2.7.1 Acoustics | Chicago Public Schools

Planning Rationale

The following recommendations constitute suggested acoustical design criteria and standard approach for the design of all schools to comply with CPS Facility Performance Standards (CPS FPS) and LEED™. Designing classrooms and educational facilities to achieve a LEED™ for Schools Certification requires meeting the Minimum Acoustical Prerequisite listed below. This prerequisite references the guidelines set forth in the American National Standards Institute (ANSI) standard ANSI S12.60-2002 Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools. LEED™ Enhanced Criteria, if elected, is also listed for additional LEED™ credits.

Criteria noted below is considered the minimum which shall be overridden by LEED™ requirements in the case of conflict with variations noted for each specific case. Additional information on design guidelines is included in the ANSI standard and may be referenced by CPS when coordinating the design of future educational facilities. Information pertaining to best practices for new & existing renovation construction is included. Recommendations for existing construction and planned renovations are for reference and should be evaluated on a case by case basis. Implementation of recommendations may be limited due to budget and practical application. For additional details pertaining to specific room types see individual room data sheets.

For general room types both LEED™ and ANSI 12.60-2010 define rooms into classrooms and core learning spaces. The following room definitions are applicable for the entire document:

Small classrooms have room volumes smaller than 10,000 ft3.
Large classrooms have room volumes between 10,000 ft3 - 20,000 ft3.
Any classroom sizes over 20,000 ft3 shall be reviewed on a case-by-case basis with an acoustical consultant.

Core Learning Space per ANSI S12.60-2010 – “Spaces for educational activities where the primary functions are teaching and learning and where good speech communication is critical to a student’s academic achievement” Core learning spaces are categorized by room volume the same as small and large classrooms noted above.
Noise Survey: For projects sites located near or within a half mile (0.5 mi.) of any major noise source (i.e. aircraft over flight – inside of 60 Ldn contour of flight path map, highways, train, and industry) an exterior noise survey should be conducted by an acoustical consultant. The noise survey should be conducted during school hours under typical conditions to capture the loudest hour (~ 8 hrs.).

Fig.2.7A Maximum Steady State Background Noise Level (NC)

Room Type	LEED v4 Enhanced / Minimum	ANSI Standard S12.60-2010	Recommended Range (CPS FPS)
Small Classroom* Large Classroom* Core Learning Space**	35 / 40 dBA (NC 30 / 35)	35 dBA (NC-30)	35-40 dBA (NC-30 to 35)
Core Learning Spaces and ancillary spaces larger than 20,000 ft³ Assembly Spaces Multipurpose Rooms	N/A	40 dBA (NC-35)	NC-35 to 40
Library	N/A	N/A	NC-35 to 40
Gymnasium/Gymnatorium	N/A	N/A	NC-40 to 45
Music Room	35 / 40 dBA (NC 30 / 35)	N/A	NC-30 to 35
Toilet Rooms	N/A	N/A	NC-45 to 50
Private Offices Open Offices	N/A N/A	N/A N/A	NC-35 max NC-40 max
Dining	N/A	N/A	NC-40 to 45
Mechanical Room	N/A	N/A	N/A

Fig.2.7B Maximum Intermittent Background Noise from Exterior Sound Sources

Room Type	LEED v4 Enhanced / Minimum	ANSI Standard S12.60-2010	Recommended Range (CPS FPS)
Small Classroom* Large Classroom* Core Learning Space**	LEED v4 Enhanced: Exterior windows/ doors must have a minimum STC 45 rating, unless outdoor and indoor noise levels can be verified to justify a lower rating. LEED v4 Minimum: High noise sites (peak hour Leq above 60 dBA during school hours) implement acoustic treatment and other measures to minimize noise intrusion from exterior sources to classrooms and core learning spaces. Projects at least 0.5 miles from noise source (i.e. aircraft over flight, highways, train, and industry) are exempt¹ .	Core Learning Space and Classrooms ≤ 20,000 ft³ – The loudest 1 hr. average Leq from an exterior noise source shall not exceed 35 dBA. Core Learning Space > 20,000 ^ft3 – The loudest 1 hr. average Leq from an exterior noise source shall not exceed 40 dBA. For projects requiring OITC refer to sections 5.4.1.1 – 5.4.1.4 of ANSI Standard S12.60-2010².	40-45 dBA

Room Type

LEED v4 Enhanced / Minimum

ANSI Standard S12.60-2010

Recommended Range (CPS FPS)

Small Classroom*

Large Classroom*

Core Learning Space**

LEED v4 Enhanced:
Exterior windows/ doors must have a minimum STC 45 rating, unless outdoor and indoor noise levels can be verified to justify a lower rating.

