Acoustical Engineering Solutions Scott Harvey, PE
Thank you for attending! ` Copyright Materials ` This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited.
` © Phoenix Noise & Vibration, LLC 2006 ` At the end of this program, participants will be able to:
1. Understand basic acoustic principals and terms 2. Define acoustics and its place in building design 3. Understand how acoustics can affect building performance 4. Design buildings with acoustics in mind ` One definition:
` the qualities or characteristics of a room, auditorium, stadium, etc., that determine the audibility or fidelity of sounds in it.
` “…the branch of physics that deals with sound and sound waves.” ` What is sound?
◦ “Any pressure variation (in air, water or other medium) that the human ear can detect.” B&K ` What is Noise?
◦ Noise is Unwanted Sound (aka my neighbor’s stereo) ` How is sound quantified
◦ Amplitude or loudness x Variation in the air pressure around us x The bigger the variation, the louder the sound
◦ Frequency or pitch/tone x How quickly we vary the pressure x The quicker the variation, the higher the tone ` Loudness measured in decibels (dB)
◦ dB = 10 x log(Pressure2/refPressure2)
◦ From this we observe: x logarithmic x simply a comparison between two numbers
` Human Range: 0 to 130 dB decibel named after Alexander Graham…
Shown here with Helen Keller and Ann Sullivan ` We measure noise in decibels or dB for a lot of reasons, two being...
◦ Broad range of numbers to a manageable scale
◦ Comparisons are easier ` Reduces the broad range of numbers to a manageable range of numbers.
◦ Humans hear from 20 to 20,000,000 micro-Pascals…
◦ In decibels, this is reduced to a range of 0 to 120 dB.
` Eases Comparisons
` Example of the logarithmic nature:
Change in dB Subjective Response 3 dB Barely Perceptible 5 dB Clearly Perceptible 10 dB Twice as Loud ` Frequency (tones) measured in Hertz (Hz)
◦ 1 Hz = 1 cycle/second
` Human range
◦ 20 Hz to 20,000 Hz ` Named for Heinrich Rudolf Hertz ` 1857-1894 ` Famous German Physicist ` First person to transmit and receive radio waves
80
70
60
50
40
30
20 Sound Pressure Level, dB Sound Pressure 10
0 63 125 250 500 1000 2000 4000 8000 16000
Frequency, Hertz
Room Acoustics Room to Room (Concert Halls plus) Noise Control
Acoustics
Background Noise Outdoor to Indoor Control Noise Control
` Traditional Acoustics ◦ Concert Halls ◦ Drama Theaters ◦ Performance Venues ◦ Houses of Worship
` But wait…
` Achieve proper acoustics by defining desired character of the space ` Maximize the acoustical efficiency within the room by controlling the “wanted” sound within the space ` Minimize “unwanted” sound (background noise) ` Reverberation time (RT) – the time it takes for sound pressure level to decay by 60 dB from its steady state value after the sound source has been terminated. ` Measured in seconds Reverberation Time
90
80 RT = 3.6 seconds 70
60
50
40
30
Sound Pressure Level, dB Sound Pressure Level, 20
10
0 0.1 0.6 1.1 1.6 2.1 2.6 3.1 3.6 4.1 4.6 5.1 5.6 6.1 6.6 7.1 7.6 8.1 8.6 9.1 Time, seconds ` What controls reverberation time?
x Room Size (Volume) x Room Finishes x Room Shape
` Therefore, we can control RT by changing either the size, shape or finishes of the room. Range of Recommended Reverberation Times 3
2.5
2
1.5
1
Reverberation Time, sec Reverberation Time, 0.5
0
Room Use
Acoustical Solutions, Inc. Reverberation Time Change with Room Volume Equal Finishes 12
10
8
6 RT, seconds 4
2
0 1,000 10,000 100,000 Room Volume, cubic ft ` Reverberation time varies with frequency…
8.0
7.0
6.0
5.0 Seconds
Time, 4.0 Measured Design Goal 3.0 Reverberation 2.0
1.0
0.0 125 250 500 1000 2000 4000 Frequency, Hz RT's of Famous Concert Halls 4
3.5
3
2.5
2 Royal Albert Hall, London
Kennedy Center, Washington, D.C. RT, seconds 1.5 Symphony Hall, Boston
1
0.5
0 63 125 250 500 1000 2000 4000 Frequency, Hz
Beranek, Music, Acoustics, and Architecture, Wiley, 1962 ` NOT JUST FOR PERFORMANCE HALLS….
