Why you need a subwoofer for music

If you are aiming for the best bass you can get, you need at least one subwoofer, even in a two channel system. When this is suggested, a common response is "my mains have enough bass!" The reasons for using a sub aren't quite so obvious.

What is required to achieve exceptional bass:

• adequate extension to reproduce bass as low as your source material demands
• adequate output to achieve the highest level you expect in your listening position with headroom
• independent level adjustment
• adequate headroom to allow for a room target curve and some EQ
• ability to place the bass speakers where they perform best 
• multiple placements - from one to five units

Obviously the bass drivers included in your existing speakers can't meet all of those requirements. In-built bass drivers on your mains are far too limited to achieve the best that is possible. In most cases, sub will work best in locations that could not be used for a full range speaker.

I use the term "subwoofer" broadly here. An active woofer not intended for home theatre use can also be used.

The main reason for using subwoofers is that they can be placed to get the best out of the room. Once properly integrated, one can achieve a much smoother response that is free from peaks and dips that plague all rooms. It isn't difficult to remove peaks with EQ, but the unique benefit to a multi-sub arrangement is the elimination of dips.