A peaceful oasis in a noisy world
Date:June 24, 2016
(Article source: Realtà Mapei Americas n.19/2014)
“Please make it stop!”
In a world filled with ever-louder demands for our attention from every direction, the most precious commodity around can often be just a little peace and quiet. Finding innovative ways to stop the pounding and tone down the volume in the home and office has been a growing concern for designers, architects, builders and owners around the globe. Many designs and construction methods have been used in the past, all with varying results and at a wide range of costs to the owners. As the industry has matured within the United States, engineers have begun to settle on specific test methods and noise-reduction requirements to bring the best value and results to the marketplace.
The science of silence
Over the years, the scientific community studying the science behind sound dampening in buildings has come to recognize that there are two very different types of sounds that must be addressed in order to make living spaces comfortable for the human ear. The first of these is impact sounds: heels striking floors, furniture dragging, machines vibrating and banging, practically any sound that results when an object comes in physical contact with a floor or wall. Such sounds that come from impacts and sound waves traveling directly through solids are classified by sound engineers as Impact Insulation Class (IIC) sounds. The second type of sounds that engineers have identified is those sounds that travel through the air initially and then pass through a floor or wall to the next room. These are the sounds of life: people talking and laughing, music playing, and the occasional baby crying.
They are not all bad, but when the neighbors upstairs are having a fight at the top of their lungs, it is not a soundtrack anyone wants to be listening to at 2 a.m. Airborne sounds are officially classified as Sound Transmission Class (STC) sounds for sound-dampening purposes. In delving a little deeper into the science, it turns out that these two types of sounds require individual tests by sound-reduction engineers because they require different strategies for sound dampening. In other words, the techniques that stop the impact (IIC) sounds do not necessarily help to kill the noise from air transmission (STC) sounds. Accomplishing both goals with one product truly required an invention that could achieve the desired reductions now being specified by engineers and zoning ordinances: a 50/50 STC/IIC rating. The 50/50 numbers come from using three very specific American Standard Test Methods – ASTM E90 to measure STC sound reduction, and a combination of ASTM E492 and E2179 to measure the IIC and DeltaIIC sound reduction respectively. Performing these tests requires highly specialized laboratories and exacting conditions that specifically test an exact construction design for its sounddampening properties. Measuring sounds over the full range of human hearing and the changes in all the harmonics involved goes into every test to determine an exact level of sound reduction. Higher test numbers are better. While the ASTM tests are very specific and exact, they do not specify or standardize the flooring or ceiling design or the exact flooring products being tested. Because there was no universal requirement, a wide variety of products was offered to the marketplace with very little, if any, exact side-by-side comparisons to allow consumers to make the best choice and to be able to compare “apples to apples.” Big numbers abounded on specifications and in product literature, but how much a sound-dampening product individually contributed to those numbers was not always clear.
A great leap forward for the marketplace occurred with the development and publication of the American National Standards Institute (ANSI) specification for sound-reduction membranes, ANSI A118.13 in 2010. For the first time, the ANSI A118.13 standard set a specification and required that sound-reduction membrane products use the same testing system – standardized construction with a simple 6” (15 cm) concrete slab and no suspended ceiling to achieve a real sound reduction using the ASTM E2179 test.
Products certified for ANSI A118.13 could now be compared in a realistic manner, and the better products could be distinguished from lesser offerings.
The challenge for scientists was to develop a product that could produce the sound reductions needed in the controlled test that met the high standards now being demanded without any added sound-dampening help to reach the desired 50/50 STC/IIC rating.
The cork is not an optimal solution
The conventional wisdom in the marketplace is that if a thin sound-reduction membrane works part of the way to reduce IIC and STC sounds, a slightly thicker version of the same membrane should also achieve the desired 50/50 rating.
In reality, this is not the case. The differences in how IIC and STC sounds must be dampened prevent a conventional membrane with a reasonable thickness from achieving both sound-reduction numbers. Standard membrane materials like rubber, bitumen, polyurethanes and the non-woven synthetic fibers used in most sound-control membranes affect the absorption and reflection of sound differently; so simply adding more material is not the solution. Mother Nature’s offering, cork, will work at the right thickness; however, it is subject to mold, mildew and swelling if it is installed on a floor that contains any moisture. Cork is, therefore, not an optimal solution for realworld floors that must stand up to all kinds of conditions.
Results shown below are from ASTM testing of sound reduction by NGC Testing Services, a leading independent laboratory. Sound-reduction ratings were measured over a 6” (15 cm) concrete slab with no suspended ceiling and using 12” x 12” (30 x 30 cm) porcelain tile.