In principle, subwoofers and speakers work exactly the same way, except that the diameter of the diaphragm is larger, usually 8 to 10 inches, and a speaker for vibration is added. .
In terms of evaluation indicators, the subwoofer is basically the same as the speaker. The specific content will not be introduced in detail here. I will only talk about the numerical requirements. The frequency response is generally below 200 Hz, and the rated impedance is also about 4Ω. , the sensitivity is generally greater than 90 dB/W/m.
At present, subwoofers can be roughly divided into two categories: active subwoofers and passive subwoofers. An active subwoofer refers to a subwoofer that has a built-in power amplifier. It does not require an additional power amplifier when used. It is usually a cylindrical shape. The shortcomings of this kind of subwoofer are that the heat dissipation is not ideal and the power is not very high. The barrel shape usually produces unnecessary vibration, which reduces the controllability of the subwoofer. In contrast, passive subwoofers require an external amplifier to work. The shape and power selection of this kind of subwoofer can be more flexible, and the effect will naturally be more ideal. In addition, active speakers can be further divided into sealed boxes and perforated boxes. The former is more suitable for deep symphony music, and the latter is more suitable for pop music.
"SubWoofer" is usually called "subwoofer" in commercial or civilian applications. In fact, the adjective "super" is incorrect. The frequency band it plays back is usually from the upper limit of 150Hz or 100Hz to The lowest is around 25Hz, which is just bass and not sub-bass. Because frequencies below 20Hz are bass that exceed the musical range of the human ear, from a scientific or professional interpretation point of view, only frequencies below 20Hz can be called "super" bass. But generally speaking, the subwoofer refers to the bass whose playback frequency is lower than 20Hz. Whether it is replaying dynamic music or movie sound effects, subwoofers are even more important than traditional floor-standing stereo speakers. This is because the special sound effects included in many pieces of music (symphonies or harp and drum music) and many movies are extremely majestic and dynamic bass. This sound effect is not just meant to be "heard" by the listener, but It is even more important to let them "feel" the atmosphere of this situation.
However, friends who play Hi-Fi have many different reactions to subwoofers. Some people feel that it is difficult to control; some people think that these are for audiophiles who are particularly experienced in playing Hi-Fi. Toy; some people think that this is a device used to solve the shortcomings of small bookshelf boxes, and you don't need to pay too much attention to its placement when adding it to the entire system; some people think that playing with this kind of equipment is thankless and the success rate is too low; and some people think that playing with this device is thankless and the success rate is too low; I feel that an ideal system does not require the addition of a Subwoofer; some people even think that the 3ubwoofer is only suitable for use in very large rooms... Although there are different opinions, the subwoofer is the least talked about and least understood item among audiophiles. Very important equipment. Through this article, I believe it can change some audiophiles’ views on subwoofer equipment. At the same time, I hope to gain some debate and jointly improve the level of fever.
1. Types of subwoofers
Subwoofers are mainly divided into two categories, they are passive (PASSIVE) and active (ACTIVE). There are currently many three-piece "3D" satellite systems (Subwoofer/Satellite System) with subwoofers and two small main speakers on the market. In this system, only one subwoofer is used, so the subwoofer is mono. Channel (L R) signal has a stereo effect only above the dividing point. This kind of system uses the volume control knob of the front stage to determine the volume of all speakers. If the sensitivity or volume of the subwoofer is not equal to that of the main speakers, it will cause confusion in the sound field, uneven frequency response, and inability to localize the sound image. , and at this time, when the placement of the subwoofer cannot solve this problem, these problems will be difficult to improve. This kind of Subwoofer usually only appears in low-level low-Fi systems.
There is also a passive subwoofer. The left and right main speakers are full-range, and the subwoofer only sounds when the bass below its upper frequency cutoff point appears. This kind of system is called a connected subwoofer system. For example, the playback frequency of the main speaker is attenuated below 65Hz, and the subwoofer's dividing point is around 65Hz. Its purpose is to connect the main speaker smoothly. The problem with this system is that although the main speaker attenuates below 65Hz, it does not mean that its low frequency begins to decrease below 65Hz. The degree of these decreases depends on the design requirements of each speaker, so Replaying with a subwoofer at 65Hz will still conflict with the main speaker. The important reason is that the subwoofer unit and the main speaker unit are different products. When two different speaker units receive signals, For example, the vibration quality of the large-diameter subwoofer unit is definitely greater than the speaker unit of the main speaker, so the sound speed must be slower, and they will definitely not sound at the same time.
So many audiophiles who play this kind of subwoofer feel that after adding a subwoofer, the effect is messier than without it. Designers of this kind of subwoofer usually try to calibrate the subwoofer's partial point to the lowest possible level to avoid conflict with the main speakers. The subwoofer crossover point of this system should only be designed for a certain pair of main speakers. When the left and right main speakers are replaced, the subwoofer crossover point must be recalibrated. Although some main speakers attenuate below 65Hz, there is still sound at 20Hz. When these speakers are coupled with a docking subwoofer, the effect may be worse. The bass is not strong enough and has no texture, and you may also feel that the bass is low. Very messy. Manufacturers that produce this type of subwoofer usually design the main speakers together. Otherwise, there will be problems with the attenuation (dB/octave) at the crossover points and their frequency cutoff points, which are also the stuff of low-price systems.
