What is the equation for decay of natural sound over time?

Click For Summary

Discussion Overview

The discussion centers around the mathematical modeling of the decay of natural sound over time, particularly in the context of sound produced by instruments like guitar strings or resonant filters. Participants explore different equations that could represent this decay, examining both theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants propose two potential equations for sound decay: y = 1/c^x and y = 1/(x+1)^c, with a preference for the first equation.
  • It is noted that the second equation may represent a translation of the first equation's graph.
  • One participant mentions that the base c in the equations is often taken to be the natural number e, suggesting that any exponential function can be rewritten using different bases.
  • Another participant introduces the concept of the decay time constant, T, which is related to the Quality Factor (Q) of the resonator, proposing that the amplitude decreases exponentially as a = e^-x/T.
  • A later reply corrects the notation of the exponential decay equation to a = e^-x/T, emphasizing the standard interpretation.
  • One participant references an article on acoustic attenuation, suggesting that it describes energy dissipation related to sound decay.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate equations for sound decay, with no consensus reached on a single equation. The discussion includes multiple competing models and interpretations of the decay process.

Contextual Notes

There are limitations regarding the assumptions made about the equations, the dependence on definitions of decay constants, and the specific contexts in which these equations apply. The discussion does not resolve these complexities.

mikejm
Messages
40
Reaction score
2
Let's say you have an impulse of noise, eg. via a guitar string, or a resonant bandpass filter, and it decays naturally. If "1" is the maximum initial amplitude of sound, and "0" is no sound at all, what is the equation for decay of sound over time (x)?

Is it:
y = 1/c^x

Or y = 1/(x+1)^c

I think it is y= 1/c^x but not sure.

What does nature do?

Thanks.

<moved from General Discussion>
 
Last edited by a moderator:
Physics news on Phys.org
mikejm said:
Let's say you have an impulse of noise, eg. via a guitar string, or a resonant bandpass filter, and it decays naturally. If "1" is the maximum initial amplitude of sound, and "0" is no sound at all, what is the equation for decay of sound over time (x)?

Is it:
y = 1/c^x

Or y = 1/(x+1)^c
Most likely the first, not the second. The second equation is the translation 1 unit to the left of the graph of the first equation.
Also, c in your equations would usually be take to be the natural number e ##\approx 2.71828##, and named after Leonhard Euler, a Swiss mathematician.

Of course, the exponent base is arbitrary, as any exponential function can be rewritten using any other reasonable base.
mikejm said:
I think it is y= 1/c^x but not sure.

What does nature do?

Thanks.
 
  • Like
Likes   Reactions: tech99 and berkeman
The decay time constant depends on the Quality Factor, or Q, of the resonator. See https://en.wikipedia.org/wiki/Q_factor. My interpretation is that the wave decreases exponentially with a certain time constant, T. If the initial amplitude is 1 and the amplitude at time x is a,
a= e^-x/T
The time constant T is equal to 2Q/radial freq.
 
  • Like
Likes   Reactions: Klystron
tech99 said:
a= e^-x/T
That would be more correct as ##e^{-x/T}##. As written above, the standard interpretation would be as ##\frac{e^{-x}}{T}##
 
  • Like
Likes   Reactions: tech99

Similar threads

  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 31 ·
2
Replies
31
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
17
Views
3K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 131 ·
5
Replies
131
Views
8K
  • · Replies 3 ·
Replies
3
Views
2K