Hearing exam 1

Sound

Sound

A vibratory energy transmitted by pressure waves through a media (like air)

Hearing

The perception of sound

Frequency tells us…

What and where and pitch

Amplitude tells us…

location

Phase tells us

Location

Spectrum tells us…

*Location

Time

How the vibrations change over time

Frequency

The rate, or frequency, of vibrations (how often it repeats)

Amplitude

The magnitude, or amplitude, of a vibration (how much energy is in the signal)

Time uses what units?

Seconds (s)

Milliseconds (ms)

Microseconds (µsec)

Frequency uses what units?

Hertz (Hz)

Kilohertz (kHz)

Megahertz (MHz)

Gigahertz (GHz)

Amplitude uses what units?

DB (db) decibels

What are the three fundamental dimensions of sound?

Mass, TIme, length

Scalar quantity

• Has magnitude

• Ex) mass, time, & length

Vector quantities

• Has magnitude AND direction

• Ex) displacement, velocity, acceleration, force, work, energy, momentum, power, intensity, pressure

Energy

Has the potential for work. Is something a body posses

3 forms of energy

Potential, kinetic and total

Power

Rate at which work is accomplished

OR

Rate at which energy is expended, transformed, or transferred

In order for sound to move it must have…

Mass and elasticity

Harmonic motion

A mechanical disturbance that is propagated through an elastic medium

Simple harmonic motion

Simple Harmonic Motion: an object moving in a harmonic motion, then changes in displacement, velocity & acceleration, creating a sinusoidal motion

Transverse wave motion

A displacement of the medium where a wave travels that is PERPENDICULAR to the direction of the wave propagation

Longitudinal Wave Motion

Particle displacement is PARALLEL to the wave of propagation.

Sounds are what types of waves?

Longitudinal pressure waves

Condensation

Compression of a medium

Rarefaction

Expansion of the medium

Waveform

How we represent change of a physical quantity as a function of time.

Phase

Indicates a certain stage in the cycle of motion by using angles from the UNIT CIRCLE

Starting phase

The displacement or location in the wave (in degrees) at the point where the vibration begins and time is 0

In phase

Same frequency & same phase

Out of phase

Same frequency & different phase

Lead

Positive Shift

Reaches peak amplitude first

Lag

Negative Shift

Reaches peak amplitude last

Instantaneous Amplitude

The magnitude of a waveform at any given moment of time

RMS Amplitude

The rms value is obtained by squaring the amplitude of each point of a waveform and then averaging those points. For complex sounds, we can use a sound level meter to calculate the rms

Wavelength (λ)**

Wavelength depends upon the medium in which it is traveling. This is in contrast with frequency which is a constant.

Higher frequencies have shorter wavelengths

Simple harmonic motion can be represented as either:

1. Sinusoid/sine wave

2. Uniform circular motion

Uniform Circular Motion

A uniform circular motion describes SHM when a body moves around the circumference of a circle at a constant rate

Propagation of Sound

When a sound source vibrates the molecules in the air, the molecules show NO NET MOVEMENT, but they vibrate with the motion of the sound source

Inverse square law

Intensity decreases proportionately to the square of the distance from the sound source

There is a rapid drop in sound intensity with increasing distance

Impedance

the total opposition to motion

*this changes the sound wave*

The difference between impedance and

will determine whether the sound wave gets REFLECTED, TRANSMITTED, or  ABSORBED by the media

Reflection

Bounces off

Transmission

Passes through

Absorption

absorbed by new medium

Constructive Interference

Results in INCREASED displacement, as the waves  add together

Destructive Interference

Results in REDUCED displacement, as the waves cancel out

Sound shadow is affected by:

1. The size of the object that the sound wave is encountering

2. The wavelength of the sound wave

Time Domain

Amplitude as a function of time (a waveform)

Frequency Domain

Fourier Series

Describes frequency, amplitude, and starting phase

1. Amplitude spectrum

2. Phase spectrum

Fourier’s Theorem

Ways we can break down complex vibrations into simple sinusoidal vibrations

Fourier Analysis

Breaking down sounds into their parts

Recovery of amplitude and phase spectra from waveform

Fourier Synthesis

Putting sounds together to make complex sounds

Add instantaneous amplitudes of waveform

Complex sounds

NOT a sinusoidal waveform

Can be defined by a line spectrum AND/OR continuous spectrum

Can be PERIODIC or APERIODIC

Periodic

Repetitive pattern

Line spectrum

Aperiodic

No repetitive pattern

Continuous spectrum

Fundamental frequency

The first harmonic

Harmonics

integer multiples of the fundamental frequency

Click stimulus

A transient stimuli– a sound that has an abrupt, quick “on” and “off”. They have a rapid onset and very short duration.

Broad continuous spectrum

Broad Band

power in a large band of frequencies

Narrowband

Power in a limited band of frequencies

Complex sounds have…

Am and Fm

Acoustic filters

Mechanism by which frequencies are selectively passed or rejected

The cochlea acts as a filter to analyze the frequencies of complex sounds, such as speech.

Cutoff Frequency:

The frequency where the filter begins to attenuate the input signal. There can be a lower and upper cutoff frequency.

Center frequency

The frequency midway between the upper and lower cutoff frequencies (for band-pass and band-reject filters)

Bandwidth

Range of Frequencies

Attenuation Rate

The amount of attenuation

We measure this in dB per octave change in frequency

Octaves

Doubling or “halfing” of a frequency

Filters Modify…

A signals spectrum and time domain waveform