Sound Energy II

1
Sound Energy II

• Or Tell me more about those scales

2
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

3
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

4

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

5
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
• What does this mean for hearing?
• Distance between ears 1 ft 1 ms

Gas Gas Liquid Liquid Solid Solid
Chlorine 206 Alcohol 1168 Lead 1200
Oxygen 313 Benzole 1324 Steel 5200
Nitrogen 336 Water 1407 Crown glass 5300
Hydrogen 1261 Glycerin 1900 Quartz glass 5370
6
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

7
Catching Up The pathway to the brain

• Cochlea lt-gt Cochlear Nerve
• Cochlear Nerve has tonotopic organization
• Coch. Nerve -gt Olivocochlear bundle x2
• Ipsi/contralateral projection
• Olivocochlear bundle -gt lateral lemniscus (STEM)
• Efferent Afferent projections
• Lemniscus -gtInferior Colliculus (MIDBRAIN)
• Lemniscus detects binaural activity, interaural
  processing

8
The End of the Pathway

• Inferior Colliculus -gt Medial Geniculate Nucleus
  (THALAMUS)
• Inferior Collic. Tightens tonotopic map
• MGN -gt Auditory cortex
• MGN tonotopic/binaural/initial multisensory
  input
• Auditory Cortex -gt Everywhere
• Primary auditory processing
• Left Speech
• Right Spatial

9
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