IDMAX 15s - Infinite Baffle – Rear Deck vs Forward Firing

[Majik]

I have been patiently waiting to install a pair of IDMAX 15s IB since the beginning of winter. Now that the weather is showing signs of cooperating (I'm in the Chicago area), my level of motivation is ever increasing.

This will be my first IB install and I’m having a hard time deciding if I should mount them on the rear deck, firing up towards the rear windshield; or forward firing through the back seats (which are leather and don’t fold down). The vehicle is a highly modified 1997 T-Bird with a large rear windshield that might provide some pseudo-horn-loading benefits, but so many of the IB installs that I see are forward firing. Is there a reason for this? Or is it just because it's easier?

After taking some trunk measurements, I can manage to install either way. However, a forward firing design would be a lot easier and much faster to build. A rear deck install is feasible but will require a lot more work. Most of the time consuming work would come from cutting the rear deck for adequate vent area...I was thinking of maybe using a hole saw and strategically 'perforating' rear deck several times over the location of the cones or cutting out a large portion and framing/welding new reinforcement...then fabbing a new vented deck cover, replacing the trunk lid torsion bars with hood struts or similar. Relocating or deleting the 3rd brake light. It all adds up. Sealing the front and rear waves is the easy part. And I fear that cutting too much material out of the rear deck will compromise it’s structural integrity…but I have seen another T-Bird owner install 3 12s in the same car with no reported issues. I don’t mind the extra work if it’s absolutely worth it, as this is my project car...and I'd like to do it once and do it right.

So is one method preferred over the other?

I guess my main question is, would the rear windshield provide any loading benefits? I recently built a pair of horn-loaded (BFM table tuba) subs for my house that are extremely efficient and benefit tremendously from corner-loading in a room. I mean, something like a +6db gain in the lower octaves just from firing them into a corner vs firing into the listening space. I was wondering if the same effect would apply to firing the IB subs through the rear deck, effectively "loading" off of the rear windshield. If so, I still might consider it. Being that this is my first IB install, I'm concerned about having enough output. Yes, this is a SQ based install, but I like it loud and would like to take advantage of any potential "free" output. Each sub will only be receiving 500w via a JL 1000/1.

[BigAl205]

Do you normally have rear passengers? You could do like the USD Grand National and remove the padding from the seat back and build a frame/webbing setup.

[Majik]

It's rare that I have passengers in the back seat. I don't think that gutting the foam would be much if any benefit to me. A traditional sealed box sounds fine in the trunk...meaning that I don't think the seats drastically inhibit the output. I'm just curious about IB orientation and whether I could expect a horn-loading effect from the rear windshield if the subs were firing towards the glass.

[subwoofery]

Daily driver or else? Do you go shopping with it? Open the trunk lid much?

If the answer is yes, I'd install on the rear deck and do whatever it takes to make it invisible to the thieves eyes.

My opinion,
Kelvin

[Majik]

No matter how I install them, it will be stealth. False wall, false floor, factory looking carpet etc. That's just how I roll. The only thing that veers from that is my pillar mounted tweets.

I just want to know if there are any acoustic benefits to rear deck mounting.

[claydo]

I've got two 8s, in sealed enclosures, firing into my rear window, and I can state that yes, there are gains to be had. Structural integrity of the rear deck needed help, and still gives me fits with flexing, causing occasional rattle hunts. I enjoy the sound of of this setup much better than the sub in the trunk route I went with first........when I went digging, and found a flat, non creased panel (not load bearing) big enuff for two 8s, the saw came out.....lol. Removing enough material for two 15" cones would be a brave endeavor....

[Hic]

It's rare that I have passengers in the back seat. I don't think that gutting the foam would be much if any benefit to me. A traditional sealed box sounds fine in the trunk...meaning that I don't think the seats drastically inhibit the output. I'm just curious about IB orientation and whether I could expect a horn-loading effect from the rear windshield if the subs were firing towards the glass.

Nodes and anti-nodes , corner loading is area size dependent. For ease of installation go rear seat area firing forward.

Hz	Inches	Feet
10	1356	113
20	680	56.5
30	452	37.66
40	339	28.25
50	271.2	22.6
60	226	18.83