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Guideline I.6: Effective Acoustics

Intent

To promote productive, supportive, and comfortable acoustic environments for all occupants and to control unwanted noise. Effective acoustics enable effective speech communications at normal speaking voice while providing for local speech privacy.

Required Performance Criteria

Guidelines apply to all New Construction projects and for Major Renovations that include replacement or construction of relevant assemblies.

  1. Newly constructed and renovated classrooms and other education facilities, including both spaces classified as occupancy group[1] E and other learning spaces and facilities for students above the 12th grade must follow ANSI S12.60–2010 Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, Part 1: Permanent Schools.
  2. Exterior-source noise control: All buildings or spaces not covered under I.6A must meet at least one of the following:
    1. A-weighted exterior-source background noise in regularly occupied spaces of the building shall be no greater than 45dBA, as evaluated after construction but prior to occupancy and tested per Annex A of ANSI S12.60–2010 Part 1.
    2. Average Outdoor-Indoor Transmission Class (OITC) rating of facades and roof assemblies shall be at least 30, or at least 40 for sites with identified risk of significant exterior-source noise. These sites include:
      1. Sites within mapped 60 dBA Day-Night Level (DNL) area for airports listed below.
      2. Sites with an identified A-weighted outdoor noise level of 65dBA or greater as surveyed during planned occupied times and evaluated as equivalent energy level (Leq) for a period of one hour during loudest time of the day.
      3. If the project includes residential use and the site has a DNL or Community Noise Equivalent Level (CNEL) of 45dBA or greater.
  3. Internal-source noise control: For buildings or spaces not covered under I.6A: Meet all of the following:[1]
    1. Air-distributed noise level from mechanical system must not exceed the following Noise Criteria (NC) levels, as estimated through the most current version of HVAC Applications HVAC Handbook, Chapter 48, Noise and Vibration Control; Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Standard 885-2008 methodology; or ANSI S12-60 Part 1 Annex A.1.
      1. Gymnasia, circulation spaces, lobbies, service areas, and sports facilities with or without seating areas: maximum of NC 45.
      2. Meeting, lecture halls not part of occupancy type E, offices of less than 300 sq. ft., and conference rooms: maximum of NC 35.
      3. All other spaces: maximum of NC 40.
    2. Reduce interior noise transfer through the following:
      1. Wall and floor/ceiling assemblies between occupancies achieves a Sound Transmission Class (STC) of at least that listed in the table below. If Apparent Sound Transmission Class (ASTC) ratings are used, subtract 5 from the listed STC minimums to determine ASTC minimums. If Normalized Noise Isolation Class (NNIC) is used for field verification, subtract 3 from the listed STC minimums.
        Note that Group E occupancies are covered under I.6A above.
        ABF IMR
        A606060606060
        B605060505050
        F606060606060
        I605060505050
        M605060505050
        R605060505050
      2. Assemblies adjacent to circulation spaces may reduce the STC requirements by 5. Spaces not regularly occupied are exempt from this requirement.
      3. Adjacent regularly occupied spaces within occupancies shall meet the following minimums:
        A55
        B45
        F50
        I45
        M45
        R45
      4. Impact Isolation Class (IIC) of floor and ceiling assemblies separating sleeping areas or dwelling units from other sleeping areas or dwelling units or other occupancies is at least 50. Assemblies separating sleeping areas or dwelling units from storage, including Group A-4 and Group S are exempt from this requirement.
      5. Ensure the following are included in the design and verified during construction:
        1. Walls continue and are sealed to bottom of floor/ceiling structure for those assemblies serving as acoustic barriers
        2. Other penetrations of intended sound barriers are limited.
        3. Consideration of other equipment or noise that will be present in the space and will be active during occupied hours. Consider separation of equipment likely to interfere with productive and comfortable acoustic environments.
      6. Ensure that wall, floor/ceiling assemblies separating mechanical rooms from other areas of the building achieve at least an STC rating of 50. If the mechanical space includes a generator, compressor, or other similar noise source, achieve an STC of at least 60 in surrounding wall and floor/ceiling assemblies. Ensure that mechanical equipment is adequately isolated to limit structure-borne sound and vibration transmission. Ensure that plumbing equipment has been adequately isolated from spaces to prevent noise transmission and noise production.
    3. Room acoustics: All regularly occupied spaces must meet one of the three paths listed below subject to the noted exceptions:
      1. Calculated reverberation time as evaluated for the 500 Hz, 1000 Hz, and 2000 Hz octave bands must be no less than 0.2 seconds and no greater than 0.7 seconds. This calculation may include furnishings if included in the project.
      2. The average area-weighted noise-reduction coefficient (NRC) of all of the interior surface materials or assemblies of the space is greater than 0.45. This calculation may include furnishings if included in the project.
      3. The average area-weighted NRC of all of the interior surface materials or assemblies of the space is greater than 0.35 for spaces with volumes less than 30,000 cu. ft. This calculation may include furnishings if included in the project.

