Download Sound Theory Questions and Answers 1. What`s the only thing that

Sound Theory Questions and Answers
1. What’s the only thing that happens to make sound? To make sound, something has to be vibrating to and fro,
creating a sequence of compressions and rarefactions that spread out through the air, forming a longitudinal wave.
2. What determines the frequency of the sound? When you pluck a stretched elastic band, it The air particles vibrate at
the same frequency as the elastic and their vibration frequency determines the pitch of the sound.
3. What determines the loudness of the sound? Plucking a guitar string just a bit causes it to vibrate just a bit and so
a small sound is released. Pluck it harder and it vibrates more and the released sound is louder. Why? The amount
the string vibrates determines the amplitude of the air particles' vibrations and this determines the loudness of the
sound. And finally, the energy of the sound waves moving through the air controls how much our eardrums vibrate
and how loud we think the sound is.
4. Can sound move through a vacuum? Recall that sound waves are a type of mechanical wave and so sound energy
must have a transmitting medium through which to move. In some space movies, we see a large space craft moving
across the screen and hear the rumble of its powerful engines. Is this accurate?
5. What is a similarity between bats and submarines? Both use echoes to look for things. Bats emit loud, high pitch
screams (good thing we can not hear at this frequency)and listen for the echoes. Their brains interpret the echoes to
help them avoid obstacles and locate food. Computers on submarines use sonar echoes in a similar way but the bat’s
brain is enormously more efficient at the task of understanding echoes. Porpoises can use their echolocation skills
to locate and even identify certain species of fish hiding in sand.
6. What is resonance? Sound waves striking a body can cause it to vibrate sympathetically if its natural vibration
frequency is the same as the sound's frequency. An example is when we feel the vibrations from a nearby loud base
speaker. Also, the windows in our house may rattle due to the low pitch sound of a powerful engine in a passing
vehicle.
7. In general, how does a clarinet or a guitar make sound? An acoustic musical instrument is basically just an air filled
cavity. Its sound is created by resonance. To play a clarinet for example, the musician first blows through the
mouthpiece to get the instrument’s resonator vibrating. The resonator is a reed – a small sliver of bamboo – and it
can emit just a tiny sound. Its vibrations move into the body of the clarinet and the air there absorbs the small sound
and begins to vibrate at the same frequency, i.e., to resonate. So, the tiny sound is magnified. A given size air cavity
will magnify one frequency best but the player wants to produce a variety of notes, all heard equally well by the
audience. So, the size of the air cavity must be changed each time a new note is to be played. The musician alters
the effective size of the air cavity by opening or closing the holes along the clarinet’s body. Resonance is important
to the operation of wind and stringed instruments which are "closed tubes", e.g., guitar, or "open tubes", e.g., tuba
8. How do we make sound? Humans make sounds when exhaled air passing by our vocal cords causes them to vibrate.
We change the pitch of our voice through tiny muscles that adjust the tension on our vocal cords.
9. What about the different pitch ranges of males and females? At puberty, hormones make the vocal cords of males
thicker than those of females and so the male voice tends to have a lower range of frequencies.
10. Can a given string release various frequencies? A string vibrating as a whole, i.e., in one segment, creates its
lowest tone, the fundamental or first harmonic. The string will have two nodes (points of no vibration) and one
antinode (a location of maximum vibration.) If the string vibrates in two segments, it has three nodes, two
antinodes and produces a sound called the second harmonic; its pitch is twice as high as its fundamental. A string
vibrating in three segments will have five evenly spaced nodes and three antinodes. Its sound is called the third
harmonic and has a pitch three times as high as its fundamental. A long string tends to vibrate in a number of these
vibration patterns all at the same time, producing a rich sound full of harmonics. Note: A sound with a frequency
double that of another sound is an octave above it.
11. What creates the harmony of two or more singers singing together? When two different pitches occur together, we
hear a new sound with a wavering or quivering quality. The pitch of this new sound, the beat frequency, is just the
mathematical difference of the two original pitches. Because our attention is drawn to the beat frequency and not
the individual original sounds, composers must anticipate what new sounds are created by groups of instruments
or voices. Certain sounds create beat frequencies that are pleasant to us and we say the sound is a consonance. If
the sound of the beat frequency is unpleasant, we call it a dissonance. The blended sound of a barbershop quartet
is a consonance.
