Pads

• A thumping subwoofer penetrates walls, ceilings and especially floors for a startling distance. If your bass speaker sits directly on the floor, you can bet that these low-end frequencies are vibrating right through the wood or concrete. An easy way to reduce this is to put a piece of rubber or foam directly beneath the speaker so that it doesn't touch the floor at all. One or 2 inches thick should be enough to make a difference, according to CNET News columnist Steve Guttenberg.
  
  

Duct Work

• An often overlooked way sound waves are transmitted is through the ductwork in your ceiling. It acts as a conduit to the rest of the house or apartment building. Installing a commercially available liner inside the ducts could contribute mightily to your soundproofing goal. So would including a few 45- or 90-degree bends in the design. Obviously, these solutions are easier to accomplish during construction than after the ductwork is installed, but not impossible.
  
  

Drywall Clips

• Drywall nailed directly to the studs of a wall frame easily translate sound waves outside the room. Building a floating system of walls and ceilings is an expensive way to reduce noise transmission, but a less costly approach is to install what are called stud clips that create a gap between the drywall and studs. This gap acts as soundproofing, trapping sound waves between the inner and outer surfaces of the wall.
  
  

Considerations

• Many people wrongfully assume that applying heavy carpet and wall coverings will help to soundproof a room. Not so, according to Guttenberg. Such measures can improve the audio quality but do little to contain it. A final tip, if you're truly concerned about incessantly annoying family or neighbors with your listening habits, wear earphones. And if you suddenly find extra money to add to your soundproofing budget, there are a host of underlayments, wall tiles and structural baffling systems from which to choose.