Sound is measured in two ways: by loudness, or decibel level,
and by frequency, or pitch.
Decibel (dB) levels run from 0, the softest sounds a human
can hear, to the truly deafening noise up around 150 dB and
beyond. The decibel scale is logarithmic, which means that
it increases exponentially, doubling in sound pressure from
one level to the next: 90 dB is twice as loud as 80, and
80 dB is twice as loud as 70.
To put it in perspective, we speak in the 40 to 60 dB range.
A telephone rings at about 80 dB, a lawnmower might register
90 dB, and a rock concert could go as high as 120 dB. Noise
levels above 80 dB are potentially damaging to hearing when
prolonged.
Frequency is measured in Hertz (Hz). Hertz is the number
of oscillations (waves) per second the air molecules in a
sound wave makes. For example, a sound that registers 300
Hz oscillates 300 times per second. The number of oscillations
also determines what sound sounds like to our ears. Think
of bass notes vs. treble notes on a piano. Low frequencies
produce lower-pitched tones, while high frequencies are higher
in pitch.
While the pure tones produced by a tuning fork, or hearing
test equipment each represent a single frequency, most sounds
we hear in everyday life, including speech, are a combination
of many frequencies. The frequencies associated with human
speech range from around 200 to 8000 Hz, though the human
ear can perceive frequencies from 20 to 20,000 Hz.
Now that you know how sound is produced, find out how it’s
experienced. Click to hear a tone at each frequency:
Note: The latest version of the Macromedia Flash
Player is required to hear these demonstrations. It can be
found here.
If you’re not able to hear all the sounds, try increasing
your speaker volume. Most computers’ internal speakers
cannot reproduce tones at lower frequencies, so unless your
computer has external, hi-fidelity speakers, you may not
be able to hear tones at 250 and 500 Hz.
