Development of subwoofer
“SubWoofer†has always been called “subwoofer†in commercial or civilian use. In fact, the adjective “super†is not very accurate. The frequency band of its playback is usually from the upper limit of 150Hz or 100Hz to the lowest of 25Hz. This is just bass instead of subwoofer. Because the frequency below 20Hz is the bass that exceeds the range of music that the human ear listens to. From a scientific or professional interpretation point of view, only frequencies below 20Hz can be called "super" bass. However, the so-called subwoofer is generally referred to as the bass with a lower repetition frequency of 20 Hz or higher. Whether it's replaying big dynamic music or movie sound, subwoofers are even more important than traditional floor-standing stereo speakers. This is because the special sound effects contained in many music (symphony or stringed drums) and many movies are extremely majestic and dynamic bass, which is not just for the listener to "listen". It is even more important for them to "feel" the atmosphere of this situation.
As early as the 1930s, the film industry was still evolving, and the subwoofer began to enter the cinema. However, at that time, the sound effects of the movie did not have independent low-frequency channels. The subwoofer was only to enhance the low-frequency performance of the two-channel system. The film really has low-frequency sound effects from the THX theater system, the first film is the 1977 "Star War." Welcome to the home theater network!
The early subwoofers were very large. If the subwoofer was to enter the home smoothly, the first condition was to reduce the volume. As a result of this progress, Servo Control played a very important role. Control technology allows smaller speakers to emit low enough low frequencies, so in the mid-1960s, home subwoofers began to enter the market, with more famous products including Infinity's Servo Static (1966), LWE (1965), PSB. Beta II (1973) and Ace Bass of The Audio Pro (1978).
Classification of Subwoofers<br> Subwoofers and regular speakers work exactly the same way, except that the diaphragm has a larger diameter and adds a box for resonance. At present, there are two types of common subwoofers: an active (ACTIVE) subwoofer with amplifier phase adjustment, which can accept direct input from the amplifier level in addition to the low frequency signal from the preamplifier. And can easily adjust the crossover point, which is currently the mainstream in the market. The other is a subwoofer that needs to be separately configured with an amplifier. It is also called a passive (PASSIVE) subwoofer. It can be combined with different styles of amplification according to the taste of the enthusiast.
In addition to these two categories, there are many two small main speakers on the market with a subwoofer system. In this system, only one subwoofer is used, so the subwoofer is a mono (L+R) signal. The stereo effect is only above the sound point. This system uses the volume control knob of the front stage to determine the volume of all the speakers. If the sensitivity or volume of the subwoofer is not equal to the main speaker, it will cause the sound field to be confused, the frequency response is not balanced, and the sound image can not be positioned. At this time, when the problem of the subwoofer cannot solve the problem, these problems are difficult to improve. This "Subwoofer" usually only appears in low-level, low-cost systems.
Subwoofers can be made in a closed or inverted form or other types, and most of them are now on the market. The ASW speakers used in foreign countries for subwoofers can easily filter out components above 200 Hz even if they do not use a frequency divider circuit. The woofer unit of this speaker is housed in a closed cabinet. The sound of the front of the horn is released in the form of a phase-inverted speaker. Since the box contains a large amount of material that absorbs high-frequency components, and the relationship between the length and wavelength of the sound path in the box, it is released from the sound hole. Only the components of the low frequency band come out. In fact, the speaker unit of the ASW speaker is not directly radiated to the surrounding like a normal speaker. It is only used to excite the air volume in the inverted speaker at the resonant frequency because The inverted speaker itself has the characteristics that it is radiated through the phase-reversed hole, and the distortion of the low-frequency component is minimized.
In 1984, BOSE designed the ACOUSTIC WAVE "Audio Waveguide" technology, a new bass playback method that produces a rich, rich bass effect from a small tube. The most straightforward example of engineering is the BOSE ACOUSTIC WAVE CANNON SYSTEM, or "AWCS". In fact, a 750px speaker is fixed in two tubes of different lengths. Its bandwidth is 25Hz-125Hz, which produces a sound level of 124dB when inputting 150W. In the 1987 Inventor of the Year Award, the "Audio Waveguide" technology caused a sensation in the scientific community, bringing the honors of Dr. AMAR and Dr. William's "Inventor of the Year Award".
The "Coronation Gun" subwoofer introduced by BOSE in the United States is another high-efficiency design. It also has the function of filtering out the medium and high frequency components. Its principle is based on the theory of sonic tube resonance. The front and back of the body are composed of acoustic tubes of different lengths. Each of the front and rear sound pipes can be regarded as a pipe that is closed at one end.
This kind of "cannon gun" subwoofer, although the effect is very good, but to send 20Hz frequency, the length of the sounding pipeline is very long, therefore, the volume is very large, more suitable for large-scale applications such as theaters. For home use, in order to reduce the size, the sound tube can be folded and fabricated like a labyrinth. Unlike the labyrinth box, the sound of the subwoofer unit is released by two folding pipes of different lengths.
About the positioning problem of the subwoofer <br> When it comes to the positioning problem of the subwoofer, we must first understand the binaural effect. When a person listens to the sound with both ears, it can improve the ability to position the sound. This listening effect is called the binaural effect. One ear can determine each property of loudness, tone, tone, and sound other than direction, but a single ear can only distinguish the direction of the sound source to a certain extent, and cannot specifically determine the direction and exact position of the sound source. When the other ear is added, since the sound waves from a certain sound source are transmitted to the two ears at different distances, the time at which the sound reaches the ears is different, resulting in a difference in time, phase, and intensity. The positioning is based on the time difference, phase difference and intensity difference between the two ears. At the same time, the ability of the human ear to distinguish the direction of the sound source varies with the frequency of the sound.
Since the distance between the two ears is about 16-450px, which is half the wavelength of the 800-1000Hz sound wave, there is no sense of direction for sounds below or equal to this frequency. It can be seen that the bass or subwoofer in the general sense has no directionality. In particular, the bass system used as a multimedia audio for computer playback can also place a subwoofer according to local conditions. It is to use the environment to accommodate it in space, and there is no big problem.
However, we should also note that the sound source has a certain radiation directivity, low-frequency sound waves, long wavelength, radiation directivity is not as obvious as high-frequency sound waves, but it is not completely absent. For example, placing a subwoofer near a glass or a place that is prone to vibration can cause noise; the subwoofer is lost near the window; the near wall can easily cause standing waves. Listening to the near point will bring direct sound. The above solution is to keep the subwoofer open as much as possible, and do not face the equipment, resulting in unnecessary resonance. Therefore, the subwoofer also has the problem of positioning. In order to achieve perfect restoration, the ideal position is also very important.
Conclusion: Someone once asked Xiaobian: Is subwoofer really necessary? As an end, we use an idealized concept to answer this question:
“Any music has harmonics and fundamentals, which are all necessary parts of the sound, and can be as low as 20Hz or lower. If you can't reproduce these frequencies, you can't reproduce it really. music!"
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