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The regular vibration of common
materials results in sound waves. Musical instruments
create sounds that can be varied in pitch and volume.
Some give off relatively pure tones, while others
consist of a pleasing mix of frequencies.
Questions you may have include:
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What are the different ways musical
sounds can be made?
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How are musical sounds amplified?
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What makes musical sounds pleasing?
Making music
The vibration of some device, such as a
wire, drum, or reed, creates musical sounds. Sometimes
moving air can be made to vibrate at certain
frequencies.
If you tie a string or wire tightly
between two posts, you can start it vibrating by
plucking or tapping it. The vibration creates
compression waves in the air, resulting in sound,
according to the frequency of the waves.
Musical instruments that use vibrating
wire to produce sound include the guitar, violin, piano
and harp.
The frequency, wavelength or pitch of
the sound depends on what the string or wire is made of,
its thickness, its length, and how tight it is strung
between the posts.
The frequency from a vibrating wire is
relative pure. In other words, it primarily consists of
one frequency. This fact is used in tuning the musical
instrument. By adjusting the tension of the wire, the
frequency can be changed slightly until it is exactly at
some set pitch.
Although some experts can tell that it
is at the correct pitch with their ears, a more accurate
way is to use a tuning fork that is calibrated at the
desired frequency. When two sounds are almost at the
same frequency, a throbbing sound is heard. It is also
called the beat frequency.
This frequency gets slower and slower as
the string reaches the same frequency of the tuning
fork. When the beat frequency disappears, the string is
tuned to the exact pitch of the tuning fork.
A drum is made by stretching some
material over a container. Striking the head of the drum
causes it to vibrate and make a sound. In reality, the
head of a drum is like a string in two-dimensions.
Being in two-dimensions, the vibration
of the drum head can be fairly complex. An interesting
experiment is to sprinkle some powder on the hear of a
drum and then strike it gently. The vibration of the
drumhead will create a pattern in the powder.
A relatively small, thin piece of
material, held in place, can be made to vibrate and make
sounds.
A simple example is putting a blade of
grass between your thumbs and blowing on it. Another
example of a reed is wrapping some wax paper around a
comb, putting it to your mouth and blowing on it to make
a sound like a kazoo.
The clarinet and harmonica are musical
instruments that use reeds to make their sound. Your
vocal cords are also a set of reed-like materials.
The act of blowing through or across a
chamber of air can create sound vibrations. The best
example of this is whistling. By changing the position
of your tongue, you can change the note of your
whistling.
If you blow across the mouth of a
bottle, you can also make a sound. By putting different
levels of water in the bottle, you can adjust the pitch.
Typical musical instruments using this
technique for creating sound are the trumpet, flute and
organ.
Amplifying music
Sounds can be amplified by trying
harder, resonance, and electronically.
One way to make the sound louder in a
musical instrument is to try harder. You can hit the
piano keys harder, strum the guitar harder, or blow
harder on the trumpet.
Another method is through using
resonance. The reason a bottle makes sound when you blow
across the top is that the air bounces back and forth
inside, amplifying the sound wave that is the length of
the depth of the bottle.
This principle is used in many musical
instruments, no matter how the sound in created. For
example, a guitar string plucked by itself makes a weak
sound. But when added to the hollow body of the acoustic
guitar, the sounds resonate and are amplified. The body
of a clarinet amplified the sound of the reed.
Electronic amplifiers use microphones
and similar devices to pick up the sound and increase
the volume. The electronics can also create special
effects, like echoes and frequency changes.
It is difficult, though, for electronic
amplification to reproduce the "character" of some
resonance amplifications.
Aesthetics
What makes a sound pleasing to the ear?
A tuning fork has a pure sound of one frequency, but
that is not necessarily pleasing or music. Early
synthetic or electronic sound was able to create and
vary many pure frequencies, but again, it wasn't too
pleasing to the ear.
One factor in musical sounds is
harmonics, or multiples of the pure tone. These
harmonics can add fullness and character to make the
tone sound better.
Certain combinations of frequencies or
pitches are more pleasing to the ear than others that
may sound "sour" or off-tune. Some of this is also
cultural, because some foreign instruments can sound
out-of-tune to someone not brought up with that type of
music.
Musical sounds are created by strings,
drums, reeds, and blowing. They can be amplified by
trying harder, resonance or electronics. Harmonics,
combinations of frequencies, and culture play a role in
what makes music and is pleasing to the ear. |
