Did a quick search, opened all the links and found this one. Brilliant page, I think we should get this page some-how stickied in this and the DIY page where people can add internet links to pages that can assist people in the design of subjects of interest.
http://www.mh-audio.nl/spk_calc.asp
For the acoustics page please sticky - It allows the calculation of various traps:
http://www.mh-audio.nl/ACalculators.asp
An amazing page, how this guy did this I do not know, but it must have taken him a few days to write this page - Calculate Reverberation time in your listening space:
http://www.mh-audio.nl/ReverberationTime.asp
http://www.mh-audio.nl/spk_calc.asp
For the acoustics page please sticky - It allows the calculation of various traps:
http://www.mh-audio.nl/ACalculators.asp
An amazing page, how this guy did this I do not know, but it must have taken him a few days to write this page - Calculate Reverberation time in your listening space:
http://www.mh-audio.nl/ReverberationTime.asp