The barking dog that keeps you awake at night ... the annoying rattle in your car's dashboard ... the sound of a photocopier just outside your office cubicle. These are just a few examples of objectionable sound or noise.

Periodic surveys conducted by the Building Owners and Managers Association (BOMA) indicate just how closely people relate sound to comfort. Year after year, survey respondents consistently identify poor indoor air quality (IAQ), uncomfortable temperatures and noise as the principal motivators for relocating from one rented space to another. It's also apparent that these factors are of relatively equal importance since their respective ranks change annually.

What's considered "acceptable" sound varies dramatically with the intended use of the finished space (see Table 2). Obviously, a factory requires less stringent acoustics than a church, while an office has a different set of requirements altogether. But it's not enough to know the type of application involved. The designer must identify the variety of spaces that exist within a particular building and determine the acoustical needs of each.

Background sound, for example, provides privacy in an open-plan office by masking the sound of voices and equipment from adjacent areas. Yet this same level of background sound would be unacceptable for conference or board rooms in that same building.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., ASHRAE, provides designers with general guidelines for HVAC system noise in unoccupied spaces (see Table 1). To better understand the nature and limitations of these guidelines, let's review some of the properties of sound.

Continue on to Sound Power and Sound Pressure.