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View Full Version : Theory behind downfiring box?



dropkick13
12-24-2007, 10:36 PM
Could someone explain the theory behind it? Basically I would think that the sub would sound like butt from it pushing air directly into the carpet....thus muffling the sound AND redirecting the air back to the sub and causing the sub to lose clarity.

Immacomputer
12-24-2007, 11:21 PM
So then by your assessment, sealed enclosures should sound horrible as all they do is push air directly into wood and then redirecting air back to the sub causing the sub to lose clarity. I guess if you put carpeting in a sealed enclosure that the sound would become muffled.

PV Audio
12-25-2007, 12:34 AM
There are really only two reasons to downfire: aesthetics, or bass enhancement. Most often, it is done because people don't want to see or think that there's a subwoofer in the room, and having the cone face out into the room makes it very obvious what it is. However, the other reason you down fire is because you can load the output off of the floor which actually makes the output greater. This only works well on hard surfaces though, but it still works nonetheless.

daniel.lindsey
12-25-2007, 04:03 PM
i think what he means is like when u have a box under a seat in the back of a truck or something, where its close to the ground and practically hitting the carpet? not sure if thats what he means though

squeak12
12-25-2007, 04:09 PM
In trucks, the often downfire so they arent right against the seat. The subs arent actually touching the ground either, theres space there so they wont hit the ground, get kicked, etc.

luvinthebass
12-25-2007, 04:11 PM
what if you had a box with a sub that was ported and u faced the port on the ground would the bass be deeper or louder or be muffled?

maldecido33
12-25-2007, 04:16 PM
it would screw up the tuning by making the port "think" its longer than it really is

dropkick13
12-26-2007, 11:25 AM
i think what he means is like when u have a box under a seat in the back of a truck or something, where its close to the ground and practically hitting the carpet? not sure if thats what he means though

This is exactly what I meant actually. I have an ext cab silverado and I'm building a box right now to go under the seat. The downfiring box is extremely common, but the typical build only leaves 1''-2'' of clearance between the sub/s' surround and the carpet. I am no acoustical expert, but I just would have thought this would make the sub sound like butt. People with these boxes do not complain though so I'm just looking for a little bit of a scientific explanation between the theory of a downfiring box and an upfiring box. I can't decide which to build.

and how does a downfiring box increase output?

tcguy85
12-27-2007, 07:17 PM
and how does a downfiring box increase output?

well for HT it is usually a really good option. the sound hits the floor and it reflected throughout the room. not sure how well this works in a car though. i have never tried it or seen it.

Immacomputer
12-27-2007, 08:40 PM
It's more about the sub being able to load off of something that is beneficial. It will work the same in a car as it does in a house. As long as the driver has something that resists movement and applies pressure back on the cone, there will be an increase in output. Just like corner loading the sub in a room.

PV Audio
12-28-2007, 12:07 AM
Bingo.

And :laugh: at your sig image.

AVX Mike
12-28-2007, 10:25 AM
You also have to leave 1/4 to 1/3 of the cones diameter for clearance other wise you will run into cancellation issues. I have recently built a center console for a F-350 with 4-8" Focal Utopia BE subs firing down with slot ports firing forward into the dash. Amazing sound!! Between loading the subs to the front and the ports, it sounds like the subs are in the dash.

dropkick13
12-28-2007, 01:59 PM
I got an RL-p12. If all I have is 1.5" for clearance between the sub and carpet, should I just upfire instead?

AVX Mike
12-28-2007, 03:57 PM
Yes, with a 12" sub you would need 3-4" of clearance between the sub and the floor.

goodstuff
12-28-2007, 04:05 PM
A friend of mine had 3 12's in a downfiring box at one point. It made my eyeballs wiggle it hit so hard.

dropkick13
12-28-2007, 06:56 PM
well no matter what, I'm only going to have about 1.5-2" of space between the sub and floor (downfiring) or sub and seat (upfiring). I realize this is not ideal by any means, but it's a unavoidable sacrifice.

Basically, I'll just go with whichever setup will produce more output. But which will that be? I can see that normally a downfiring setup will have more output but I can't see the sound waves bouncing well off the body of my truck with the 'squishy' carpet in the way muffling the waves. Yes, the seat will be in the way of the sub in an upfiring box but it is basically hollow.

So, with 1.5-2" clearance, which setup will have more output?

nineballsafety8
12-29-2007, 09:57 PM
it has nothing to do with the distance the enclosure sits from the ground... what you have to think about is the surface area of the opening that the sub it using to transfer the energy into the cabin.
so basically what i am saying is say a box that is 1ft^3 with a ten in it... the box would be 13.5X13.5X13.5, so if you calculate the cone area your looking at roughly 75 sq in. so.... if you take the perimeter of the box (from above) you get 54", therefore your opening needs to be ATLEAST 1.388 in tall. so you would just raise the box up, say an 1.5 inches or so...
so in theory the bigger the box, the less heighth you need to raise the box off the floor...
HOWEVER... in all cases you need to account for the exursion of the driver, so if you do the math and it says your enclosure only needs to be be 3/4" off the floor you are WRONG... your sub needs a MINIMUM of an inch of space to breath when the cone is fully exurted (not sure on spelling)... so if you have a sub with an Xmax of a 1.5 inches you need atleast 1.75 inches of space for you sub to breath (xmax divided by 2= one way excursion plus the inch minimum for your sub to breath)

that is the theory of the how to downfire an sub.