LEED v4 Minimum:
High noise sites (peak hour Leq above 60 dBA during school hours) implement acoustic treatment and other measures to minimize noise intrusion from exterior sources to classrooms and core learning spaces. Projects at least 0.5 miles from noise source (i.e. aircraft over flight, highways, train, and industry) are exempt¹ .

Core Learning Space and Classrooms ≤ 20,000 ft³ – The loudest 1 hr. average Leq from an exterior noise source shall not exceed 35 dBA.

Core Learning Space > 20,000 ^ft3 – The loudest 1 hr. average Leq from an exterior noise source shall not exceed 40 dBA.

For projects requiring OITC refer to sections 5.4.1.1 – 5.4.1.4 of ANSI Standard S12.60-2010².

40-45 dBA

For projects sites located near or within a half mile (0.5 mi.) of any major noise source (i.e. aircraft over flight – inside of 60 Ldn contour of flight path map, highways, train, and industry) an exterior noise survey should be conducted by an acoustical consultant. The noise survey should be conducted during school hours under typical conditions to capture the loudest hour (~ 8 hrs.).
Projects requiring OITC should retain an acoustical consultant to review.

Fig 2.7C Minimum STC Ratings Floor-to-Ceiling Assemblies

Room Adjacency	LEED v4 Enhanced / ANSI Standard S12.60-2010	Recommended Range (CPS FPS)
Classroom to Classroom³	STC-50	STC-45 to 50
Classroom to Toilet Room¹	STC-53	STC-55 to 60
Classroom to Corridor, Office, Library	STC-45	STC-40 to 45
Classroom to Music Room, Gymnasium, Mechanical Room	STC-60	STC-60
Music Room to any other occupied adjacent space ⁴	STC-60	STC-55 to 60²
Mechanical Equipment Rooms	STC-55 to 60	STC-55 to 60²
Minimum Exterior Wall / Window Construction	STC-45	STC-35 to 45+ TBD based on nature of exterior noise

Projects requiring OITC should retain an acoustical consultant to review.
Projects requiring OITC should retain an acoustical consultant to review.
Where restroom sink/toilet chase walls backup against an occupied space, a double stud partition (STC 60 should be used.
Depending on the proximity to the nearest adjacent occupied space (i.e. music room or mechanical room not adjacent to classrooms or core learning space) the recommended STC rating may be relaxed to STC 55, to be evaluated on a case by case basis.
Partition type includes operable partition separating classrooms or other core learning spaces.
Additional Music Room isolation shall be determined on a case by case basis.

Fig 2.7D Minimum IIC Ratings of Floor-Ceiling Assemblies

Room Type Range	ANSI Standard	Recommended
Classroom	IIC-45 to 50	IIC-45 to 50
Library	IIC-45	IIC-45
Gymnasium	IIC-50 to 70*	IIC-50 to 70*
Music Room	IIC-50	IIC-50
Toilet Room	IIC-50-70*	IIC-50-70*
Offices	IIC-45	IIC-45
Dining	IIC-50-70*	IIC-50-70*
Mechanical Room	IIC-45	IIC-45

*Upper range of criteria shall be utilized when space in question is above a classroom
IIC 70 – Minimum if renovation to existing gymnasia, dance studios, and similar rooms located above core learning space less than 20,000 ft3 . IIC 65 - for spaces greater than 20,000 ft3 .
Refer to Best Practice Guidelines for additional details.

Fig. 2.7E Maximum Reverberation Time (RT₆₀)

Room Type	LEED Minimum	ANSI Standard S12.60-2010	Recommended Range
Small Classroom* / Core Learning Space**	Reverberation Times are the same as ANSI Standard S12.60-2010 for Small and Large Classrooms / Core Learning Spaces. Conformance Criteria: Rooms < 20,000 ft3 Option 1: For each room, confirm total surface area (wall panels, ceiling finishes, and other finishes) should equal or exceed the total ceiling area with a minimum NRC 0.7. Option 2: Confirm through calculation in ANSI S12.60-2010 that rooms are designed to meet reverberation time requirements. Equation 1 below satisfies stipulation 5.3.2 from ANSI S12.60-2010 for core learning spaces less than 10,000 ft3 to be readily adaptable to reduce reverberation time to 0.3 seconds. (Eq. 1) A ≥ kV/T60. A = total absorptive surface area, k = 0.049 ft. /s, V = volume ft3, T60 = target reverberation time.	0.6 Seconds	0.6 Seconds
Large Classroom* / Core Learning Space**		0.7 Seconds	0.7 Seconds
Classroom* / Core** Learning Spaces larger than 20,000 ft³	Rooms greater than 20,000 ft3 to meet the recommended reverberation time for classrooms and core learning spaces outlined in NRCCNRC Construction Technology Update No. 51, Acoustical Design of Rooms for Speech (2002).	N/A	TBD on case by case basis
Gymnasium	N/A	N/A	< 1.5 Seconds
Music Room	See classroom / core learning space requirements above.	N/A	TBD on a case by case basis
Dining	N/A	N/A	< 1.5 Seconds

Fig. 2.7F Classroom Audio Distribution Systems

Room Type	ANSI S12.60-2010
Classrooms/ Core Learning Spaces	For adaptable/flex classrooms that include an audio system, the following criteria shall apply: The system shall have uniform coverage within ± 2.5 dB for octave-band sound pressure levels within midband frequencies of 500, 1000, 2000, and 4000 Hz.

