Hi Charlotte,
Consider your ears’ sensitivity to sound in the short term and long term. Something abruptly louder for a short amount of time allows you time to recover to the norm. Something increasingly louder over a period of time may require a little while for you to notice that your ear has been exposed to louder and louder noise, but depending on how much louder will require a logarithmic scale than a linear scale to be useful. As a wave metaphor, consider seismic wave measurements that are logarithmic rather than linear, like the Richter scale. Why are these waves measured logarithmically rather than linearly? Is frequency and intensity of occurrence important for designing structures in high seismic zones?
A decibel is literally 1/10th of a bel, which is a relative unit used to express the ratio of one value of a power or root-power quantity to another, on a logarithmic scale. So, these are used to quantify the range of sounds that impact human hearing. Like earthquake measures on a Richter scale describe potential impacts to buildings, decibels measure impacts to our ears on a standard scale.
An increase of 3dB doubles the sound intensity but a 10dB increase is required before a sound is perceived to be twice as loud. Therefore a small increase in decibels represents a large increase in intensity. The so-called, “3db rule” addresses the human perception and impact of sound (or noise, which is any unwanted sound) on the ear’s “structure.”
Architectural design presumes, typically, to provide a healthful environment. When data provided in terms of exposure are presented in decibels, we can select materials with various sound absorbing qualities and arrange them in deflective geometries to mitigate unhealthful noise.
-Coachglenn