Hi, im new to this stuff and ive seen on some car shows where they install the subs backwards/upside down (where the cone is facing inward)... I was thinking about doing this because I have little space in my trunk and currently my sub and box is on top of my only access point to my spare tire, so i was going to make a custom box and mount them backward so they will fit....
so would i be sacrificing sound/ efficiency by doing this... and would porting my box still make it hit harder?
also would the major reduction in the size of the box make a big difference?
Inverting a speaker is the term used when a subwoofer is mounted "backwards" so the magnet structure is exposed outside of the enclosure to show off the size of the magnet, or the chromed basket and so forth. Mounting a speaker this way has absolutely NO effect on the output of the system. Doing this does not make the sub any louder or quieter. Inverting a sub does however change the volume of the box, since you're moving the mass of the driver's motor structure outside of the enclosure, effectively increasing the net air space inside the enclosure. This can alter the response of the box, or change the tuned frequency of any ports.
So, to answer this commonly asked question, no inverting a speaker doesn't effect the output in any significant way. It's mainly done for looks and bling factor.
Do note that some woofers make mechanical noise, more so than others and that may be a factor in doing this type of mount. Also the important components of the sub are open to foreign objects which can result in damages to the sub.