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

`

1. 2. 3. 4.

At the end of this program, participants will be able to: Understand basic acoustic principals and terms Define acoustics and its place in building design Understand how acoustics can affect building performance 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

Sound Pressure Level, dB

70 60 50 40 30 20 10 0 63

125

250

500

1000

2000

Frequency, Hertz

4000

8000

16000

Room Acoustics (Concert Halls plus)

Room to Room Noise Control

Acoustics Background Noise Control

Outdoor to Indoor 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

Sound Pressure Level, dB

80

RT = 3.6 seconds

70 60 50 40 30 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

Time, seconds

5.6

6.1

6.6

7.1

7.6

8.1

8.6

9.1

`

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

Reverberation Time, sec

3 2.5 2 1.5 1 0.5 0

Room Use Acoustical Solutions, Inc.

Reverberation Time Change with Room Volume Equal Finishes

12 10

RT, seconds

8 6 4 2 0 1,000

10,000 Room Volume, cubic ft

100,000

Reverberation time varies with frequency… 8.0 7.0 6.0 Reverberation Time, Seconds

`

5.0 4.0 Measured Design Goal

3.0 2.0 1.0 0.0 125

250

500

1000

Frequency, Hz

2000

4000

RT's of Famous Concert Halls 4 3.5

RT, seconds

3 2.5 2

Royal Albert Hall, London Kennedy Center, Washington, D.C.

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

RT, seconds

2.5 2.0

Carpeted Floor,

1.5

NRC = 0.55

1.0 Carpeted

0.5

Flr/Acoustical Tile Ceiling, NRC

0.0 125

250

500

1000

Frequency, Hz

2000

4000

= 0.57

` ` ` `

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 Design Goal

3 2 1 0

125

250

500

1000

2000

4000

Range of Recommended Reverberation Times

Reverberation Time, sec

3 2.5 2 1.5 1 0.5 0

Room Use Acoustical Solutions, Inc.

8 7 6 5 4

Ceiling/Wall Absorption Measured

3 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

50

42-45

Loud speech can be heard with some 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 (Dietrich RC Deluxe)

Double Legged, RX-2

`

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 x x x x

Other employees Phones, printers, copiers, keyboards, etc. Cubicle partition heights Open plan office design HVAC

`

Exterior Sources x x x x

`

Transportation Schools/Daycare centers Mechanical Equipment 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 Adjustment Factor, dB

`

0 -10 -20 -30 -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 Exterior Walls Brick Vinyl Siding Vinyl Siding w/RC

STC Rating 56 39 45

Construction 2 x 4 wood studs, an exterior layer of ½” OSB or plywood, 3” of fiberglass batt insulation, 5/8” 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, Insulated Window

35

Two 1/8” panes laminated together, 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 Aweighted 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, Insulated

35

31

` ` ` `

Restrictions on Exterior Façade Finishes Lots of Glass High STC Rated Windows and Doors = $$$ Green Building Design ◦ Bigger Windows ◦ Fresh Air Openings

Room Acoustics (Concert Halls plus)

Room to Room Noise Control

Acoustics Background Noise Control

Outdoor to Indoor Noise Control

Questions?

Lunch?

Discussion?

Acoustical Engineering Solutions