Sound Deadening Properties of Materials

Testing Sound Deadening Properties

• The American Society for Testing and Materials, a nationally recognized organization for the testing of sound and sound deadening material, has established a simple numbering system for sound deadening and a list of the sound deadening properties for various materials. The testing process involves taking simultaneous measurement in decibels inside a structure and outside. The Sound Transmission Rating is the number of decibels the intervening wall subtracts from the outside measurement. An STC rating of 1 is barely perceptible, a rating of 5 is noticeable and a rating of 10 is twice as loud. The decibel scale is logarithmic. Each whole number is ten times the previous whole number. Going from a decibel reading of 38 to a reading of 28 means that 90 percent of the noise is removed.

Mass

• The more dense a material is, the better it insulates. Thicker concrete walls deaden sound more effectively than thinner walls. Doubling the mass will usually result in an STC rating of 4 or 5.

Air

• Double glazed windows have two panes of glass separated by and air space and are effective enough that the Government of Canada has mandated double-glazing in all new homes. Double glazing increases the STC by five.

Insulation

• The use of insulation is complicated because it doesn't affect noise transmitted through the structural members around the insulation. Generally, insulation works best in reducing mid and high frequency sounds. Adding insulation to a wall will give the wall an STC rating of 4 to 6.

Mechanical Decoupling

• Mechanical decoupling means interposing material which carries sound well with material which deadens sound. Cars use mechanical decoupling to reduce noise as well as vibration by putting rubber anti-vibration mounts between the engine and the frame of the car. The number and kind of applications of mechanical decoupling are highly varied.