.93Ω, indicating that the impedance of the speaker under test is 8Ω.

3. Judgment of good or bad

We put the multimeter in the "R × 1" block, connect one terminal of the voice coil (coil) with a red test lead, and click on the other terminal with a black test lead. If the speaker can make a "click" sound, it means that the speaker is normal; otherwise, it means that the voice coil or lead wire of the speaker is open.

Methods and skills: If you don't have a multimeter at hand, you can also use a No. 5 battery and a wire to judge whether the voice coil of the speaker is normal. The method is to connect the negative pole of the battery to one terminal of the voice coil, connect the positive pole of the battery to one end of the wire, and use the other end of the wire to click on the other terminal of the voice coil, and the speaker can make a "click" sound under normal conditions.

Ⅴ. Methods of purchasing speakers

1. When purchasing a speaker, we must first check whether the nominal impedance and rated power marked on the trademark of the loudspeaker itself are what you need. Then conduct appearance identification to observe whether the speaker leads are intact, whether the paper cone is damaged or broken, whether the basin frame is glued firmly, etc.

2. When checking the speaker, we can gently press down on the paper cone evenly with both hands, and listen carefully for the rubbing sound of the voice coil and the iron core. When we press the paper cone, don't use too much force to avoid damaging the paper cone.

3. When the above content inspection meets the requirements, we can conduct an audition inspection. We connect the speaker to the power amplifier circuit whose impedance and power meet the requirements, and listen to the sound from the speaker for hoarseness, harshness and other undesired sounds. The sound from a good speaker should be layered, full, harmonious, clear, pleasant, and comfortable. When we audition and check, it is best to choose music that we are familiar with.