1. Decibels and Intensity
Sound
Decibels and Intensity

2. Decibels – a measure of the relative intensity of sounds.

3. Normal Conversation – 60 dB

4. 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.  

5. Loudest Sounds Ever! dragster 155-160
400,000 Watt speakers decibel
fireworks
dragster
Space shuttle
blue whale 188
The Tunguska event 315 June 30, 1908

6. 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

7. 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

8. 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.

9. Beats

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

11. Sonometer

12. Sound Frequency = Average Beat Frequency = Difference

13. 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.