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2005 Pontiac GTO
350 Posts
Discussion Starter · #1 ·
I've owned this car since 2010, and it's been through a lot of iterations over those 11 years. For 3-4 years, it was a dedicated road course car even ... but I retired it from the track in ~2014, and converted it back to mostly stock form, to turn into a nice daily driver (even though it only gets driven a 2k miles a year or so).

Back then, I put a Pioneer 80PRS head unit it, and dug out my old amps and installed them as well. A Rockford Fosgate Punch 250a2, and a PPI 4240. Definitely two old school amps :) I also threw some MB Quart components up front, some Tang Band 6.5" subs in the rear deck, and disconnected the rear speakers all together. For power, I installed a two-fuse block under the hood, and ran two 8ga power wires back to the trunk.

So here is where I started this refresh from:

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... And this is how the car has been since 2014 until just a few months ago when I decided to refresh the system due to me driving the car a lot more often lately.

At 1st, I just wanted better bass in the car, so I replaced the Tang Band subs + RF Punch 250a2 setup with a Rockford Fosgate P300-12, which is a self-contained 12" woofer and 300w amp, in a sealed enclosure. I also moved the RF amp to the 6.5" door speakers, to give them more wattage, since the punch 250 delivers 50wx2 vs the PPI which is 30wx4.

Here was the result:

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This definitely added the low extension I was looking for, but it still wasn't up to par on what I was looking for in terms of clarity.

So the next thing I decided to do was replace the components with something higher end, and get a single 4-channel amp with more power, to simplify the amp setup and significantly clean up the trunk space.

So I picked up some Hertz Cento components, and decided to try the new Toro class A/B amplifier as well. So my end state at that time, was to arrive at the following:

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As I started reading more, and planning the install ... I decided that I should do some sound treatment while the doors were apart ... which led me to gutting the interior and treating everything (not just the doors) with second skin CLD, MLV and CCF. Man, what a slippery slope this can be!

Then I started thinking about the power, and questioning the two 8ga power runs to the trunk. Learning about CCA vs OFC, and everything else which comes along with that topic. Having a power distribution like this:

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... while it may technically "work", I began to realize it was far from ideal and wouldn't provide me with any room to scale up in the future. So I decided to replace the power and ground wires too ... I mean, I'm in this far, right? So why not ....

So I ended up swapping out the two 8ga CCA runs with a single 2ga OFC run, added two distro blocks in the trunk, 4ga OFC runs to the amps ... for both the power and the ground wiring ... resulting in this:

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Ok, so this is pretty good, right? The sound definitely improved all around .... sound deadened, MLV blocking road noise, CCF removing rattles, Hertz components, more power on tap ... I even upgraded the grounds under the hood ... but ... still, I felt the clarity wasn't quite what I wanted.

So more reading, more research, and of course ... I need to tune the system with more than just my ears ....

2005 Pontiac GTO
350 Posts
Discussion Starter · #2 · (Edited)
So, time to break out REW, as I have experience with it from tuning my home theater as well as live venues, since as a musician, I've often times had to setup live sound .... but, my rig for HT and live sound is a Tascam interface with a phantom power microphone, with all the signal and power requirements that come along with that ... and man, that's just a lot to manage for tuning the car.

Then I find this cool Dayton Audio iMM-6 calibration mic, that'll work with my phone and the AudioTools app ... sure, that'll be enough :)

So I pick one up, along with a lightening to 1/8" TRRS adapter, and an extension cable ... NOW I can get that clarity I'm looking for, right?

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Armed with the measurement setup and the 80PRS capabilities, I get to tuning ... and man, the system takes another leap forward in terms of clarity.

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But am I now completely satisfied?? Naa, of course not! It must be the cheap Toro amp, right? I mean, it sounds better than the setup when I had the old PPI and RF amps in play ... but that must be due to the Hertz speakers, the sound deadening, and the power upgrades, right?

So I start thinking way down the road ... What if i were to replace the 80PRS with a nice modern touch screen, with backup cam, navigation, wireless carplay, etc, etc ... But then I'd need to find a HU with all those features, which can also match the SQ capabilities of the 80PRS.

And then I ran into the world of DSPs ... Nice! With one of these, I can offload all the SQ processing out of the headunit, freeing up my HU selection to focus more on the usability features and less on the SQ capabilities.

That leads me into more reading, more research .. and wouldn't you know it, there are DSPs which also have integrated amps! Whoah, ok ... so now I can not only address the future scalability of the HU, but I can also get the cheaper Toro amp out of there at the same time ... and, now that I'm thinking long term, it sure would be nice to reclaim my trunk space so I can actually fit my guitar and gear in there when I need to drive the GTO to an event...

Does the rabbit hole even have a bottom??

So all of this thought process leads me to a Helix V-Eight DSP MK2 ... nice, this thing not only has 10 channels of DSP capability from one of the leaders in the space ... but also has an integrated 8 channel amplifier built in. And ... it'll fit in the same place where the GTO's OEM amp was mounted for the stock 6" subs which came in the rear deck.

