you MAY get 3db when you add another cone
BUT, adding the cone area IS NOT WHY you get 3db!!!!!!!

Mark Zarella wrote:

Actually, doubling the cone area (adding a second sub) should raise
the output by 3dB,

http://www.installer.com/tech/conearea.html


Where in your tutorial do you refute what was said about adding cone area by
adding a second sub?