Purpose

• Subwoofers enhance the sound field in your room by providing low-frequency bass and alleviating the workload of your primary speakers. In addition to creating a more enveloping sound field, subwoofers create a physical rumble in your house.
  
  

Power Types

• The basic types of subwoofers are passive and powered. Passive subs are powered by the stereo receiver itself, while active subs are powered by their own internal amplifier. The extra power allows powered subs to provide a larger and louder sound.
  
  

Firing Types

• Subwoofers can be front firing, meaning the sound is projected outward from the sub, or down firing, meaning the sound will be projected toward the floor.
  
  

Enclosure Types

• Subwoofers come housed in a variety of enclosures. The type of enclosure can greatly affect the sound. Types include free air, sealed and ported.
  
  

Costs

• Subwoofer range in cost and quality. A moderate sub can be purchased for around $50, and a high-end sub can cost thousands. Good value subs from reliable manufacturers like Velodyne can be had for around $150.