Elenco Snap Circuits® Deluxe Sound & Light Combo - Manual (Page 17)

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Sound in Our World
Sound is a variation in air pressure created by
a mechanical vibration. See projects 13 & 51
for a demonstration of this. These air pressure
variations travel across the room like waves,
so we call them sound waves. You “hear”
sound when your ears feel these air pressure
variations, and convert them to nerve pulses
that your brain interprets. Eventually the
energy of a sound wave is absorbed, and
becomes heat.
Sound waves can also be thought of as waves
of temporary compression that travel through
materials. Notice that at a loud concert you can
sometimes feel the pressure waves, in
addition to hearing them. Sound waves can
travel through liquids and solids but their
speed may change and their energy may be
reduced, depending on the characteristics of
the material. Sound waves can only travel
through a compressible material, and so
cannot travel through a vacuum. Outer space
is silent, because there is no air or other
material for sound waves to travel through.
The “hearing” part of your ear is inside your
skull; the flaps you see are just funnels to
collect the sound and pass it along to your
eardrum inside. When you were young your
brain learned to interpret the difference in the
information collected from your two ears, and
use it to know which direction a sound came
from. If one of your ears is clogged, then it is
difficult to determine a sound’s direction.
You can compare sound waves from your
voice to waves in a pond. When you speak,
the movements in your mouth create sound
waves just as tossing a rock into the pond
creates water waves. Sound waves travel
through air as water waves travel across the
pond. If someone is nearby, then their ears will
feel the air pressure variations caused by your
sound waves just as a small boat at the other
side of the pond will feel the water waves.
If the mechanical vibration causing the sound
wave occurs at a constant rate, then the sound
wave will repeat itself at the same rate; we
refer to this as the frequency of the sound
wave. Nearly all sound waves have their
energy spread unevenly across a range of
frequencies. When you say a word, you create
a sound wave with energy at various
frequencies, just as tossing a handful of
various-sized rocks into the pond will create a
complicated water wave pattern.
Frequency measures how many times
something occurs per second, expressed in
units called hertz (Hz). The metric prefixes can
be used, so 1,000 repetitions per second is 1
kilohertz (kHz) and 1,000,000 repetitions per
second is 1 megahertz (MHz). The range of
frequencies that can be heard by the human
ear is approximately 20 to 20,000 Hz and is
referred to as the audio range.
Just as there are sound waves caused by
mechanical vibrations, there are also electrical
waves caused by electrical variations. Just as
sound waves travel through air, electrical
waves travel through wires. A microphone
senses pressure variations from sound waves
and creates electrical waves at the same
frequencies. A speaker converts electricity into
sound, by using the energy in electrical waves
to create mechanical vibrations (sound waves)
at the same frequencies.
How does the speaker make sound? An
electric current flowing through a wire has a
very, very tiny magnetic field. Inside the
speaker is a coil of wire and a magnet. The coil
of wire concentrates the magnetic field from
the flowing electric current, enough to make
the magnet move slightly, like a vibration. The
magnet’s vibration creates the air pressure
variations that travel to your ears.
Your speaker can only create sound from a
CHANGING electrical signal, for unchanging
electrical signals it acts like a 32 ohm resistor.
(An unchanging signal does not cause the
magnet in the speaker to move, so no sound
waves are created). Electrical variations at
high frequencies (referred to as radio
frequencies) cannot be heard by your ears, but
can be used to create electromagnetic radio
waves, which travel through air and are used
for many forms of communication. In AM and
FM radio, voice or music is superimposed on
radio waves, allowing it to be transmitted over
great distances, to later be decoded and
listened to.
Sound and water waves
Speaker
sound waves
SCC-350_Manual_Part_A.qxp 7/25/14 2:39 PM Page 17