Introduction to Acoustics€¦ · types • Discuss the importance of acoustics in the built environment • Describe design considerations to pass a post-construction compliance

INTRODUCTION TO ACOUSTICS: How I Learned to Stop Worrying and Love the Sound Level Meter | 07.14.20151

Veneklasen Associates Consultants in Acoustics | AV | IT | Environmental Noise

Introduction to Acoustics:How I Learned to Stop Worrying and Love the Sound Level Meter

Samantha Rawlings, LEED AP BD+C

For IFMA New Mexico 07.14.2015

INTRODUCTION TO ACOUSTICS: How I Learned to Stop Worrying and Love the Sound Level Meter | 07.14.2015INTRODUCTION TO ACOUSTICS: How I Learned to Stop Worrying and Love the Sound Level Meter | 07.14.2015

ACOUSTICAL IMPACT

Why Do I Care about the Acoustical Quality of the Built Environment?

• What happens if a building has NEGATIVE acoustical attributes?

- Greater tenant turnover

- Lessened productivity

- Less restful

• What if a building has POSITIVE acoustical attributes?

- Pleasing work/learning environment

- Good speech intelligibility

- Increased comfort

When the Acoustics are correct, occupants will never even consider sound quality.


Learning Objectives

• Review the role of data, statistics, and

analytics in acoustical building science

• Understand regulation of acoustical

performance within several building

types

• Discuss the importance of acoustics in

the built environment

• Describe design considerations to

pass a post-construction compliance

review

OVERVIEW


Acoustical Metrics and Terminology


METRICS & TERMINOLOGY

What is Sound?

• Sound is a pulsation of air pressure, a fluctuation that propagates through the air, that is capable of being heard.

• Usually generated by vibrating surfaces that in turn vibrate the air.

a



What is a Decibel?

• dB=20log(p/pref)

• Logarithmic quantity: 93 dB + 93 dB = 96 dB

• Increase of 10 dB sounds twice as loud

• Smallest perceivable change is 3 dB



Frequency Spectrum


ARCHITECTURAL ACOUSTICAL RATINGS

STC Sound Transmission Class

Airborne sound insulation

IIC Impact Insulation Class

Impact sound insulation

NRC Noise Reduction Coefficient

Average absorption

CAC Ceiling Attenuation Class

Sound isolation for ceiling tiles thru ceiling plenum

COMMON ACOUSTICAL METRICS


Acoustics and Codification


• Multifamily residential construction (IBC / HUD)

• Schools (LEED / CHPS)

• Healthcare (LEED - FGI)

• Secure Government Facilities (GSA)

• Court Facilities (USAOC)

• Environmental Noise & Vibration (FAA / FTA / State and Local Ordinances)

Where does acoustical design appear as a requirement?

ACOUSTICAL CODIFICATION


• LEED: Commissioning

• CHPS

• Design/build contracts

On the Horizon – Verification of Minimum Performance



Everyone Loves a Good Story

• Private corporations with government contracts– Hired D/B contractor, including acoustical design

– Complaints resulted, inadequate privacy

– 5+ years of testing and reconstructing

– $5M lawsuit

• CHPS Verification– Consultant measured post-construction reverberation

time, exceeded criteria by 0.01 seconds.

• State University D/B contract



D/B contract verification language

“Airborne sound isolation measurements for 20 partitions or floor ceiling assemblies…Should any of the tested areas not comply with the requirements indicated in this report the Design Build team shall have the burden of modifying the space until the specifications are met...This shall continue until all tests performed comply with the project criteria.”

Is this level of precision realistic?

If we examine the statistical outline of the data…



μ = 48.0

σ = 2.6

Field Tests

(NIC Ratings)



Acoustical Design Basics and Practice


So the Process Seems Obvious

1. Select criteria.

2. Select assemblies that meet that criteria.

3. Build assemblies correctly.

ACOUSTICAL DESIGN BASICS AND PRACTICE


Why Does This Not Work?

1. Select criteria.

2. Select assemblies that meet that criteria.

3. Build assemblies correctly.

1. The tests are not as precise as you think

2. The test report may not be for the assembly that you think!



Precision in Acoustical Testing

• The range of values that will be achieved for a given assembly is 5 points at a minimum

• You can’t tell if two assemblies are different unless the results differ by at least 5 dB

• Or, you need to compile many tests and average:

This is ESPECIALLY IMPORTANT when the assembly

is only slightly above the requirement.



