# intensity and loudness of sound

## decibel levels

The Figure 1.1 shows decibel levels of several different sounds. As decibel levels get higher, sound waves have greater intensity and sounds are louder. For every 10-decibel increase in the intensity of sound, loudness is 10 times greater. Therefore, a 30-decibel quiet room is 10 times louder than a 20-decibel whisper, and a 40-decibel light rainfall is 100 times louder than the whisper. High-decibel sounds are dangerous. They can damage the ears and cause loss of hearing. Q: How much louder than a 20-decibel whisper is the 60-decibel sound of a vacuum cleaner? A: The vacuum cleaner is 10,000 times louder than the whisper!

Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity of the sound waves. Intensity is a measure of the amount of energy in sound waves. The unit of intensity is the decibel (dB).

## amplitude and distance

The intensity of sound waves determines the loudness of sounds, but what determines intensity? Intensity results from two factors: the amplitude of the sound waves and how far they have traveled from the source of the sound. Amplitude is a measure of the size of sound waves. It depends on the amount of energy that started the waves. Greater amplitude waves have more energy and greater intensity, so they sound louder. As sound waves travel farther from their source, the more spread out their energy becomes. You can see how this works in the Figure 1.2. As distance from the sound source increases, the area covered by the sound waves increases. The same amount of energy is spread over a greater area, so the intensity and loudness of the sound is less. This explains why even loud sounds fade away as you move farther from the source. Q: Why can low-amplitude sounds like whispers be heard only over short distances? A: The sound waves already have so little energy that spreading them out over a wider area quickly reduces their intensity below the level of hearing.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

intensity is a measure of a sound waves

``````a) speed.

b) frequency.

c) wavelength.

-->  d) energy.
``````

an 80-decibel sound is 20 times louder than a 60-decibel sound.

``````a. true

-->  b. false
``````

the intensity of sound depends on the

``````a) amplitude of the sound waves produced by the sound source.

b) distance the sound waves have traveled from the sound source.

c) speed at which the sound waves traveled from the sound source.

-->  d) two of the above
``````

as distance from the sound source increases, the area covered by the sound waves decreases.

``````a. true

-->  b. false
``````

amplitude is a measure of the size of sound waves.

``````-->  a. true

b. false
``````

which sound is considered to be extremely loud?

``````a) dishwasher

-->  b) lawn mower

c) vacuum cleaner

d) two of the above
``````

## diagram questions

No diagram questions associated with this lesson