Most main speakers are typically passive. But most subwoofers include a power amplifier, creating the raw power needed to provide deep bass, without taking away any excessive amplifier power from the receiver. Subwoofers usually handle frequencies below 150 Hz or so.
Most subwoofer are designed to deliver accurate musical bass from a small enclosure. Small enough to be placed behind furniture or tuck into a corner and not be obvious from view. But its big bass output will be able to deliver all the visceral gut rumble for the action movies as well as tight, accurate bass precision for music.
The trend toward small, easily concealed main speakers has fueled an increase in the use of subwoofers. Compact main speakers, and in-wall or in-ceiling speakers, are often bass-shy. Large, costly floor-standing speakers often have plenty of bass, but they may be cosmetically unacceptable. Also, the speaker room placement that results in the best stereo imaging is almost never the best placement area for reproducing deep bass.
So don’t make the front stage speakers do all the work. Instead, add a subwoofer to the system. This will free up the front stage to be more dynamic and expansive by letting the subwoofer take over the low frequency effects, the thrills of movies and the deep bass of soundtracks. The design of the intelligent amplifiers in subwoofers basically filters the low frequencies cleanly and smoothly, for better blending with the full audio spectrum being reproduced the main speakers. Easily accessible, professional-grade connections will give multiple options for hookup, so that one can tweak the performance according to the system needs. Adding a subwoofer, or two. will make TV watching into a wild ride, and music listening into a real live-on-stage experience.
It is also important to note that a subwoofer’s deep bass is nondirectional. Therefor some care and planning is advised when considering where to place the subwoofer when installing the home theatre system.
By finding the best location for placing the subwoofer, it can make a dramatic difference in the sound. Corner placement is the de facto strategy for most people, possibly because the subwoofer will then be out of the way and almost always produces the most bass, but corner placement may not yield the most accurate bass, or smoothest transition to the speakers. The subwoofer and main speakers have to work together as a team, and ideally one should never hear the subwoofer as a separate sound source. All of the bass should appear to come from the main speakers.
With small speakers, it’s best to keep the subwoofer within 1m or 1.5m of the front left or right speakers. Once the subwoofer is a lot farther away, it will be harder to maintain the illusion the bass is coming from the speakers. For really small speakers or skinny sound bars, keep the subwoofer as close as possible to the speaker(s).
For larger speakers (with 10cm or larger subwoofers), some placement experimentation may be useful. By playing music with lots of deep bass and keep repeating the sound as you move the subwoofer to all of the visually acceptable locations in the listening room provide the listener to gauge how different the bass sounds in different locations. Some location may give a muddy effect while other locations may give the effect that the sound is louder, and yet some other location will reduce the bass volume. The goal is to get the best balance of deep bass from the subwoofer and still have the mid and upper bass from the speakers in equal proportions (adjust the subwoofer volume control in each new position). In some rooms, smooth bass response won’t be all that hard to achieve, but be prepared that there may be “problem” rooms where the bass always sounds boomy or muddy.
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