Ozarks Technical Community College
HIS 110: Acoustics & Psychoacoustics
Intensity and Loudness
Recall that intensity is an acoustic property of sound
that can be physically measured
Unit of measure is the decibel (dB)
Loudness is a psychoacoustic property of sound, in
that it represents our human perception of how “loud”
or “soft” sounds of various intensities are.
Units of measurement include the phon and sone
Things to remember…
Ours ears do NOT have a flat frequency response
They are more sensitive in the mid-frequencies (500-
5000 Hz) than at other frequencies
the average normal hearing person has a threshold of 7
dBSPL at 1000 Hz, but it requires almost 50 dBSPL to
hear a sound at 125 Hz.
What is a phon?
A basic measure of loudness
The loudness of a 1000 Hz pure tone at 40 dB=40
The 40 phon curve represents the sound intensity that
is required at each frequency to sound equally loud to
a 1000 Hz tone at 40 dB.
Refer to Figure 7.1 (Lass & Woodford)
Equal Loudness Contours
by Fletcher and
pressure level and
loudness of the
The curves show
how loud a sound
must be in dB SPL
to be perceived as
being of the same
loudness as a 1
kHz tone of a
Image from: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/
How was the phon scale developed?
Basically, you have a patient in the soundfield and you
present a 1000 Hz tone at 40 dBSPL.
The patient has a turn-dial knob and they are
instructed to adjust the volume of the subsequent
sounds of different frequencies until it is equally as
loud at the 1000 Hz tone at 40 dBSPL.
This created the 40 phon curve.
This process was repeated at the different input levels.
(i.e. 1000 Hz tone at 70 dBSPL to create 70 phon curve)
Phon vs. Sone
The phon scale provides us with a basic scale of
loudness. It tells us that one sound is louder than
The sone scale can tell us how much louder one sound
is than another. (i.e. 2x as loud, 4x as loud).
1 sone=40 phons
A change of 10 dB results in a doubling or halving of
the perceived loudness.
A 1000 Hz tone at 40 dB is perceived as being half as
loud as a 1000 Hz tone at 50 dB.
Keep in mind…
Practically speaking, you will never use these
They are more important to audio engineers who are
developing high-end audio equipment and sound
The psychoacoustic unit of measure to quantify a subjects
perception of the noisiness or annoyance of a sound is
termed the NOY.
The noy includes the presence of high frequency
components, intermittent presentation, changes in
frequency and intensity, and impulse components that all
contribute to the perceived “noisiness” of a sound.
Due to its limited research, this is enough said, regarding
One person’s “music” is another person’s “noise”.
Frequency and Pitch
Recall that frequency is an acoustic property of sound
that can be physically measured
Unit of measure is the hertz (Hz)
Pitch is a psychoacoustic property of sound, in that it
represents our human perception of how “high” or
“low” sounds of various frequencies are.
Unit of measure is the mel
What is a mel?
The mel scale was developed in 1937 by S.S. Stevens
The pitch of a 1000 Hz tone at 40 dB SPL=1000 mels
2000 mels is equivalent to a pitch that sounds twice as
loud as a 1000 mel tone
The mel scale is not linear
Doubling the perceived pitch does not equate to doubling the
i.e. 1000 mels=1000 Hz, but 2000 mels is NOT equal to 2000
How was the mel scale developed?
By “fractionalization” of a pure tone pitch
a pure tone pitch at forty phons of loudness was
presented and the subject was instructed to turn the
dial to find a pitch that was half the pitch of the first, a
third the pitch of the first, etc.
Pitch Perception Phenomena
When two tones of different frequencies (i.e. 500 and 700 Hz) are
simultaneously presented at high intensity levels, a low frequency
difference tone may be heard (i.e. 200 Hz) by the listener.
A summation tone may occur instead of a difference tone. For
example, a 1000 Hz tone plus a 500 Hz tone may be perceived as a 1500
Hz tone. This is not as commonly occurring as a difference tone.
The greater the intensity of a frequency the more likely it is perceived
at either a lower or higher frequency pitch.
Lower pitched tones are perceived to be of a lower frequency with
Higher pitched tones are perceived to be even higher with greater
This pitch change by intensity has little effect in the frequency areas
between 500Hz and 2KHz.
Timbre is composed of the whole spectrum of sound—
not just the pitch.
It is what differentiates musical instruments.
A trumpet, a piano, and a flute each produce a pitch of C
on the musical scale; however, each sounds differently
due to its TIMBRE.
Take Home Message
Though you will likely never use the phon, sone, or
mel clinically, it is very important to understand that
loudness, pitch, and complex noise perceptions vary
by frequency and from person-to-person.
All of these measurements were made on NORMAL
This will become critical when applying amplification
to pathologic residual hearing ability.