Sound energy ii
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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)

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Sound Energy II

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Sound energy ii

Sound Energy II

Or Tell me more about those scales…


Why is db spl considered flat

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

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


How does sound travel

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


Sound mediation

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

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

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

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


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