In the active ACTIVE (dual amplifier) ??subwoofer system, the signal goes directly into the preamp with active crossover. Frequencies below 100Hz are amplified by the bass amplifier and sent to the subwoofer speaker for broadcast. Frequencies above 100Hz are sent to the rear stage of the main speaker after frequency division, and are amplified and played out by the main speaker. At this time, there must be a volume control to control the ratio of the subwoofer volume to the volume of the main speakers. In addition, there must be a phase adjustment knob that can adjust the phase of the bass amplifier from 0-180. school. Because the power amplifier of the subwoofer amplifier and the main speaker may be of different designs, they are not in the same phase in most cases. The listening effects of different phases will make the listener feel different. This phase adjustment knob is used To achieve the same phase effect as the subwoofer and the main speakers. When adjusting from different phases to the same phase, the volume will feel louder and the bass will be more solid (rich). When the phase is reversed to 180 degrees, the sound effect will be slightly slower.
To use the subwoofer correctly, the author believes that the subwoofer system must have the following five properties: 1. The subwoofer must have its own power amplifier; 2. There must be independent volume control; 3. There must be phase control; 4. The subwoofer must be placed in an independent position; 5. The main speakers must work above the crossover frequency of the subwoofer (for example, above 100Hz or 120Hz).
2. Reasons to use subwoofer Why use subwoofer?
Most readers who play subwoofer think that subwoofer is used because the bass of small speakers is not enough. As for the large speaker floor-standing box, there is no need to use a subwoofer. In fact, playing with a subwoofer is not as simple as using it to assist the bass. There are only a handful of traditional speakers on the market that can faithfully reproduce the bass sound found in movie sounds, and most even mid- to high-priced AV surround amplifiers do not have enough power to drive subwoofers. If active subwoofers are used, the above two problems can be easily solved.
The so-called "active active" means that the subwoofer itself has a specially designed power amplifier, so the signal source it requires only comes from the general level of the AV surround amplifier. Signal. Active active subwoofers are easy to match with other audio equipment. No matter what the sensitivity or low-frequency response of the speakers they are paired with is designed, it can handle it by adjusting itself. In addition, no matter whether it is facing the sound field from the front or facing away from the sound field, there is no need to move its position, just adjust the phase. The subwoofers discussed below are all active subwoofer systems.
The advantages are:
1. The main speakers do not need to work below 100Hz. Therefore, the distortion of this speaker above 100Hz will be reduced. Usually the distortion played back by the speaker is due to the frequency distortion above 100Hz due to the need to reproduce the bass. If there is no need to push signals below 100Hz, this unit's ability to reproduce sounds above 100Hz will be enhanced and the distortion will be lower.
2． Because the subwoofer has its own power amplifier, the power amplifiers of the left and right main speakers do not need to push frequencies below 100Hz, but only need to work above 100Hz. Just because there is no need to push these basses, the "power" of this amplifier above 100Hz will be two to four times greater than before. At this point, a little more explanation is needed in this context. If the power of the power amplifier is 50W, that is to say, when the amplifier operates within the operating range of 20-20000Hz, its driving power is 50W (the manufacturer will never say in advertisements that if their power amplifier is There are sayings such as 200w when working above 70Hz), and when we talk about the power output capability of a power amplifier, it only means that when the amplifier works between 20 and 20000Hz, it can have an output of 50w and so on. But when a 50W power amplifier only works above 100Hz, its power (above 100Hz) is the same sound level capability as a 100W to 200w amplifier that reproduces frequencies of 20-20000Hz! But if this originally It is 50W. Now, if the amplifier that has been upgraded to 100-200W due to reproducing frequencies above 100Hz operates in the full frequency band, its power will return to its original form and become the original 50W. When working above 100Hz, it will become double or quadruple, depending on the frequency of the replayed music. If most of the music is high-pitched, it will be four times; if most of the music is mid-bass, it will be double. . The power amplifier has not changed, but when it works within different frequencies, its driving capabilities will be different, because the energy in the entire frequency band is mostly concentrated in the mid-low frequency and low frequency bands. If a power amplifier only works below 10000Hz, its "power" will not change much. It will only affect its "power" when there is no need to push the bass;
3. Because The subwoofer can be separated from the main speakers and placed elsewhere. The bass we hear in the room is mainly due to the response of these bass in the room, so the placement of the subwoofer in the room has a great impact on the bass effect. Some speaker designers place the left and right main speakers on top of the subwoofer. This design does not take into account the advantages of separate subwoofer and main speakers. Some people may think that one-piece speakers look better, but if they are one-piece speakers, why bother with a subwoofer? In terms of speaker placement, most of the positions that are suitable for high-midrange speakers will not be suitable for bass speakers. The subwoofer should usually be placed behind the left and right main speakers. Because the subwoofer can be separated, the sound field and positioning created by this playback system are incomparable to a pair of left and right main speakers (no matter what level your speakers are). Many people feel that the bass is not enough when playing with large floor-standing speakers. They feel that there is no bass or that the bass is too heavy and muddy. The subwoofer system discussed in this article has an independent bass adjustment, which can be used to adjust the volume ratio between the bass and the main speakers. , In addition, it can have an independent position, so this subwoofer will never have the problem of too heavy or insufficient bass.
The above are the three major advantages of using subwoofer speakers.