ph 105 dr. cecilia vogel lecture 4. outline room acoustics concert hall properties
Post on 21-Dec-2015
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Reverberation Time Reverberation time
V, volume of room A, the absorption area = sum of
aS for all surfaces a from table for material, S = surface
area
Na for all seats a from table for seat, N = # of seats
aV a from table for air, V = volume
K is a constant: 0.161 for mks units
VRT K
A
Absorption example A 10 mX10mX4m room currently has a
RT of 1.0 s for sounds at 500Hz. What change will be made by covering five 1.2mX0.5m glass windows with heavy drapery?
The current absorption, A, can be found V
RT KA
A =
Example cont’d Lose the absorption of glass, add the
absorption of drapery: the absorption for each is aS, a from
___________, S =
A = 64.4m2 A =
VRT K
ART
Properties of Concert Halls “Intimacy”
means _____________ between direct and early sound is
sounds like “Liveness”
level of adds to
Properties of Concert Halls “Clarity”
more important in keep reverb
“Warmth” level of drapery, carpet
“Loudness” total
Properties of Concert Stage “Balance”
keep appropriate relative level of instruments
“Blend” mix of sound from
“Ensemble” can performers hear
Whispering Gallery A curved reflecting surface can focus sound
it sounds like it comes from
There are spots in the science bldg where you hear a voice think it’s but actually The sound was reflected and focused, making an
Diffraction When a wave meets an obstacle
that doesn’t totally or one that
it can diffract or to get
video
Diffraction SometimesNote that a wave will not diffract,
if its wavelength is
Ex: Visible light has wavelengths ____________ than a meter,
do not see through a doorway, or around a tree
Ex: Audible sound has wavelengths ______a meter
you can hear through doorway, or around a tree.
Ex: in lab, to see _________ without too much __________, must use ultrasound
“ultra” meaning high high freq corresponds to
SuperpositionWhen two disturbances (or waves)are at the same place at the same time,total disturbance is the sum of the two.
watch impulsive waves
InterferenceBecause of superposition,Waves, when they meet
can add or interfere constructively so the total is if they happen to have the same phase
periodic waves, when they meetcan cancel or interfere destructively so the total is if they happen to have opposite phase
InterferenceWaves from two source,will have places where they interfere constructively
what does it sound like with sound?what does it look like with light?
and other places where they interfere destructively
what does it sound like with sound?what does it look like with light?
video
SummaryUsing RTConcert hall qualities definedDiffraction is the bending of wave around an obstacle or through an opening
if obstacle or opening is similar in size to wavelength of the wave
Interference is the addition of waves at point where they meet
constructive interference means they add to larger wave (louder)destructive interference means they add to smaller wave (quieter)