| 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.