All HVAC noise criteria should be expressed in terms of single number NC ratings.
Diffusers, Grilles & Registers shall be selected with no damper in diffuser necks or at plenum connections.
Diffuser, grilles, and registers are to be selected at least 5 NC points below the room design criteria. Plaque or perforated face diffusers shall be selected 10 NC points below the criteria.
Volume dampers within each branch to diffusers shall be minimum 3 feet from diffusers and grilles.
Pressure Reducing Box and/or Fan Units serving individual classrooms shall be located outside the projected area of sensitive space with approximately 3-10 feet of ductwork and one horizontal elbow before entering the projected area.
Perimeter ‘console’ type through the wall HVAC units shall not be utilized due to difficulties in implementing effective noise control for these types of units.
Medium pressure ductwork over classrooms shall be avoided.
Use of either internal acoustical duct lining or sound attenuator devices shall be considered for noise control of main air handling units, fans, and other HVAC equipment
Typical sound attenuator sizing recommendations:

0.25” w.g. max for medium pressure ductwork
0.10” w.g. max in low pressure ductwork
Lower pressure drops will result in lower noise reduction for a given attenuator size

Pack-less sound attenuators be avoided whenever possible. These types of silencers provide minimal noise reduction, particularly at relatively low pressure drops. Hospital grade duct silencers are acoustically preferred if contact between the fiberglass media and airstream is not permitted.
All rotating mechanical equipment shall be provided on vibration isolation devices.
Elevators or supporting mechanical rooms shall not be located adjacent to any classroom.
Ductwork from new roof-mounted mechanical equipment shall be installed and configured/routed to minimize transference of sound through the ductwork.
Where restroom hand dryers are located, they should be placed at a level to maximize distance and oriented away from students’ ears to minimize direct exposure

Enhanced design criteria of exterior wall and roof construction may be needed to meet the background noise level requirements noted above due to proximity of airport flight paths, train tracks or other noise generating sources.
Window upgrades incorporating insulated assemblies and possibly use of laminated glass may be needed to meet the background noise level requirements. Projects shall be accessed on a case-by-case basis.

See Figure 2.3.5C for Minimum STC ratings of Partitions
STC-40: Single layer of drywall on either side of metal studs erected to underside of ceiling, with acoustical batt insulation between studs.
STC 45: Single layer of drywall on either side of metal studs erected full height to the structural slab above with full depth acoustical batt insulation between studs.
STC 50: Single layer drywall on one side of metal studs with double layer on opposite side (3 layers total) erected full height to the structural slab above and below, or to a raised floor system capable of meeting a minimum STC-50 rating; with full depth acoustical batt insulation between studs.
STC 55: Double layer of drywall on either side of metal studs (no bridging of studs permitted) erected full height to the structural slab above and below with full depth acoustical batt insulation between studs.
STC-60: Two layers of drywall on separate rows of independent metal studs separated by minimum 1 inch gap erected full height to the structural slab above and below with full depth acoustical batt insulation in both stud cavities.
All partitions shall be constructed full height from floor to ceiling including acoustical sealant(s) treatment
STC rating of metal stud partitions listed above are based on 25 gauge studs spaced 24 inches on center. Lower gauge studs and closer spaced studs will reduce the STC performance.
All operable partitions should be STC 50 minimum.

Recommendation for full acoustical door seals and drop bottom on all doors between classroom and corridor and within the music suite.

Doors for spaces with STC-50 or higher rated partitions shall consider the following:

Solid core wood or hollow metal door and frame packed with insulation
Head and Jamb: Acoustical gasketing around the head and jamb
Door Bottom: Acoustical drop bottom. ½” continuous sill applied with a bulb neoprene gasket, or minimized undercut of ¼” or less.
Threshold: Low profile neoprene bubble gasketed only to be used at specific areas. (i.e. music room, dance studio to adjacent sensitive space). To be evaluated based on the adjacent space(s) programming needs.

See Figure 2.3.5D for Minimum IIC Ratings
Any room above a classroom needs to meet the minimum criteria listed above and if there is no carpeting the minimum is raised by 5 points. Carpet is typically not used except in limited locations such as administrative suite, offices, and library/media centers.
With hard surface flooring there may be a need to provide a resilient underlayment below the finished floor to meet the requirements listed above. F
High floor impact rooms of any type in new Construction shall not be located above classrooms or other core learning spaces (Gymnasium, Dance Studio, etc.).
Areas that are stacked conditions such as restrooms or corridors do not need additional mitigation.

