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Industrial

Military Aviation

HVAC

OEM

Architectural

EnvironmentalMarine

ASHRAE Chapter MeetingASHRAE Chapter Meeting

HVAC Noise & Vibration ControlHVAC Noise & Vibration Control

Best PracticesBest Practices

Presented By

Noise & Vibration Control, Inc.

610-863-6300

www.brd-nonoise.com

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Why Acoustics Matter!Why Acoustics Matter!

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☺ Introduction to Acoustics

☺ Fundamental Design

Questions

☺ Acoustic Materials

TopicsTopics

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Important Acoustic Terminology

• Loudness vs. Pitch

• Tonal Content

• Decibels: Sound Power vs. Sound

Pressure

• Decibel Weighting Networks

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Loudness = Quantity of Sound

Pitch = Quality of Sound

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What Is The Decibel Scale?

The decibel (dB) is a dimensionless unit calculated using the ratio of a

measured value (p) to a reference value (ref). The values of sound

pressure of most interest range from the threshold of hearing at about 20

µPa to a level of extreme danger at about 200 Pa. This range of

variation translates to 7 orders of magnitude with the high level being

10,000,000 times that of the lower threshold. The use of a logarithmic

scale compresses the unit of measure to a manageable range in order to

simplify calculations, computations and quantitative manipulation of data.

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200

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

108

105

104

103

102

101

100

10-1

10-2

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10-11

10-12

100,000,000

100,000

10,000

1,000

100

10

1

0.1

0.001

0.0001

0.00001

0.000001

0.0000001

0.00000001

0.000000001

0.0000000001

0.00000000001

0.000000000001

0.0000000000001

Saturn Rocket

Turbojet Engine

Jet Aircraft at Takeoff

Turboprop at Takeoff

Prop Aircraft at Takeoff

Large Pipe Organ

Small Aircraft Engine

Blaring Radio

Automobile at High Speed

Voice, Shouting

Garbage Disposal Unit

Voice Conversation Level

Ventilation Fan

Office Air Diffuser

Small Electric Clock

Voice, Soft Whisper

Rustling Leaves

Human Breath

Threshold of Hearing

Decibel re: 1012 WWatts – ExponentialWattsSource

200

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

108

105

104

103

102

101

100

10-1

10-2

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10-11

10-12

100,000,000

100,000

10,000

1,000

100

10

1

0.1

0.001

0.0001

0.00001

0.000001

0.0000001

0.00000001

0.000000001

0.0000000001

0.00000000001

0.000000000001

0.0000000000001

Saturn Rocket

Turbojet Engine

Jet Aircraft at Takeoff

Turboprop at Takeoff

Prop Aircraft at Takeoff

Large Pipe Organ

Small Aircraft Engine

Blaring Radio

Automobile at High Speed

Voice, Shouting

Garbage Disposal Unit

Voice Conversation Level

Ventilation Fan

Office Air Diffuser

Small Electric Clock

Voice, Soft Whisper

Rustling Leaves

Human Breath

Threshold of Hearing

Decibel re: 1012 WWatts – ExponentialWattsSource

Actual Scale versus Decibel Scale

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Sound wavelengths are the linear measurement

of one full cycle of displacement where the motion

of air molecules is first compressed and then

expanded (forming a pressure pulsation). The

wavelength is determined by the ratio of the speed

of sound to the frequency.

Wavelength (ft)

= Speed of Sound (fps) / Frequency (Hz)

The rate at which these pulsations occur is

called the frequency and is described in

cycles per second (1 cycle per second equals

1 Hz). Each cycle is one complete expansion

and compression.

Frequency and Wavelength

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A 1K Hz tone at 60 dB would require a

102 dB tone at 20 Hz to sound as loud to

the human ear.

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Decibel Addition:

10 log (10dB/10 + 10dB/10 + …)

For example, 87 dB + 87 dB

= 10 log (1087/10 + 1087/10)

= 10 log (108.7 + 108.7)

= 10 log (1.00237 x 109)

= 10 (9.00103) = 90 dB

Calculation Tools

Sound Power to Sound Pressure:

dB = Lw – ((20 Log dist in ft) - 2.4)

For example, at 30'

dB = Lw – ((20Log30) - 2.4)

= Lw – ((20*1.477) - 2.4)

= Lw – (29.5 - 2.4) = Lw - 27.1

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A-weighting network is designed to approximate the human hearing response.