12. What is the Doppler Shift about? When a sound source is motionless, its sound waves spread out in evenly spaced
circles. But, if the sound source is moving, the waves in front of it become squished and the waves behind it
become elongated. People in front of the moving sound source are in the path of the compressed sound waves and
hear a higher than normal pitch; people in the path of the elongated sound waves behind the moving sound hear a
lower than normal pitch.
13. Name the main ear parts. The ear has three major sections: the outer, middle and inner ear.
14. What happens in the outer ear? The pinna is the fleshy outermost part of our ear. It collects sound waves and
directs them into the auditory canal. The auditory canal then directs the sound to the middle ear.
15. In the middle ear? The tympanic membrane (eardrum), the start of the middle ear, vibrates as the sound waves
strike it. Attached to the inside of the eardrum are the three ossicles, the tiniest bones in our body. As they vibrate
and transfer sound energy to the inner ear, they magnify it 1.5 times. When a sound reaches a certain intensity, two
tiny muscles pull the last ossicle back from the inner ear and this reduces the chance of damage there.
16. And in the inner ear? The last ossicle transmits its vibrations into the cochlea, a spiral shaped structure filled with
liquid and lined with about 22 000 vibration sensitive nerve hairs. The nerve hairs are grouped into thousands of
small rows, each one containing hairs sensitive to a certain frequency. Finally, the auditory nerve gathers all the
impulses from the nerve hairs and carries them to the brain’s auditory center where we “hear”.
17. Contrast the units of decibel (dB) and hertz (Hz). The decibel scale, dB, is used to measure sound intensity.
Frequency is measured in Hz. If sounds are loud enough, the extreme frequency range of a very sensitive the
human ear is from 20 to 20 000 Hz.
18. What is an ultrasonic sound? Sounds with frequencies above 20 000 Hz are called ultrasonic sounds.
19. An infrasonic sound? Sounds with frequencies below 20 Hz are called infrasonic sounds.
20. Do we hear all sounds the same? Within the audible frequency range, we do not hear all frequencies equally well.
21. Know the following hearing safety chart. Audiologists have published charts listing the intensity of common
sounds to help people judge the safety of certain sound environments. Note: do not confuse the pitch of a sound
(Hz) and its loudness (dB.) Loudness is aspect of a sound that causes the greater damage.
Sound source
threshold
whisper
normal conversation
traffic
pain
rock concert
dB
0
10 - 20
60 - 70
70 - 80
120
100 - 150
22. What is tintinitis? If a sound is loud enough, it causes the eardrum to vibrate so far back and forth that pain is felt.
Note that pain can be caused by the loud sounds from a rock concert. In addition to hearing loss, exposure to loud
sounds can cause another permanent hearing disorder called tintinitis. The symptom is a constant ringing sound.
Sleep is possible only by masking the ringing with louder but soothing sounds, e.g., water sounds.
23. Do animals have different hearing ranges than us? Elephants can make and hear infrasonic sounds. When they are
lying in water, getting washed by their trainers, you can see energy ripples moving out from their foreheads but we
can not hear the sound. They use infrasonic sounds to communicate with other elephants as far away as 500 miles.
Pigeons can hear the infrasonic sounds made by wind rushing through mountain passes thousands of
kilometers away. They use these sounds to help them navigate.
Another long distance listener is the whale. They can also hear infrasoninc sounds made thousands of
kilometers away. We think they use these low frequency sounds for communication and navigation.
24. What was a strange sound “weapon”? A bizarre use of infrasonic sound was as a weapon of war. A giant coach’s
whistle powered by a huge compressor sent out infrasonic sounds that disoriented the enemy. But, after just a few
trials, the sound weapon was taken out of use. Because the sound waves diffracted around the weapon, the
operators were subjected to the same energy and became too ill to use it.
25. What is one job related hearing loss? Television technicians repairing vacuum tube powered picture tubes used to
suffer hearing loss at one specific frequency. It was later realized that one of the TV’s transformers (called a fly-by
transformer) gave off a constant 15 000 Hz barely audible squeal. After years of exposure, the technician’s
cochlear cells sensitive to that frequency were wrecked.
26. What are some uses of ultrasonic sounds? These super high frequency sounds have a number of uses. They can be
used to clean jewellery, measure heart performance, reveal the hidden world of unborn babies, zap painful
gallstones into much less painful grit and, as “silent” dog whistles to command trained animals, e.g., dogs, goats.