Sound Flashcards
Origin of sound
- most sounds are waves produced by vibration of material objects
- vibrating material sends a disturbance through the surrounding medium, in the form of longitudinal waves
- in most cases, frequency of vibrating source and frequency of sound waves produced are the same
Pitch
Our subjective impression about the frequency of sound
- young person can hear 20-20000 Hz
- this range gets smaller with age
Infrasonic
Below 20 Hz
Ultrasonic
Above 20000 Hz
Pulse
No periodic sound
Compression
Condensed region of medium through which a longitudinal wave travels
Rare fraction
Reduced pressure of the medium through which a longitudinal wave travels
- it is not the medium that travels across the room but the energy carrying pulse
Elasticity
Ability of a material that has changed shape in response to an applied force to resume its initial shape once the distorting force is removed
Media that transmit sound
Relative to solids and liquids, air is a poor conductor of sound
- liquids and crystalline solids are generally excellent conductors of sound
- speed of sound is generally greater in solids than in liquids, and greater in liquids than in gases
Speed of sound
- depends on wind conditions, temperature, and humidity
- it DOES NOT depend on the loudness or frequency of the sound
- sound travels through warm air faster
- for each degree rise in temperature above 0C, speed of sound increases by 0.6m/s
Echo
Reflection of sound
Transmitted wave
Sound energy not carried by the reflected sound wave
Reverberations
Multiple refelctions
Acoustics
Study of sound properties
Refraction
When sound waves bend when parts of the wave fronts travel at different speeds
- sound travels slower at higher altitudes and bends away from the ground
- reflections and retractions of ultrasonic waves are used in diagnositc imaging
- when high frequency sound (ultrasound) enter the body, it is…
Energy in sound waves
- only a small amount of energy is needed to produce sound
- sound energy dissipates to thermal energy while sound travels in air
- for waves of higher frequency, the sound energy is transformed into internal energy faster than for waves of lower frequency
Forced vibration
Setting up of vibrations in an object by a vibrating force
Natural frequency
Frequency at which an elastic object naturally tends to vibrate if it is disturbed and the disturbing force is removed
- some factors that contribute to the natural frequency of an object are elasticity and shape of object
Resonance
When the frequency of forced vibrations on an object matches the object’s natural frequency and a dramatic increase in amplitude occurs
- tuning forks tuned to the same frequency and spaced about 1m apart from each other
Constructive interference
Waves arrive in phase and interfere constructively when the path lengths from the speakers are the same
(Crest meets crest, trough meets trough)
Destructive interference
Waves arrive out of phase and interfere destructively when the path lengths differ by half a wave length
(Crest meets trough)
Interference
If a range of sounds with different frequencies are emitted, only some waves destructively interfere. There is usually enough reflection of sound to fill in cancelled spots
Dead spots
Occur when sound aves reflect off walls and interfere with non-reflected waves to produce zones of low amplitude
- good anti-noise technology
Beats
Periodic variation in the loudness of sound
- they are due to interference
- the sound that reached our ears throbs between max and min loudness
- when frequencies are identical, the beats disappear
