Noise Control with Concrete Masonry
Unwanted noise can be a major distraction, whether in the home or the work environment. Concrete masonry walls are often used for their ability to isolate and dissipate noise. Concrete masonry is an excellent noise control material in two ways.
First, masonry walls effectively block sound transmission over a wide range of frequencies.
Secondly, concrete masonry can effectively absorb noise thereby diminishing noise intensity. These abilities have led to the successful use of concrete masonry in applications ranging from party walls to hotel separation walls, and even highway sound walls.
Sound transmission class (STC) provides an estimate of the performance of a wall in certain common sound insulation applications.
Many sound transmission loss tests have been performed on various concrete masonry walls. These tests have indicated a direct relationship between wall weight and the resulting sound transmission class—heavier concrete masonry walls have higher STC values.
The International Building Code contains requirements to regulate sound transmission through interior partitions separating adjacent dwelling units and for those separating dwelling units from adjacent public areas, such as hallways, corridors, stairs or service areas. Partitions serving the above purposes must have a sound transmission class of at least 50 dB for airborne noise when tested in accordance with ASTM E 90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions.
In the absence of test data, standard calculation methods exist, although these tend to be conservative. Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls, TMS 0302 contains procedures for determining STC values of concrete masonry walls.
According to the standard, STC can be determined by field or laboratory testing in accordance with standard test methods or by calculation. The calculation in TMS 0302 is based on a best-fit relationship between concrete masonry wall weight and STC based on a wide range of test results, as follows: STC = 21.5W0.223 [SI: STC = 15.1W0.223] where W = the average wall weight based on the weight of the masonry units; the weight of mortar, grout and loose fill material in voids within the wall; and the weight of surface treatments (excluding drywall) and other components of the wall, psf (kg/m2).
Resource: www.ncma.org – Concrete Masonry Designs – Jan 2008