Detecting Sound Waves
by Ron Kurtus (revised 1 December 2009)
Sound waves are detected by the fact that the waves can cause objects to vibrate. The vibrations from the sound waves must be converted into a signal and then amplified and processed.
Your ear and a microphone are common detectors of sound.
Questions you may have include:
- How does sound cause vibrations?
- How is sound processed?
- What are some devices to detect sound?
This lesson will answer those questions. Useful tool: Units Conversion
Sound causes objects to vibrate
Just as a vibrating object creates sound, thus forming compression waves in air or some other medium, sound is also detected by the waves causing a back-and-forth vibration of some object in its path.
What is happening is that the sound in traveling from the air into the object, just like you can hear sound going through the walls or windows in your house.
Since the vibrations are so small in most situations, you cannot tell that the object is actually vibrating. However, you can feel how sound can cause other things to vibrate by standing in front of some loudspeakers when music is being played very loud. You can actually feel the vibration on your skin and chest.
Loud sounds in a room can cause the windows and even walls to vibrate noticeably at the frequency of the waveform.
Vibration must be processed
The detection of sound waves requires transferring the vibration it causes into some sort of signal that can be processed and used.
Feeling the vibration of a wall when loud music is being played in the other room is detecting the sound, by changing the vibration into signals to your brain from your sense of touch. But that isn't very useful information.
Your ear or a microphone can convert the vibration into a signal, which can then be processed into a form that can duplicate or reproduce that sound.
The type of signal that the vibration creates is usually an electrical signal. Processing can almost duplicate the original sound, except for some distortions.
(See Reproducing Sounds for more information.)
There are a number of devices used to detect sound. The most common are the ear and the microphone.
How the ear works
The ear has a small membrane called an eardrum. Sound causes to the membrane to vibrate, which in turn cause tiny hairs in your inner ear to vibrate, according to their designated frequency. Each hair sends an electrical impulse to the brain, where the signals are process and turned into the perception of sound.
(See Hearing and Sensing Sound for more information.)
How a microphone works
The most common mechanical detector of sound is the microphone. It has a membrane that is made to vibrate by the sound. That vibration is changed to electrical signals, which are then sent to a processor or electronic circuitry for amplification or such.
The electrical signal can then be sent to a loudspeaker to create sound at a greater volume, to a tape recorder, or to send out radio or TV signals.
(See Magnetism for more about how a microphone works.)
Sound waves can cause some objects to vibrate, allowing for detection of the sound. The vibrations from the sound waves must be converted into a signal—usually an electrical signal—and then amplified and processed. Your ear and a microphone are common detectors of sound.
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Resources and references
The Power of Hearing - From PhysicsWeb magazine
Mircophones - From HyperPhysics
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Detecting Sound Waves