|dB (Decibel) - a term used to describe sound pressure level.
||3dB - the smallest amount of sound pressure change average people can hear.
||To hear a 1dB change in sound, you need to be in a recording studio or similar room.
|An increase of 3dB in sound pressure level is twice the power.
||A decrease of 3dB in sound pressure level is cutting the power in half.
||To double the (perceived) loudness of sound, you need to increase the power 3 times, or 9dB.*
|When you double the distance from a given point, the sound level decreases 6dB. *
||When you half the distance from a given point, the sound level increases 6dB.*
||Sound travels through water faster than through the air. Sound travels faster as humidity increases.
|Sound travels at 1130 feet per second.
||Frequency is "vibrations per second", which in turn is called "Hertz" (Hz).
The human voice has a range of 80Hz to 1200Hz.
|The tone of a sound is called "frequency".
||Harmonics are multiple vibrations of the fundamentals.
||Harmonics are what make each voice and instrument different sounding.
|The human voice has both fundamental vibrations and harmonic vibrations.
||ESSS sounds in speech are often caused by the spaces in a person's teeth.
||ESSS sounds are from 5,000Hz to 9,000Hz.
|Harmonics extend the range of the human voice up to 6,000Hz.
||The wavelength of 200Hz is 5.63 feet.
||The wavelength of 2,000Hz is 6.75 inches.
|The wavelength of 80Hz (the low end of a persons voice) is 14.06 feet.
||For a surface to control a frequency, it has to be as thick as 1/4 the wavelength. (Carpet 3/4-inch thick with 1/2-inch underpad begins to absorb sound above 2,000Hz.)
||Carpet absorbs sound above the speech range, makeing carpet a poor controller of speech in a large room. This also kills the musical aspect of the room.
|To create a sound, an object has to vibrate a full cycle of movement which involves a push and pull motion.
||Building acoustical control into a church when it's being built often doesn't cost the church anything extra except for the knowledge of how to do it.
||What is not absorbed by a surface (like carpet) is reflected back into the room.
*In a closed room, these rules don't always apply.
This information adapted with permission from the Church Sound Network & EdB Sound, Acoustics, 1997 edition.