Questions and Answers on the Basic Knowledge of Speaker Purchase

What parts of the speaker?

The speakers on the market come in all shapes and colors, but no matter which one, they are composed of the two most basic parts of the speaker unit (the term is called the speaker unit) and the cabinet. In addition, most speakers use at least two or more The speaker unit implements the so-called multi-channel crossover playback, so the crossover is also an indispensable part. Of course, there may be other components in the speaker, such as sound-absorbing cotton, inverted tube, folded "labyrinth pipe", ribs/reinforced partitions, but these components are not indispensable to any speaker, the most basic composition of the speaker The element has only three parts: speaker unit, cabinet and crossover.

●Why do some speakers use two speaker units, while others use three, and some speakers use four or five speakers. Is it okay to use one?

The speaker unit plays the role of electric-acoustic energy conversion and converts the electric signal sent by the power amplifier into sound output. It is the most critical part of the speaker. The performance index and sound quality of the speaker greatly depend on the performance of the speaker unit. , The prerequisite for making a good speaker is to select a speaker unit with excellent performance. The performance requirements of the speaker unit can be summarized as high load power, low distortion, wide frequency response, good transient response, and high sensitivity. However, it must take into account distortion at the same time in the wide frequency range of 20Hz-20kHz. Performances such as, transient, and power are very difficult. Just like road police, if the tube is too wide, it will definitely lose sight of the other. It is much easier to manage one section of each section. The speaker unit is the same reason. The most effective solution is sub-band playback. For this reason, the speaker factory has produced different types of units. Some are only responsible for playing bass, called woofers, those that play midrange are called midrange units, and tweeters are only responsible for playing treble. The performance of this unit is relatively good.

Therefore, although a full-band speaker can be used to design the speaker, for the above considerations, the design method of using a combination of multiple units to cover the entire audio frequency band still accounts for the vast majority. The specific number of units used depends on the frequency division method of the audio range. If it is a two-way speaker that is simply divided into two sections of treble and bass (or mid-low), choose one high and one low (or mid-low) two speakers. Enough; if it is a three-way speaker with three sections of high, medium and low, then at least three units must be used. Now the design of two woofers working in parallel is also very popular, so the total number of units may reach Four; the frequency bands of some large speakers are more finely divided, and if the design of units working in parallel is adopted, the total number of speaker units will be more. There are usually words like "X-way X-unit" in the information or manual of the speaker, which is a specific description of the number of frequency divisions of the speaker and the total number of units used. For example, "three-way four-unit" indicates that this is a three-way design. For the speakers, a total of four speaker units are used, and the rest can be deduced by analogy.

●What is the purpose of the frequency divider?

Since almost all current speakers adopt the design method of multi-unit sub-band playback, there must be a device that can divide the full-band music signal sent by the amplifier into treble, bass output or treble, midrange, and bass output as needed. In order to connect with the corresponding speaker unit, the crossover is such a device. If the full-band signal is directly sent to the high, medium, and woofer unit without distribution, the part of the "excess signal" outside the frequency response range of the unit will have an adverse effect on the signal restoration in the normal frequency band, and may even cause The tweeter and midrange unit are damaged.

From the perspective of the circuit structure, the frequency divider is essentially an LC filter network composed of capacitors and inductors. The treble channel is a high-pass filter, which only allows high-frequency signals to pass through and blocks low-frequency signals; the bass channel is just the opposite, it only lets Bass passes through and blocks high-frequency signals; the midrange channel is a band-pass filter, except for the frequency between the two crossover points, one low and one high, which can pass, high-frequency components and low-frequency components will be blocked. In the actual frequency divider, sometimes in order to balance the sensitivity difference between the high and woofer units, an attenuation resistor is also added; in addition, some frequency dividers also add an impedance compensation network composed of resistors and capacitors, the purpose of which is Make the impedance curve of the speaker as flat as possible to facilitate the power amplifier drive.

●What types of speaker units are there?

There are many types of speaker units, and their classification methods are also different. If divided according to the principle of electro-acoustic conversion, there are different types of units such as electromagnetic, electric, electrostatic, piezoelectric, etc. The most commonly used is the electric unit; according to the shape of the unit diaphragm, there is a cone Unit, flat unit, dome unit, belt unit and other types, of which cone unit and flat unit are more suitable for bass and midrange, while dome unit and belt unit are more suitable for tweeter, and some midrange units use ball Top-style design; from the frequency band covered, the speaker unit can be divided into woofer, midrange, tweeter and full-band unit.

