咩叫subwoofer?

Subwoofer 中文名稱是： 超低音揚聲器。
Subwoofer 種類： 1. 有源 2. 無源
有源 Subwoofer： 內置6至18吋揚聲器；內置功率擴音機；內置分音器。
無源Subwoofer: 祇內置6至18吋揚聲器。
分音器頻率範圍： 一般是 120 Hz - 20 Hz. (可調分頻點)
有源Subwoofer功能： 1. 可調分頻點 2. 可調音量 3. 可調相位 4. 可旁路內置擴音機、分音器
Subwoofer於Surround用途：連接環迴效果擴音機 (Surround amp.)之超低頻輸出接口 (Subwoofer out)，對應 Lucas film THX 80 Hz 以下要求。
調節Surround amp： A. 於surround amp之speaker set up選定為 THX speaker(若不選THX speaker, 需於subwoofer set up調節為80 Hz，目的是將amp 80Hz以下頻率交給Subwoofer；選THX speaker則自動輸出80 Hz))。 B. 調音壓於75db.(需借助音壓儀)。C. 調節聆聽位置與Subwoofer距離。
調節Subwoofer分頻點: 將分頻點調到120 Hz.或旁路。
調節Subwoofer 音量：因每隻DVD超低頻輸出量不盡相同，盡管已於Surround amp調節成75 db.，還需適當調節音量。
Subwoofer相位調節： 視乎擺位方向、位置；一般是 0, 180 度。
Subwoofer於兩聲道音響用途： A. 調較分頻點以配合左，右揚聲器最低截止頻率，以增加低頻段。B. 視乎環境調較音量。
每款擴音機、 Subwoofer不盡相同，上列是基本Subwoofer的功能及調較方法，以作參考。

A subwoofer refers to either a driver, or a complete loudspeaker dedicated to the reproduction of bass audio frequencies, typically from 150 Hz down to 20 Hz. In the case of a rotary woofer, it is possible to reproduce frequencies down to 1 Hz. Bass frequencies below about 80Hz become increasingly difficult for typical floorstanding or bookshelf loudspeakers to reproduce at high playback levels (100 dB or more) because they do not have large enough drivers to generate the required amount of air displacement. Therefore, subwoofers are useful for augmenting main loudspeakers by providing playback of low bass frequencies at high levels.

History
The first subwoofer was developed during the 1960s by Ken Kreisel, currently president of Miller & Kreisel Sound Corporation in Los Angeles. Kreisel's business partner, Jonas Miller, owned a high-end audio store in Los Angeles, and customers buying some of the high end electrostatic speakers complained about a lack of bass response in the electrostatics, compared to conventional loudspeakers; Kreisel's solution was to design a powered loudspeaker that would reproduce only those frequencies that were too low for the electrostatic speakers to convey and thereby fill in the missing sonic information.[1]. Infinity's full range electrostatic speaker system of about the same time also used a subwoofer to cover the lower frequency range the electrostatic arrays did not handle adequately.

The first use of a subwoofer in a recording session was for mixing the Steely Dan album Pretzel Logic when recording engineer Roger Nichols arranged for Kreisel to bring a prototype of his subwoofer to Village Recorders. Further design modifications were made by Kreisel over the next ten years (and continuing to the present day), and in the 1970s and 1980s by engineer John P. D'Arcy; record producer Daniel Levitin served as a consultant and "golden ear" for the design of the crossover network (used to partition the frequency spectrum so that the subwoofer would not attempt to reproduce frequencies too high for its effective range, and so that the main speakers would not need to handle frequencies too low for their effective range).

Subwoofers came into greater popular consciousness in 1974 with the movie Earthquake which was released in Sensurround. Sensurround was initially installed in 17 U.S. theaters. Six very large subwoofers were driven by a pair of 1600w amplifiers that were triggered by control tones printed on one of the audio tracks on the film. Four of the subwoofers were positioned in front of the audience under (or behind) the film screen and two more were placed together at the rear of the audience on a platform. Energy in the range of 5 Hz to 40Hz was generated at the level of 110-120 dB. Much publicity was given to the new low frequency entertainment method and the film was a box office success. More Sensurround systems were assembled and installed. By 1976 there were almost 300 Sensurround systems leapfrogging through select theaters. Further films to use the effect include Midway in 1976 and Rollercoaster in 1977. [2]