AUD202
Audio and Acoustics Theory
Reflections
Diffraction
Diffusion
Sound Observations Report
Last Week >
The Doppler Effect
Delay Perception
SPL Meters
Upcoming Events
18 Days - Sound Observations Report
28 Days - Exam
Topics So Far
The Decibel
Sound Properties
White and Pink Noise
Wavelength
Envelope of Sound
Frequency
Anatomy of the Ear
Amplitude
Hearing Protection
Period
OH&S principles
Comb Filtering
SPL Meters
Speed of Sound
NIHL
Wave Interaction
Phase Concepts
Standing Waves
The Inverse Square Law
Harmonics and Overtones
Psychoacoustics
Waveforms
Masking
Reflection
Diffraction
Diffusion
Haas Effect
Doppler Effect
Delay Perception
Beat Frequencies
Loudness Curves
Ranges of Hearing
Delay Perception
up to 10ms – comb filtering effects
from wave interaction
10-40ms – a ‘thickening’ effect
40ms and over – a distinct repeat or
echo of the sound
COMB FILTERING
Comb Filtering
When a delayed version of a sound interacts
with the original sound causing constructive
and destructive interference
Write down three situations where this
could occur
Comb Filtering
If two identical signals are shifted against
each other in time some frequencies will
be cancelled and some will be reinforced
Odd harmonics of the fundamental frequency of
cancellation will cancel
Even harmonics of the fundamental frequency of
cancellation will reinforce
Comb Filtering
How to Calculate the fundamental frequency
of cancellation of a comb filter:
Find the longest wavelength that can occur
between two points (a 2m room will have a
4m wavelength), from that find the frequency
of the full wavelength. This is your
fundamental frequency of cancellation.
Comb Filtering
Given the following room length axis
measurements, calculate the fundamental
frequency of cancellation
5 meters
7 meters
1 meter
Comb Filtering
Remembering that odd harmonics
cancel and even harmonics reinforce,
what are the first 3 cancellations for the
following fundamental frequencies:
100Hz
2500Hz
600Hz
REFLECTION
Reflection
Sound acoustics is the field primarily
concerned with the reflections of sound.
Reflected sound reveals the size and
materials within a space. Changing the
size or materials will alter the quality and
amount of reflections.
Reflection
Direct sound is the
original sound
Early Reflections
are the first
reflections you hear
after the direct
signal.
Direct Sound vs. Reflected Sound
Reflection
The diffuse field is where the reflected
sound is higher in level than the direct
sound.
The near field is where the direct sound is
the louder.
Reflections
Sound bounces off reflective surfaces in the
same behaviour as light – and follows the law
"angle of incidence equals angle of reflection"
Reflections
Reflected waves can interfere with incident
waves, producing constructive and destructive
interference which can result in standing waves
Standing Waves
What can be done to combat standing
waves?
Reflections
Reflection from a HARD boundary
Reflections
Reflection from a HARD boundary
DIFFRACTION
Diffraction
Diffraction is the bending of waves around
small obstacles and the spreading out of
waves beyond small openings.
Diffraction
Diffraction
When sound passes through a hole in a
barrier, the hole becomes a new ‘point
source’ and the sound will spread out from
that point.
DIFFUSION
Diffusion
In acoustics, diffusion is the scattering of
sound waves to reflect them in different
directions. Or breaking the soundwaves into
smaller pieces.
Diffusion is commonly used to reduce
specular reflections and echo. Also to direct
sound energy to specific areas.
Diffusers
The purpose of a diffuser is to break up sound
waves and disperse them in various directions.
There are two main types of diffuser, the barrel
diffuser and the quadratic diffuser.
Adding sound diffusion to your acoustic room
treatment can improve the speech and instrument
intelligibility and improve the overall listening
environment within the room
Barrel Diffusers
Quadratic Diffusers
Quadratic Diffusers
SPL METERS
SPL Meters
A weighting is based on the human perception of
loudness (e.g. the equal loudness curves) and is
used for most situations.
SPL Meters
C weighting provides a flatter response and is
useful for peak sound analysis
Next Week >
Reverberation Parameters and Concepts
Absorption Co-Efficients