Firing Subs down

Yes, I asked JL Audio about placing my subs firing down toward the floor (since I have JL Audio subs, hehe). They gave me the "rule of thumb" about 60% of cone area, etc. I am assuming that this rule of thumb would apply to all speaker brands, not just JL Audio subs. However, he did say that he knew of a person doing the same setup as mine that only had 1.5" of clearance between box and floor without any adverse effects, but I would still use the rule just to be safe, unless you have time and money to experiment with different setups.VEHICLE: 2002 GMC Sonoma ZR2

Alpine CDA-7940

AudioControl EQT x2

JL Audio 1000/1

JL Audio 10W6 (originals) x3

Kicker ZR120

Kicker ZR460

Polk GXR-6 x4

Polk GXR-4 x2

Like all "rules of thumb" they are a good starting point.  I've built down-firing loudspeaker systems with as little as 1" between the cone plane and the "floor," and some with as much as 5X the woofer diameter.  It all depends on the woofer and the application.  Getting it to sound OK is easy.  Getting any system to sound its BEST is very hard and requires lots of time, patience, experimentation with different setups and yes, money.  It all depends on what you want.Support the12volt.com

Well, what I want is to get it to sound its best but i dont have a lot of time and money. Thats why im trying to boil it all down right now before I build this box. If not perfect I want real good. As flawless as I can without investing the time and money it takes to expirement. From what I heard from the JL tech guy is that I want at minimum 80% of the cone surface area. This is information he said has come from the engineers. In any case I am taking as many steps as I can to get the information I need previous to building a mediocre box.