` LEED for Schools specifies ` ◦ 0.6 seconds for core learning space < 10,000 ft3 ◦ 0.7 seconds for core learning space >10,000 ft3 but < 20,000 ft3 ` Room Finishes
◦ Absorbers ◦ Reflectors ◦ Diffusers ` Sound Absorbers – surfaces which absorb sound and prevent reflections ◦ Generally Soft Materials ◦ Sound Absorption Coefficient ◦ NRC ◦ The perfect absorber is an open window Absorption Coefficient – a measure of the sound absorbing property of a surface. More specifically, absorption coefficient is defined as the fraction of the incident sound energy absorbed (otherwise not reflected) by a surface.
Noise Reduction Coefficient (NRC) –a single number rating derived from measured values of sound absorption coefficients of a material at 250, 500, 1000, and 2000 Hz. NRC is an estimate of the sound absorptive property of an acoustical material. ` Open Window NRC = 1.0 Marble Floor NRC = 0.01 Change in RT with Treatment 1000 cu ft, gyp bd walls
3.5
3.0 Concrete Floor, NRC = 0.02 2.5
2.0 Carpeted Floor, 1.5 NRC = 0.55 RT, seconds
1.0
Carpeted 0.5 Flr/Acoustical Tile Ceiling, NRC 0.0 = 0.57 125 250 500 1000 2000 4000
Frequency, Hz ` Reflectors are opposite absorbers ` Also ranked using NRC scale ` Used to direct sound ` Caution: Avoid large, parallel reflective surfaces
Kinetics Noise Control ` Diffusers – scatter the sound energy ` Used to enhance acoustical quality of a listening room ` Studios, practice rooms, recital halls, concert halls ` Carpet
` Absorber ` Painted Gypsum Board
` Reflector ` Painted CMU
` Reflector ` Acoustical Tile Ceiling
` Absorber ` Metal Decking
` Reflector?
` Or Diffusor? ` Plywood
` Reflector ` Glass
` Reflector ` People
` Absorber ` Acoustical Metal Decking
` Absorber ` Unpainted CMU
` “Resorber”????? ` 8,100 ft2 ` 277,000 ft3 ` Wood Floor ` Gyp Walls ` Metal Ceiling 8
7
6
5
4 Measured 3 Design Goal
2
1
0 125 250 500 1000 2000 4000 Range of Recommended Reverberation Times 3
2.5
2
1.5
1
Reverberation Time, sec Reverberation Time, 0.5
0
Room Use
Acoustical Solutions, Inc. 8
7
6
5
4 Ceiling/Wall Absorption 3 Measured
2
1
0 125 250 500 1000 2000 4000
8.00
7.00
6.00
5.00
4.00 Wall Absorption Measured 3.00
2.00
1.00
0.00 125 250 500 1000 2000 4000 8
7
6
5
4 Measured Design Goal 3 Tectum Roof Deck
2
1
0 125 250 500 1000 2000 4000
` Sound Transmission Class (STC) ` Ceiling Attenuation Class (CAC) ` Impact Insulation Class (IIC) ` Sound Barrier – device used to block sound transmission from one point to another.
◦ Transmission Loss per frequency
◦ Sound Transmission Class (STC) – a single number rating of the partition’s ability to block speech frequencies from one side to another.
` There are noise barriers and there are noise absorbers. ◦ Barriers are not absorbers. ◦ Absorbers are not barriers. ◦ Many times the absorber is somewhat transparent.
` Barriers are generally composed of dense, heavy material layers. (Quiz Later) ` Barrier or Absorber?
` Barrier ` Barrier or Absorber?
` Absorber ` Barrier or Absorber?
` Barrier ` Barrier or Absorber?
` Absorber ` Barrier or Absorber?
