– by Julie Fischer INCE, LEED AP BD+C
Although acoustics is one of the top complaints in occupied buildings, it is typically a secondary consideration due to its non-visual nature. In some cases, acoustical design provides an overall auditory improvement to a space. In other cases, acoustics can have a much greater impact on the overall functionality of the space. With today’s project budgets having to stretch further, convincing a design team or hospital to spend valuable construction money on improving an acoustical condition can be a tough sell. In complex situations, utilizing an innovative approach to showcase the acoustical implications on a project often makes the best argument.
One example of this outside-the-box approach took place on a recent project consisting of a new medical building, which included a rooftop helipad. The building will be part of a larger medical campus that already has some helicopter activity. However, the building under design would create a significant increase in the number of flights per day. Adding further complications, patient rooms would be located directly underneath the helipad, with windows having a direct line of sight to the flight approach and takeoff.
After analyzing the current window and façade construction, it was obvious that the overall exterior assembly should be upgraded to achieve the recommended acoustical performance in the patient rooms. However, this upgrade, which would consist of more substantial windows, would represent a significant price increase. Our findings were presented in a typical acoustical report showing graphs of the anticipated sound levels vs. average patient room background noise levels, as well as discussing the overall noise levels vs. the criteria put forth in the Facility Guidelines Institute ‘Guidelines for the Design and Construction of Hospitals.’ It quickly became clear that the hospital was going to need to have a deeper understanding of the issue if they were going to make an educated decision.
When acoustical data is presented for these kinds of decisions, it is often presented in terms of dB(A) or Noise Criterion (NC) curves. It can be difficult for a person to understand exactly what that means in terms of the impact of sound on the surrounding environment. Everyone has seen the typical noise chart where various decibel levels are equated to common household activities — 80 dB is equivalent to a vacuum cleaner; 60 dB is equivalent to a typical conversation — but, in our case, that chart does not accurately tell the whole story. How will a patient, whose recovery is directly tied to rest and quality of sleep, react to a sudden increase in noise created by a helicopter passing directly outside their window?
We asked ourselves, how do we best help the hospital to understand the rationale behind upgrading six stories’ worth of windows on a tower building by using written words in a report? The answer is we don’t. Instead, we created a simulated environment, called an auralization, which allowed the hospital to experience the noise levels themselves. This live auditory experience enabled them to make an informed decision as to what is right for their patients and project.
The process to accomplish was straightforward. First, we needed an accurate recording of a helicopter taking off and landing. In our case, this recording was made in the field at an adjacent building on the same medical campus. Measuring at the same facility gave us confidence that the frequency spectrum of the helicopter sound would be equivalent to what would be present at the new building. Factors such as type of helicopter, speed of rotor, and distance from the patient room can all affect the overall character of the sound.
Next, we needed to understand how much sound mitigation the glazing at the patient rooms would provide for helicopter noise levels. Using a computer program, we were able to calculate the sound transmission loss at various frequencies provided by the glazing assemblies under consideration. Using this transmission loss, we calculated the overall noise reduction and the reduction in each frequency band provided by each glazing assembly. This is important as the human ear reacts differently to various frequencies of sound. Lower frequency sounds are typically not heard as well as higher frequency sounds. If the noise in a space is comprised of mostly lower frequency sound, it will be perceived as less annoying than noise that is the same overall level but is comprised mostly of higher frequency sound.
Once we had our octave band frequency sound levels, we were ready to perform our auralization. To accomplish this, we located a room that was similar in size and treatment to a typical patient room. Two speakers were positioned in adjacent corners of the room to get a diffuse sound field throughout the space. A sound level meter was then used to calibrate the signal emanating from the speakers, aligning it to the calculated values in each frequency band. This calibration included matching both the overall loudness and the frequency spectrum of the calculated values.
Finally, the main stakeholders were brought into the room and allowed to listen to a side-by-side comparison of the differences between the various glazing options. This approach was invaluable to the hospital and the design team as it allowed them to experience what a patient might encounter during a helicopter fly by. In the end, the decision to upgrade the exterior glazing construction and improve the acoustical condition of the patient rooms was easy and well worth the cost.
With all building elements demanding a piece of the budget, it is more important than ever to help end users make an educated choice when it comes to acoustics. With acoustics being among the highest complaints in occupied buildings, being open to deviating from the standard design process to educate, inform, and demonstrate is a vital part of the design process.
Julie Fischer INCE, LEED AP BD+C is a Principal Consultant in the Washington DC office of NV5 Engineering & Technology (formerly Sextant Group). Julie directs our acoustics practice and is a leader and mentor for our team of acoustical consultants across North America.
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