As sound travels through any material it decays. The nature of the decay depends upon the substance itΓÇÖs travelling through. Air is a satisfactory medium for maintaining the balance of original qualities in a sound. A singerΓÇÖs body tissues are not. The soft tissues filter out high frequencies, the bony structures have their own resonances which corrupt the sound spectrum as it passes through. The same applies to the air and liquid cavities of the body. So, before the sound from the vocal folds reaches the eardrums, it is substantially transformed. As singersΓÇÖ voices grow more expansive, more and more sound reaches the eardrums in this way.
HereΓÇÖs an experiment. Put your hands over both your ears and sing softly, then as loudly and fully as you can. Repeat the sounds with open ears. You should notice a bigger difference between the volume of the two sounds with your ears covered, than with them open. The proportion of sound transmitted through the body, rather than through the air, rises with the volume. To counteract this effect, singers sometimes cup a hand over one ear when practising. To try and pick up more sound from the air, and hear what they really sound like to their audience.