` ???? STC ASTC Subjective Description 30 22-25 Most sentences clearly understood
40 32-35 Speech can be heard with some effort
Loud speech can be heard with some 50 42-45 effort 60 52-55 Loud speech essentially inaudible 70 62-65 Loud music heard faintly 75+ Most noises effectively blocked
Credit: Architectural Acoustics: Principles and Design 1999
¾ STC developed for speech, applied to many other noise sources such as:
¾Mechanical ¾Transportation ¾Music ` One cost effective way to add STC points to a wall system is through the use of Resilient Channel
` Cost effective but
` NOT SO SIMPLE…
` (This really needs much more time…) Single Legged, RC-1 Double Legged, RX-2 (Dietrich RC Deluxe)
` Ceiling Attenuation Class (CAC) – the measure for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent close spaces. (Architectionary)
Diracdelta.co.uk ` CAC is similar to STC ` Applied primarily to lay in ceiling tiles ` CAC < 25 considered poor ` CAC > 35 considered good ¾ Impact Insulation Class (IIC) - A single number rating used to compare the effectiveness of floor-ceiling assemblies in providing reduction of impact-generated sound such as footsteps.
¾ The popularity of hard surfaced floors and condominiums has brought a lot of attention on IIC ratings.
¾Most Any Carpet and pad > 60 IIC ¾Hard floors < 40 IIC ¾IBC /IRC standards are 50 IIC
•Hard surfaces •Low partition heights •Small-ish cubicles
` Background noise in non-residential buildings is influenced by a variety of sources ` Interior Sources x Other employees x Phones, printers, copiers, keyboards, etc. x Cubicle partition heights x Open plan office design x HVAC ` Exterior Sources x Transportation x Schools/Daycare centers x Mechanical Equipment x Construction/Landscaping ` Have the most design capability on HVAC components and mechanical equipment (emergency generator, cooling towers, elevators, etc.) ` Single number ratings describing the relative loudness and speech interference properties of a given noise spectrum ` Used to specify background noise levels for various space uses, mainly HVAC and mechanical noise ` Noise Criteria (NC) ◦ Simple ◦ No assessment of sound quality ` Room Criteria (RC) Mark II ◦ Evaluates sound quality ◦ Diagnostics
` Airborne ◦ Equipment location ◦ Duct break out ◦ Air flow ◦ Diffusers ` Structure Borne ◦ Proper Isolation x Springs x Pads x Roof Curbs Courtesy of ASHRAE Courtesy of ASHRAE
Courtesy of ASHRAE
` Transportation Noise ` Computer Modeling ` Building Shell Analysis ` Common Building Elements ` Windows and Doors: The Weak Link ` OITC ` Planes, Trains, & Automobiles ` On-site measurements ` Computer Modeling ` HUD Noise Guidebook ` Ldn in dBA ` Typically measured using the “A-weighted” dB scale or “dBA” ` The A-weighting simulates human hearing and is generally used for overall, environmental noise measurements.
A-Weighting
10
0
-10
-20
-30
Adjustment Factor, dB Factor, Adjustment -40
-50
Frequency, Hz
` Calculates a room’s interior noise level based upon: ◦ Exterior Noise Level ◦ Composite STC Rating x Windows, Doors x Walls, Roof x Miscellaneous ◦ Room Size & Volume ◦ Room Absorption ` Can be either very general or very detailed Building Element STC Rating Construction Exterior Walls 2 x 4 wood studs, an exterior layer Brick 56 of ½” OSB or plywood, 3” of Vinyl Siding 39 fiberglass batt insulation, 5/8” Vinyl Siding w/RC 45 interior layer of drywall ½” Insulated Window 28 1/8” glass, ¼” air space, 1/8” glass 1” Insulated Window 35 ¼” glass, ½” air space, ¼” glass 5/8” Laminated, 35 Two 1/8” panes laminated together, Insulated Window ¼” air space, 1/8” glass Standard Patio Door 29 ½” thick glass lite mounted in polystyrene frame Upgraded Patio Door 36 1” dual glazed unit composed of 3/8” laminated glass, ½” air space, and 1/8” double strength glass
` Outdoor-Indoor Transmission Class: an A- weighted single number rating of the transportation sound reduction effectiveness of a partition that separates an indoor space from the outside. ` STC – Speech Frequencies ` OITC – Transportation Frequencies
Window STC Rating OITC Rating ½” Insulated 28 26 5/8” Laminated, 35 31 Insulated ` Restrictions on Exterior Façade Finishes ` Lots of Glass ` High STC Rated Windows and Doors = $$$ ` Green Building Design ◦ Bigger Windows ◦ Fresh Air Openings Room Acoustics Room to Room (Concert Halls plus) Noise Control
Acoustics
Background Noise Outdoor to Indoor Control Noise Control Questions?
Lunch? Discussion? Acoustical Engineering Solutions