Note that curve is similar but opposite the equal loudness contours.

Octave Band Center Frequency, Hz

31.5 63 125 250 500 1000 2000 4000 8000

A-weighting -39 -26 -16 -9 -3 0 +1 +1 -1

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What is the overall dBA level?

Octave Center Unweighted A-weighting A-weighted Overall

Band Frequency Sound factor (dB) Sound Resultant

Pressure (dB) Pressure (dBA) Level

1 63 94 -26 68

2 125 86 -16 70

3 250 85 -9 76

4 500 89 -3 86 91 dBA

5 1,000 89 0 89

6 2,000 77 1 78

7 4,000 75 1 76

8 8,000 76 0 76

86

89

Decibel

Addition

72

86

89

79

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Why is it important to know dB versus dBA?

946170808589898785dBA

94626979859298103111dB

-1

8k

110-3-9-16-26A-scale

Total

dBA4k2k1k50025012563

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What is Sound Pressure?Decibels of sound pressure (Lp) have a universally

accepted reference pressure of 2.0 x 10-5 Pascals (Pa).

Lp = 20 log10 [Root Mean Square (RMS) Sound Pressure]

2.0 x 10-5 Pa (Reference Pressure)

What Is Sound Power?Decibels of sound power (Lw) have a universally accepted

reference value of 10-12 watts (1 picowatt).

Lw = 10 log10 Watts Sound Power

10-12 Watts (Reference Value)

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PWL vs. SPL Power vs. Pressure

Cause vs. Effect

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Extreme Danger

Threshold of Pain

Threshold of Discomfort

Very Loud

Moderate

Faint

Threshold of Hearing

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

200.0

63.2

20.0

6.3

2.0

0.6

0.2

0.06

0.02

0.006

0.002

0.0006

0.0002

0.00006

0.00002

Military Jet Takeoff @ 100 ft

Artillery Fire @ 10 ft

Passenger Ramp at Airport

Loud Rock Band

Platform of Subway Station

Large Diesel Engine @ 130 ft

Computer Printout Room

Freight Train @ 100 ft

Conversation Speech @ 3 ft

Window Air Conditioner

Quit Residential Area

Whisper @ 6 ft

Buzzing Insect @ 3 ft

Threshold of Good Hearing

Threshold of Youthful Hearing

Subjective Reaction

Sound Pressure Level dB

SoundPressure

Pa

Typical Sound Pressure Levels

Extreme Danger

Threshold of Pain

Threshold of Discomfort

Very Loud

Moderate

Faint

Threshold of Hearing

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

200.0

63.2

20.0

6.3

2.0

0.6

0.2

0.06

0.02

0.006

0.002

0.0006

0.0002

0.00006

0.00002

Military Jet Takeoff @ 100 ft

Artillery Fire @ 10 ft

Passenger Ramp at Airport

Loud Rock Band

Platform of Subway Station

Large Diesel Engine @ 130 ft

Computer Printout Room

Freight Train @ 100 ft

Conversation Speech @ 3 ft

Window Air Conditioner

Quit Residential Area

Whisper @ 6 ft

Buzzing Insect @ 3 ft

Threshold of Good Hearing

Threshold of Youthful Hearing

Subjective Reaction

Sound Pressure Level dB

SoundPressure

Pa

Typical Sound Pressure Levels

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Sioux Falls, SD Municipal Code defines tone as:

“any sound which can be distinctly heard as a single pitch or set of single pitches…. and shall exist

of the one-third octave band sound pressure level in the band when the tone exceeds the arithmetic

average of the sound levels of the two contiguous one-third octave bands by five dB for frequencies

of 500 Hz and above, eight dB for frequencies between 160-400 Hz, and by 15 dB for frequencies

less than or equal to 125 Hz.”

Tonal Noise

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Recommended NC levels for various room uses

• OSHA, MSHA, etc.

