Units of loudness of sound, being a subjective quantity

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Discussion Overview

The discussion revolves around the nature of loudness as a subjective quantity in sound perception, contrasting it with the objective measure of sound intensity. Participants explore the implications of having units for loudness, such as decibels and phons, and how these relate to human perception.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how loudness, described as a subjective sensation, can have measurable units like decibels and phons.
  • Another participant asserts that decibels measure a characteristic of sound, but acknowledges that perception of loudness can vary between individuals.
  • A different viewpoint suggests that while loudness is subjective, it can be quantified through experiments where people rate sounds, similar to the development of the magnitude system for star brightness.
  • One participant explains that sound intensity in decibels measures changes in air pressure, while loudness scales (in phons) are based on human perception and vary with frequency and age.
  • Additional notes mention that the relationship between perceived loudness and frequency can change, affecting how sounds are judged at different volumes.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between subjective loudness and its measurable units, with multiple competing views presented regarding how loudness can be quantified despite its subjective nature.

Contextual Notes

The discussion highlights limitations in understanding the definitions of loudness and intensity, as well as the variability in human perception that affects measurements.

Manraj singh
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I am learning sound. My teachers and textbook say loudness of sound is a subjective quantity, it is different for every person, while intensity is the objective quantity. The first section says intensity is a measurable quantity, WHILE LOUDNESS IS JUST A SENSATION. On the very next page they have given the units of loudness of sound, decibel and phon. Don't the two contradict each other? If loudness of sound is just a sensation, how does it have units to measure it? This has completely boggled my mind. Please help
 
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Decibels are an absolute measure of a characteristics of a sound. How your particular set of ears perceive a given decibel level is objective and can differ from mine.
 
While it may primarily be a subjective quantity, you can still take people and have them rate how loud a sound is and then take those results and assign a value to the measurements.

This is identical to how the magnitude system was initially developed to measure the brightness of different stars. For example, a magnitude 0.0 star is 2.5 times brighter than a magnitude 1.0 star, but the early magnitude system claimed it was only 2.0 times brighter since it looks only twice as bright to the eye.
 
Sound intensity (in decibels) is just a different scale for measuring the change in air pressure in a sound wave.

The scale for sound loudness is different for each person, and changes as the person gets older. The scale for loudness (in phons) was made by doing experiments with people, asking them to adjust to amplitude of sounds so that two sounds of different frequencies had the same loudness, or to adjust sounds at the same frequency so one was "twice as loud" as the other. The standard scale for loudness in phons is the average of those experiments on many people, and is defined as a set of curves relating phons to decibels.

eqlou.gif

(from http://hyperphysics.phy-astr.gsu.edu/hbase/sound/eqloud.html)

Note that the shape of the curves varies with the sound level, and the intensity (in dB) for equal loudness changes with the frequency of the sound.

FWIW there is a similar effect for the pitch of a sound as judged by humans, compared with the frequency as measured by the number of vibrations per second. Low pitched sounds appear to get lower as they get louder, high pitched sounds appear to get higher.

pitchloud2.jpg

(from http://acousticslab.org/psychoacoustics/PMFiles/Module05.htm)
 
Thank you
 

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