|MLA Citation:||Bloomfield, Louis A. "Question 694"|
How Everything Works 22 Jan 2018. 22 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=694>.
A sound's volume is determined by the extent to which the air pressure fluctuates as the sound passes. A loud sound involves a stronger pressure fluctuation than a soft sound. Soundproof materials are ones that decrease the volume of the sound passing through them by weakening the pressure fluctuations. There are two ways to decrease the volume of sound passing through a material: by absorbing the sound or by reflecting it. Soft materials such as carpet or foam rubber absorb sound by allowing the sound's pressure fluctuations to waste their energies bending the materials. The sound's energy is converted into thermal energy. Hard, dense materials reflect sounds by making the sounds change speed. Sound travels quickly through most solids and liquids—typically about 5 to 10 kilometers per second. Whenever a wave changes speed in passing from one medium to another, part of that wave is reflected. Thus as sound speeds up in entering a hard surface from the air and as that sound slows down when reentering the air, much of the sound reflects.