MemberThat is true, but for T, in particular if it is narrowband (and, to the extreme, a pure tone), we can actually match it to a real sound in term of dB perceived, so we can match it to a scientifically measurable power output.
Scientists do that all the time in T studies, in particular to determine the evolution of the volume perception. Of course, one can claim that 5 dB is deafening, and another one that 50 dB is a whisper, but having an objective scale to compare takes away these considerations and helps us understand volume in isolation, without the subjective interpretation of it.
The second aspect of this is the actual type of T vs typical ambient noise: in many cases, T is a high frequency noise, which is spectrally quite separate from environmental noises (including voices), so it will stand out even when the environment seems loud. As an example, I hear my T when a F-22 Raptor makes a surprise fly-by with its afterburner during Fleet Week in San Francisco. And clearly, that afterburner roaring is quite loud (most people, including me, were covering their ears after the "element of surprise"), but I was clearly able to hear my T because the roar has high density of energy in the low frequencies and almost nothing in the high frequencies, where my T is located.
I have another T in the low frequencies (as part of the cocktail), and I can generally not hear it during the day because it blends well with environmental noises.
So, intrusiveness may be determined by disjointed energy distributions as much as volume. A dentist drill will stand out in my household even with the TV on. The fridge, even if it were as loud as the dentist drill (in terms of sound power emitted), would likely be drowned by the TV and be imperceptible.
