Subwoofer box, enclosure

Friday, 19 January 2007

Subwoofers are audio speakers that operate in the low frequency or bass range. Due to inadequate low-frequency characteristics, many loudspeakers do not respond well to input signals of very low frequencies. Thus, a high quality audio system may include a separate, specialized speaker, termed a subwoofer, which is designed to more accurately reproduce the lower frequencies of the full sound spectrum. Speakers for high-fidelity sound reproduction are commonly divided into high-frequency tweeter speakers, mid-range speakers, and low-frequency woofer or subwoofer speakers. In the field of high fidelity sound reproduction, a high quality audio system is normally comprised of a signal source which is generally music or soundtracks, a preamplifier which receives signals from the signal source and provides an audio signal to a power amplifier which amplifies the signal, and loudspeakers that can reproduce the sound from the signal source. Generally, loudspeakers are single enclosures designed to produce most of the audible frequency range, which is from 20 Hz to 20,000 Hz. There used to be very little need to reproduce intense levels of sound down to 20 Hz (the low range for human hearing) because available programming sources were incapable of recording such frequencies. Modern recording technologies have allowed music and film producers to make recordings having wider dynamic ranges and more extended frequency response. With the advent of more dynamic recording techniques, however, the ability of a subwoofer box to reproduce low frequency input signals without distortion has become a highly desirable objective in the industry.

In response to the increased low frequency sound in recordings, a growing number of audio systems are adding an additional type of loudspeaker to their existing array of loudspeakers. Subwoofer speaker systems are designed to reproduce the lowest bass frequencies in music and sound, such as audio frequencies below 35 Hz. These low frequencies are difficult for many full range loudspeakers to reproduce because the bass drivers for full range loudspeakers must handle a wider frequency range. A common limitation of loudspeaker systems, particularly those intended for high quality stereo sound reproduction, is relatively inadequate low frequency performance. Adding a subwoofer to an audio system relieves the full range loudspeaker from reproducing the lowest frequencies, thereby improving its performance. Like any speaker, a subwoofer requires an audio amplifier which produces electrical impulses that alternate from positive to negative voltages and create an electromagnet when they reach a "voice coil" inside the speaker. The voice coil is suspended between the pole pieces of a permanent magnet motor structure. Sub-woofers are used with stereo amplifiers or home entertainment systems to give an enhanced, realistic listening experience in which these lower frequencies can be heard and felt by the listener. In some instances, a subwoofer is used in conjunction with a crossover. The crossover separates, with respect to a crossover frequency, the full sound spectrum into low-frequency components and high-frequency components. The crossover then directs the low-frequency components to the subwoofer and the high-frequency components to the main speaker. Various forms of loudspeaker systems have been developed, and the types of speakers as well as the technologies involved pertaining to woofers, tweeters, mid-range and other forms of speaker systems are well known. A speaker system is commonly hooked up to an audio system such as those typically found in desktop and laptop computers to enhance the listening experience. A typical computer based speaker system generally may include left and right satellite speakers typically placed on either side of the computer, and possibly a subwoofer is usually located nearby. The subwoofer enclosure may house a power amplifier and controls for the speaker system. Stereo sound systems using front speakers with subwoofers, along with rear and side speakers, have become prevalent particularly for sound systems used to reproduce sound in home theater systems for playing back video motion pictures and similar program material. The typical installation comprises a pair of front speakers positioned to either side of the TV screen, preferably with a center speaker and a subwoofer, and along with a pair of right and left side speaker and/or a pair of left and right rear speakers.

Subwoofer speaker systems are known to consist basically of familiar, expected and obvious structural configurations. Sub-woofers are designed to be either powered or passive. The powered subwoofer system has a built-in power amplifier to drive the sub-woofer speaker. Powered subwoofer boxes typically find use in applications where a local amplifier of a stereo or home entertainment system is limited in its output power and cannot drive the sub-woofer to its full efficiency. The powered sub-woofers therefore increase the capability of the local audio source amplifier by providing remote amplification of audio signals generated by the audio source through the use of the built-in power-supply and amplifier at the speaker. Passive subwoofers, on the other hand, do not have built-in power supplies or amplifiers, but rather rely on the amplifier of the audio source to drive the sub-woofer audio driver. Therefore, passive sub-woofers are generally not able to produce the same sound level as powered sub-woofers due to the limited output power of most conventional stereo amplifiers. Subwoofer systems designed to produce frequencies in the lower bass frequency range typically employ a bass reflex enclosure system using a single transducer (drivers or cone drivers) placed in a large chamber having a port to tune the system to a desired low frequency. The speaker system of multimedia computer speaker systems includes a pair of amplifiers that provide. amplified right and left audio signals to corresponding ones of the wide-band. speakers. The subwoofer receives an audio signal that typically is generated from the right and left audio channels. The left and right audio channels are summed, and the sum is passed through a low pass filter to a subwoofer amplifier. The subwoofer amplifier is coupled to the sub-woofer and drives it with a sum of the low-frequency components of the right and left audio channels.

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