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  1. Acoustics Or How to make a client happy

  2. Fundamentals of Architectural Acoustics Acoustics

  3. Sound is a longitudinal wave. • Remember that longitudinal waves are made up of areas where the wave is compressed together, and other areas where it is expanded. • Sound can be vibration which is pressure – felt but not heard. • We will look in detail at three fundamental characteristics of sound: Speed, Frequency, and Loudness. * Acoustics

  4. Speed • The speed of sound in air actually depends on the temperature of the air. • The sound travels faster through media with higher elasticity and/or lower density. • Speed of sound is 1130 feet per second or 344 m/s • Light is 186,000 miles per second Acoustics

  5. Acoustics

  6. Frequency • Most often we will be looking at sound waves that humans can actually hear, which are frequencies from 20 – 20,000 Hz. • Infrasonics -20 Hz - Ultrasound 20,000Hz • Frequency is sometimes referred to as pitch. Acoustics

  7. Loudness • The loudness of a sound depends on the wave’s amplitude. • This is why a stereo system has an “amplifier”, a device that increases the amplitude of sound waves. • The louder a sound, the bigger the amplitude. • This is also a way of measuring the amount of energy the wave has. Acoustics

  8. Loudness • The system used to measure the loudness of sounds is the decibel system, given the unit dB. • The decibel system is based on logarithms, which means for every step up by one, the sound is actually ten times louder. For example, a 15dB sound is ten times louder than a 14dB sound. * Lesson 49: Properties of Sound by Mr. Clintberg’s Study Physics Acoustics

  9. Acoustics • One of the loudest man-made sounds 215 dB • That much sound energy creates heat. • Water is used to absorb the energy • That’s steam you see. It’s not all smoke. • If they did not use water to absorb the sound, the shuttle and tower would fail due to the energy generated from 215 dB.

  10. Acoustics Noise pollution is huge especially in our cities

  11. Acoustics

  12. Inverse Square Law • Not in textbook Acoustics

  13. Chapter 18 Sound in Enclosed Spaces Acoustics

  14. Sound Absorption • Noise Reduction Coefficient (NRC) Verses • Sound Transmission Coefficient (STC) (textbook class it Sound Transmission Class) Acoustics

  15. Acoustics

  16. Acoustics STC

  17. Acoustics NRC

  18. Acoustics

  19. Acoustics

  20. Acoustics

  21. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • See Handout in class • Also available on line at Arch 433 - Web Site Acoustics

  22. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Submittals • Ceiling Samples – tile and grid • Tile 6 inch square samples Grid boxes – 3 samples each • Follow directions in section 01330 – Submittal Procedures • Ceiling layout – drawings – 3 sets • Attachment methods Acoustics

  23. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Quality Assurance • Class “A” • Coordination – Anything above the ceiling • Extra Material Acoustics

  24. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Manufactures - Panels • Mineral Base • Type III (see slide 24) • Pattern EI (see your handout for “E”+ “I” • STC -35 • Tegular Edge • Size 24”x 24” • Manufacture – Armstrong – Cirrus 584 (or equal) “by” • Celotex or USG Acoustics

  25. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Types of Material • There are 20 types • A Type III • Mineral base with painted finish; • Type includes: • Form 1 Nodulated, cast, or molded • Form 2 Water felted • Form 3 Dry felted Acoustics

  26. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Manufactures – Grid • Direct Hung • Powdered-Actuated Fasteners in Concrete - OK • Wire – 12 gauge • Hold Down Clips – Yes • Grid – 15/16” • Manufactures – Armstrong, Chicago, Interiors Inc. Acoustics

  27. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Acoustical Sealant • At perimeter joints and openings • Flame spread & smoke development < 25 per ASTM E84 • Exposed • At perimeter joints and openings • Flame spread & smoke development < 25 per ASTM E84 • Concealed • BA-98 Pecora or Tremco Act. Sealant • AC-20 FTR or Sheetrock Act. Sealant, USG Acoustics

