I have an exsisting 12" powered sub with a 16"x16"x16" box and a 200w rms plate amp. The sub is boomy and has no low end extension. I need help finding a driver that would be appropriate in the box and would work with the 200w plate amp. The box has a 4" port (length unknown) and is front firing. I've been learning to use WinISD and playing around with different drivers and the 12" Atlas appears to work well in small enclosures (website recommends a sealed box). I could remove the port and seal the box up and have probably a 55-60L sealed box. Any suggestions on drivers besides the 12" Atlas? Just looking for a low cost alternative for better bass without building a diy sub from scratch (plan on one though in the future).