Introduction to Acoustics:

Transcription

1 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 Veneklasen Associates INTRODUCTION Consultants in TO Acoustics ACOUSTICS: AV IT How I Environmental Learned to Stop Worrying Noise and Love the Sound Level Meter

2 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.

3 OVERVIEW 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

4 Acoustical Metrics and Terminology

5 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

6 METRICS & TERMINOLOGY What is a Decibel? db=20log(p/p ref ) Logarithmic quantity: 93 db + 93 db = 96 db Increase of 10 db sounds twice as loud Smallest perceivable change is 3 db

7 METRICS & TERMINOLOGY Frequency Spectrum

8 COMMON ACOUSTICAL METRICS ARCHITECTURAL ACOUSTICAL RATINGS STC IIC NRC CAC Sound Transmission Class Airborne sound insulation Impact Insulation Class Impact sound insulation Noise Reduction Coefficient Average absorption Ceiling Attenuation Class Sound isolation for ceiling tiles thru ceiling plenum

9 Acoustics and Codification

10 ACOUSTICAL CODIFICATION Where does acoustical design appear as a requirement? 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)

11 ACOUSTICAL CODIFICATION On the Horizon Verification of Minimum Performance LEED: Commissioning CHPS Design/build contracts

12 ACOUSTICAL CODIFICATION 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

13 ACOUSTICAL CODIFICATION 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

14 ACOUSTICAL CODIFICATION μ = 48.0 σ = 2.6 Field Tests (NIC Ratings)

15 Acoustical Design Basics and Practice

16 ACOUSTICAL DESIGN BASICS AND PRACTICE So the Process Seems Obvious 1. Select criteria. 2. Select assemblies that meet that criteria. 3. Build assemblies correctly.

17 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!

18 ACOUSTICAL DESIGN BASICS AND PRACTICE 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.

19 ACOUSTICAL DESIGN BASICS AND PRACTICE Field Tests on RC Assembly

20 ACOUSTICAL DESIGN BASICS AND PRACTICE 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!

21 ACOUSTICAL DESIGN BASICS AND PRACTICE Effect of Stud Gauge and Spacing o.c. STC o.c. STC ga. 20 ga STC

22 ACOUSTICAL DESIGN BASICS AND PRACTICE 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

23 ACOUSTICAL DESIGN BASICS AND PRACTICE Results of Laboratory Testing

24 ACOUSTICAL DESIGN BASICS AND PRACTICE Placement also matters! 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

25 ACOUSTICAL DESIGN BASICS AND PRACTICE Sandwich Installation

26 ACOUSTICAL DESIGN BASICS AND PRACTICE 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

27 ACOUSTICAL DESIGN BASICS AND PRACTICE Single Metrics DO NOT Tell the Whole Story Impact sound pressure level (db) Frequency (Hz)

28 ACOUSTICAL DESIGN BASICS AND PRACTICE 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.

29 Down-to-Earth Application

30 APPLICATION What can I do? 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. Sound level shall not exceed X decibels. Occupant shall not cause a disruption. 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 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.

31 APPLICATION What can I do? 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.

32 CONCLUSIONS 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.

33 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 Veneklasen Associates INTRODUCTION Consultants in TO Acoustics ACOUSTICS: AV IT How I Environmental Learned to Stop Worrying Noise and Love the Sound Level Meter Thank 33you!