Decibels and Intensity

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Presentation transcript:

Decibels and Intensity Sound Decibels and Intensity

Decibels – a measure of the relative intensity of sounds.

Normal Conversation – 60 dB

85 decibels - prolonged exposure can cause gradual hearing loss 85 decibels - prolonged exposure can cause gradual hearing loss. 100 decibels - no more than 15 minutes prolonged exposure recommended 110 decibels - regular exposure of more than one minute risks permanent hearing loss without hearing protection.

Loudest Sounds Ever! dragster 155-160 400,000 Watt speakers 135-145 decibel fireworks 145-150 dragster 155-160 Space shuttle 165-170 blue whale 188 The Tunguska event 315 June 30, 1908

Important Decibel Ideas This is a “relative” (comparing) scale. Humans can distinguish about 1 dB. 10dB higher “sounds” 2x louder. Logarithmic, not linear. 10x more energy = 10dB higher 100x more energy = 20dB higher 1000x more energy = 30dB higher 10,000,000x more energy = 70dB higher

Bettendorf – measured 4 ft above the ground at property line Residential (7am-10pm) 60dB (10pm-7am) 50dB No lawn mower, trimmer chain saws Commercial (all times) 65dB Industrial (all times) 75 dB

Loudness The intensity of a sound is proportional to the square of the amplitude of a sound wave. Decibel (db)—the unit of intensity. Loudness—a physiological sensation that differs from person to person. Loudness varies nearly as the logarithm of intensity. 0 db = the lower threshold of hearing for a normal ear. 10 db is 10 x more intense than 0 db. 20 db is 10 x more intense than 10 db and 100 x more intense than 0 db.

Beats

Two similar sounds played together 33 waves 30 waves 31.5 waves (average) 3 beats (difference)

Sonometer

Sound Frequency = Average Beat Frequency = Difference

Forced Vibration and Natural Frequency Forced vibration—the vibration of an object that is made to vibrate by another vibrating object. Example: the strings on a guitar cause the wooden body of the guitar to vibrate. Natural frequency—the characteristic frequency of an object, which requires minimum energy to produce forced vibrations and the least amount of energy to continue this vibration.