The loudness of noise is measured as a sound pressure level in decibels. The decibel is a logarithmic scale, which means that every ten decibel rise in sound pressure roughly doubles the loudness we hear while increasing the sound power tenfold. Because of this, the gap between 30 and 60 decibels is far wider than the numbers make it look.
To match the way our ears respond, measurements often use A weighting, written as dB(A). It weighs the signal according to how sensitive the ear is at each frequency, so it reflects how loud something actually feels. Useful reference points are a quiet bedroom at around 30 decibels, normal conversation at around 60, a busy street at around 80, and long exposure above 85 decibels, which can begin to harm hearing.
In industrial and product testing, the task is often to measure a faint sound against a very low background, and this is exactly where anechoic chambers, soundproof rooms and silent boxes earn their place. A well designed acoustic laboratory can press the background noise down to twenty or thirty decibels, so that the acoustic character of the product under test stands out clearly.