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On the previous page Audible Levels, I examined the 'subjective loudness' of sound. In this context, we realize how our sense of hearing interprets an increase in decibel levels. As our eyes co-ordinate different 'receptors and processors' for seeing in dim and bright light levels, so do our ears utilize different 'receptors and processors' for hearing in low and high sound levels. It is because of these selective sensory receptors that our primary senses are able to subjectively function over such a wide range of levels. While our sense of hearing can subjectively adapt to considerable variations in decibel levels, the balance of our biological functions are not subjectively adaptive. Just like the rest of the physical and biological world, the rest of our bodies have to respond objectively to the true energy levels of sound, whether audible or inaudible. If one found the progressive rate of the subjective loudness of increasing decibels of audible sound to be surprising, then that of the true energy level of increasing decibel levels of all sound will be even more so. Whereas the subjective increase of loudness was "double for each increase of 10 decibels", the actual objective increase in energy imparted is "double for each increase of 3 decibels (approx.)". It's this amazing rate of increase in sound energy levels that has the potential to impact heavily upon the human body. As shown in the following diagram, while 70 decibel sound is subjectively (filtered by the hearing process) only 8 times louder than 40 decibel sound, it actually bears 1,024 times as much real energy!  |
A reference for these distinctly different rates of increase in 'subjective loudness' and 'objective energy' are described thusly ... "... as you double the sound pressure (or the energy in the sound) the index increases by approximately 3. A sound level of 100 dB(A) thus contains twice the energy of a sound level of 97 dB(A). The reason for measuring sound this way is that our ears (and minds) perceive sound in terms of the logarithm of the sound pressure, rather than the sound pressure itself ... Most people will say, that if you increase the dB(A) by 10, you double the subjective loudness of the sound." ... at the Danish Wind Industry Association website.
It is crucial at this point, to repeat that just like the rest of the physical and biological world, all the other organs and processes of our bodies have to respond objectively to the actual unfiltered energy levels of sound, regardless of it being audible or inaudible.
energy.htm (2013 Update - January 5th, 2013)