AFMG Network Forum

arvinsr · Member

hey, I need to make some approxiamtions for some materials. Could anyone give me the best possible material that i could approximate for the plexiglass light diffuser used under commercial fluorescent lighting fixtures. Also could somebody tell me the difference between a student on a wooden chair and public on upholstered chairs.
thanks
arvin

Jim Mobley · Member

Hi Arvin,

If I had to guess, the closest material to the plastic lenses would be one of the sheet goods like 1/8 inch hardboard, though I suspect hardboard's absorption peak is lower in frequency than the plastic.

Generally, though, you can ignore the light fixtures in your model, they seldom compose enough of the overall surface area to worry about.

As for the difference in the Students in Wooden Chairs material and the Public in Thickly or Thinly Upholstered Chairs, the two data sources are different, one from the NIOSH Handbook and one from David Eagan's book, Architectural Acoustics. Looking at the data, I would surmise that the students had greater spacing between them as the LF absorption is less.

The materials database was updated to include better attribution, the materials in the directory C:\EASE40Data\Global Materials40\American Base\Manufacturers\Generic include source data in the "details" field.

Ron Sauro · Member

Hi Arvin.... Sorry about the late answer... The database update was a project of mine over the last few years and many of the old materials were left out because there was not a traceable test for it ....There were a few frequently used materials left in because they are use too often and there is not a test directly attributable for them.

Your first question about the plastic panels for lights is frequently asked because of large fresnel plastic screens used on rear projection systems.
I recommend the simple Generic single strength window glass. The LF component is closer to what we have seen in a typical room with large expanses of this material.... If the material makes up more than 10% of the ceiling plane then coating these areas might make sense.

The student in a wooden chair has much different densities than upolstered seats ... The assumption in these measurements is that the seating is distributed right next to each other. There are materials for single seats in the database..

As a Laboratory doing material measurements we are working with ASA to arrange measurements of "standard Items"

Ron Sauro
NWAA Labs