See Figure 2.3.5E for maximum RT
Ceilings shall have no less than 50% sound absorptive acoustical treatments. For ceiling with 50% sound absorptive material, see Figure 2.3.5E above for additional acoustical treatment requirements.
Classrooms may need acoustical wall treatment based on room size and percentage of ceiling that is acoustically treated to meet the RT60 criteria noted above.
When provided, new ceiling material shall have a minimum NRC 0.7 or higher.
Where required to reduce reverberation within auditoriums, music rooms, and libraries, as well as improve speech intelligibility, surfaces within these spaces shall receive some sound absorptive materials.
Refer to individual room data sheets for more specific design criteria.
For classrooms that need enhanced acoustics for auditory impairments or special needs refer to Figure 2.3.5E – conformance option 2 - for improved reverberation time requirements (0.3 seconds). An alternative to this option is the implementation of audio assistive listening devices.

A-Weighted Decibel (dBA): The human ear does not perceive sounds at low frequencies in the same manner as those at higher frequencies (i.e., sounds at low frequency do not seem as loud as those of equal intensity at higher frequencies). Thus, the A weighting network is provided in sound analysis systems to simulate the response of the human ear. A weighted sound levels are expressed in units of decibels (dB). The engineer to evaluate hearing damage risk and community annoyance impact uses these levels in dB.
Background Noise: The recommended criteria range for the standards noted are provided due to the fact that in our experience, achieving the more stringent requirements of the ANSI standard are not necessarily required for all projects and in some cases, meeting the ANSI standard can be cost prohibitive. Other “Industry Standard” criteria for classrooms, as published by ASHRAE and other industry driven organizations, is a background sound level of about 40 dBA (NC- 35). There are no specific criteria set for the level of exterior noise intrusion but a commonly used acoustical rule of thumb is that exterior noises should not exceed the interior background sound level by greater than 5 to 8 dB so as not to become obtrusive and distracting. Therefore, the relevant criteria for any CPS elementary school project shall be decided upon on a case-by-case basis. If strict adherence to the ANSI standard is not specifically met, achieving a LEED innovation credit for acoustics may not be granted for a particular project.
Impact Insulation Class (IIC): A single number utilized to describe the level of attenuation of structure borne sound between floor and ceiling assemblies, as measured in a laboratory. The higher the number, the better the attenuation.
Sound Transmission Class (STC): A single number rating which is the transmission loss adjusted for room interior acoustical properties. The (STC) tests are performed in laboratory environments on doors, partitions, and roofs. The higher the STC value the more attenuation of sound afforded by the partition.
Laboratory vs. Field Ratings: Please be advised the Sound Transmission Class (STC) and Impact Insulation Class (IIC) ratings noted in this document are the ideal laboratory rated value, and shall be used to define the level of effort and detail required for the barrier constructions. These values shall NOT be used for installed final performance criteria. Field installation is typically 3-6 points below ideal laboratory values.
Noise Criteria (NC):

A single number, which attempts to describe the level of sound as heard by humans. It is determined by comparing the sound level within individual octave band frequencies against a series of standard Noise Criteria curves. The highest curve intersected within any octave band determines the resultant NC level.
The family of NC curves closely resemble equal loudness within the individual octave band frequencies, and therefore allows higher sound levels within the lower frequencies than the higher frequencies. Humans are much more sensitive to higher frequency sounds; such as a child’s voice, siren, etc.
Equivalent NC levels do not necessarily sound the same. An NC controlled by low frequency sound (such as centrifugal fan ‘rumble’ or ‘drone,’ or aircraft engine takeoff) actually “sounds” much different than an equivalent NC level controlled by high frequency sound (such as diffuser/air “hissing,” or railroad/subway metal track “squeal”). NC levels are normally used to describe interior sound levels caused by mechanical equipment or transmitted from outside sources. Typical design goal NC levels for continuous sound for various spaces are noted in the following sections of this document (adapted from ASHRAE Applications Handbook and/or ANSI standard referenced above)

Reverberation Time (RT60): The time in seconds that it takes sound to decay 60 dB from its original level within the 500 Hz octave band frequencies. Decay times in other frequencies are important and shall be considered as well, however, the formal RT60 is measured within the 500Hz octave band.
Outdoor-Indoor Transmission Class (OITC): A single number rating which rates the effectiveness of a building facade element at reducing transportation noise intrusion.
Core Learning Space: A space for educational activities where the primary functions are teaching and learning and where good speech communication is critical to a student’s academic achievement” Core learning spaces are categorized by room volume the same as small and large classrooms noted above.