Heavy rail, light rail, and freeway noise isolation
To determine the noise impact to the site from heavy rail and freeway traffic, one-third octave band maximum sound pressure level measurements were undertaken at the site. As the LRT is not yet present at the site, sound pressure level measurements were undertaken of some existing light-rail pass-bys at a location beside an existing line in south Calgary.
The engine pass-by sound levels of the diesel locomotive on the CP Rail line had significant low-frequency energy levels similar to the aircraft. The noise from freeway traffic heard at the site was generally lower than the aircraft and heavy rail noise; the loudest freeway noise events were from trucks and motorcycles. Therefore, the noise isolation required for the aircraft would provide sufficient noise isolation for the heavy rail and freeway noise. The LRT pass-by measurements also indicated high maximum noise levels because of the close proximity of the proposed right-of-way to the science centre.
The science centre’s most critical room with regard to the future LRT line is the Presentation Theatre, located on the east side, directly adjacent to the proposed LRT right-of-way. The design target in this theatre was a maximum NC of 30. Calculations indicated three layers of 16-mm gypsum board on metal studs with acoustic insulation in the stud space would provide the required noise isolation.
Based on the LRT sound level measurements, two layers of 16-mm gypsum board on metal studs were used for the upper gallery exterior walls, and one layer of gypsum board on top of a 13-mm plywood layer on metal studs for the lower portion of the gallery walls. This assembly provides the flexibility to construct classrooms along the science centre’s east exterior wall in the future and meet a maximum NC of 35.
The windows were also reviewed, and the windows and skylights in the classrooms required an upgrade to meet ABC and the target background NC levels. As the design progressed, the skylights were removed from the classrooms. With their elimination, and substituting a layer of laminated glass for one of the panes in the sealed double-pane window assemblies located in the classroom, the exterior walls met the ABC requirements. Further upgrades to the windows, such as laminating both panes and providing a larger air space were reviewed. As the most critical rooms—the Dome Theatre and the Presentation Theatre––did not have windows, it was decided further noise isolation upgrades to the windows for other less noise critical spaces would not be incorporated into the design.
The exterior building envelope noise isolation measures incorporated into the building design ensure the sounds heard within the building are those of the various displays and programs rather than the noise from the surrounding planes, trains, and automobiles.
Cliff Faszer, P.Eng., is the president and founder of Calgary-based FFA Consultants in Acoustics and Noise Control Ltd. He has been an acoustical consultant for 35 years. Faszer is a member of the Association of Professional Engineers, Geologists, and Geophysicists of Alberta (APEGGA), the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC), the Canadian Acoustical Association (CAA), and the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE). He can be contacted via e-mail at firstname.lastname@example.org.