I'm trying to find some pics of a down firing sub box. I know I've seen one or two on the boards but i could not find them with the search button. TIA

 

http://www.nloc.net/gallery/album.php?id=563

 

Why do you want it to fire down???

 

IMO The best sounding sub enclosures are downfiring. It helps diffuse cone noise and helps build the pressure wave by having a surface to fire into. My rule of thumb is to have about a fist distance to the floor. Other rules of thumb are keep the speakers close together so that they tend to act as one and try to corner load them. Both of these are hard to do in a regular cab truck. In general want you try to make the sound travel the longest path it can so that the sound wave can develop, ie. firing the subs backward to the rear in the trunk of a car.

 

actually it doesn't matter how long the soundwave travels, you just want it in phase with the front soundstage so it blends in, instead of hearing the bass coming front the back. you use speaker positioning and wiring polarity to try to get it as close as possible to being in phase.

downfiring is just another way to load a sub. it reflects the sound waves off of the floor, but you need to make sure that you have ample room under the sub or you will end up with a 4th or 6th order bandpass box. feet are the best way to go, you don't want just a small opening in the front or it will affect the frequency response and spl of the enclosure.

Downfiring the woofer has one detrimental effect and that is SAG due to gravity which causes Xmax to be reached earlier, and may add slightly to distortion. this will show how to calculate if a woofer is acceptable for downfiring: http://www.adireaudio.com/Files/Tech...rientation.pdf
and here is a calculator built with those equations: http://www.accelerator-pedal.com/sag.htm