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Designing for optimum Performance
The performance of single wythe CMU walls has proven that the mass of concrete masonry results in high STC ratings. A recent study was conducted by the
Institute for Research in Construction (I.R.C.) as part of a research study sponsored by the Ontario Concrete Block Association. This study found that when concrete blocks are used in conjunction with furring,
insulation, and drywall, the masonry advantage becomes even clearer.
Wall mass has been proven to be inversely proportional to sound transmission through that mass. This new research shows that this is not the only
factor that should be observed. When sound vibrates one side of a wall, the more massive the wall, the less vibration will be translated through the wall. When furring and drywall are introduced into the system, the
sound waves vibrate through the mass of the block, then through the air in the cavity, and finally through the drywall into the listening area. An enclosure as such has a specific frequency at which sound energy is
magnified, its resonance frequency. As the volume of air within the cavity, increases, the resonance frequency of that enclosure is lowered. This type of technology is used to optimize the performance of high
fidelity audio speakers. As the air space in a cavity wall is increased, the STC rating will increase as well. This is known as the Mass-Air-Mass factor. Overall conclusions of this study are the following:
1. Concrete block wall systems can reach very high sound insulation values.
2. Measurements made to one octave below standard limits prove that block walls have good resistance at low frequencies.
3. Cavity walls (for interior use can achieve STC values up to 79).
4. A simple chart method for predicting transmission loss values for several block systems was validated.
The data contained in this brochure were obtained using the results of this study. They show the value of masonry wall systems as sound insulators.
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