# Robert Harleys RT60 equation does not work

After reading "The complete guide to Home Theater" by Robert Harley I have noticed quite a few discrepencies. After carefully plotting in all square footages and using his equation on page 113 I got RT60 times of 0.001476 to 0.001292. I have a 6460 cubic foot room (34x19x10). All surfaces were drywall except for the floor which was carpet. How is this possible in a room of this size??
bnauka595f
2 responses
 03-19-2003 1:39pmHi Bnauka:I don't have his book and have not read it. If you are like me you made a mistake the first time around.(hehe) It is difficult to believe that the book has an error because it has been through several editions hasn't it?The numbers you got are too low. Your room can't be that dead? Everest (Master Handbook of Acoustics)presents a graph of average living rooms and it was .69s at 125hz and .4s at 8khz. You didn't mix up feet and meters or use a wrong absorption coefficient? What equation does he present in the book?There is not to much to mess up in the basic formula. RT60 = k*(V/Sa). k is a constant that equals 0.161 when the units of measurement are metric (in meters for our use) and 0.049 when units are expressed in feet. Sa is the total surface absorption of a room expressed in Sabins. V is room's volume. Is this the equation Harley uses?Double check it with an online calculator.http://www.csgnetwork.com/acousticreverbdelaycalc.htmlorhttp://www.trinitysoundcompany.com/rt60.htmlThe Linkwitz site is good on this too.http://www.linkwitzlab.com/rooms.htmI remain, 03-20-2003 7:26amYeah, you screwed up the equation somehow. You might have messed up the Sabines/Absorbtion Co-efficient thing likely. The "Sa" part of the equation is better described in F.Alton Everest Master Handbook of Acousics. It works perfect for me every time basically.