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Sound Image 1 - Basic Physics

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jedi bunny

on 6 August 2017

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Transcript of Sound Image 1 - Basic Physics

we hear before we see:
- reactive listening begins at around 16 weeks, even though the ear is not fully developed until 24 weeks
- sight is the last sense to be developed and is not fine-tuned until after birth; eyelids don't usually open until 7th month.

there is a difference between hearing and listening
sound has physical or acoustic dimension but still seems abstract
sound engages imagination and emotions
with film and video, the brain sees one image at a time
sound can be layered, the ear can process many sounds at once: speech, noise, music
Acoustical phase:
The time relationship between 2 or more soundwaves at a given point in their cycles. Waves are repetitive and occur at regular intervals, which you can measure in degrees.

In phase:
If 2 identical waves begin at the same time, the intervals will coincide. They reinforce each other and increase in amplitude.
This is constructive interference.
 
Out of phase:
If the 2 identical waves begin at different times, the intervals will not coincide and could decrease each other's amplitude.
This is destructive interference.
Timbre
refers to the specific color or tonality of different sounds,
despite
having same pitch. Timbre is related to harmonics, the material of vibrating object, how sound is made: struck, plucked, blown, etc.

Sound Pressure Level or SPL:
the relative intensity of acoustic pressure

Audible dynamic range:
Humans hear from 0dB to 120dB, from quiet to deafening.

Threshold of Hearing:
quietest sound we can hear
 
Threshold of Pain:
loudest sounds we hear, causing pain & hearing loss
This indicates the number of cycles the vibrating object completes in one second.
The number of cycles per second is expressed in hertz or kilohertz.

Audible frequency range:
The range of frequencies between 20hz to 20kHz that the human ear should be sensitive to. Frequencies at high and low end are felt rather than heard.

Pitch:
The way the brain perceives frequency; highness or lowness; treble or bass.
 The air molecules don't move
with
the sound wave, they eventually slow down and settle into an average resting place until another wave comes.

Sound moves in longitudinal waves, like vibrations through the coils of a Slinky toy.

Compression:
As a vibrating object moves outward,air molecules are more densely squeezed together into areas of increasing air pressure
Rarefaction:
As a vibrating object moves inward, air molecules are pulled apart and the molecules thin out, resulting in decreasing air pressure

When a vibration has undergone one back and forth motion it completes one
cycle.
The Sense of Hearing
attack
- first sound emitted when object starts vibrating
initial decay
- slight decrease in amplitude as sound reaches momentum
sustain
- how long the sound stays at stable amplitude or volume; the body of the sound
final decay or release
- how long it takes for sound to go from stable vibration to silence
The diagrams we've been looking at have been of simple, single frequency soundwaves, pure tones called
sine waves.
 
But sound consists of several frequencies at various amplitudes with a unique structure.
This is called a
complex or composite waveform.
Equal Loudness Principle:

We do not hear high and low frequencies at equal loudness as midrange freqs.

Our ears are most sensitive at 3kHz. You'd have to boost a sound 70dB to hear lower, bassier frequencies.
For example:
A 20 Hz sound is 55 feet in wavelength; a 8kHz sound is 1.5 inches in wavelength.
This will be important in acoustics because short, high freqs generally bounce; long, low freqs tend to bend around and under objects and barriers.
Sound is created by a vibrating object. Air molecules closest to the object are set in motion. A sound wave is created as these molecules move back and forth in response to vibration. Momentum is transferred to adjacent molecules and propagates the wave, carrying sound to your ear. This is possible because of the elasticity of air itself.
 

Harmonic Partials
SOUND IMAGE:
BASIC PHYSICS

In physics, resonance is a phenomenon in which a vibrating system or object drives another system to vibrate with greater amplitude at specific frequencies.
 
An acoustically resonant object usually has more than one resonance frequency, especially at its harmonic frequencies. 

It will easily vibrate at those frequencies, and vibrate less strongly at other frequencies. It will "pick out" its resonance frequency from the sound waves around it. In effect, it is filtering out all frequencies other than its resonance.
What is the Speed of Sound?
In everyday speech,
"speed of sound"
refers to the speed of sound waves in air. However, the speed of sound varies from substance to substance, and with temperature. Sound travels
faster
in liquids and non-porous solids than it does in air, and
faster
in warmer temps than in cold.
In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s).
In fresh water, sound travels at about 1497 m/s (4911 ft/s) at 25 °C.
In salt water free of air bubbles or suspended sediment, sound travels at about 1560 m/s. (5118 ft/s).
In brick, sound travels at 4176 m/s; in steel at 6100 m/s; and in glass at 3962 m/s.
Demonstration
basic ideas about sound
We get 2 kinds of information from sound:

COGNITIVE INFORMATION,

which
relates to knowledge, reasoning, memory
and judgement

AFFECTIVE INFORMATION:

which
relates to feelings and emotions
Audible frequency bands:

low bass
-
20 to 80Hz
- Gives sound power, boom, fullness; but could cause rumble or distortion.
upper bass
-
80 to 320Hz
- A foundation frequency that gives warmth to sound; but could sound muddy or thick.
midrange
-
320 to 2360Hz
- Gives intensity and presence; but could sound brassy or harsh.
upper midrange
-
2kHz to 5kHz
- Gives clarity/definition, especially to speech; but could sound lispy, swishy.
treble
-
5kHz to 20kHz
- Provides brilliance, brightness; but also range of hiss and noise.
Amplitude
is the measure of acoustic pressure or how many molecules are being moved by a vibrating object. It describes the size of the sound wave.
https://soundcloud.com/jedibunny/freq-for-class
How is sound created?
Frequency of Sound
Wavelength of a Sound
The length of one cycle, from one point of compression to one point of rarefaction.

Amplitude of Sound
Loudness
is how the brain perceives amplitude.

Decibels or dB

refers to how we measure loudness
Every complex sound has a base frequency called the
fundamental.

In music,
harmonics
refers to whole number multiples of the fundamental frequency
Timbre of Sound
The Sound Envelope
Sound Envelope describes the changes in sound's loudness or volume over time.
In this video you can hear and see the interference patterns between 2 soundwaves.
Resonance
What does it mean when something "resonates" with you?
Common sounds and their frequency ranges
Full transcript