Basics of Sound

Question 0

What are the components of a sound wave?

Answer 0

• 1/2 compression (higher pressure molecules)
• 1/2 rarefaction (lower pressure molecules)
• Amplitude; loudness; amount of particles in motion
• Frequency; rate of pressure fluctuation; Hz; cps
• Period; spc; 1/ frequency
• Wavelength; distance covered by one complete cycle; speed of sound/ frequency

Question 1

What is sound?

Answer 1

An acoustic wave that forms when there is a periodic disturbance of molecules transmitted through an elastic medium and the interaction of those disturbances with the environment

Question 2

What is the speed if sound?

Answer 2

1130 ft/ sec @ sea level, 68 degrees F, 40% humidity
-for every degree change, velocity will change +/- 1.1 ft per sec.

4800 ft/ sec through water

Even faster through solids esp. glass or steel

Question 3

What is an audio signal?

Answer 3

An electrical representation of sound in a proportionately fluctuating current with the signal level measured in dB

Question 4

Sound waves vs. electromagnetic waves

Answer 4

Sound waves: acoustic, longitudinal (all energy travels in the same direction)

Electromagnetic waves: transverse (2 forms of energy travel at right angels to one another)
Electrical (up/ down) and magnetic (forward/ back) waves will transverse

Question 5

6 motions of sound waves

Answer 5

Diffraction: bend around object and continue in the original direction
Reflection: bounce off object, reflected direction is angle incident
Diffusion: scattering of waves, rarely happens naturally, not angle incident
Absorption: stopping waves energy completely
Transmission: moves right through object
Refraction: ability to change directions

Question 6

What is a standing wave?

Answer 6

Reflected waves that reflect at 90 degrees between parallel surfaces
-turns into a flutter echo at 2.5 K, when the wave length becomes too short/ weak to support itself as a standing wave

Question 7

What is an acoustic envelope, what comprises it?

Answer 7

Parts of a sound measured overtime from beginning to end

Attack: amount of time from silence to peak loudness
Decay: amount of time from peak loudness to avg. level
Sustain: time of avg.
Release: amount of time from avg. to silence

Attack function of compressor: amount of time to reach maximum reduction after signal crosses threshold

Question 8

Infrasonic vs. ultrasonic frequency ranges

Answer 8

Infra: 0-20 Hz, can be perceived if loud enough
Ultra: >20K, perceived psychoacoustically

Question 9

What are the increments of loudness?

Answer 9

0 dB-SPL: threshold of hearing 
80 dB-SPL: comfortable listening level
118 dB-SPL: threshold of feeling
120 dB-SPL: threshold of pain
150 dB-SPL: threshold of permanent hearing damage
180 dB-SPL: threshold of deafness
220 dB-SPL: threshold of death

Question 10

What are the 3 interaural differences?

Answer 10

Intensity differences: 2k- 20k, horizontal, skull casts an acoustic shadow of high frequencies and one side of the head perceives these frequencies with greater intensity
Time differences: 20Hz- 2k, horizontal, can diffract but it takes a moment of time, so one ear will hear the low frequencies before the other
Spectral differences: full range, vertical, the way the pinnae color the sound; if the sound is in front, there will be no coloring, making it sound normal