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My wife had some 4" thick foam left over from a project she was doing, and I cut two circles out of it. It was white though, so I topped them with black second skin closed cell foam I had left over ... so when the rear deck cover is in place, you don't see anything through the speaker grills. The OCF and CCF combo blocks out the noise from my stock fuel pump. When I 1st put everything together, I just left the holes open, and the fuel pump noise was too much. The foam circles did the trick though, since the frequency of the fuel pump is so high.



Yes, the fuel tank is lurking behind that panel ... scroll up and see my post above.

The fuel tank in these cars is located in the trunk.
Dawwwwwww. Well, that rules out a giant sub in the center.
 

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2005 Pontiac GTO
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Unless...you built a slanted baffle and used the two 8" holes as vents. You could still keep 95% of your trunk, too. Just have a baffle at a slight angle to force the sound through the rear deck?
The fuel tank is in the trunk, behind that flat panel, under the rear deck. It extends from the right to the left, taking up the entire space under the rear deck, and extends toward three rear of the car, past the 3rd brake light in the rear window.

There’s really no opportunity for a slanted baffle to vent through the rear deck.

The car is actually a Holden Monaro, rebadged as a Pontiac GTO. The story is that GM was forced to relocate the fuel tank into the trunk to meet USA regulations. Apparently the tank hung too low with the Aussie design?
 

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2018 VW Passat, Helix M Four DSP, Gladen Zero Pro 165.4, Gladen Zero 10 Pro
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They aren’t flimsy. 85% infill. Gyroid pattern. 1/4” thick plastic and the flange has a fillet in it.
Certainly no expert on the sound stuff, but I know 3D printing pretty well. Those look like really solid adapter rings but I wonder if they are causing an issue by tunneling the sound waves. Kinda like yelling down a paper towel tube.
For IB don’t you want as much open space behind the subwoofer as possible?
 

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Discussion Starter · #27 ·
Certainly no expert on the sound stuff, but I know 3D printing pretty well. Those look like really solid adapter rings but I wonder if they are causing an issue by tunneling the sound waves. Kinda like yelling down a paper towel tube.
For IB don’t you want as much open space behind the subwoofer as possible?
you could be on to something. Maybe I should try opening the holes up in the back deck.
 

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you could be on to something. Maybe I should try opening the holes up in the back deck.
Have you thought about building enclosures for the 8" woofers, to fit behind the rear sail panels? I think you would get more of what you're looking for by doing that, instead of trying to make an IB setup work in the rear deck.

There's a guy in Australia who printed enclosures for 9" woofers to fit that space ... He's a great guy too, and might be willing to share his 3D printer files with you? Let me know if you want his contact info.

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If you don’t mind opening them up so they can mount flush without the adapters it would probably be worth it.
There's not enough depth to flush mount anything back there. There really is no room under that rear deck.
 
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Discussion Starter · #31 ·
Have you thought about building enclosures for the 8" woofers, to fit behind the rear sail panels? I think you would get more of what you're looking for by doing that, instead of trying to make an IB setup work in the rear deck.

There's a guy in Australia who printed enclosures for 9" woofers to fit that space ... He's a great guy too, and might be willing to share his 3D printer files with you? Let me know if you want his contact info.

View attachment 310806



There's not enough depth to flush mount anything back there. There really is no room under that rear deck.
I can’t imagine the sound being able to make its way out of that little 4-4.5” grill on the side panel...and it not rattle badly.
 

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I can’t imagine the sound being able to make its way out of that little 4-4.5” grill on the side panel...and it not rattle badly.
Subwoofers work very well in that location. The sound doesn't need to make its way out of the 4.5" grill, as sub frequencies are not stopped by the trim panel.

Many guys have installed 8", 10", 12" and even 13" shallow subs in there with great results. Hendrix engineering used to make fiberglass enclosures for it even, but they stopped offering them a few years back due to such low demand (ie: limited number of GTOs on the road).
 

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Discussion Starter · #33 ·
Subwoofers work very well in that location. The sound doesn't need to make its way out of the 4.5" grill, as sub frequencies are not stopped by the trim panel.

