Last week, I introduced the decibel (dB). This week, I’m turning my attention to an intriguing question that frequently comes up in my line of business: How much of a dB change is actually noticeable?
The standard definition of a decibel indicates that it’s roughly the smallest amount of volume change that a person can subjectively perceive. That means variations of up to 1 dB ought to be pretty much imperceptible, while those at or beyond 1 dB are noticeable.
However, I’ve sometimes heard people claim that even a 3 dB volume change is only just noticeable. Based on my experience with sound masking systems, I actually find it rather dramatic. So do visitors to our office when I demonstrate such a volume adjustment using our system.
Why this seeming disagreement?
I think it comes from using a different set of test conditions. If, for example, people in a lab are exposed to two sounds that are separated by a break, then it’s possible that some (because hearing ability varies) will find it challenging to say which of the two was louder. However, in my business, we’re more concerned with variations in volume across a facility and over time because the masking sound is continuously present. Under these conditions, it’s much easier and much more likely that a person will perceive a difference as small as a single dB.
To look at this question another way, let’s consider the sound energy and loudness measures that I introduced last week. A 1 dB change in a sound equates to about a 26% difference in sound energy (remember that a 3 dB difference is a doubling of energy levels). In terms of subjective loudness, a 1 dB change yields just over a 7% change. A 3 dB change yields a 100% increase in sound energy and just over a 23% increase in loudness.
Variations in sound masking volume not only affect how noticeable a system is, but also how consistent the masking’s effectiveness is. The greater the variation in volumes, the more likely it is that the sound masking system will be noticed by occupants and the less consistency there will be in terms of the masking effect (noise control and speech privacy).