  28. Review Specification • CSI Division 09511 – Acoustical Panel Ceilings • Execution • Balance boarders • Splay hangers • Sealant @ wall angle • Screw attach wall angle • Cleaning Acoustics

  29. Let’s do a sound absorption problem!!!! Acoustics

  30. Carpenter Hall Room 102 Foot print of Carpenter Room 102 32’ x 98’ Ceiling Ht. 14’ to 10’ average 12’ Sound Absorption @ 500Hz Sound Absorption

  31. The Formula T = .05 V/a and NR = 10log (a2/a1) We’ll get to the formulas later Sound Absorption

  32. I can explain everything

  33. Walls Plaster, gypsum or lime on brick = ά .02 Floor Wood = ά .10 Ceiling Plaster, gypsum or lime = ά .06 (See handout) ά = Noise Reduction Coefficient (NRC) or Sound Absorption Coefficient This is similar to the example on page 791 Sound Absorption

  34. What is the reverberation time with no finishes? Walls ά Sabins Back 10’x 32’= 320 sf Front 14’x 32’= 448 sf Sides (12’ave. x 98’) x 2 = 2,352 sf 3,120 sfx ά .02 = 62.4 Floor 31 x 98 3,038sf x ά .10 = 303.8 Ceiling 31 x 98 3,038 sf x ά .06 = 182.3 Total 548.5 Sound Absorption

  35. Sound Absorption T = .05 V/a Wallace Clement Sabine Father of Architectural Acoustics

  36. The Formula T = .05 V/a T = Time of Reverberation V = Volume a = Sabins  Sound Absorption

  37. The Formula T = .05 V/a V = Volume of room 31’x 98’x 12 a = sabins of = 548.5 T= .05(31’x 98’x 12’)/ 548.5 T= .05(36,456)/548.5 T= 3.32 seconds Sound Absorption

  38. With acoustical tile & carpet, what would be the reverberation time? Sound Absorption

  39. Walls άSabins Back 10’x 32’= 320 Front 14’x 32’= 448 Sides (12’ave. x 98’) x 2 = 2,352 3,120 sf x ά .02 =62.4 Floor with Carpet 31 x 98 3,038 sf x ά .14 = 425.32 Ceiling - Acoustical tile (5x7) 8 each 280 sf x ά .85 =238 3,038 sf – 280 sf 2,758 sf x ά .06 =165.5 w/o carpet (769.7) Total891.22 Sound Absorption

  40. The Formula T = .05 V/a V = Volume of room 31’x 98’x 12 a = sabins of 891.22 T= .05(31’x 98’x 12’)/ 891.225 T= .05(36,456)/ 891.22 T= 2.04 seconds Sound Absorption

  41. 3.32 seconds vs. 2.04 seconds Sound Absorption

  42. What! 2.04 vs. 3.32 seconds

  43. Is this a big enough difference?

  44. NR = 10log (a2/a1) NR = Noise reduction a2 = 2.04 seconds a1 = 3.32 seconds Sound Absorption

  45. NR = 10log (a2/a1) NR = 10 log (2.04 / 3.32) NR = 10 log (.614) NR = 2.11 Noise Reduction of = 2.11 db Acoustical tile alone = 1.48 db Sound Absorption

  46. WHAT! Sound Absorption Is this enough?

  47. Let’s look at a rule of thumb.

  48. Sound Absorption Change in Intensity Level, db 1 3 5 10 18 Change in Apparent Loudness Almost imperceptible Just perceptible Clearly noticeable Twice as loud Very much louder

  49. For a noise reduction of 2.11! Carpet 3,136 sf of carpet or 348 sy at $22.00 sy = $7,666.00 Acoustical Ceiling Tile 280 sf x $2.25 = $630.00 Total cost furnished and installed $8,296.00 $8,296.00 for an imperceptible noise reduction! (For 1.48 db reduction just for the acoustical tile) Sound Absorption

  50. Doesn’t make a lot of sense