      Exceptions:

      • Concert halls or other music performance auditoria, laboratory spaces, aquatic facilities, and gymnasia are exempt from this requirement.
      • Open-office floor plans may have a reverberation time of up to 0.8 seconds or an area-weighted NRC as low as 0.30.
  4. Adequate acoustic conditions of gathering spaces and accommodation for hard-of-hearing: This is coordinated with Minnesota Statute §16C.054. For all spaces which accommodate and are intended for gatherings of 15 or more people and where audible communications is integral to the use of the space:
    1. Include audio-induction loops to provide an electromagnetic signal for hearing aids and cochlear implants if a permanent audio amplification system is present in the space.
    2. The space must meet the American National Standards Institute Acoustical Performance Criteria, Design Requirements and Guidelines for Schools for:
      1. Maximum background noise
      2. Reverberation times
  5. Implement sound masking if any of the following condition are met:[1]
    1. Internal-source noise control: Projects which are not compliant with I.6A, I.6B, or I.6C where other sound-privacy measures have not been met. It is not necessary or advisable to implement sound masking in all spaces not compliant with listed guidelines, though should be implemented in non-compliant open-plan office areas, libraries, and other areas where the need for speech privacy and masking exceeds the need for speech intelligibility.
    2. Spaces which have been identified as requiring additional sound privacy, or where the productivity benefits of sound masking are desired in areas that are anticipated to be over-quiet.

Sound masking system should not exceed 45dBA and should be broad spectrum.

Recommended Performance Criteria

  1. Confirm performance under I.6A for educational facilities by performing noise measurement as outlined under ANSI/ASA S.12.60-2010 Annex A.
  2. Articulation Index (AI) must be less than 0.30 for open offices, where speech privacy is desired, and greater than 0.70 for enclosed offices or other spaces where a high level of speech intelligibility is desired. Compliance with this requirement involves:
    1. Identification of at least two areas of indented speech privacy and areas of desired communicability.
    2. Documentation that the design meets the AI for these identified spaces.

Indoor acoustic environments have been identified as an area many surveyed occupants find dissatisfactory. Improving the indoor acoustic condition is generally done by the consideration of controlling noise (i.e., unwanted sound) and by supporting the transfer or reverberation of desired sound. As the appropriate level of these criteria varies with different outdoor conditions, occupancy types, noise source and space types, there are an array of strategies necessary to help ensure a productive, supportive, and comfortable indoor environment.

Early in the design process identify which of the guidelines will be required for each room and wall/room assembly. Develop a list of occupancy types if more than one occupancy type is present in the project. In particular, note that education spaces (occupancy type E) and other classroom and learning environments must meet the listed ANSI Standard, which includes requirements for core learning spaces (under 20,000 cu. ft.) and ancillary learning spaces. List specific room criteria for each of the space types (i.e., classrooms, conference rooms, etc.) and verify that the anticipated schedule of finishes, wall, and floor/ceiling types will be anticipated to meet these criteria. Adjust design as necessary to meet criteria, including reverberation time, AI (if pursuing I.6G), and sound insulation requirements of interior and exterior wall and floor/ceiling assemblies. List anticipated wall types expected to be used in the project and ensure that they meet the sound insulating requirements laid out in I.6A through I.6C.

Evaluation of the noise present on the site may be done by use of an integrating-averaging sound level meter, which can record and evaluate the sound on the site. This measurement can be used both for the evaluation of Leq levels and DNL levels to determine if OITC ratings must be addressed. Currently the only available airport DNL mapping is the Minneapolis-Saint Paul International Airport (MSP), which is listed below under Additional Resources.

Calculation of airborne noise from HVAC systems may be done per the AHRI 885 methodology using the spreadsheet-based calculator listed below (under Additional Resources) for air terminal units or by using the ASHRAE Handbook – Fundamentals methodology listed for other system types. Here the source noise and effect of duct size, characteristics and distribution is used to calculate the NC in the resulting space. This additionally permits designs that test with NC over the allowable limit to quickly evaluate potential remedies that would bring the receiving space into compliance. Use of this calculation method may influence duct sizing and layout and as such is best done as early as feasible in the design and mechanical layout process to avoid redesign. Projects may evaluate compliance with I.6C.1 based on representative spaces rather than calculating each room in the project.

Limiting undesirable long reverberation times in larger, more “live” spaces may necessitate additional consideration of interior finishes and furnishings. Projects may evaluate the design of representative spaces for reverberation times if their interior finish materials are predominately the same and square footages and ceiling heights are within 20%. Areas with different floor or ceiling finish types may not be considered to be acoustically representative. Smaller spaces may be able to meet the reverberation time requirements with a lower average NRC through a calculation of reverberation time than they can through the prescriptive approach through I.6C Part 3ii. A simple reverberation time calculator is listed below under Additional Resources.

