Figure 2.0, Loudness Curves (Fletcher-Munson Curves)
Perception
of Sound Waves
The
perception of sound by the listener is
directly
related to the physical characteristics of
the sound
wave. For a given frequency, the greater the
pressure
amplitude of a sound wave, the greater the
perceived
loudness.
An important factor that contributes is that the ear is not equally sensitive to all frequencies in the audible range. A sound at one frequency may seem louder than one of equal pressure amplitude at a different frequency.
The curves shown in Figures 2.0 indicate how the perceived loudness is a function of both the frequency and the amplitude of the sound wave. The unit used is the called a .phon.. At 1 kHz the phon and the dB Sound Pressure Level (SPL) are identical. As frequency varies, the phon follows the contour curve while the dB remains constant.
These curves tell us in some frequency regions the sound wave amplitudes must be increased to be perceived as equally loud as a sound of 1 kHz, while other wave frequencies must have their amplitude attenuated for the same perception.
| The frequency range your hearing accentuates coincides with the frequency range in which important lingual sounds have their major spectral contents. Sounds like .p. and .t. have very important parts of their spectral energy within the .accentuated. range, making them more easy to discriminate between. To hear sounds in the accentuated range is vital for speech communication. |
Figure 2.0, Loudness Curves (Fletcher-Munson
Curves)
If the curves are turned upside down, as in Figure 2.1, the curves tell give us an idea of how the human hearing attenuates and accentuates parts of the audible frequency range.
