<< Chapter < Page Chapter >> Page >

A unit called a phon    is used to express loudness numerically. Phons differ from decibels because the phon is a unit of loudness perception, whereas the decibel is a unit of physical intensity. [link] shows the relationship of loudness to intensity (or intensity level) and frequency for persons with normal hearing. The curved lines are equal-loudness curves. Each curve is labeled with its loudness in phons. Any sound along a given curve is perceived as equally loud by the average person. The curves were determined by having large numbers of people compare the loudness of sounds at different frequencies and sound intensity levels. At a frequency of 1000 Hz, phons are taken to be numerically equal to decibels.

The graph is the plot of sound level in decibels versus frequency in Herz. Data for 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 phons is plotted. Data is plotted as curved lines stacked one a top of other.
The relationship of loudness in phons to intensity level (in decibels) and intensity (in watts per meter squared) for persons with normal hearing. The curved lines are equal-loudness curves—all sounds on a given curve are perceived as equally loud. Phons and decibels are defined to be the same at 1000 Hz.

Measuring loudness

(a) What is the loudness in phons of a 100-Hz sound that has an intensity level of 80 dB? (b) What is the intensity level in decibels of a 4000-Hz sound having a loudness of 70 phons? (c) At what intensity level will an 8000-Hz sound have the same loudness as a 200-Hz sound at 60 dB?

Strategy

The graph in [link] should be referenced to solve this example. To find the loudness of a given sound, you must know its frequency and intensity level, locate that point on the square grid, and then interpolate between loudness curves to get the loudness in phons. Once that point is located, the intensity level can be determined from the vertical axis.

Solution

  1. Identify knowns: The square grid of the graph relating phons and decibels is a plot of intensity level versus frequency—both physical quantities: 100 Hz at 80 dB lies halfway between the curves marked 70 and 80 phons.
    Find the loudness: 75 phons.
  2. Identify knowns: Values are given to be 4000 Hz at 70 phons.
    Follow the 70-phon curve until it reaches 4000 Hz. At that point, it is below the 70 dB line at about 67 dB.
    Find the intensity level: 67 dB.
  3. Locate the point for a 200 Hz and 60 dB sound.
    Find the loudness: This point lies just slightly above the 50-phon curve, and so its loudness is 51 phons.
    Look for the 51-phon level is at 8000 Hz: 63 dB.

Significance

These answers, like all information extracted from [link] , have uncertainties of several phons or several decibels, partly due to difficulties in interpolation, but mostly related to uncertainties in the equal-loudness curves.

Got questions? Get instant answers now!

Check Your Understanding Describe how amplitude is related to the loudness of a sound.

Amplitude is directly proportional to the experience of loudness. As amplitude increases, loudness increases.

Got questions? Get instant answers now!

In this section, we discussed the characteristics of sound and how we hear, but how are the sounds we hear produced? Interesting sources of sound are musical instruments and the human voice, and we will discuss these sources. But before we can understand how musical instruments produce sound, we need to look at the basic mechanisms behind these instruments. The theories behind the mechanisms used by musical instruments involve interference, superposition, and standing waves, which we discuss in the next section.

Questions & Answers

What is angular velocity
Amara Reply
refer to how fast an object rotates ot revolve to another point
samson
An object undergoes constant acceleration after starting from rest and then travels 5m in the first seconds .determine how far it will go in the next seconds
Sophy Reply
x=x0+v0t+1/2at^2
Grant
what is the deference between precision and accuracy
ShAmy
In measurement of a set, accuracy refers to closeness of the measurements to a specific value, while precision refers to the closeness of the measurements to each other. 
Grant
Thank you Mr..
ShAmy
Are there is a difference between Error and Relative Error...
ShAmy
An aircraft flies 300km due east and 600km due north. determine the magnitude of its displacement
Sophy Reply
670.8km
iyiola
which formula did you use
Sophy
X^2=300^2+600^2
iyiola
what is Fermat principle.
Madhu Reply
find the angle of projection at which the horizontal range is twice the maximum height of a projectile
Akaji Reply
impulse by height fomula
Tigst Reply
Hello
Madue
what is impulse?
Tigst Reply
impulse is the integral of a force (F),over the interval for which it act
Agbeyangi
What is significance of vector?
jagan Reply
magnitude and direction
Chris
what is impulse?
Enimini Reply
the product of force and time
Robert
find the flow rate of a fluid of viscosity 0.0015N-s/m³ flowing through a pipe of radius 50cm and length 100m at a pressure differential of 200000N/m²
Okoli Reply
friend ,what is the equation your question
lasitha
What is victor
Moses Reply
How are you all?
Giorgi Reply
what is the formula for momentum?
Chisom Reply
p=mv
Grant
what is the formula for angular displacement ?
lasitha
angular displacement = l/r
anand
friend ,what is the " l "?
lasitha
I have another problem,what is the difference between pure chemistry and applied chemistry ?
lasitha
l stands for linear displacement and l>>r
anand
r stands for radius or position vector of particle
anand
pure chemistry is related to classical and basic concepts of chemistry while applied Chemistry deals with it's application oriented concepts and procedures.
anand
what is the deference between precision and accuracy?
ShAmy
I think in general both are same , more accuracy means more precise
anand
and lessor error
anand
friends,how to find correct applied chemistry notes?
lasitha
what are the main concepts of applied chemistry ?
lasitha
anand,can you give an example for angular displacement ?
lasitha
when any particle rotates or revolves about something , an axis or point ,then angle traversed is angular displacement
anand
like a revolving fan
anand
yeah ,I understood now, thanks!
lasitha
o need this application in French language
Diacre Reply
Why is it that the definition is not there
Bello
what is physics
mesfin Reply
the study of matter in relation to energy
Robert
Ampher law
Zia
Practice Key Terms 8

Get the best University physics vol... course in your pocket!





Source:  OpenStax, University physics volume 1. OpenStax CNX. Sep 19, 2016 Download for free at http://cnx.org/content/col12031/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 1' conversation and receive update notifications?

Ask