Field Tests on RC Assembly

0

1

2

3

4

5

6

7

40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55



Test Reports Often Do Not Give the Details

1. Material properties • Gauge of studs

• Weight of gypsum board

• Type x or type c?

2. Assembly details • Screw spacing

• Number of studs

3. Mounting conditions

(Some of) the Details Matter!



0

10

20

30

40

50

60

70

63

80

100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

5000

25 ga. @ 24” o.c. STC 52

24” → 16” o.c.

STC 49

25 ga. → 20 ga

STC 48

Effect of Stud Gauge and Spacing



Resilient Channel

• Commonly used in North America

• Nominal 25 gauge steel, ½” thick, Z shape

• Also “double leg” resilient channel or “hat channel”

• Resilient channel has become a commodity product, but there is no specification



Results of Laboratory Testing



• RC should be attached directly to framing

• Common error to install over solid surface, often plywood shear panel

• 2x6 stud wall, R19 batt insulation

• RC sandwiched between 2 layers of gypsum board on one side

• 1 or 2 layers of gypsum board on other side

Placement also matters!



Sandwich Installation



Single Metrics DO NOT Tell the Whole Story

• Single-number metrics ease comparison, code language

• BUT, not indicative of details in specific frequency ranges

• Single-number ratings only cover part of audible frequency range

– Typical frequency range of interest: 50 Hz – 5000 Hz

– STC frequency range: 125 Hz – 4000 Hz

– IIC frequency range: 100 Hz – 3150 Hz

Conclusion: Consider octave-band data as well as single-number ratings



10

20

30

40

50

60

70

31 63 125 250 500 1000 2000

Frequency (Hz)

Imp

ac

t so

un

d p

res

su

re l

eve

l (d

B)

Single Metrics DO NOT Tell the Whole Story



Summary: Why You Don’t Design From a List of Ratings

1. A test result actually represent a range of values.

2. The more differences in the condition, the wider the range.

3. Details like stud gauge and screw spacing may not be reported but can significantly affect the result.

4. Determining which details are important requires systematic testing and compiling the data.



Down-to-Earth Application


• Take steps to prepare for performance verification testing:– Review performance verification language carefully. Do not accept

language that opens you or your client to unreasonable expectations. Ensure language is specific.

What can I do?

APPLICATION

“Sound level shall not exceed X decibels.”

“Sound level shall not exceed X decibels, when measured on an A-weighted scale.

Measurement shall be completed for a period of Y minutes, with fast time constant. Metric shall be the Equivalent Sound Level (Leq).

Measurements shall be performed only by an individual with Z qualifications.”

“Occupant shall not cause a disruption.”

“Occupant shall not persist in activities that are disruptive to persons of normal sensitivity. Landlord shall determine whether a sound is

reasonably disruptive. ”

“All test results shall meet criteria.”“An arithmetic average of test results shall

meet criteria.”


• Take steps to prepare for performance verification testing:– Review performance verification language carefully. Do not accept

language that opens you or your client to unreasonable expectations. Ensure language is specific.

– Review standard design to obtain realistic idea of field performance. Consult more than one source for performance. Be aware of common pitfalls that will reduce acoustical performance.

– Be especially careful when design is close to criteria. Inform client of risk involved with design vs. considering a degree of overdesign.

– Ensure good QA during construction. Avoid compromise.

– Consider voluntary post-construction verification testing when not required to obtain understanding of your standard systems’ performance.

What can I do?

APPLICATION


• With appropriate acoustical environment,

TENANTS STAY LONG-TERM and buildings

have longer lives.

• Acoustical GUIDELINES appear for schools,

healthcare, security/government, projects

within noisy exterior environments, and

multifamily residential.

• Understanding and avoidance of elements

that compromise acoustical performance,

ensuring high-quality field QA, and advance

assessment of post-construction

performance enable PASSED COMPLIANCE

REVIEWS.

CONCLUSIONS

INTRODUCTION TO ACOUSTICS: How I Learned to Stop Worrying and Love the Sound Level Meter | 07.14.201533

Veneklasen Associates Consultants in Acoustics | AV | IT | Environmental Noise

Introduction to Acoustics:How I Learned to Stop Worrying and Love the Sound Level Meter

Samantha Rawlings, LEED AP BD+C

For IFMA New Mexico 07.14.2015

Thank you!

Documents

Introduction to Acoustics€¦ · types • Discuss the importance of acoustics in the built environment • Describe design considerations to pass a post-construction compliance