We are currently calculating our sound absorption coefficients for LEED for Schools 2007 EQ Prerequsite 3 and have formulated a couple questions.
1: Should we include built-in casework in our calculations? This would include a) subtracting their volume from the total volume of the room, b) including their surface area in the surface area calcuations, and c) determining the sound absorption coefficient for them.
2: Does anyone know of a reference with an expanded list of products and their sound absorption coefficients at 500, 1000, and 2000 Hz.? In addition to those listed in the LEED for Schools reference guide, we need coefficients for whiteboards, smart boards, etc.
Any help you can provide will be greatly appreciated! Thank you for your time in advance.
Daniel Hicks
Daniel Hicks, E.I., INCEGeiler & Associates
267 thumbs up
August 4, 2010 - 5:53 pm
Hi Breana:
If there is a significant amount of casework, I would include it in the calculations. There is a point, however, where adding or subtracting items in the room will be negligible in determining the reverberation time. You might try modeling the room both ways to see if it is really necessary.
Some items like the whiteboards and smartboards simply do not have absorption coefficients because it costs money to get testing and the items aren't considered "acoustical". Similar to the casework, these items are probably negligible in terms of calculating the reverberation time and could be omitted from the calculations. I would just model the walls bare. If there are acoustic tests for items like whiteboards, I am not aware of them.
Hope this helps,
Daniel
Breana Detzler
Project DesignerRisinger + Associates
68 thumbs up
August 5, 2010 - 10:18 am
Daniel,
Thank you for your response. We are following your advice and calculating the walls without whiteboards and smart boards. We are going to include the casework, since we have almost a full wall of built-in units in our classrooms.
Do you, or anyone else, know if there is a resource anywhere that we can find a sound absorption coefficient for plastic laminate? A casework manufacturer? A countertop manufacturere? Another architectural acoustic reference? For our draft calculations we plan to use the plywood paneling number provided in the LEED reference guide as it appears to be the closest material. If we can get a more accurate number though, it would be very helpful.
Thanks again for your response!
Breana
Joseph F. Bridger
Stewart Acoustical Consultants7 thumbs up
August 5, 2010 - 10:50 am
I would add, that if you are willing to use an NRC 70 ceiling panel, and avoid use of soffits etc., no calculations are necessary.
If you are trying to avoid NRC 70 panels or have to do calcs due to design, consider the shortcut method described in the classroom standard (ANSI S12.60) which simply allows for all residual sound absorption (chairs, floor, hard surfaces on walls) to be 0.15 times the floor area. This makes the calculation very simple and applicable to all rooms without significant calculation efforts. Page 18 in the 2002 version of the standard describes it.
In English Units, T60 = 0.049 x V/A, where A = a(ref)S(ref) + a(act)S(act) + a(residual)S(residual). Ref = reflective part of ceilings (lights/diffusers/gypsum). ACT = Acoustical Ceiling Tile. Residual = rest of room (assumes no acoustical treatments, just chairs etc.). a = alpha (absorption coefficient) for the specific frequency (500, 1K or 2K). S = Surface area of finish. aS(residual) = .15S(floor area) per p. 18 (if not carpeted). If V = hS(floor), this T60 simplifies to:
T60 = .049 H/{.15S(floor)+a(ACT)S(ACT)+a(Ref)S(Ref)} OR .049 H/{.15S(floor)+a(ACT){S(floor)-S(ref)}+a(ref)S(ref)}
where a(ref) is generally taken to be 0.05, so that all you need to know is the floor area, area of lights/diffusers/gypsum, absorption coefficient for ACT, and ceiling height. Watch out for the 10,000 and 20,000 c.f. thresholds. There are more tips and tricks... but hopefully this gets you started.
Joseph F. Bridger
Stewart Acoustical Consultants7 thumbs up
August 5, 2010 - 11:05 am
For more tables of data, you need a good architectural acoustics book. We have a list here: http://www.sacnc.com/books.html
Breana Detzler
Project DesignerRisinger + Associates
68 thumbs up
August 5, 2010 - 12:02 pm
Joseph,
Thank you for your input. We do have an NRC 70 tile in our ACP ceilings. However, many of the classrooms also have gypsum board soffits. Do you know if we need to calculate the reverberation time for our classrooms without soffits if we are using the calculation method for those that do have them? Or can we combine the two approaches and only calculate those spaces with a combination of ceilings types?
Thanks for your help,
Breana
Joseph F. Bridger
Stewart Acoustical Consultants7 thumbs up
August 5, 2010 - 4:10 pm
you can combine... the main thing is when submitting I used narrative format to explain things.. but under GBCI they may be changing things... for me the templates (as an acoustical consultant) were busywork... the narrative with some form of documentation was much easier.
I do know they permit either method (NRC 70-full ceiling or calculations) and it is not an exclusive choice.
BTW- You can still avoid calculations if you simply add wall panels NRC 70 or better of the same square footage as the soffits.
I would do a sample calculation in one of the soffit rooms to see how much (if any) additional wall panel area is needed to meet the calculation requirement versus just providing equal NRC 70 wall panel square footage to soffits. Then choose the most effective route given the calculation effort required and results. Good luck!