Mounting Comps Free-Air

[Subz 10+ year member]

Does anyone have any input on how two Kicker 10" Comps would sound mounted free-air behind the seat of a truck? My plans are to build a box just big enough to hold the sub, but not put a left or right side on it. I'd end up going with two of these if you guys think it'd sound pretty good.

The main thing I'm looking for is good rumble and loudness but they don't have to have 8" in a sealed box accuracy at all.

They'd be run at recommended RMS.

What could I expect?

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[DiamondFanatic 10+ year member]

You should put them in a fully enclosed box. Are you trying to save money on MDF or what? My friend's dad messed up when he built a box for his 10 in the same truck you have and did it free air and he wound up with no bass and it sounded like crap.

 

[Subz 10+ year member]

Nah, mounting them free air keeps me from having to supply the subs with the correct size box. The specs for the Comp 10's say their suitable for a free application, but I'm guessing it's not the way to go?

What about putting two Kicker Comp VR 8" in a .57CuFt sealed box? The subs require a minimum of .4, so what would happen if I put two in the .57 box with no separator? I'm still new to a lot of this stuff so please don't go off if that's a very stupid question, lol.

Thanks

 

[Rodge 10+ year member]

That would be way too little air space for those subs. You'd effectively cut the box volume in half for each sub. I had a 91 Toy Pickup. I fit a 10 behind the seat with little loss of leg room. Then again I'm only 5'9". I know with my truck, if I would of wanted to, I could of fit two tens, or three eights with ease. It's all about how much leg room you're willing to give up. Besides, a ten filled the cabin with plenty of bass.

 

[406er 10+ year member]

if u dont have enough space put some polyfill in there

 

[SAG3 5,000+ posts]

do the 2 8's with more space

 

[helotaxi 5,000+ posts]

Nah, mounting them free air keeps me from having to supply the subs with the correct size box. The specs for the Comp 10's say their suitable for a free application, but I'm guessing it's not the way to go?

They may be suitable for "free-air" but what you think of as "free-air" and what Kicker was thinking of when they say "free-air" are two completely different things. When kicker is saying "free-air" they are talking about an infinite baffle. The front and rear wave of the sub must be completely isolated from each other. Basically free air is a sealed box large enough that the air inside the box provides no damping on the suspension of the sub. From an efficiency standpoint, free air subs are great. The speaker is not fighting the air in the box and will reach its maximum excursion with relatively little power, but since the air in the box is not providing any damping, the mechanical power handling is greatly reduced. It becomes very easy to exceed the max excursion capability of the sub and blow them from over-excursion. Since you have to isolate the front and rear waves of the sub for them to produce output, the only way to do an IB setup in a truck is by cutting sheetmetal. You would need to cut out the rear of the cab and the front of the bed, seal the gap between them in the cutout area, and mount the subs on a baffle in the cutout. You would really want a cover of some sort over the bed to protect the subs from the elements and you would need some kind of physical protection for them to keep items in the bed from damaging them. If you're going to that kind of trouble, you are basically better off doing the cutout and putting the subs in and appropriately sized enclosure in the bed firing through the cutout.
What you are describing is only marginally better than just setting the subs behind the seat without a baffle or anything. The front and rear pressure waves of the subs are not isolated and cancellation will be almost total. The result will be no usable sub output and a high chance of blowing the subs from over-excursion. Your best bet with ther space you have is to run a single sub in the correct enclosure. It will almost assuredly outperform 2 subs with way to small and enclosure and will flat destroy what you are proposing.

 

[86yota 10+ year member]

Its better for them to have less air than needed in a BOX, than them being free-air. Do 2 8"s with polyfill in the boxes.