Spray booth plenium design

hey all!
im in the final stages of designing my spraybooth, and have a question regarding the plenium (sp?)...
ok, i know that its purpose is to even out the air flow across the booth
what i wanna know is whats the best way to design one...
a recess in the booth, (basically just making the booth a bit deeper) and mounting the fan in the middle? (like the one on here http://modelpaint.tripod.com/images/image3a.gif )
or a pyramid style plenium with the fan mounted ontop of the pyramid (sorry i cant seem to find a pic)
also, if i were to go the pyramid route, would it matter if the fan was mounted to the bottom of the booth,? ive included a sketch to help describe wot im getting at, hope u guys can make it out coz its not da best drawing
http://i4.photobucket.com/albums/y143/tw080/Image1.jpg

and as usual, thank you very much for the help!!!

I don't think it will make a huge difference, especially since you'll have a filter element between the booth area and the plenum. You could even make it a box and not deal with all the fabrication.

Just be sure to use a powerful enough blower, or even an over-powered one and vent the plenum for proper airflow.

One thing I’d throw out there is that the position of the fan and the shape of the plenum will affect the airflow. It may not sound like much but depending on the size of your box it could make a difference. Be sure to check out the tutorial at Brian’s Models on booth design.http://www.briansmodelcars.com/tutorials/tutorial.asp?TutorialID=23&CurPage=1

If you have room, run the fan under the floor of the booth. If you must put the fan in the back, arrange the plenum so that the air is sucked from the front of the floor. This way the overspray coming out of the booth is what's sucked by the fan. Any extra air drawn by the fan will go under the booth before it reaches your model. On the lower right drawing of yours, run a "floor" right above the fan and place your subject there.

Old setup, bad idea. I could see the dust specks fly into the model, I might as well have painted without the booth.
http://images2.fotki.com/v21/photos/4/43509/245233/P5050040-vi.jpg

Semi-current setup. Note how the opening is at the bottom front of the booth. Dust goes in there, not on my models. The "box" is made up of foam board from Target. The floor is a wall-mounted shelf unit and is sturdy enough to hold the fan/plenum that is screwed into it from below. The Pampers container is my CSC tub.
http://images9.fotki.com/v184/photos/4/43509/381975/P1010008-vi.jpg

Updraft booths can sprinkle bad stuff like dust, dried paint, etc. over your paint job. Crossflow booths with fans and openings in the rear draw air and dust right across your model. Work with gravity, not fight against it. You'll lose.

thanks ppl
steve: im not filtering it at all, just venting it straigh outta window. i figured this would b cheaper in the long run and easier to build. howerver, i am contemplating using a cloth(old shirt) to catch the larger(first?) particles, but i will see how i go...
runflat: thats the faq i used to build mine, and it is very helpful and concise. i just though that a sloped plenium would provide an evener air flow, but from what ive heard, it dosnt really matter. the main downfall in most booths is the ducting AFTER the fan, and if the fan is capable of pushing that air thru the ducting. that faq has a section on it.
on a side note, i have spoken to klaus(if u read this, a BIG THANKYOU!) (author of the faq) and he has told me that he has since upgraded his fan, coz he wasn happy with the 75FPM, so if ur gonna build one, aim for the proper FPM....

hey 008, we must have posted the same time coz i didnt see ur reply...
cool booth, so its kinda like a trough (sp? like the thing horses drink outta) on the front of the booth right?
i originally wanted to go with the downdraft booth, coz like u said, gravity will always win, but i couldnt coz of space restrictions....
anyways, i have mounted the fan on the bottom of the booth, so hopefully thatll minimize dust, im also gonna keep it covered while not in use...ill see how i go, but i think my will be ok for the mean time...
008, if u can be bothered could u take some more pics of ya setup, coz i really like the look of it, and the logic behind it....
cheers!!