Fascinating facts about acoustics February 25, 2007Posted by grhomeboy in Science.
• “Acoustics” comes from the Greek words, “akoustikos,” which pertains to hearing, “akoustos,” which means “heard” or “audible,” and “akouein,” which means “to hear.”
• The ancient Greeks are credited with the first acoustically-conscious theaters. Studies have found that they placed sound-reflecting surfaces, such as stone floors, near performers to keep their voices from being lost as soon as lines were spoken. The Greeks also elevated their stages, which caused the actors’ voices to radiate well over the audience instead of being absorbed by the bodies in the front rows.
• The first English usage of the term “acoustics” can be traced back to 1683.
• The modern definition of “acoustics” is the science of sound, including its production, propagation, and effects.
• Some of the most common sub-disciplines of acoustics include:
– Aeroacoustics: The study of aerodynamic sound generated when fluid flow interacts with a sold surface or with another flow. Examples include the sound made by jets and the physics of shockwaves.
– Architectural acoustics: The study of how sound and buildings interact, including the behavior of sound in concert halls and auditoriums, as well as in office buildings, factories, and homes.
– Bioacoustics: The study of the use of sound by animals such as whales, dolphins, and bats.
– Biomedical acoustics: The study of sound in medicine. For example, the use of ultrasound for diagnostic and therapeutic purposes.
– Loudspeaker acoustics: The engineering discipline behind the design of loudspeakers.
– Psychoacoustics: The study of how people react to sound, hearing, perception, and localization.
– Physical acoustics: The study of the detailed inter-action of sound with materials and fluids.
– Vibration/structural acoustics: The study of how sound and mechanical structures interact. For example, the transmission of sound through walls and the radiation of sound from vehicle panels.
• Reverberation, which is the decay of sound after the sound source has ceased, is the oldest and one of the most important measures of acoustics.
• An overly long reverberation time can make sounds blend together too much, making it difficult to distinguish individual sounds. Different musical styles often require different reverberation times.
• An echo is a soundwave that has been reflected by a discontinuity in the propagation medium, and returns at a level and with enough delay that the listener can decipher the sound.
• The human ear can’t distinguish an echo from the original sound if the delay is less than 1/10th of a second. Because the velocity of sound is about 1,125 meters per second at normal room temperature, a reflecting wall must be more than 53 feet from the sound for a person at the source to hear the echo.
• Wallace Sabine is credited with founding the field of architectural acoustics during the 1890s.
• Sabine discovered that he could manipulate the reverberation time in a room using sound absorbing materials. This discovery led him to be hired as an acoustical consultant for Boston’s Symphony Hall, the first concert hall in which measurable acoustic characteristics were part of the design process.