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.