Soundproofing Flanking Noise, Part 2:
Major Noise Flanking Paths Requiring Soundproofing

Floor Framing System Under the Wall Flanking Path

In some construction, floor joist systems can travel under the offending wall. The floor systems on either side of the wall is therefore connected, so while there is no actual open air path from his side to yours, the floor framing itself can conduct the vibration from his side to yours and soundproofing is required.

Ceiling Joist System Noise Flanking Path

There are times when an attic area is common to both rooms and soundproofing is necessary. Vibration from the offending room are transmitted via airborne path or conducted through the ceiling joists themselves.

Side Walls Noise Flanking Path

Walls in your unit are usually directly connected to the next door unit.  Sound is easily conducted through a single stud wall, and can be soundproofed.

Minor Noise Flanking Paths Requiring Soundproofing

Ductwork Flanking Noise

How many times have you been able to listen to a conversation going on in another room by sticking your ear by the air vent?  Standard ductwork is metal, and therefore very conductive of sound. Ductwork has smooth, hard surfaces and can therefore bounce sound inside from one room to another. For soundproofing, try lining the rigid ducts with a 1” compressed duct liner, generally available through any heating and air conditioning distributor.

Flanking Noise from Doors

Whether residential or commercial, most doors are poor isolators of airborne sound. Two main reasons for the limited performance are poor seals and lack of mass. For soundproofing, try a heavy exterior door. A heavy exterior door has mass and weatherstrip to seal it up.

Seal up Holes to Stop Flanking Noise

Outlets and gaps are all holes that can transmit sound, especially high frequencies. Use a standard latex caulk or sealant where the drywall meets the floor behind the base molding to help with soundproofing.

Seal the outside surface of the outlet box with a heavy putty pad or use a plastic electrical box designed for use in vapor barriers (they’re sealed).

Seal the junction of the drywall and electrical box with caulk or a foam energy-saving gasket.

Make sure the wall is insulated and that the insulation is tucked in behind the electrical box.

All of the simple soundproofing above should help with noise flanking caused by holes.

Summary of Noise Flanking Soundproofing

By considering the less obvious pathways that sound can travel, you will have a better ability to stop it by applying the above soundproofing treatments. If the noise flanking situation becomes too much to deal with, you could consider contacting a professional Acoustical Consultant.

Contributing Soundproofing Expert:

Ted White
Soundproofing Company, Inc.