Can Decibels Measure Sound Wave Loudness?

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Discussion Overview

The discussion revolves around the measurement of sound wave loudness, exploring various methods and units used in quantifying loudness, including decibels (dB), phons, and sones. Participants delve into the mathematical aspects of loudness measurement and the subjective nature of sound perception.

Discussion Character

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

Main Points Raised

  • Some participants suggest that sound loudness is commonly measured using sound level meters that report in dB.
  • Others argue that loudness perception is frequency-dependent, noting that units like phons and sones are relevant, with some uncertainty about which is the standard unit.
  • It is mentioned that conventional studies often use dB, but the ear's interpretation of sound requires adjustments through weighting filters (A, B, C, D weightings), with dBA being the most commonly quoted.
  • One participant explains that sound intensity in dB is relative to the minimum perceivable sound intensity, providing examples of how dB levels correspond to multiples of this minimum level.
  • Another participant seeks a mathematical approach to compare the loudness of two sound waves with similar frequencies, questioning whether an integral of wave amplitude or another norm is needed.
  • Concerns are raised about the practicality of comparing different waveforms, such as square waves versus sine waves, due to the subjective nature of loudness perception and the complexities of sound pressure fields.
  • One participant asserts that loudness is fundamentally a function of amplitude and relates this to the logarithmic nature of human hearing, which aligns with the decibel scale.

Areas of Agreement / Disagreement

Participants express differing views on the best methods and units for measuring sound loudness, with no consensus reached on the mathematical operations required to compare the loudness of different sound waves.

Contextual Notes

Participants highlight the subjective nature of loudness perception and the influence of frequency on how sound is experienced, indicating that the discussion may depend on specific definitions and assumptions about sound measurement.

yetar
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How do you measure a sound wave loudness?

Thanks in advance.
 
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A sound level meter that measures sound pressure levels is the most common.
 
In dB I think.
 
Mk said:
In dB I think.
You would think so wouldn't you, but not quite. Loudness is usually quoted with a frequency since the ear does not perceive all frequencies equally. The phon and the sone are common units of loudness, although I believe the sone is the standard unit, but I could be wrong.
 
Hootenanny said:
You would think so wouldn't you, but not quite. Loudness is usually quoted with a frequency since the ear does not perceive all frequencies equally. The phon and the sone are common units of loudness, although I believe the sone is the standard unit, but I could be wrong.
Most conventional studies are indeed done in dB. However, the ear's interpretation of sound requires the altering/filtering of the source measurements. Hense the A, B, C and D weightings. The A weighting being the filter used most commonly and thus why most readings being quoted in dBA. Sones are used, but I think the dB rules supreme in this area.
 
Normally sound intensity is measured in dB relative to the minimum perceivable sound intensity of the human ear measured in units of W/m^2 (which turns out to be 1x10^-12 or something of that order).

So a sound level of 20 dB means that the sound intensity is 100x the minimum aubible level. 30 dB means the sound intensity is 1,000x, 40 dB 10,000x and so on.

As has been pointed out, this is not the only way to measure sound 'loudness', but this is the most common way it is measured in my experience as a layperson.

Claude.
 
This is not exactly what I ment.
It is true that the human ear percieve sound loudness relative to its frequency and relative to the average sound in the environment.
However, I want to know the mathematical side of sound loudness.
Lets say we have two different sound waves that have a very close frequency.
What mathematical operation we need to do on the two sounds to tell which one is louder? Is it an integral on the absolute value of the wave amplitude?
Is it some other norm?
For example, if we have two sound waves that have the same frequency, one is a square wave and the other is a sin wave, who will be louder?
 
A square sound wave? That would imply an almost infinite acceleration of the sound producing device/thing. The forces generated would be huge. I don't think it's practical to look at it like that.

Since the interpretation of loudness is highly subjective, I would say that two things would be required. The first is a thorough understanding of the pressure field created by the source. The second is to understand the filtering characteristics of any of the weighting schemes.
 
Is it an integral on the absolute value of the wave amplitude?
It's just a function of the amplitude:

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l2c.html

Since our hearing is basically logarithmic (similar to most of our senses, which allows a large range of input), the decibel scale is the same.
 
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