At present, the most common bass unit and midrange unit are electrodynamic speakers in terms of the principle of energy conversion. They mostly use cone-shaped diaphragms because the diaphragms of this shape are mature in design and perform well. Diaphragm materials are diverse, including traditional paper diaphragms, diaphragms made of polymer synthetic materials (such as polypropylene), and diaphragms made of metal materials such as aluminum and magnesium. The requirements for the diaphragm are good rigidity (not easy to produce split vibration), light weight (good transient response), and proper internal damping characteristics (resonance suppression), but these requirements are not easy to meet at the same time. The weight of the paper diaphragm And damping characteristics can meet the requirements, but the rigidity is not strong enough; the rigidity of the metal diaphragm is very good, but the damping is not good; the polypropylene diaphragm has a good balance of all aspects, and has obtained more applications in recent years. In addition, some manufacturers use very complex processes to manufacture the diaphragm. The "sandwich" composite structure is one of them. The middle layer of the honeycomb structure is sandwiched between its upper and lower surfaces, which has high rigidity as a whole and at the same time. It has the characteristics of light weight and good damping, which is very promising.

The most commonly used tweeter is the dome tweeter, which is also an electric unit in terms of working principle. The diaphragm of the dome tweeter can be made of metal materials (such as aluminum, titanium, beryllium, etc.), called hard dome, or made of soft fabric (such as silk, chemical fiber), called soft dome, usually hard ball The high-frequency response of the dome is better, and the sound of the soft dome is softer. In recent years, ribbon tweeter and electrostatic tweeter have also been used to some extent. Their common advantage is that the diaphragm is particularly light, so the high frequency response is excellent, and the sound is slim and transparent. However, the production of these two tweeters is not as easy as the dome tweeter. , The application is not very popular. There is also a kind of horn tweeter, which is composed of a dome-type driving part and a horn-shaped horn. It is characterized by strong sound directivity and high efficiency, so it is widely used in speakers in the professional amplifying field.

There is also a coaxial unit, which is actually a combination of bass and tweeter. For specific features, please refer to the relevant Q&A.

●Why should the speaker unit be packed in a box? Is it okay to not pack them, such as using a bracket to fix them?

No, to be precise, the woofer must be boxed, and the treble can be installed or not. There are two reasons why the bass unit must be installed in the box: one is to eliminate the "acoustic short circuit" phenomenon; the other is to suppress the low-frequency resonance peak of the speaker unit. Let me talk about the first reason. When the diaphragm of the woofer moves back and forth, in addition to the sound waves radiating forward, there are also sound waves radiating backward. The phase of the sound radiation in the two directions is exactly opposite, that is, the phase difference is 180 degrees. Due to the long wavelength of the low-frequency sound wave, its diffraction ability is very strong, that is to say, the directionality of the low-frequency sound wave is very weak. If the speaker unit is not packed, the sound wave radiated in the backward direction will circle to the front to meet the front. The radiation out-of-phase cancels out, and the overall forward acoustic radiation energy is greatly weakened. This phenomenon is called "acoustic short circuit". The phenomenon of "acoustic short circuit" must be eliminated, otherwise the low frequency cannot be radiated effectively. If the speaker unit is installed in a box, the radiation behind the diaphragm will be blocked by the box, and there will be no "acoustic short circuit".

The second reason is that every electric low-frequency unit has a low-frequency resonance point, at which the output reaches a peak, but the distortion is also very high, and the transient response is very poor. If this resonance peak is not suppressed , It is bound to seriously affect the sound quality of playback. If the unit is packed in a box, the stiffness of the air in the box will inhibit the movement of the diaphragm, thus achieving the purpose of suppressing the resonance peak and improving performance. In addition, by reasonably selecting the structure and parameters of the cabinet, the purpose of widening the low-frequency response can be achieved. Well-designed inverter cabinets, passive radiator speakers, and transmission line speakers can all achieve this effect.

Why can the tweeter not be packed in the box? Because the tweeter has a short wavelength and weak diffraction ability, there is no "acoustic short circuit" phenomenon, and there is no need to suppress low-frequency resonance peaks like a woofer. Therefore, for the tweeter, the role of the speaker is only a support.

●What materials are generally used for the box body?

