please tell me if I am doing this wrong
Starting at the bottom,
(little triangle) 130 X 225 = 29250, 29250/2= 14625
(rectangle above it) 565 X 225 = 127125
(area in driver cutout- do you include this?) 490 X 36 = 17640
Total area = 159390 mm2
If 600mm internal width- 95.634 L
Ah yes, though it looked like the narrowest point. So your horn starts at the 149 line. Everything above is the rear chamber (the volume you need to calculate).
Also now we get to the point where you should consider if the throat is too narrow for this driver.
14.9cm x 60cm = 894cm2.
I still recommend to get it at around 1200cm2 to get proper low bass response. What is the maximum inner width you can tolerate?
I don't mind making it wider (as long as I can get it thru a door) but to get that to 1200cm2 (keeping it at 14.9cm) it would have to be 805 mm wide (31inches)
So can I make the rear baffle shorter?
If I make the internal width 630, then I only need the horn path to start at 190mm instead of 149. Which can probably be achieved by chopping an inch off the rear baffle length.