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Designing Acoustic Controls

The design phase is the best spot to address acoustic issues. If steps are not taken at this point to identify potential acoustic problems, they will surface after the building is occupied with the possibility of making it unusable without a major retrofit.

The first issue is to understand that sound control can be addressed in three areas: the source, the path, and the receiver. Controlling noise at the source is the optimum solution, but in designing a building, architects can typically control only acoustic conditions through the receiver and the path.

Excessive traffic noise is the greatest irritant for most Americans and the one that affects more people than any other environmental noise source. It can affect the ability to work, learn, relax, etc. And if the noise continues to be an irritant it can lead to health problems such as nerve damage to the ear or issues related to high stress. For buildings located near high traffic areas, some measures may control exterior sounds, including: adding a barrier wall, increasing isolation quality of the structure, masking the noise, or controlling the source.

 

Creating air space between glass panes can improve the STC.

But these may not be feasible, or may only solve part of the problem. Noise from the outside may still reach a building. When it infiltrates it and becomes a distraction, the windows or doors are often blamed because they have many more components and operational elements than other parts of the structure through which sound may pass. For example, exterior walls typically block between 45 to 50 decibels (dB) of sound and a superior quality window may block under 40 dB. But if a door or window is not sealed properly, air—and sound—can get around or through the seal.

Successful design of non-residential buildings depends on recognizing situations that may increase noise levels, and choosing windows and doors that help reduce sound transmission.

Understanding and Measuring Sound

To help in understanding how to control unwanted noise, let’s first define what we are considering. Sound energy is a wave form that travels through matter. It begins when a sound source vibrates or otherwise disturbs the air immediately surrounding the source. Because sound is a wave form, it can travel through air and building materials.

Sound intensity is measured by observing sound energy passing through an area per unit of time. The frequency of sound, or its pitch, is measured in cycles per second, or hertz (Hz). One Hz equals the cycles per second (cps) of air pressure. Frequency is the measure of tonal or pitch quality of sound; a higher frequency indicates a higher pitch. The human ear can hear between 20 Hz and 20,000 Hz.

The intensity of sound is measured in decibels (dB), but a decibel does not quantify other sound characteristics. A higher dB signifies louder sound. The faintest sound detectable by the human ear is 0 dB; the loudest is more than 180 dB, which is the noise level at a rocket pad during launch. The loudest intensity the human ear can tolerate without pain is about 120 dBs.