Many guys have installed 8", 10", 12" and even 13" shallow subs in there with great results. Hendrix engineering used to make fiberglass enclosures for it even, but they stopped offering them a few years back due to such low demand (ie: limited number of GTOs on the road).
How does the plastic panel not rattle tho? For that matter, I bet I could stuff some bazooka tubes in there. I’m kidding. Wait...am I? I need to do some measuring now..... that wouldn’t be a bad idea.....
 

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How does the plastic panel not rattle tho? For that matter, I bet I could stuff some bazooka tubes in there. I’m kidding. Wait...am I? I need to do some measuring now..... that wouldn’t be a bad idea.....
You just deaden the panel.

Here's some info I found a while back, when I was researching it. This guy put 8" woofers inside MDF boxes he built for the space. I think the 3D printed designs are MUCH better, but this gives you an idea of what can be done with the space.

Rectangle Parallel Font Circle Plot


Audio equipment Wood Automotive tire Gas Loudspeaker
 

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Discussion Starter · #35 ·
You just deaden the panel.

Here's some info I found a while back, when I was researching it. This guy put 8" woofers inside MDF boxes he built for the space. I think the 3D printed designs are MUCH better, but this gives you an idea of what can be done with the space.

View attachment 310809

View attachment 310811
Yea I saw those boxes long ago, I have that picture of the measurements saved in my phone. I never really considered that because I thought the panels would rattle.
 

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Yea I saw those boxes long ago, I have that picture of the measurements saved in my phone. I never really considered that because I thought the panels would rattle.
I think as long as you treated the area appropriately, it would be fine.

For my car, I put CLD on anything which seemed to resonate ...

Automotive tire Motor vehicle Hood Automotive design Bumper


.... then I followed it up with MLV inside the cavity, and CCF anywhere the trim panel made contact with the body. I actually don't have these rear speakers even hooked up, but ... all rattles and vibrations were removed from doing this. It also significantly cut down on rear tire noise coming into the cabin (due to the MLV)

Automotive tire Motor vehicle Trunk Automotive design Hood
 

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Maybe I missed it, but I dont see anything here about a SS filter. With only 2 8in subs for your sub-stage you don't have nearly enough displacement for anything below 40hz with any sort of authority.
So you are probably distorting them to death and running them hard into xmax when you touch your gain knob.
You have no sort of air spring on the cone. So it wants to move like crazy. Unless you limit that, it's going to sound rough at high volumes if there is any sub 40hz content in the music you are listening to.
If you want to run IB and not make an enclosure for them, your gonna have to fab something up for larger drivers with more displacement imo.
 

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Discussion Starter · #38 ·
So I just got through taking it all apart again. I yanked one of the audiophile subs out and replaced it with a Blaupunkt. Did some swapping back and forth testing. Now I see why I took the Blaupunkts out. No matter what, they bottom too easy. Even with all the deadening and sealing I did. And the dsp. Dont matter. The audiophile subs pretty much trounce them. I’m leaving my interior apart and order a few other subs to try. No point in trying the 6.5’s I have because I remember the Blaupunkts beat those. I think I’m gonna order some cerwin Vega Vegas to try and some kicker comp c’s. I may order one of each. Skar has an 8” sub so I may order that too. I’m determined to make this work. I dunno why. I guess I’m seeing it as a challenge at this point.
 

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Think of it in terms of displacement alone. You have four 6.5in mids, each of them has a cone area of 132cm each. Then you have two 8 in subs with a cone area of roughly 216cm each. You have 18% more cone area with your mids than you do with your subs. So it's not a surprise your mids are giving you nearly what you want and the subs are underwhelming.
132 x 4 = 528cm vs 216 x 2 = 432cm

That doesn't take into account linear travel, but even if your subs have 2x the xmax of your mids, that's still only 60% more air moved at xmax.
With have the same SPL level at one octave lower, you need to move 4x the amount of air.
So if you wanted to be able to match the spl capability of your mids running at 80hz @ xmax w/ 528cm, you would need to be displacing 2112cm. Drop that down to 30hz and you need 4224cm displaced. That also doesn't take into account the rise in the lower octave that is typically wanted.
Moral of the story, if you want to keep up with the 4 6.5in mids, you need to displace much more air than two 8in subs will provide when running in IB without a SS filter in place.
 
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