One of the interesting areas of sound is sound level measurement and the effects sound can have on people and physical objects. Sound waves can be incredibly powerful. One of the loudest sounds on the planet is the space shuttle at liftoff. According to NASA, 800 feet is the closest distance a sound-pressure meter has ever been placed to the launch pad. NASA engineers determined that if they placed the meter any closer, the sound waves from the launch would destroy it. The sound-pressure reading at 800 feet from the base of the launch pad at liftoff is an incredible 195 dB-SPL.

Within seconds of a shuttle launch, one-half million gallons of water dumps onto the launch pad and into the flame tunnel. Contrary to popular belief, this water is not to cool the launch pad from the flames of the shuttle's engines and solid rocket boosters. The water is part of the sound suppression system. The water absorbs and breaks up the powerful sound waves from the shuttle's solid rocket boosters and three main engines so that the sound cannot reflect off the launch pad and strike the shuttle. If the sound waves were allowed to reflect off the launch pad and impact the shuttle, the shuttle could literally be shaken to pieces upon liftoff. It is not that the shuttle is that fragile—the sound waves are that powerful.

This chapter mentions that sound-pressure meters need adjusted or weighted electronic filters so that they would register sounds like humans hear them because of the equal-loudness principle. Sound-pressure meters use three filters to measure the loudness of sound. The "A-weighted" filter is the standard filter used to approximate human hearing at lower levels. The B filter is a close approximation of the human ear at higher sound levels, and the C filter is a filter used to measure very loud sound levels.