# Pontiac G8 GT – 2,000 watt system – IB Subs



## BadSS (Feb 2, 2008)

I finally started the stereo install and I hope to finish things up over the next couple weekends.

Head Unit – Stock Blaupunkt with incorporated HVAC controls
Processor – JBL MS-8
Tweeters – Vifa XT-25s – stock dash location – fires at an angle under the grill opening
Front MidBass – Alpine SPX-17Pros – stock location
Center Speaker – Morel Tempo 4 – stock dash location
Rear Doors – JBL P550 woofers, Vifa XO Tweeters, Altec Passive Crossover
Subs – 2) IDMAX 12D4 V.3, free-air under rear-deck firing up into stock location
Amps
Hifonics Gen X Goliath, 500 watts, 125 x 4, tweeters and rear doors
Hifonics Gen X Saturn, bridged, 400 watts, 200 x 2, front door mid-bass
Hifonics Series VIII Pluto, bridged, 120 watts, center speaker
Hifonics Gen X Zeus, 1,000 watts, 500 x 2, subs wired to 2-ohms

The stock G8 system is the worst I’ve ever heard in a car since the 70’s – absolutely horrid speakers. It’s also not a very stereo installation friendly car. Flimsy sheet metal rear deck, water pours in the doors, and the HVAC controls are incorporated into the stock head-unit. I seriously considered an Alpine of Australia dash kit for the Holden VE, but the stock unit is a decent sounding Blaupunkt 6-disk changer,, and I found a good deal on the MS-8.










Center Speaker – Morel Tempo 4C

I originally thought I could get a low profile 5.25” speaker to fit up top, but there is just not enough room/depth under there. While I didn’t think I could get it to fit under the grill,, I found a deal on a single Morel Tempo 4C, and it was cheap enough to try. I’m glad I did, because tonal quality is very good with surprising bass from such a small woofer. Long story short, I ended up cutting and bracing the stock grill and mounting the Tempo 4 on top. While this is the first visible speaker in any of my cars since 1985,, and I’m not all that happy about it,,,, it was the best I could do and get the sound I was looking for. Closely matching interior spray paint was used on the Morel grill to help it blend in the best it can. 










Rear Door Speakers – JBL 550s with Vifa XO Tweeters and Altec Lansing Crossovers

Since I was impressed with the Morel Tempo 4, I bought a set of Tempo 6 coaxial speakers for the rear doors, but didn’t particularly care for them. I tried a number of other speakers, then out of pure frustration I broke out a set of new old stock JBL P550 components that I bought years ago. I didn’t particularly care for the JBL’s tweeters or crossovers, but after swapping those for a set of Vifa XO tweeters and Altec Lancing crossovers I had laying around,, the combination sounded better to me than the Morel Tempo 6. Plus,,, the cone area of their “plus-one” 5.25” woofer is almost as much as the 6” Morel. In fact I was rather shocked to find the P550’s woofer sounds very similar to the 7” Vifa MG driver that I had originally hoped to use - just not quite as much bass and lacking a little bit of detail. 

OK,, that brings me to the stock G8 mounts. They’re rather flimsy and that water deflector adds some nasty and unwanted reflection to the back of the speaker cone. I fixed the flimsiness by using epoxy putty to fill in the openings then sanded the mounting surface flat. To tame the unwanted reflection, I added thin adhesive backed closed cell foam to the inside of the water deflector.










Full Dynamat on the outside door skin as well as the inside of the inside door skin,, where I could put it,, and of course the outside of the inside door skin. Dynamat was also used on the inside of the door panel’s “reservoir” that fits inside the large opening at the bottom of the door.

I cut a hole in the stock P550 grill, painted it black and mounted the Vifa tweeter as low as I could without the back of the tweeter coming in contact with the woofer cone under full excursion. A little notch in the bottom part of the grill lets the wires run through it and keeps them off the surround. I’m extremely pleased with the sound from this Frankenstein of a combination.


