/
Sound Absorption and Anechoic chambers Sound Absorption and Anechoic chambers

Sound Absorption and Anechoic chambers - PowerPoint Presentation

festivehippo
festivehippo . @festivehippo
Follow
343 views
Uploaded On 2020-08-27

Sound Absorption and Anechoic chambers - PPT Presentation

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: 804298

energy sound room absorption sound energy absorption room time surface noise acoustic space air building vol open metamaterial absorbed

Share:

Link:

Embed:

Download Presentation from below link

Download The PPT/PDF document "Sound Absorption and Anechoic chambers" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.


Presentation Transcript

Slide1

Sound Absorption and Anechoic chambers

Kris Gill

Slide2

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

Slide3

Two 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)

Slide4

Sound 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

Slide5

Types of reflected Sound

Slide6

Reverberation 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”

Slide7

Anechoic 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

Slide8

How 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

Slide9

Quieter 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

Slide10

This 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

Slide11

Any 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. .