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How important is a Subwoofer in a Home Theatre System ?

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Even though your primary (Left/Right) speakers may have an impressive bass response, they won't be able to reproduce the very low frequencies delivered by a good subwoofer. And most importantly, not at an adequate power level.

Also worth noting is that, though sound becomes less directional as the frequency decreases, it is for all practical purposes not "non-directional", as some may claim. So, the appropriate positioning of a subwoofer can make a big difference to your enjoyment of the Home Theatre and Surround Sound audio experience.

Home Theatre is not just a matter of sitting down and watching a movie ... Home Theatre is all about the total experience of the movie and the action. In other words, Home Theatre is about audio immersion and getting involved in the atmosphere created by the Surround Sound system. And a subwoofer is an essential component of the total package to achieve total immersion.

What is a Subwoofer?
A subwoofer is a speaker that is designed to reproduce very low bass frequencies. These bass frequencies are usually in the range between 20 Hz (sometimes less) and 125 Hz. At these very low bass frequencies, sounds are often felt as much they are heard. So the subwoofer is used to provide the powerful audio rumble and punch which is now commonly found in movies and music videos, in particular for dramatic effects associated with crashes and explosions.

Though subwoofer speakers may come in a variety of diameters and may be found in enclosures of various sizes, subwoofer speakers tend to be relatively large in size, between 8" (20.3cm) and 15" (38.1cm) in diameter. A larger speaker diameter is naturally inclined to reduce high frequency response, while also providing a longer throw (the distance a speaker can move back and forth). With the often large speaker diameter and matching enclosure in mind, it is no surprise then that even a well designed subwoofer package can take up quite a bit of space in your listening environment.

There are no fixed rules for placement of the subwoofer, other than a subwoofer should be placed directly onto the floor. This assists with the transmission of the sound from the subwoofer into a vibration that will be felt as well as heard.

That said however, some of the following tips may prove helpful to improve the bass response of your Home Theatre environment, especially one that is “bass shy” or naturally lacking in bass.

  1. Placing the subwoofer close to a wall
    By placing the subwoofer enclosure close to a wall, the long bass frequency sound waves coming from the rear and sides of the subwoofer enclosure will be reflected from the wall. Since these sound waves will be almost in phase, this will appear to magnify the overall bass level.

  2. Placing the subwoofer near a corner
    In a manner similar to the above (close to the wall) point, placing any speaker near a room corner can also provide a perceivable improvement in bass response. You may however need to experiment with the distance used because the size (dimensions) of the subwoofer enclosure will also have an effect.

  3. Place the subwoofer within the frontal audio field
    Where possible, avoid placing the subwoofer enclosure to either side or the back of your listening environment. This point will be more significant for larger and more powerful subwoofers (and obviously at higher audio levels). For example putting the subwoofer behind your couch may work for you, but at the output levels required to "make it work", your neighbours may be less impressed.

  4. Consider using 2 smaller subwoofer enclosures rather than a large single enclosure
    This suggestion is really for those who are into DIY (Do It Yourself) and are adding a subwoofer to an existing Home Theatre or Surround Sound system. If having one large central subwoofer enclosure is not practical, consider having two slightly smaller subwoofer enclosures placed in close proximity to your main Left and Right speaker pair. Having the two subwoofers will get rid of any directionality you might otherwise experience.

  5. Use a Dedicated Subwoofer Amplifier
    Many Surround Sound amplifiers do provide a line level subwoofer output for precisely this purpose. This allows to drive your subwoofer speaker (or speakers, if using dual subwoofer enclosures) from a dedicated mono or stereo amplifier. In most cases, once you have tweaked the level on this subwoofer amp, you can set and forget, since the actual level control will come from the Surround Sound amplifier.

Of course bass output also will depend largely on the shape and size of the room, furniture placement, the capabilities of the subwoofer itself, the subwoofer crossover adjustment and the available amplification.

Poor subwoofer placement and adjustment is a leading cause of disappointment with Home Theatre performance. A little experimentation, even with furniture placement, can often provide improved results. Though I prefer to place the subwoofer somewhere between the main front left and right speakers, subwoofer placement is a matter of personal preference and practicality.

Keep in mind that maxing out the volume level on your subwoofer may create dramatic effects but there is no substitute for correct placement of home theatre components ... especially the subwoofer ... for the total Home Theatre experience.

Essence Audio - Music First!
Incept: July 2008

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