heres the two setups:

old: 2 10" kappa perfects sealed 2cu^ft box @ 2 Ohm off zapco 1100.1

new: 15" JBL GTI W15 3cu^ft tuned to 25 Hz @ 3Ohm off zapco 1100.1

i was expecting a massive increase in loudness but did not get it, i may of gotten a bit but still, i will say the new setup sounded better but i wanted to go deaf or something.

things that may be causing the problem: most of the new box is made of 3/4" particle board type stuff. AND because i was in a rush i used aproximatly 14 AWG wire over about 5 feet. i had 8 AWG to my 10's Also the 15" is facing sideways into one of the trunk panels, again due to un-completeness

eventually (a long way away) i want to get a zapco 9.0X for the sub

 

Tune it 10hz higher and it will be much louder and still musical

 

Why did you think it would be louder?

 

well for one thing, you're getting less power to the sub now at 3 ohms. The box positioning can make a huge difference as well. But i bet it plays deeper now though. Try moving the box around cause that sub should stomp those two tens

 

you almost did not gain any cone area combined with lot less power produced by the amp. infact it should be less loud with a single 15.

also, you need to tune much higher, try 35-37 hz tuning on the 15.

 

^ I agree with Yuli in that a single 15 isn't much more cone than the 2 10s and with a slight power dip, it really shouldn't be any louder.

 

Oh and as worldind indicated, you're tuned too low.

 

!!!If you want a zapco 9.0... you had best have it on order no more will be made!!!!

the cone surface area for two 10" is 157 cu in and one 15" is 176.7 cu in. is what you gained

you gave up amplifier power
you gave up efficiency (electrical)

Particle board or MDF?

throw some power at the sub and it should scream and if your box is tuned to 25 Hz your port is longer than your intestines so I am guessing you dont really have 3 cubic feet either I agree with a higher port freq