But, I need a way to control it from the driver's seat ... Hmm, the URC, the Helix Director, the Helix Conductor, or WiFi control ... more reading, more research ... I decide the Conductor is the way to go for me. and I rip the system apart yet again ...

To mount it, I attach two strips of wood to the bottom, with 4 philips head screws exposed for mounting to the OEM location

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Yep, perfect fit! Everything wired up, cables ran, and it's a nice clean install in an out-of-the-way location, perfect! :)

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So the conductor, hmmm ... There's this perfect place next to my window switches, but it's a self contained module. Ahh, but that doesn't stop me ... I pull the window switch module out, and hack it open and start modifying. It really is a perfect fit!

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So now I need a way to tune the system easily, and opening the trunk, pulling back the panel, and plugging a USB cable in isn't really easy.

To solve this, I ran a USB extension cable into the center console, and installed a USB jack for connecting my laptop.

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For the power, I ended up relocating everything to be nicely hidden behind the trunk panels.

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The 2ga power from the battery comes through the hole at the top left of this picture, then there's a 3-way distribution box hidden by the fuel filler hose, which splits the power out to the two circuit breakers. There is a very conveniently located channel across the entire back of the car, and you can see where I ran the cables for the Helix DSP through it.

Just a quick look at the underhood changes as well ... The blue line shows where I installed additional 2-awg tinned OFC ground from the battery to the chassis and the engine block ... and you can see the single fuse block now, with 2-awg tinned OFC power wire as well.

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So now I need to tun this thing, but the little iMM-6 mic with AudioTools seems inadequate now LOL ... it probably would have been fine, but I really wanted a way to use REW ... which leads me to picking up a dayton UMM-6 USB mic.

Here is what I end up with after this phase ...
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... and wow, after tuning, the system takes yet another leap forward in clarity!

2005 Pontiac GTO
350 Posts
Discussion Starter · #3 · (Edited)
But I'm not at the bottom of the rabbit hole yet, so why would I stop? Heck, I still can't even see the bottom from here!

After all, I have a 10 channel DSP now, with 8 amplified channels and 2 preouts .... and I still have 4 of the amplified channels going unused.

Hmm .... rear fill sound like a really good idea now ... and heck, this thing has the "Real Center" processing on it ... sure, that's what I need next ... some rear fills and a center.

Rear fill? Easy enough... I pick up the matching 6.5" coax Hertz Centos, and mount them up in the rear side panels.

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So now for the center .... which is not so easy. The GTO doesn't have a center, and no options exists for a center ... but it does have this nifty top trim plate which seems like the perfect place to install one.

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So I picked up an AudioFrog GS25, and got to modifying ...

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And then I modified a parts express speaker bezel, and molded it to fit into the hole ... came out pretty good I think :)

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then finally, a little but of routing setup ....

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... and real center enabled

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And I arrive at this:

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... all I can say is, WOW! The system sounds really, really good after I went through a full tuning session.

So am I done? Nope ... I would still like to recover my trunk space, and have some plans to try and accomplish that. But that'll be an update for this thread at some point in the future.

for now, the system is sounding really, really great! :)

2005 Pontiac GTO
350 Posts
Discussion Starter · #7 ·
Nice progression and pictures! I've always been a fan of the GTOs. Almost ended up with one on a trade deal 2 years ago but the owner backed out of the deal.
Thanks, me too! A nice clean GTO is getting harder and harder to find these days. For a while, they got pretty cheap (like under $10k) and a lot were bought up and heavily modified. I've tried to keep mine "collectable" through the years, even when it was dedicated to track duty. I only did mods which were reversible so I could go back to OEM.

Nice thread, nice work (y)
Thanks, it's been a fun experience :)

You had me at GTO! Wasn't '05 the first year for the LS2 or am I remembering wrong?
LOL ... ya, 2004 had the LS1, and 2005/06 had the LS2. For me, the lack of hood scoops and dual exit exhaust made the 2004 a no-go when I was looking for one back in 2010. The 50 extra horses of the LS2 was just a bonus :)

The last dyno was 386 ft/lbs @ 4292rpm and 366hp @ 5931rpm at the wheels with all stock internals. Just a different air intake to make room for a laminova engine cooler (for road course use), some dyno tuning, and a removed catback ... since who needs the extra weight when it was a track car being trailered everywhere LOL!

It was definitely fun times, but the risk of body damage was too much, considering how much parts for these cars are going for now, if you can even find them. I lost a side mirror to some track debris one day on track, and it was over $300 for the mirror. I ended upprincing out different parts ($600 for a headlight!) and decided it was too costly to continue to run it.

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2005 Pontiac GTO
350 Posts
Discussion Starter · #10 ·
Very nice work! I love your “Rabbit Hole” comments...are we ever done?
Thanks! I'd say it's probably never done, although there does come a time when it's "done enough" LOL! I'm pretty satisfied with everything right now, except the loss of my trunk space and the dated head unit. I plan to replace the HU when these supply chain issues resolve and they become reasonably priced again ... and for the trunk space, I'm going to try IB 8's in the rear deck to see how they do, and then long term, put 10's behind the rear seat panels and move the rear fills to the rear deck.

