Sound Level Terminology

  • Absorption Coefficient- Denoted by alpha (units of inverse meters) and “a” (dB/m). This constant measures the sound-absorbing ability of a material. The values go from about 0.01 for marble slate to almost 1.0 for the long absorbing wedges that are used in some anechoic sound chambers.
  • Anechoic Sound Chamber- room in which the walls, ceiling, and floor all are covered with sound absorbing materials shaped to maximize sound absorption. Echoes effectively do not exist in such a chamber
  • Decibel- logarithmic unit used to gage sound level. Subtracting three decibels translates to reducing the intensity by 50%. Human ears, however, perceive sound that is 10 times less intense as being half as “loud”. In other words, a difference of 10 dB will seem to be twice as loud or quiet.
  • Hertz- unit of frequency (inverse seconds). AKA cycles/second.
  • Infrasonic- sound lower than 20 hertz
  • Medium- the material that something travels through
  • Octave- difference in pitch equal to a doubling of frequency
  • Threshold of pain- 120 dB- the level that goes from discomfort to pain and hearing loss
  • Tone- a definite pitch
  • Ultrasonic- frequencies about 20,000 Hz (20 kHz)

Decibel Level Sound
10 Light Whisper
20 Soft Conversation
30 Normal Conversation
40 Light Traffic
50 Loud Conversation
60 Busy Office
70 Traffic, train
80 Subway
90 Heavy Traffic, Thunder
100 Jet Plane takeoff
120 Pain Threshold

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Absolute Zero

Absolute Zero also known as 0 degrees Kelvin or -273.15 degrees Celsius describes the theoretical temperature at which particles have zero thermal energy- meaning that velocity of the particles goes to zero. Thus the velocity of the particles corresponds to temperature.

Absolute Zero was, previously thought to be the temperature at which an ideal gas would decrease to zero volume. At lower temperatures the velocity of the particles is lower which corresponds to lower volume. It now finds use as the bottom of an absolute temperature scale.

The Low Temperature Laboratory in the Helsinki University of Technology, Finland reached 2 x 10^-9 degrees Kelvin in 1989.