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The Audible Frequency Range |
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We find as we go to lower frequency sounds, the ear becomes less
sensitive. If we go to low enough frequencies, we find that a
vibration in the air is not heard at all, so for our purposes
it is no longer what we would call sound. This lower frequency
limit for audible sounds is difficult to determine precisely.
For one thing, like most hearing phenomena, it will vary considerably
from person to person. Also, it is difficult to tell when a vibration
stops becoming a sound and becomes a feeling instead. Furthermore,
it is difficult to produce pure tones of considerable intensity
at low frequencies, and if harmonies are present in the tone,
the ear will think it is hearing the fundamental. However, as
a rough average figure, we may take the lower frequency limit
of sound to be about 15 cycles per second. Musically, the actual
value of the lower limit is immaterial. Pitch discrimination,
the ability to distinguish two tones of nearly the same frequency
as different in pitch, is very poor near the lower limit. The
lowest frequency tone at the piano is 27.5 cycles per second,
and even at this higher value pitch discrimination is not too
good. Hence we may consider the frequency range of musically
useful sounds to start at about where the piano does - at about
27 cycles per second. Going now to frequencies, we find there is also an upper limit to the frequencies the ear will hear as sound. This limit is even more indefinite than the lower limit. Not only does it vary widely from one person to another, but in given individual it will change with age: Young people can hear sounds of frequencies up to 17-18 kilocycles per second or higher; in older people this will drop to 12 kilocycles per second or lower. This hearing loss at high frequencies, called presbycusis, is a part of the normal aging process.. As a practical upper limit to sound frequencies, we may take an average of 15 kilocycles per second. The total frequency range of audible sounds is then 15 to 15,000 cycles per second. The ear can thus handle frequency range 1000 to 1. This is considerably smaller than the sound pressure range it can handle which is about 1 million to 1. As with very low frequencies, pitch discrimination is very poor at high frequencies; it is essentially nonexistent above about 10 kilocycles per second. |
Frequency Range of Musical Sounds |
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Measurements have been made on the sounds of musical instruments
to determine the frequency ranges they cover. It is found that
most instruments produce very little sound above 10 kilocycles
per second and what is produced in this region is associated
with noises such as bow scrapings, clinking of keys, and so forth.
For perfect reproduction of instrumental sounds, particularly
for percussion instruments, the whole audible frequency range
is necessary. However, the tone quality of most instruments is
very little affected by cutting off all frequencies above 10
kilocycles per second. This is why normal presbycusis is of no
consequence to the musician. The useful range of fundamental frequencies of tones produced by musical instruments is considerably less than the audible frequency range. The highest tone of the piano has a frequency of 4186 cycles per second, and this seems to have evolved as a practical upper limit for fundamental frequencies. The high-frequency region above this is necessary - in sound-reproducing equipment, for example - to accommodate the harmonics of the high tones. The working range of fundamental frequencies, the range of tones produced on musical instruments, is then approximately 27 to 4200 cycles per second. |