Bad Speaker Box Design?

Great feedback. Everyone's got some great ideas!!!!

My $.02

Either xover will work. Just use one or the other,not both.

Downfiring depends on the driver/enclosure. Also, its best that space in front of driver be 10-12% driver diameter. Also best if it fires into a firm surface. use MDF for enclosure (I would use at least 3/4" for a 12). Add internal bracing if sides are unusually wide or long (eliminates ringing). Direction of driver is really personal preference of what you want it to sound like.

Keep plugging a way at it. Most of the best systems went through many changes a little at at time.

8 ohm load on a 4 ohm amp won't "hurt" it. The amp just won't give full rated output (some higher end units will give same rated output over a range of loads).

Thanks for all the input. I am pretty sure that the crossover is setup correctly. i haven't a chance to look it at it all really since i got it in there. I will try playing around with the firing direction.  I will first try putting a scrap piece of MDF underneath it to see if that improves the wave dispersion. The box is really built quite well from the construction standpoint, but probably not so great as far as size and shape goes. It is made with High density MDF and is totally sealed with silicone. although it is an 8ohm driver it seems to get plenty loud, just doesn't have the tight response that I am looking for. As for airspace, someone told me that it is safer to have the box be a little bit smaller than recommended for the driver as opposed to be too big, a problem that can't be fixed :)

Thanks for all your great input. I will try several things and let ya know how it turns out.

THanks

Brad

Be sure to let us know what you decide and if you can solve the problem, Brad. 

Enclosure design is just as much trial and error as it is how to use formulas and how to cut and glue.  I must have parts from twenty different failed enclosure designs in my garage!  Sometimes bad sound is caused by enclosure geometry, sometimes it is poor construction, sometimes too many baffles, other times too few, and many times (indeed, more often that not) it is the wrong driver for the enclosure I want to build.  Sometimes playing with the stuffing will help.  Sometimes swapping the woofer solves all the problems. 

I once built a nice octogonal enclosure for a customer's $1200 MTX sub that looked really cool but sounded like crap, with poor response and flabby bass with no punch at all.  Since I had spent 40 hours on the enclosure I tried to fix it.  During trouble shooting (looking for air leaks) I didn't want to risk the expensive sub so I swaped in a $20 Pioneer POS sub I had laying around.  Suddenly it sounded GREAT.  Awesome, in fact.  That cheap-ass Pioneer was pumping out 100 db @ 50 hz with a 100 watt amp and sounded very tight for a 15".  I had simply built the wrong enclosure for the MTX.  I built another, more conventional shaped one and voila, the MTX rocked.  I sold the Pioneer system to someone else!

Sorry about the long story, the moral is keep trying and see if you can make your plans work.  If you are serious about staying with a down-firing design, read THIS web page from my friends at Parts Express to help you decide which driver would work best.

Cheers

phase and cancellation. if 2 speakers are 180degrees out of phase, then 100% cancellation will occur.

cant play with one without affecting the other.

nope. a speaker is just as loud from the front as it is from the back. Ever seen subs mounted with the magnet  mounted outside the box with the cone facing in? makes no difference to the sound volume which way the cone moves.

as for which speakers put out sub bass? none, but your other speakers do put out bass (50Hz - 100Hz) which is what is cancelling.