Kris Gill What is Sound Absorption Any technique used to manage the reflection of sound off of a surface causing sound energy to be dissipated Absorption Reflection Diffusion Two types of sound absorption ID: 804297
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Slide1
Sound Absorption and Anechoic chambers
Kris Gill
Slide2What is Sound Absorption?
Any technique used to manage the reflection of sound off of a surface
causing sound energy to be dissipated.
Absorption
Reflection
Diffusion
Slide3Two types of sound absorptionPressure ActivatedEnergy below 100HzReally long oscillating waves (L)Excites air space between wallsCreates distortions, room modes
Requires a pressure related treatmentDiaphragmatic, Helmholtz, Membranes
Velocity/Air Movement (Molecular Movement)Energy above 100HzMiddle and High frequenciesRaysRequires Foam and Limp Mass MaterialsRate and Level (R&L)
Slide4Sound Absorption Quality
Noise Reduction Coefficient (NRC)
Scalar representation of the amount of sound energy absorbed upon striking a particular surface
Provides a single-number rating for sound absorption (higher values are better).
Average of 4 spot frequencies, gives equal weighting across the frequency range
Not as accurate as
α
Sound Absorption Coefficient (
α
)
Defined as the ratio of sound energy absorbed by its surface to total sound energy on the surface
6 spot frequencies
α is dependent upon material as well as frequency of sound
Slide5Types of reflected Sound
Slide6Reverberation time (RT)
Reverberation: Amount of sound in a room that persists over a definite period of time after the source has stopped.
RT = Amount of time sound bounces around before absorption
RT-60: Time it takes for energy to decay 60dB
Can be controlled preciselyVolume of the roomType of materials
Surface area of materialsAffects how well one can hear and understand speechCan change how music soundsOptimal RT for general auditoriums ~2sShorter = More clarity
“Longest Echo”
Slide7Anechoic Chambers
Space in which there are no echoes or reverberations from the walls, ceiling, or floor.
Engineered specifically to eat sound.
Surfaces absorb all sound, reflect none.
99.5% of radiated sound energy absorbed
Constructed as a room within a room
Majority = 3 walls, Microsoft’s Building 87 has 6
Chamber floats on an independent foundation
Decoupling it from building vibrations
Slide8How do they work?
what are they used for?
The panels deaden sound by absorbing soundwaves
Panels are wire mesh containing porous material
Energy squishes material and dissipates as heat
Angles of the foam
Bouncing soundwaves = no reflected energy out
Free-field Conditions
Used for psychoacoustic work relating to loudness
Testing loudness of equipment
Loudspeaker and Microphone directivity and frequency response functions
Astronauts – space adaptation
Concert/Auditorium acoustics simulations
Slide9Quieter than dead silence
Ambient noise at the Quietest Place on Earth
Quieter than complete silence
Normal Conversation +60 dB
Human whisper +30 dB
Calm breathing +10 dB
Dead Silence +0 dB
Building 87 -20.6 dB
Brownian Motion, the noise produced by colliding air molecules at room temperature is ~ -23 dB
Vacuum of Space
“We are used to every sound producing a small echo from the world around us,” he points out. “In these chambers, there is just dead sound. It is just like going into a dark room, at first you cannot see anything but over time your eyes adapt.” Suedfeld
Slide10This month: Researchers develop 'acoustic metamaterial' that cancels sound
Silences noise using an open, ring-like structure, created to mathematically perfect specifications, for cutting out sounds while maintaining airflow.
Transversely placed bilayer medium,
Large degrees of contrast layers' acoustic properties
Asymmetric transmission
High-performance sound silencing
Large degree of open area – air permeable
Shape is completely customizable - cube or hexagon
Demonstrates a reduction in the transmitted acoustic energy of up to 94%
Possible applications
Smart sound barriers, fan or engine noise reduction, etc.
https://phys.org/news/2019-03-acoustic-metamaterial-cancels.html
Slide11Any questions?
Thank you.
Citations:
ISO-354, “
Measurement of sound absorption in a reverberation room”
.
Reza
Ghaffarivardavagh
et al, Ultra-open acoustic metamaterial silencer based on Fano-like interference,
Physical Review B
(2019).
DOI: 10.1103/PhysRevB.99.024302
Ressl
, Marc S. S, and Pablo E. E
Wundes
.
Proceedings of the 11th WSEAS International Conference on Acoustics and Music: Theory and Applications, AMTA '10
, 2010, pp. 18–23.
Cox, Trevor J, and Allan Kilpatrick. “A Record ‘Longest Echo’ within the
Inchindown
Oil
Despository
.”
The Journal of the Acoustical Society of America
, vol. 137, no. 3, 2015, pp. 1602–4.
Xu, Qian, et al. “Building a Better Anechoic Chamber: A Geometric Optics-Based Systematic Solution, Simulated and Verified [Measurements Corner].”
IEEE Antennas and Propagation Magazine
, vol. 58, no. 2, 2016, pp. 94–119.
Ellingson, Roger M. M, and Patrick V. V
Helt
.
Proceedings of Meetings on Acoustics, vol. 19, no. 1, 2013, pp. .