• Company policy

• Bldg criteria for human comfort

• Local ordinance:

generalcode.com

municode.com

noisepollution.org

amlegal.com

Outdoor Objective Criteria

State, City, Township Ordinances

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www.generalcode.com

www.municode.com

www.noisepollution.org

www.amlegal.com

Researching Outdoor Objective

Criteria

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System Problems Require System

Solutions

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System Problems Require System

Solutions

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(Sound Levels 270 ton Air Cooled Chiller)

-37-37-37-37-37-37-37-37-37Loss100’

1008185929497999890Lw

634448555760626153Lp

A8K4K2K1K50025012563Freq (Hz)

1. Where are we now?

2. Where do we need to be?

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13182022171410----Needed

Attenuation

502628334046526167Ordinance

634448555760626153Chiller

A8K4K2K1K50025012563Freq (Hz)

3. How much noise reduction is required?

4. What needs to be done to achieve compliance?

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ABSORBERS BARRIERS COMPOSITES

DAMPING ELECTRONIC FLOW CONTROL

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Covers Discharge StacksSilenced Discharge

Stacks

Wall Treatments Barriers Enclosures

Air-Cooled Chillers

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Covers Soft Enclosures Hard Enclsoures

Covers Acoustic CurbsDischarge Stacks and

Acoustic Screens

Water-Cooled Chillers

Rooftop Units

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A Specification Should Provide

“Just the Right Prescription”

• Accountability

• Cost Control

• Predictable Performance

• Review of subjective and objective noise

criteria

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Common Specification Common Specification

StrategiesStrategies

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Common Spec Strategies on Noise

Sensitive Projects• Specify sound data for lowest rated model as

equipment basis of design

• Specify all available OEM equipment low noise options

• Specify an equipment model that is not tonal

• Specify the same treatment used on the last noise sensitive project

• Retain an acoustical consultant to write the specification

• Specify base equipment and address any

noise problems at start-up

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Sound Pressure Data for property line 80’ away

(No OEM Sound Kit Options)Overall

A-Wtd

63 125 250 500 1000 2000 4000 8000 (dBA)

1 61 58 56 61 54 52 48 46 61

2 66 67 63 63 62 58 51 48 66

3 31 34 43 47 53 55 52 44 60

4 57 63 61 64 61 55 52 44 66

Sound Pressure Levels 5 (dB) @ 80'

Octave Band Center Frequency (Hz) 4 Different Chiller

Manufacturers &

Models (Screw

and Scroll

Designs)

Sound Pressure Data for property line 80’ away

(with factory OEM options)Overall

A-Wtd

63 125 250 500 1000 2000 4000 8000 (dBA)

63 57 57 59 54 48 44 42 60

52 60 61 59 56 54 46 41 62

31 33 43 46 49 51 48 42 56

57 63 61 61 60 55 52 42 64

Sound Pressure Levels 5 (dB) @ 80'

Octave Band Center Frequency (Hz)

4 Different Chiller

Manufacturers & Models

(Screw and Scroll

Designs)

None of the chillers will comply with typical nighttime

noise ordinance values of 50 to 55 dBA.

Common Specification Strategies:

� Specify sound data for lowest rated model as equipment basis of design

� Specify all available OEM equipment low noise options

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Scroll Chiller Sound

Pressure Levels

Z C A 12

16

20

25

32

40

50

63

80

100

125

160

200

250

315

400

500

630

800

1k

1k25

1k6

2k

2k5

3k15

4k

5k

6k3

8k

10k

12k5

16k

20k Hz

30

40

50

60

70

80

90

100dB

Screw Chiller Sound

Pressure Levels

Common Specification Strategies:

� Specify an equipment model that is not tonal

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Best Practices

Acoustic Design

• Answer 4 design questions

1. Where are we now?

2. Where do we need to be?

3. What needs to be done to get there?

4. How much will that cost?

• Use 3-5 dBA safety factor

• Cursory review on every project, in depth review when

warranted

• Assess site ambient noise levels

• Evaluate airborne and structure-borne transmission

• System problems require system solutions

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Best Practices

Specifications

• Job specific combined design/performance specs

preferred over generic performance specs

• Evaluate project specific objective and subjective criteria

– Indoor criteria: NC, RC, NCB, RC Mark II

– Outdoor criteria: Zoning and ordinance criteria

• Place in Division 15/23 with equipment

• Specify single source for system acoustic performance

• Specify turnkey where installation critical

• Require submission for approval as “or

equal” 10 days before bid date

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