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Acoustics and Classroom Sound Issues


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Explains basics about sound and what classroom issues are present due to sound effects which causes problem for students to hear teacher properly.
Explains concept of reverberation and other issues and suggests about its solution for better classroom sound efficiency

Published in: Education
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Acoustics and Classroom Sound Issues

  1. 1. Acoustics Reverberation andClassroom Issue Ashvary Jain 0201ME101017 BE III sem, Mechanical Jabalpur Engineering College
  2. 2.  IntroductionAcoustics and Classroom Problems in a classroom• Room Noise• Reverberation• Speaker Listener Distance Reverberation – In Detail SolutionsSummary
  3. 3. Introduction Sound .• It is a mechanical wave that undergo oscillation.• Transmits through solid liquid or gas.• Composed of frequencies within range of hearing or create sensation of vibration.
  4. 4. Acoustics• Study of all mechanical waves in gases, liquids, and solids.• Including vibration, sound, ultrasound and infrasound.• Everything related to hearing and speaking comes in its scope.
  5. 5. What happens to sound when it hits a barrier?• Transmitted (pass through)• Absorbed• Reflected• Diffracted
  6. 6. Acoustics and ClassroomImportance of hearing/listening• Approximately 45% of school time spent listening• Approximately 30% speaking• Approximately 16% reading• Approximately 9% writing
  7. 7. • Elements of Listening• Detection – Identifying the sound• Discrimination – Differentiating between various words• Recognition – Catching the exact word• Comprehension – Noting correct thing
  8. 8. Problems in ClassroomOften students are not able to get what teacher is speaking, sometimes even misinterpreted. The main reasons behind this are • Room noise • Speaker-listener distance • Room reverberation Lets discuss these problems individually….
  9. 9. RoomNoise • Acoustical noise is any unwanted sound • Could be external or internal • Includes whispers, shut noises, external disturbances. • Noise is around 55-60 dB in classroom
  10. 10. Speaker ListenerDistance• Audibility decreases as the distance from the speakerincreases• About a 6dB drop for every doubling of distance.• At certain distance, background noise can mask speaker’svoice.• A typical teacher’s voice measures 60 to 65dB at a distance of1m/3ft.
  11. 11. • Noise is generally at 55-60 dB in a classroom.• First row student gets decent sound, about 65 dB• Forth row student get 60 dB of voice signal, same as noise• For back-row students, teacher is at 53dB, receive 55% of thespeech signal, and achieve just 60% word recognition
  12. 12. Reverberation
  13. 13. Reverberation• It is the persistence of sound in a particular spaceafter the original sound is removed.• Large number of echoes build up and then slowlydecay as the sound is absorbed• Causes prolongation of sound.• Longer the reverberation the more “smear” of speechsounds.
  14. 14. Reverberation Time•Time it takes a sound to stop reflecting•Is the time in seconds for a sound to reduce 60 dB inintensity once the generation of sound has stopped•Hard room -> long RT time•RT of room alters the effect of the speaker-listenerdistance upon sound intensity
  15. 15. Sound Source
  16. 16. Classroom study of Reverberation
  17. 17. Classroom CalculationsTime Difference Calculations• Assuming the dimensions of a class room to be – 15 x 10x10 metres.• Speed of light = 330 m/sT1 = Time taken by sound to travel via 10m straight pathT2 = Time Take by sound to travel via 12+12m reflected pathTime = Distance /Speed
  18. 18. T1 = 10/330 = 0.0303 secT2 = 28/330 = 0.0727 secT2 – T1 = .0424 sec 10m 12mTime difference of .0424sec between two soundwaves cause the confusionwhile detecting thespeech 10m
  19. 19. Reverberation Time Calculations Sabine equation RT60 - Reverberation Time in sec V - Volume of Room in cubic metres S - Total Surface Area in square metres c – Speed of Light in metres a – Average Absorption Coefficient
  20. 20. By using a pre buildReverb Timecalculator andputting data closeto the reality, thereverberation timewas found to bearound 1.8 seconds
  21. 21. In general, for a class room, the reverberationtime must be between .4 to .6 sec
  22. 22. Solutions for Better AcousticsImportance of Better Acoustics• Improvement in speech recognition• Improvement in speech recognition• Reduced vocal strain and voice fatigue for teachers• Increased teacher mobility Some of the solutions for better Acoustics are -
  23. 23. 1. False Ceiling• Decreases the volume of room.• Time variation between two rays also reduces• Acoustical ceiling tiles in the room to decrease reverb due to absorption• Available in panels, which are installed using a grid attached to the existing ceiling.• Wood planks provide a similar benefit as acoustical ceiling tiles.• Thermocol sheet also help for the purpose
  24. 24. Acoustic Tiles used as False Ceiling
  25. 25. 2. Carpeting Floor•Helps in absorption of reverb sound.•Replace hardwood, laminate, tile or cement floorswith carpet•cover the floors with area rugs.•More open area on floor = more reverberation
  26. 26. Room with good False Ceiling and Carpeting
  27. 27. 3. Heavy Fabric on Windows•Cover windows with heavy drapes.•Drapes made from soundproofing material areavailable but are costly•Instead choose a heavy fabric that covers the entirewindow•Also cover walls with heavy fabric or velvet•Appears similar to Movie Theatre fabrication
  28. 28. Drapes in an AuditoriumMovie Theatre Fabrication
  29. 29. 4. Mic and Speaker System• This is specially for classrooms.• Speakers are installed in various part of the room• Teacher is supposed to speak on mic•Appears as teacher being near to most of thestudents•Reduces the Speaker – Listener Issue as if teacher isjust near to him.•Background noise is suppressed.
  30. 30. An Auditoriumwith perfectuse of AcousticFundamentals
  31. 31. Summary• Acoustics make big impact on any vocal oriented operation• Classrooms often suffer with poor acoustics• Classroom related issues include – Room Noise, Speaker-Listener distance, Reverberation• Various measures could be taken to enhance acoustics• For Classrooms, this include False Ceiling, Carpeting, Drapes and Speaker-Mic system
  32. 32. Thank You