What Does a Graph of Sound Wave Pressures in the Atmosphere Reveal?

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Discussion Overview

The discussion revolves around understanding sound wave pressures in the atmosphere, specifically regarding the relationship between sound pressure levels (SPL) and atmospheric pressure. Participants explore the definitions, measurements, and implications of sound pressure in various contexts, including street noise and the energy required to produce sound at different decibel levels.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about a graph showing the highest and lowest atmospheric pressures for sound waves at various decibel levels.
  • Another participant provides a reference defining the 0-dB sound pressure level in air and suggests using a table or formula for other SPLs.
  • There is confusion regarding the interpretation of 'street traffic' noise pressure being stated as 2 Atm, with multiple participants questioning this figure and its implications for high and low pressure regions.
  • One participant clarifies that the pressures are given in Pascals (Pa) rather than atmospheres (Atm), while another insists on their conversion to Atm.
  • A participant challenges the conversion factor used, stating that 0.2 Pa for street noise is significantly less than 1 atm.
  • Another participant explains that the pressures listed in the table represent amplitudes of pressure variations around the ambient pressure, emphasizing that these variations are small compared to atmospheric pressure.
  • Several participants express interest in graphs related to the energy or power needed to produce sound at specific decibel levels, with one noting the distinction between energy and power.

Areas of Agreement / Disagreement

Participants express disagreement regarding the interpretation of sound pressure levels, particularly the claim of 'street traffic' noise being 2 Atm. There is no consensus on the correct interpretation or conversion of sound pressure measurements, and the discussion remains unresolved.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about sound pressure levels and the definitions of terms like energy and power. The conversion factors and the context of atmospheric pressure versus sound pressure are also points of contention.

physea
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Sound waves transmit in atmosphere as dense and thin areas of air. Is there a graph showing the highest and lowest pressure of atmosphere for sound waves of various decibels?
 
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According to this page:

http://www.acoustic-glossary.co.uk/sound-pressure.htm

the 0-dB sound pressure level (SPL) in air is defined as 2 x 10-5 Pa. This is the root-mean-square difference between the instantaneous pressure and the ambient pressure (the pressure that you would have if there were no sound at all). For other SPLs, you can use the table or the formula given on that page.
 
I see 'street traffic' noise pressure is 2 Atm. What does that mean? That pressure the high pressure regions and what the low have in the atmosphere?
 
physea said:
I see 'street traffic' noise pressure is 2 Atm. What does that mean? That pressure the high pressure regions and what the low have in the atmosphere?
The pressures are given in Pa and not atmospheres.
 
nasu said:
The pressures are given in Pa and not atmospheres.

I already know that and I converted them to Atm.
 
Check your conversion factor. 0.2 Pa (which the table shows for "street noise") is much much less than 1 atm.
 
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physea said:
I see 'street traffic' noise pressure is 2 Atm. What does that mean? That pressure the high pressure regions and what the low have in the atmosphere?
Atmospheric pressure is about 105Pa and traffic noise is about 0.2Pa, which is a tiny fraction of that. I can't think where you got your "2 Atmospheres" from.
 
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The pressures in the table are the amplitudes of the pressure variations around the average value (the pressure in the air without sound waves, po).
A value of 2 Pa in the table means that the pressure in the sound wave can be between p0-2Pa and p0+2Pa . Even for the noise so strong that it can damage the ear, the variation are very small compared with the atmospheric pressure.
 
I am looking for a graph of the energy we need to produce a sound of x dB with current technology. Any hint?
 
  • #10
physea said:
I am looking for a graph of the energy we need to produce a sound of x dB with current technology. Any hint?
You would mean Power, not Energy. (Important distinction).
Did you ever try this wiki link?
 

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