Nice work!! Can you comment on those Tang Bands you had on the rear deck?
Thanks, and sure ... anything particular you'd like to know? The model # on them is Tang Band w6 1139sif. The specs are pretty impressive for a cheap 6.5" sub, and they were one of the very few which dropped right in to the rear deck location.

The issue with the GTO is the fuel tank is in the trunk, and is located right under the rear deck; so there's not a lot of room to work with. When these were in there, and being fed by the RF punch 250a.2, they worked well for the mid bass region. Of course, I didn't get much below 50hz or so with them installed like I had them. Not I didn't do any sealing of the rear deck or wall between the trunk and the cabin when I installed these either, so I wouldn't say it was a "good" IB install. At the time, I was just looking for something better than the OEM, which would drop right in.

Here's a pic from the trunk side, when they were installed. It's tough to tell, but I had to trim the fuel tank strap with a 4" grinder just to get these to fit in there.

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To fit 8's in there, a fellow DIYMA member with a GTO designed some 3D printed adapters to replace the OEM 6.5" adapters.

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The added height from the adapters provided the necessary clearance for these Cerwin Vega 8" subs to fit nicely

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I also went through and sealed up the holes in the deck, rear wall, and other places where the trunk and cabin were venting. I'm waiting on the amp I chose to be delivered now, and will give them a go when it is. My hope is they'll be good enough to keep me satisfied with the 12" sealed box removed from the trunk, but we'll see.

Like I said, long term plan is to get custom boxes built to allow installation of 10" subs behind the rear seat side panels, as there's plenty of room in those locations.

Here's a pic I took before any sound deadening or rear speaker work, showing how much room is available .... I don't see any reason why a couple of 10's (one on each side) wouldn't work perfectly here, so long as I can build (or have built) the right enclosures for them.

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I was thinking maybe ported enclosures, with the port exit lining up with the 6" hole where the OEM speaker grill is located? Or, sealed enclosures with the 10" woofer face overlapping with that grill ... not sure yet, as I'm still thinking through it.

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2005 Pontiac GTO
350 Posts
Discussion Starter · #12 ·
My Jaguar has the gas tank behind the rear seat like your GTO and I never could get decent sounding bass in to the cabin from the trunk area so I gave up on that. It all started when the factory 6x9 "sub woofer" gave up the ghost as the foam surround crumbled. I ended up removing the stock sub, fabricated a new mounting ring and replaced it with a PowerBass 6x9 sub that does pretty decent for what it is. My car also has solid steel between the rear seat nd the gas tank with a lot of sound insulation and I don't know if the GTO is like that or not?

I hope that in the end two 8" woofers IB works as I can't live without a trunk, need space for golf clubs. I think that if my Jag had two 6x9 subs it would be decent enough as I don't want to modify it to that degree either due to the nature of them getting harder to find in good condition.
Ahh, so you understand the dilemma :)

The 12" Rockford sealed sub does really well in the trunk, especially when I had the rear deck 6.5" holes open. Well, almost open ... I ended up making two circles out of open cell foam, with a thin layer of CCF on top and vinyl tape on the bottom. These were just to block the fuel pump noise from the cabin, and still allow the bass to pass through.

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With the 8" subs in there now, I'm still getting good bass into the cabin. I do run it pretty maxed out, and crossed over at 63Hz, but it's very well balanced. I've been really impressed from this Rockford Fosgate P300-12 all-in-one setup

The GTO also has a steel wall between the trunk and cabin, but there's quite a lot of holes in it. The rear seat is very thick though, and does a decent job of insulating the cabin.

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When I treated the interior, I 1st put Second Skin CLD on that wall, sealing up the holes in the process

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Then I added a layer of mass loaded vinyl over the top

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Then with the rear seats in place on top, it worked out really well.

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This next pic gives you a sense of how thick the rear seats really are ... they're solid foam, covered with softer foam, then the leather.

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All in all, the sound treatment completely transformed the driving experience. Maybe my age is showing, but out of everything I've done to this car, I enjoy the result of the sound treatment the most :)

2005 Pontiac GTO
350 Posts
Discussion Starter · #14 ·
You basically answered my question about the Tang Band subs. You weren't getting enough down low output with them.

I have 6x9 openings in my rear deck that are utilized as subs in IB. Looking for anything that can fit in there with some adapter plates that I can buy that will give me enough low end to fill up the cabin.

i posted a thread about it but like others suggested I will need to make a custom adapter plate if I wanted a decent dedicated subwoofer. My problem is I don't have the fabricated tools lol
Gotcha. If you have available trunk space, some 6.5" subs in the rear deck, with small enclosures mounted to the underside of the deck to enclose the backside of the 6.5" subs, would work really well.

The vented F3 of these little 6.5" subs is 38Hz ... so they can reach down pretty low, when installed in an appropriate enclosure.

The issue I have is there is no room to do something like that in my trunk, and an IB setup is more akin to a sealed enclosure. So the F3 of these in a sealed enclosure is 70Hz. Hence, I wasn't able to really get any volume below 50Hz or so.

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