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Sound Energy II
Or Tell me more about those
scales…
Why is dB SPL considered flat?
dB scales


Ratio scale
Psychophysical
Based on human hearing
dB SPL (Sound Pressure
Level


Based on hearing threshold
at 1000 Hz
Flat energy for all
frequencies
dB HL (Hearing Level)

Based on hearing threshold
at every frequency
Variable energy across
frequencies

Equal loudness contours
preserved
Why are multiple scales needed?
Example 1: Psychoacoustic
Research

How loud was the clicker in the HUW
experiment?
Comparable across all sounds

Was the intensity the same under
water?
Measure intensity at the ear

Same if SPL, different if HL?
Example 2: Clinical Audiology

How much hearing loss at 2 kHz?
Comparable to other listeners

Is this the same amount of hearing
loss as at 200 Hz?
Same if HL, different if SPL
dB SPL
Source
0
Threshold of hearing
10
Human breathing at 3 m
20
Rustling of leaves
40
Residential area at night
50
Quiet restaurant
70
Busy traffic
80
Vacuum cleaner
90
Loud factory
100
Pneumatic Hammer at 2 m
110
Accelerating motorcycle at 5 m
120
Amplified music concert
130
Threshold of pain
150
Jet engine at 30 m
180
Rocket engine at 30 m
How Does Sound Travel?
Impedance Experiment

When was sound loud?
Change in spectra?

Why is there a difference?
Speed of sound typically
345 m/s in air
Gas
Liquid
Solid
Chlorine
206
Alcohol
1168
Lead
1200
Oxygen
313
Benzole
1324
Steel
5200
Nitrogen
336
Water
1407
Crown
glass
5300
Glycerin
1900
Quartz
glass
5370
Hydrogen
1261
What does this mean for
hearing?

Distance between ears 1 ft ~
1 ms
Sound Mediation
Movement of sound may be affected by affected by
medium

Distance of travel
Sound diffusion

All freq
Absorption by media


High freq
Change to greater density
Reflection & Scatter


High freq
Change to less density
Diffusion

Asymmetrical density
Diffraction


Changes shape of the waveform
Low freq
Catching Up: The pathway to the
brain
Cochlea <-> Cochlear Nerve

Cochlear Nerve has tonotopic
organization
Coch. Nerve -> Olivocochlear
bundle x2

Ipsi/contralateral projection
Olivocochlear bundle ->
lateral lemniscus (STEM)

Efferent & Afferent projections
Lemniscus ->Inferior
Colliculus (MIDBRAIN)

Lemniscus detects binaural
activity, interaural processing
The End of the Pathway
Inferior Colliculus -> Medial
Geniculate Nucleus
(THALAMUS)

Inferior Collic. Tightens tonotopic
map
MGN -> Auditory cortex

MGN tonotopic/binaural/initial
multisensory input
Auditory Cortex -> Everywhere

Primary auditory processing
Left: Speech
Right: Spatial
Big picture of the Physiology
Outer Ear: Spectral filter for direction
Middle Ear: Attacks impedance
problem
Inner Ear: Converts sound to nerve
impulse
Brainstem to Midbrain (olivocochlear
bundle): Bilateral effects
Cortex: Higher-level auditory
processor