How Does Amplitude Affect Frequency in Sound Waves?

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    Amplitude Frequency
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Discussion Overview

The discussion centers around the relationship between amplitude and frequency in sound waves, particularly in the context of vibrating strings. Participants explore the mechanics of string vibration, the implications of amplitude on sound pressure, and the speed of sound, while addressing misconceptions about how these factors interact.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant asserts that while a higher amplitude does not equate to a higher frequency, hitting a string harder increases its amplitude and may imply a faster motion, raising questions about the relationship between amplitude and the speed of sound waves.
  • Another participant agrees with the initial description but emphasizes that higher amplitude leads to greater pressure variations without necessitating a change in frequency.
  • Questions arise regarding the derivative of pressure with respect to time, with one participant seeking clarification on its implications for pressure change and sound wave propagation.
  • Concerns are expressed about the misconception that higher amplitude increases the speed of sound, with a request for a mathematical relationship between amplitude and sound speed.
  • Participants discuss the potential for frequency to change under non-linear conditions, such as when amplitude exceeds a certain threshold, but clarify that this is not directly related to the original question.
  • There is a suggestion to explore the ball and spring model to understand the forces and motions involved in wave propagation and how they relate to amplitude and frequency.

Areas of Agreement / Disagreement

Participants generally agree that higher amplitude does not inherently lead to higher frequency, but multiple views remain regarding the implications of amplitude on sound wave characteristics and the speed of sound. The discussion includes unresolved questions and varying interpretations of the mechanics involved.

Contextual Notes

Participants note that the speed of sound is not dependent on amplitude until a certain threshold is reached, beyond which non-linear effects may occur. The discussion highlights the complexity of the relationship between amplitude, frequency, and wave propagation without reaching a definitive conclusion.

  • #31
JohnnyGui said:
I did indeed mean to talk about fixed amplitudes and changing the frequency. So since a higher frequency gives a higher max velocity to the air molecules and a higher pressure difference, can I say that a higher frequency has a higher power?

no, because you are forgetting that
1) speed of sound, regardless of freq, in a given medium is constant
2) at the higher freq, the molecules of air move back and forwards a much shorter distance due to the higher freq oscillation
3) The amplitude of sound waves is independent of their frequency. The amplitude determines the strength (volume) of the waves.

If so, does this mean that a higher frequency can be heard at longer distances than lower (since it possesses more kinetic energy)?

no that is incorrect
you still seem to be hung up on your original premise ... higher freq = higher amplitude with equates to higher power.
you have to get over that incorrect assumption

lower frequencies will travel longer distances as, in general, they will suffer less attenuation than higher frequencies.
this applies to both audio and RF frequencies ... there are natural and manmade examples of this

a natural example is the booms from volcanic eruptions ... in 1883 Krakatoa in the Sunda Strait, Indonesia erupted. The low freq booms and rumbles were heard up to 3000 km away in central Australia.
a manmade example ... ask yourself, when your neighbour is having a noisy party, what frequencies of sound do you hear from his stereo system inside your house ? they are the lower ones huh ... the thud thud of the bass guitar and the drums
Dave
 
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  • #32
davenn said:
ask yourself, when your neighbour is having a noisy party, what frequencies of sound do you hear from his stereo system inside your house ? they are the lower ones huh ... the thud thud of the bass guitar and the drums
It's not easy to compare situations when there are so many different factors. High and low frequency sounds are absorbed differently on the way through buildings (and in the open air) and you get transmission by diffraction of low frequencies more than high frequencies. Also, loudspeakers can couple low frequency sound directly to the building and that energy will propagate directly to the neighbours.
Our 'experiences' of sound are not good 'experimental' evidence of theory. The great thing about mathematical descriptions in Physics is that they can just show one relationship at a time. In cases like this, the arm waving can easily lead to invalid conclusions.
 

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