Include performance criteria necessary to meet guideline requirements in the construction drawings and specifications of the project. Ensure that details have been developed that avoid sound transmission. Note that uncontrolled sound transfer can easily occur at the joint of wall/ceiling assemblies if not properly detailed, and at the connection of interior to exterior wall assemblies.

Predesign:

  • 6B: Identification of whether the project is a high-risk outdoor noise environment.

Design:

  • 6A: Identification of spaces required to meet guideline, if any. Provide list of spaces identified as core learning spaces and ancillary learning spaces with background noise level, reverberation time, and other room and assembly acoustic criteria as defined in ANSI Standard. List the A-weighted outdoor noise level as measured under Part 5.4.1.1 of the guideline and the resulting OITC requirement.
  • 6B: Identification of whether the project is high-risk outdoor noise environment, included documentation of selected method of compliance, including enclosure OITC rating.
  • 6C: List preliminary wall types and wall/ceiling assemblies in project compliant with STC rating requirements. List rooms in project and preliminary assessment of reverberation times and NC. List spaces identified as exempt from reverberation time requirements. If multiple spaces have generally equivalent size, wall assemblies, and finishes, then representative calculations can serve in lieu of calculation of every space in the project.
  • 6D: List gathering spaces of project which trigger guideline requirements and preliminary planning for required system and noise control.

Final Design:

  • 6A: Identification of spaces required to meet guideline, if any. Provide list of spaces identified as core learning spaces with background noise level, reverberation time and other room and assembly acoustic criteria as defined in ANSI Standard. List the A-weighted outdoor noise level as measured under Part 5.4.1.1 of the guideline and the resulting OITC requirement.
  • 6B: Identification of whether the project is a high-risk outdoor noise environment, included documentation of selected method of compliance, including enclosure OITC rating.
  • 6C: List wall types and floor/ceiling assemblies in project compliant with STC rating requirements. List rooms in project and assessment of reverberation times and NC. List spaces identified as exempt from reverberation time requirements. If multiple spaces have generally equivalent size, wall assemblies, and finishes, then representative calculations can serve in lieu of calculation of every space in the project.
  • 6D: List gathering spaces of project which trigger guideline requirements. Describe design of induction loop system and evaluation of reverberation time and outdoor noise control for required spaces.
  • 6G: List open and enclosed office spaces and anticipated AI.

Closeout:

  • 6A: Verification of installed condition meets requirements for core and ancillary learning spaces.
  • 6B: Verification of final enclosure OITC rating(s).
  • 6C: Verification that installed wall types and wall/ceiling assemblies in project compliant with STC rating requirements. Verification or updating of calculated reverberation times based on installed condition.
  • 6D: Verification of installation of required systems.
  • 6F: Documentation of verification of conformance with ANSI/ASA S.12.60 per Annex A.
  • 6G: List open and enclosed office spaces and measured AI (if documenting compliance through measurement).

I.6 – ‘Effective Acoustics’ Training Session Video (YouTube)

I.6 – ‘Effective Acoustics’ Training Session Slides (PDF)

AHRI 885 Calculator (calculates the discharge, radiated, and room sounds for various duct sizes and arrangements using AHRI 885 methodology): https://www.krueger-hvac.com/public/software/885%20calculator.

AHRI Standard 885: https://www.ahrinet.org/search-standards/ahri-885-2008-procedure-estimating-occupied-space-sound-levels-application-air-terminals-and-air

IRCAM (French research project with useful publications and free software): www.ircam.fr.

SARA (Spatial Audio & Room Acoustics Project from the Academy of Finland): www.acoustics.hut.fi/~vpv/projects/sara.htm.

The Engineering Toolbox Architectural Acoustic Calculator: http://www.engineeringtoolbox.com/room-absorption-sound-d_69.html.

Minneapolis-Saint Paul 2017 International Airport (MSP) 2017 Annual Noise Contour Report: https://www.macnoise.com/pdf/final-msp-2017-annual-noise-contour-report-web.pdf.

ODEON Room Acoustics Modeling Software: www.odeon.dk.

Regularly Occupied Space:

Any space that is occupied by one or more persons for more than one hour during days the building is in use. Note that this includes spaces which may be irregularly occupied but, when occupied, a typical occupant would spend more than one continual hour in the space. Excluded from calculation of continuously occupied spaces are:

  • Spaces with uses that only require minimal lighting and in which the primary activity intended for the space would be harmed by daylight (this exclusion does not apply to spaces with ultraviolet light concerns) – note that this only applies to the calculation of regularly occupied spaces with respect to the daylighting requirements.
  • Spaces that do not meet the minimum occupancy outlined above during daylight hours) – note that this only applies to the calculation of regularly occupied spaces for the daylighting criteria with respect to the daylighting requirements.

Spaces where no individual occupant spends at least one continual hour during days the building is in use.

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