Acoustics Flashcards
The Boston symphony hall was acoustically designed by _______
Wallace Sabine
DEF: antinode
the point where the amplitude of a standing wave is at is maximum
DEF: node
point of no vibration, essentially the zero crossing of a waveform
DEF: mode
a room resonance, a standing wave
DEF: axial modes
a resonance between two room parallel surfaces (one pair)
DEF: tangential modes
a resonance between four room surfaces (two pairs)
DEF: oblique modes
a resonance between all six room surfaces (3 pairs)
The Schroeder Frequency of a room determines:
the point at which resonances become less problematic reflections
Reduction of reflections to an imperceptible loudness is called:
RT60
DEF: RT60
The time requird for the sound in an enclosure to decay 60 dB from an initial steady-state level
An absorption coefficient of 0 equals:
total reflection
In order to take an impuse response a room may be excited by ________
a sine sweep or a loud click (ie. gunshot)
In order to catch a wavefront at maximum velocity an absorber must be equal to what fraction of a wavelength?
1/4 wavelength
How does an air cavity between an absorber and a boundary affect its acoustic performance?
It increased the performance at lower frequencies
Describe a Tom Hidley control room design
a reflective front wall
In a control room do you want parallel or non-parallel surfaces?
Non parallel
What is the Sabine Equation?
What do we use Sabine’s equation to calculate?
reverb time
Identify the type of control room design
a Tom Hidley design
How does thickness of a material affect it’s absorption coefficient at lower frequencies?
thicker abosrbes more of lower frequencies as they have larger physical soundwaves
DEF:
absorption
When sound energy is converted into heat energy as it passes through a medium
how can you increase diffusion?
- non parallel surfaces
- use of geometric irregularities
- use of concave surfaces or diffusion panels
- use of every day objects (ie. book cases)
name this diffuser
MLS ( Maximum length sequence) Diffuser
DEF:
room mode
the normal modes of vibration in an enclosed space
name this diffuser
skyline diffuser
name this diffuser
QRD (Quadratic Residue Diffuser)
name this diffusor
Schroeder’s Diffusor
What constitutes a perfectly diffuser environment?
- no measured frequency or level irregulariries
- smooth reverberation decay
- same rever decay for all frequencies and from all directions
- same reverb time at all points in the room
name this acoustic treatment
bass trap
name this acoustic treatment
perforated panel absorbers
name this acoustic treatment
Helmholtz Resonator
name this acoustic treatment
Helmholtz Resonator
What equation is used to calculate the maximum frequency that can be absorbed by a substance?
with porous absorbers, what dictates the degree of absorption?
the space between the fibres
if fibres are not packed closely enough, little energy will be lost as heat
if fibres are packed too closely, sound may not penetrate absorber sufficiently
name this acoustic treatment
porous absorbers
DEF:
acoustic absorption
the process by which a medium takes in sound energy as opposed to reflecting it. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body
What word do we use to discribe the sound energy that has been converted to heat via acoustic absorption
energy transformed into heat is said to have been ‘lost’
Who developed the quadratic residue diffuer (QRD)?
Manfred R. Schroeder
In a QRD the well depth dictates _______
the lowest frequency for diffusion
In a QRD the well width dictates the ________
highest frequency for diffusion
what equation is used to calculate the well depth sequence in a QRD?
what does the ‘modulo’ refer to?
the remainder
What is the use of a Helmholtz resonator?
used to achieve absorption at lower frequencies
DEF:
STC
Sound Transmission Class
a single number used to describe a series of transmission loss measurements made at frequency intervals throughout the frequency range. A standardised class system based on how well a medium attenuates sound.
what does MLS stand for?
Maximum length sequence
What are the three godlen room ratios?
What equation is used to calculate a room mode?
What equation is used to calculate the Schroeder frequency?
What equation do you use to calculate standing waves?
DEF:
standing wave
a resonance condition in an enclosed space in which sound waves travelling in one direction interact with those travelling in the opposite direction , resulting in a stable condition
DEF:
reflection
sound is reflected much like light, with the angle of incidence equaling the angle of reflection
DEF:
Helmholtz resonator
a reactive, tuned sound absorber
