PPD Practice Exam 1 Q91

The questions is number of acoustic panels are needed to have total absorption of 65 sabins. The question include the selection of the panel but not including the finish of the panel. How do we know we know which NRC value in this case using 1.05 value is correct one to select? The light spray paint finish has the best sound absorption but in the scenario or other information does not mentioned the selection. Only location it has mentioned is in other question of this case study. Do we assume or use the information from other questions?

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@smoriny that’s a great question. @coachlizschneider do you mind helping with this one?

@smoriny Thank you for the question.
Generally, it’s not a bad strategy to use info from other questions to help you answer items on the exam. You will want to be careful that the info is applicable to the question you are answering though and that the scenario hasn’t shifted between questions. For this question without looking at the other questions in the case study, choosing the highest NRC value for the panels will give you the lowest number of required panels while still meeting the requirement. So since the question does not specify a finish, you know at a minimum 11 panels are required. If another finish is selected by the architect or client that number will increase.

Dear @smoriny. ARE provides a Reference for Sound that NRC = average of sound absorption coefficient (SAC) for frequencies 250, 500, 1000, 2000 Hz. The spec provided provides NRC for those frequencies, when calculating the average (adding all the values for 250, 500, 1000, 2000 Hz), it does not equal to the 1.05 that is the “correct” SAC to solve the problem. Q: should one find the average by adding the Hz together or select the highest NRC value as you recommend? Follow up Q: then when one uses the average of Hz for SAC? Thx!

@themariangirls Thank you for the follow up question. Because the spec provides you with the NRC, which as you note is the average of the SAC at 250Hz, 500Hz, 1000Hz, and 2000Hz, you don’t need to calculate the average. By providing you with an NRC value they spec has already completed this calculation for you.
Because the question doesn’t ask for you to provide the number of panels at a specific frequency, you should use the NRC or average value in your calculation.
And because you want the required number of panels, selecting the finish with the highest NRC will give you the minimum required number of panels.

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