Friday, December 18, 2015

Acoustics Resources–Sabin RT60 Calculator

When I taught “Acoustics” and, later, Room Acoustics at McNally Smith College of Music, many of my assignments directed my students to fool around with some spreadsheets I’d created to experiment with the effects of building materials and acoustics tactics. One of the most popular was an Excel file called “Sabin RT60 Calc.” I started work on this spreadsheet on the Office version that came about the time Office appeared on Windows for Workgroups v3.01, back in the late 80’s. It took a serious upgrade with Office XP and a bunch of additions in Office 2003, where its development stopped when Microsquash removed Visual Basic macros from Office. To use the whole "tool," you'll need to enable the macros when you open the file. is a bit of a pain to use as a cloud resource, but at the top right of the screen you'll find a "Download" button. You can ignore the bit about creating a Dropbox account, if you like, and just download the file to your computer.
The first tab in the spreadsheet is the “Sabin Calculator.” However, the coolest thing (IMO) about this spreadsheet is the “Materials List” tab, which contains data for 280 different acoustic materials from really slick RPG specialty absorbers to empty theater seats and wall board. The idea is that you can cut-and-paste the “Material” through the “8k” data into the “Sabin Calculator” room surface fields and build a pretty detailed estimate of your proposed room’s reverberant characteristics. I’ve used it in all sorts of room designs and, outside of room mode problems, it is very accurate.
If your room is relatively dead (<1.0S) or small (<3,000 cubic feet), the next tab, “”Norris-Ering Calculator,” uses the “Sabin Calculator” data to more accurately estimate the reverberation. The flaw in the Norris-Ering formula is that it can not cope with absorbtivities >1.0, which isn’t often a problem but can rear its ugly head with some exceptional specific frequency absorbers.
The “Measured RT60” tab is a place where you can put three sets of measured RT60 test data in a spreadsheet for averaging.
Finally, the “Helmholtz Absorbers” tab contains a spreadsheet with calculators for two different sorts of Helmholtz absorber designs, perforated panels and tube traps.
Best of all, it’s free and easily modified. If you add anything cool to the spreadsheet, I’d appreciate it if you would send me an updated version and I’ll put it on the site and if you “sign” your update it will remain on the spreadsheet.

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Wirebender Audio Rants

Over the dozen years I taught audio engineering at Musictech College and McNally Smith College of Music, I accumulated a lot of material that might be useful to all sorts of budding audio techs and musicians. This site will include comments and questions about professional audio standards, practices, and equipment. I will add occasional product reviews with as many objective and irrational opinions as possible.