## Decibels, Loudness

From woodleywonderworks on flickr

When someone returns from a heavy metal concert they don’t usually comment loudly about how many Watts per meter squared they experienced.

Decibels might make sense.  People tend to know that 120 Decibels is a lot.

This system has been devised and units of decibels measure perceived loudness.

It increases on a logarithmic scale, so something that seems twice as loud really has 10 times the intensity.

Position also can vary the perception of sound such as when a noise emitter comes nearer to you the frequency seems greater and the pitch higher (Doppler Effect).

## 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