Shape of the Body The body on an instrument absorbs the vibrations coming from the strings and transmits them back through the bore. The air inside the body will also pick up the vibrations from the strings and begin to resonate. The body of an instrument is often shaped with curves. This helps to amplify the low pitches. The high pitches are simply reflected off the top of the instrument while the low pitches are caught by the body. The low pitches are then transferred into the oscillating air inside the body and then out of the bore. An example of low frequencies traveling inside of an acoustic guitar. Picture taken from UNSW