| Themes > Science > Physics > Acoustics > Physical Characteristics of sound > Sensations of Tone > Sensations of Tone |
If the ear of an average young person is tested by an audiometer, it will be found to be sensitive to all sounds from 15 to 20 Hz to 15,000 or 20,000 Hz. The hearing of older persons is less acute, particularly to the higher frequencies. The ear is most sensitive in the range from A above middle C up to A four octaves higher; in this range a sound can be perceived hundreds of times fainter than a sound an octave higher or two octaves lower. The degree to which a sensitive ear can distinguish between two pure notes of slightly different loudness or slightly different frequency varies in different ranges of loudness and frequency of the tones. A difference in loudness of about 20 percent (1 decibel, dB), and a difference in frequency of 1/3 percent (about 1/20 of a note) can be distinguished in sounds of moderate intensity at the frequencies to which the ear is most sensitive (about 1000 to 2000 Hz). In this same range, the difference between the softest sound that can be heard and the loudest sound that can be distinguished as sound (louder sounds are "felt," or perceived, as painful stimuli) is about 120 dB (about 1 trillion times as loud). All of these sensitivity tests refer to pure tones, such as those produced by an electronic oscillator. Even for such pure tones the ear is imperfect. Notes of identical frequency but differing greatly in intensity may seem to differ slightly in pitch. More important is the difference in apparent relative intensities with different frequencies. At high intensities the ear is approximately equally sensitive to most frequencies, but at low intensities the ear is much more sensitive to the middle high frequencies than to the lowest and highest. Thus, sound-reproducing equipment that is functioning perfectly will seem to fail to reproduce the lowest and highest notes if the volume is decreased. |
|
|