The box body is generally made of wood materials, because wood is easy to process, and after surface treatment, it can get the same texture as furniture, and it is easy to harmonize with the living environment. At present, the most commonly used material is man-made medium density fiber (MDF) board. This material has high strength, is not easy to deform, does not crack, and the surface is very flat. It can be directly pasted with veneer or PVC decoration without sanding. Some speakers also use particleboard to make the cabinet. The particleboard has the characteristics of not easy to deform and crack, and the surface is flat. The strength is also good, but it is easy to damage when it gets wet, so it is usually only used for cheap low-end speakers. There are also cabinets made of natural solid wood panels, but natural solid wood costs are relatively high, and improper handling is prone to cracking and deformation, so in recent years, the application has become less and less, and it is generally only used for high-end speakers, mainly because the texture of solid wood is relatively high ( Especially precious wood) this advantage. Of course, the cabinet does not have to be made of wood, plastic, metal or even slate can be used, but speakers made of these materials are not common.

●Is the sound of solid wood speakers better than wood-based speakers?

Can't say that. In theory, as long as the box is strong enough to not vibrate, it makes no difference what material is used. The sound of the speaker is mainly determined by the three elements of the speaker unit, the cabinet structure design, and the frequency divider, and it has nothing to do with whether the cabinet material is made of solid wood or wood-based panels, or even plastic or metal.

●How are speakers classified?

The classification of speakers has different angles and standards. According to the acoustic structure of the speakers, there are airtight boxes, inverted boxes (also called low frequency reflection boxes), passive radiator speakers, and transmission line speakers. See their respective characteristics in detail. Related questions and answers. The inverter box is the mainstream in the current market; from the perspective of the size and placement of the speakers, there are floor-standing boxes and bookshelf boxes. The former is relatively large and is generally placed directly on the ground. Sometimes, shock-absorbing feet are also installed under the speakers. nail. Due to the large volume of the cabinet and the convenience of using larger and more woofers, the floor-to-ceiling box usually has better low frequency, higher output sound pressure level and strong power carrying capacity, so it is suitable for larger listening areas or more comprehensive requirements For occasions. The bookshelf box is small in size and usually placed on a tripod. It is characterized by flexible placement and does not occupy space. However, due to the volume of the box and the limitation of the size and number of the bass unit, its low frequency is usually lower than that of the floor box, carrying power and output sound pressure The level is also smaller, suitable for use in a smaller listening environment; according to the narrow bandwidth of the playback, there are wideband speakers and narrowband speakers. Most speakers are designed to cover the widest possible frequency band. , Belongs to broadband speakers. The most common type of narrow-band speakers is the subwoofer (subwoofer) that emerged with the home theater, which is only used to restore the ultra-low frequency to a very narrow frequency band; according to whether there is a built-in power amplifier, it can be divided into passive speakers and Active speakers, the former does not have a built-in amplifier and the latter has. At present, most home speakers are passive, but subwoofers are usually active.

●What are the characteristics of a closed box?

The horn unit of the airtight sound box is installed in a completely airtight box. In this way, the reverse phase sound wave radiated by the diaphragm is completely blocked by the box, and it will not go outside the box and cancel out the positive phase sound wave in front of the diaphragm. Solve the "acoustic short circuit" problem, so that the bass can be effectively radiated. The low-frequency attenuation characteristics of a closed box are gentler than those of other types of speakers, and are similar to the attenuation curve of a second-order low-pass filter, which means that it has the best transient response among all types of speakers. At the same time, the air enclosed in the box forms a strong "air spring", which can effectively restrain the displacement of the diaphragm at the resonance frequency and reduce nonlinear distortion. However, the stiffness of the air also increases the low-frequency resonant frequency of the speaker unit, which increases the overall low-frequency limit of the speaker unit under free space conditions. Compared with the design of the inverter box and transmission line speaker, the low-frequency of the closed box The lower limit is relatively worse. In addition, the rearward radiation of the diaphragm is not used, resulting in a lower efficiency.

●Are air-cushioned speakers and airtight speakers the same thing?

The air-cushion speaker was first proposed by H. Olson and his partner J. Preston in the United States and was patented. It was promoted by AR in the 1950s. The representative product was the well-known AR-3 at the time (the Hong Kong and Taiwan enthusiasts called it " Brother A"). Air-cushioned speakers are a kind of airtight box. It is characterized by the use of high-compliance speaker units and the design of the box body small enough so that the stiffness of the air in the box is much higher than the stiffness of the unit vibration system (generally more than 3 For the vibration system of the unit, the air in the box acts like an elastic and strong air cushion, and this kind of speaker is named after it. Air cushion speakers have low distortion and very good transient performance. They were once popular. However, due to the use of high-compliance units, the sensitivity of such speakers is generally low.
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