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Chapter: 06. Sound
Musical Instruments: Stringed vs. Percussion vs. Wind vs. Reed
Category
Vibrating Part / Sound Mechanism
Structural Features
Examples Mentioned in Text
Stringed Instruments
Stretched strings vibrate when plucked or stroked with a bow.
Stretched strings and a hollow body that traps an air column to enhance sound.
Veenas, santoors, guitars, harps, and tanpuras.
Percussion (Membrane) Instruments
Tightly stretched skin or membrane vibrates when struck.
A hollow frame with a tightly stretched skin/membrane across openings.
Tabla, drums.
Wind Instruments
Air columns vibrate when air is blown into them.
Not mentioned in text
Flutes, bugles.
Reed Instruments
Metal reeds vibrate when air is blown through them.
Contain metal reeds.
Harmoniums, trumpets, and mouth organs.
Characteristics of Sound: Loudness vs. Pitch vs. Quality (Timbre)
Characteristic
Definition
Determining Factors
Vibration Properties
Loudness
The ear’s perception of a sound as loud or soft depending on its intensity (energy).
• Amplitude (directly proportional to square of amplitude)• Distance between listener and source• Area of vibrating body• Sensitivity of listener’s ear
• Large amplitude/intensity = loud sound• Small amplitude = soft sound
Pitch
The characteristic of sound that determines its shrillness.
Frequency (rate at which vibrations are produced).
• High frequency = high-pitched (shrill) sound• Low frequency = low-pitched (flat) sound
Quality (Timbre)
The characteristic enabling distinction between sounds of the same pitch and loudness from different sources.
The source producing the sound.
Not mentioned in text
Wave Media Comparison: Sound Waves vs. Light Waves
Feature
Sound Waves
Light Waves
Speed in Air
Approximately 340 m/s
3 × 10⁸ m/s
Relative Speed
Slower (takes more time to travel)
Faster (travels faster than sound)
Propagation Medium Requirement
Requires a material medium; cannot travel through a vacuum.
Can travel through space/vacuum; does not require a material medium.
Dependency of Speed in Air
Varies according to atmospheric conditions (temperature, pressure, and presence of moisture).
Constant
Speed of Sound across States of Matter
State of Matter
Relative Speed
Typical Examples & Speeds at 0°C
Propagation Capability
Solids
Fastest
• Glass: 5500 m/s• Steel: 5100 m/s• Copper: 3560 m/s
Excellent
Liquids
Faster than gases, slower than solids
• Water: 1450 m/s• Turpentine: 1325 m/s• Alcohol: 1210 m/s
Good
Gases
Slowest
• Hydrogen: 1270 m/s• Air: 340 m/s• Carbon dioxide: 260 m/s
Poor
Vacuum
Cannot propagate
Not applicable
Absent (cannot travel due to complete absence of particles)
Reflection of Sound: Good Reflectors vs. Bad Reflectors
Property
Good Reflectors
Bad Reflectors
Surface Characteristics
Hard and rigid surfaces
Soft, fluffy, or porous surfaces
Sound Absorption Level
Low absorption (bounces/reflects most sound waves)
High absorption (absorbs most striking sound waves)
Common Materials
Metals (e.g., aluminum door)
Clothes, cork, paper, wool, wood, sponge, thermocol, carpets, rough materials, thick curtains
Common Applications
Large reflectors (e.g., mountains, big buildings) are useful for producing echoes
Covering walls, ceilings, and floors of auditoriums and cinema halls; window curtains to block unwanted sound
Ranges of Sound: Sonic vs. Ultrasonic vs. Infrasonic (Subsonic)
Sound Type
Frequency Range
Human Audibility
Examples of Animals Sensitive to It
Practical Uses / Features
Sonic (Audible)
20 Hz to 20,000 Hz
Audible
Humans
Enables the general sensation of hearing.
Ultrasonic
Greater than 20,000 Hz
Inaudible
Dogs, leopards, monkeys, deer, bats, whales, seals
• Medical diagnostic imaging (sonogram/echocardiogram)• Relieving muscle/joint pain• Cleaning utensils with ultrasonic vibrators• Detecting faults/cracks in metal sheets• Mixing milk powder with fat• Grease/dirt/tartar removal• Locating shoals of fish
Infrasonic (Subsonic)
Less than 20 Hz
Inaudible
Not mentioned in text
Not mentioned in text
Vocal Cord Configurations: Tight & Thin vs. Loose & Thick
Vocal Cord State
Frequency of Vibration
Resulting Voice Characteristic
Tight and Thin
High frequency
High-pitched / shrill
Loose and Thick
Low frequency
Low-pitched / flat
Larynx and Voice: Males vs. Females
Gender
Relative Larynx Size
Voice Quality
Males
Bigger
Low-pitched / less shrill
Females
Smaller (relative to males)
High-pitched / shrill
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