Sound Wave, Microphone and Electromagnetic Induction

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Discussion Overview

The discussion revolves around the functioning of microphones, specifically how sound waves induce an electromotive force (emf) in a microphone's coil. Participants explore two scenarios involving a tuning fork and a louder sound source, questioning how the amplitude of the induced emf changes with variations in sound intensity while keeping the frequency constant.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes a microphone's mechanism, noting that the vibrations from a tuning fork induce an alternating emf in the coil due to the movement of a magnet.
  • Another participant argues that when a louder sound source replaces the tuning fork, the stronger acoustic pressure waves will exert greater force on the microphone's mechanism, resulting in a higher amplitude of the induced emf while maintaining the same frequency.
  • A question is posed about whether the frequency of the sound wave corresponds to the frequency of the induced current and if the amplitude of the sound wave correlates with the amplitude of the induced emf.
  • Participants confirm that, ideally, the frequency and amplitude relationships hold true, although they acknowledge that microphone quality can affect these outcomes.
  • There is curiosity about the factors that differentiate high-quality microphones from lower-quality ones.

Areas of Agreement / Disagreement

Participants generally agree on the relationship between sound wave characteristics and induced emf in microphones, but there is no consensus on the implications of microphone quality or the specific factors that influence performance.

Contextual Notes

Participants reference ideal conditions for microphone performance, suggesting that real-world factors may complicate these relationships. There is also mention of varying microphone specifications that may affect sound capture quality.

Who May Find This Useful

This discussion may be useful for individuals interested in audio technology, microphone design, or the principles of sound wave interaction with electronic devices.

wlng81
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Dear all, I have encountered an issue in understanding how microphone works and I hope you guys can assist.

There are two scenarios involved.
In the first scenario, there is tuning fork and a microphone. The microphone contains a small disc attached to a magnet and a fixed coil. (Please refer to here: http://www.flickr.com/photos/11353862@N02/10851144236/)
It is mentioned when the tuning fork vibrates, an alternating induced emf is induced in the coil.

In the second scenario, the tuning fork is replaced a source that produces a sound of greater loudness but the same pitch.

The question is: How will the amplitude of the induced emf change?

I had thought the magnitude induced emf should remain the same since the pitch (hence frequency -> rate of change of magnetic flux) was the same. But I also came across some audio websites saying the amplitude induced emf would increase.
As a result, I am utterly confused now...:confused:
 
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Remember that the acoustic waves that propagate from the source (tuning fork) to the detector (microphone) are pressure waves. When they strike that disc they push and pull the magnet, which induces the current in the coil.

When the tuning fork is replaced with a louder source, the acoustic pressure waves will be (louder) stronger and so will push and pull that mechanism in the microphone with a greater force than the tuning fork did. So, the alternating current in the coil will be the same frequency, and a greater amplitude.
 
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Hi Bobby, can I say that the frequency of the sound wave is reflected in the frequency of the induced current and the amplitude of the sound wave is reflected in the amplitude of the induced emf?
 
Yes and yes.
 
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At least ideally. That's why some microphones are better (and more expensive) than others. :wink:
 
jtbell said:
At least ideally. That's why some microphones are better (and more expensive) than others. :wink:

Out of curiosity, what are the factors that separate a good mic from a lousy one?
 

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