Lecture 2: Basic Sound Waves

Why do we care?

-foundation of hearing: we can’t understand hearing without understanding how sound is produced, transmitted, and perceived, we cannot understand hearing

-speech and language depend on (access to) sound

-diagnosing disorders: knowing the properties of sound help pinpoint where in the auditory system breakdowns occur

-designing solutions (cochlears, hearing aids, etc.)

-collaborations with SLPs and other professionals

What is Sound?

-Psychologically: sensation we feel when acoustic energy enters our auditory system

-Physically: energy in the form of oscillating particles in a medium that carry energy from one place to another

**What Sound Needs in Order to be Produced**

1. an energy source

   -energy source depends on vibrating body; no energy = no vibration = no sound

2. an elastic medium

Medium/Elastic Medium

-medium: the substance through which sound energy propagates

• can be solid (like steel; elastic = soft/squishy)

• can be insubstantial and invisible (*air)

-elasticity: how well something bounces back to its original shape after being disturbed

• elasticity of a medium will increase as the distance b/w molecules decreases (solid > liquid > gas)

Propagation

-sound doesn’t travel but propagates

-vibration at source causes subsequent molecules to vibrate (chain reaction) until a destination is reached

Free Vibration

-when something is set into motion and then left to move on its own until it eventually dies out

• ex. plucking a guitar string and letting it ring out, pushing swing and letting it stop on its own

Forced Vibration

-an outside energy source keeps the object put in motion moving

• ex. continuing to play the guitar or push the swing

• free vibration will commence once outside energy source is removed

!!!Waves (refer to notes)

-wave: a series of impulses set up vibration

-compression: (push molecules together ?)

-rarefaction (pull apart?)

Two Types of Waves

Transverse: molecules moving up and down while the wave itself moves side to side (ex. water dripping into a pond)

**Longitudinal: molecules move along the same direction as the wave itself (ex. sound waves)