Sound Energy II Or Tell me more about those scales…

Why is dB SPL considered flat? dB scales Ratio scale Ratio scale Psychophysical Psychophysical Based on human hearing dB SPL (Sound Pressure Level Based on hearing threshold at 1000 Hz Based on hearing threshold at 1000 Hz Flat energy for all frequencies Flat energy for all frequencies dB HL (Hearing Level) Based on hearing threshold at every frequency Based on hearing threshold at every frequency Variable energy across frequencies Equal loudness contours preserved Equal loudness contours preserved

Why are multiple scales needed? Example 1: Psychoacoustic Research How loud was the clicker in the HUW experiment? How loud was the clicker in the HUW experiment? Comparable across all sounds Was the intensity the same under water? Was the intensity the same under water? Measure intensity at the ear Same if SPL, different if HL? Same if SPL, different if HL? Example 2: Clinical Audiology How much hearing loss at 2 kHz? How much hearing loss at 2 kHz? Comparable to other listeners Is this the same amount of hearing loss as at 200 Hz? 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? When was sound loud? Change in spectra? Why is there a difference? 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 Distance between ears 1 ft ~ 1 ms GasLiquidSolid Chlorine206Alcohol1168Lead1200 Oxygen313Benzole1324Steel5200 Nitrogen336Water1407 Crown glass 5300 Hydrogen1261Glycerin1900 Quartz glass 5370

Sound Mediation Movement of sound may be affected by affected by medium Distance of travel Distance of travel Sound diffusion All freq All freq Absorption by media High freq High freq Change to greater density Change to greater density Reflection & Scatter High freq High freq Change to less density Change to less densityDiffusion Asymmetrical density Asymmetrical densityDiffraction Changes shape of the waveform Changes shape of the waveform Low freq Low freq

Catching Up: The pathway to the brain Cochlea Cochlear Nerve Cochlear Nerve has tonotopic organization Cochlear Nerve has tonotopic organization Coch. Nerve -> Olivocochlear bundle x2 Ipsi/contralateral projection Ipsi/contralateral projection Olivocochlear bundle -> lateral lemniscus (STEM) Efferent & Afferent projections Efferent & Afferent projections Lemniscus ->Inferior Colliculus (MIDBRAIN) Lemniscus detects binaural activity, interaural processing Lemniscus detects binaural activity, interaural processing

The End of the Pathway Inferior Colliculus -> Medial Geniculate Nucleus (THALAMUS) Inferior Collic. Tightens tonotopic map Inferior Collic. Tightens tonotopic map MGN -> Auditory cortex MGN tonotopic/binaural/initial multisensory input MGN tonotopic/binaural/initial multisensory input Auditory Cortex -> Everywhere Primary auditory processing 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