Sound Energy IISound Energy II

Or Tell me more about those Or Tell me more about those scales…scales…

Why is dB SPL considered flat?Why is dB SPL considered flat?dB scalesdB scales

Ratio scaleRatio scale PsychophysicalPsychophysical

Based on human hearingBased on human hearing

dB SPL (Sound Pressure dB SPL (Sound Pressure LevelLevel

Based on hearing threshold at Based on hearing threshold at 1000 Hz1000 Hz

Flat energy for all frequenciesFlat energy for all frequencies

dB HL (Hearing Level)dB HL (Hearing Level) Based on hearing threshold at Based on hearing threshold at

every frequencyevery frequencyVariable energy across Variable energy across frequenciesfrequencies

Equal loudness contours Equal loudness contours preservedpreserved

Why are multiple scales needed?Why are multiple scales needed?

Example 1: Psychoacoustic Example 1: Psychoacoustic ResearchResearch

How loud was the clicker in the HUW How loud was the clicker in the HUW experiment? experiment?

Comparable across all soundsComparable across all sounds Was the intensity the same under Was the intensity the same under

water?water?Measure intensity at the earMeasure intensity at the ear

Same if SPL, different if HL? Same if SPL, different if HL?

Example 2: Clinical AudiologyExample 2: Clinical Audiology How much hearing loss at 2 kHz?How much hearing loss at 2 kHz?

Comparable to other listenersComparable to other listeners Is this the same amount of hearing Is this the same amount of hearing

loss as at 200 Hz?loss as at 200 Hz?Same if HL, different if SPLSame if HL, different if SPL

dB SPLdB SPL SourceSource

00 Threshold of hearing Threshold of hearing

1010 Human breathing at 3 mHuman breathing at 3 m

2020 Rustling of leavesRustling of leaves

4040 Residential area at nightResidential area at night

5050 Quiet restaurantQuiet restaurant

7070 Busy trafficBusy traffic

8080 Vacuum cleanerVacuum cleaner

9090 Loud factoryLoud factory

100100 Pneumatic Hammer at 2 mPneumatic Hammer at 2 m

110110 Accelerating motorcycle at 5 mAccelerating motorcycle at 5 m

120120 Amplified music concert Amplified music concert

130130 Threshold of painThreshold of pain

150150 Jet engine at 30 mJet engine at 30 m

180180 Rocket engine at 30 mRocket engine at 30 m

How Does Sound Travel?How Does Sound Travel?

Impedance ExperimentImpedance Experiment When was sound loud?When was sound loud?

Change in spectra?Change in spectra? Why is there a difference?Why is there a difference?

Speed of sound typically Speed of sound typically 345 m/s in air345 m/s in air

What does this mean for What does this mean for hearing?hearing? Distance between ears 1 ft ~ Distance between ears 1 ft ~

1 ms1 ms

GasGas LiquidLiquid SolidSolid

ChlorineChlorine 206206 AlcoholAlcohol 11681168 LeadLead 12001200

OxygenOxygen 313313 BenzoleBenzole 13241324 SteelSteel 52005200

NitrogenNitrogen 336336 WaterWater 14071407 Crown Crown glassglass

53005300

HydrogenHydrogen 12611261 GlycerinGlycerin 19001900 Quartz Quartz glassglass

53705370

Sound MediationSound Mediation

Movement of sound may be affected by affected by Movement of sound may be affected by affected by mediummedium

Distance of travelDistance of travelSound diffusionSound diffusion

All freqAll freqAbsorption by mediaAbsorption by media

High freqHigh freq Change to greater densityChange to greater density

Reflection & ScatterReflection & Scatter High freqHigh freq

Change to less densityChange to less densityDiffusionDiffusion

Asymmetrical densityAsymmetrical densityDiffractionDiffraction

Changes shape of the waveform Changes shape of the waveform Low freqLow freq

Catching Up: The pathway to the Catching Up: The pathway to the brainbrain

Cochlea <-> Cochlear NerveCochlea <-> Cochlear Nerve Cochlear Nerve has tonotopic Cochlear Nerve has tonotopic

organizationorganization

Coch. Nerve -> Olivocochlear Coch. Nerve -> Olivocochlear bundle x2bundle x2 Ipsi/contralateral projectionIpsi/contralateral projection

Olivocochlear bundle -> Olivocochlear bundle -> lateral lemniscus (STEM)lateral lemniscus (STEM) Efferent & Afferent projectionsEfferent & Afferent projections

Lemniscus ->Inferior Lemniscus ->Inferior Colliculus (MIDBRAIN)Colliculus (MIDBRAIN) Lemniscus detects binaural Lemniscus detects binaural

activity, interaural processingactivity, interaural processing

The End of the PathwayThe End of the Pathway

Inferior Colliculus -> Medial Inferior Colliculus -> Medial Geniculate Nucleus Geniculate Nucleus (THALAMUS)(THALAMUS) Inferior Collic. Tightens tonotopic Inferior Collic. Tightens tonotopic

mapmap

MGN -> Auditory cortexMGN -> Auditory cortex MGN tonotopic/binaural/initial MGN tonotopic/binaural/initial

multisensory inputmultisensory input

Auditory Cortex -> EverywhereAuditory Cortex -> Everywhere Primary auditory processingPrimary auditory processing

Left: SpeechLeft: SpeechRight: SpatialRight: Spatial

Big picture of the PhysiologyBig picture of the Physiology

Outer Ear: Spectral filter for directionOuter Ear: Spectral filter for direction

Middle Ear: Attacks impedance Middle Ear: Attacks impedance problemproblem

Inner Ear: Converts sound to nerve Inner Ear: Converts sound to nerve impulseimpulse

Brainstem to Midbrain (olivocochlear Brainstem to Midbrain (olivocochlear bundle): Bilateral effectsbundle): Bilateral effects

Cortex: Higher-level auditory Cortex: Higher-level auditory processorprocessor