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## BadSS (Feb 2, 2008)

Dash Tweeters - Vifa XT-25

The stock 2.3-ohm tweeters with a 3.3mF cap are a joke,, doing the math, that’s -6dB around 21,000 Hz. However, luckily the small format XT-25s fit right in the stock location and after playing with the firing angle through the stock grill cover, this is where I ended up with them. I tried a set of Seas Neo Textile tweeters as well and I thought they sounded fractionally better over 10K or so,,, as off-axis as they are. However,,, the XT-25s had a little better detail in the lower end of the spectrum and I’m hopeful the processor can “fix” the higher-end frequency response.










Front Door Mid-Bass – Alpine SPX-17PRO

I really wanted to run the 7” Vifa MG woofers, but due to the water coming in the doors,, I needed to find something that would fit inside the stock mounts with the water deflectors. I could have made custom baffles out of plastic cutting boards and rigged up custom water baffles, but decided to see what was the biggest and “best” I could find that would fit the stock mount. After a good bit of research trying to find something decent that would fit in a 133mm opening,, I ended up taking a chance on a set 17PRO woofers with the mounting hardware. Even though I had seen a few bad reviews on the woofers, on paper they have a respectable displacement potential due to an X-max of 6.3mm with an effective piston area, Sd, of 133cm2. 

I did an A-B comparison in speaker boxes with the Vifa MGs and the 17PROs are not quite as transparent as the MGs, a little veiled in comparison, but most are. Still overall detail is very good and the midrange is better than most I’ve heard. Also,, while the MGs are not known for their bass output, I did not expect the difference in low-end bass production, especially after hearing a lot of criticism of the 17PRO’s bass output. In fact, I think the 17PROs dig as deep as any 6.5” or 7” speaker I’ve heard with a mounting depth under 2.75”. As far as fitment, after mounting the adapter ring to the stock mount the Alpines didn’t quite seat. Here’s a shot with the inside of the stock mount ported enough to give the speaker a little wiggle room.










Since the mounts are so flimsy, I used epoxy putty to strengthen them by filling the hollow portion that’s on the backside of the mount – the hollow area is topside for the rear mounts.










Epoxy putty was used to fill in and “expand” the area under the Alpine’s adapters as well as in other areas to make the mount more rigid.










Here’s the front door fully deadened, speaker installed, and ready for the door panel










I used a lot of Dynamat on the doors,, including the inside of the door panel. I noticed with the stock speakers there was a high frequency vibration at the thin plastic map pocket. I didn’t think that was good and the Dynamat fixed that. I also used it in other parts of the door panel,, but it was probably over kill.










Whether it was overkill or not - the end appears to justify the intent. Overall, I’m extremely impressed with the sound using just the stock radio and passive crossovers until I can finish up the rest of the install. I used an 8-ohm resister on the Morel Tempo 4 center speaker,,, and have Altec Lansing crossovers running the 17PROs and XT-25 tweeters in the dash for now.


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## BadSS (Feb 2, 2008)

I plan on working on getting the amps in over the weekend and possibly the subs.

Wiring run to the rear – SpeedWire to MS-8, 12 gauge to tweeters, mid-bass, and rear doors. 14 gauge to the center speaker.










Mock up of the amp rack that’ll go behind the rear seats.










Rear deck IB for the two IDMAX 12s – firing up through stock 8” sub opening.










Added bracing welded,, still a little worried about the weight though. They do not build them like they used to – lol.


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## optimaprime (Aug 16, 2007)

this gonna be cool i really love those cars what color is it?


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## LS1 Sounds (Dec 12, 2009)

Cool build! I also have a 2009 Pontiac G8 GT, but with a very modest system. I'm always looking for upgrade ideas.  Subscribed!


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## BadSS (Feb 2, 2008)

optimaprime said:


> this gonna be cool i really love those cars what color is it?


Thanks, I had something similar to this system in my old 97 Thunderbird and I thought it was pretty cool,, if I do say so myself - lol. Here's a shot of the trunk,, semi-finished Rockford made MB Quart 15s firing into the seats, MB Quart 10's top mounted on the rear deck, and a mixture of HiFonics Gen X and Rockford built MB Quart RAA reference amps. I'm hoping the G8 will hang with it.










The G8 is silver. I'll take a couple pictures and post them once I clean it up,,,, after I get the stereo in.



LS1 Sounds said:


> Cool build! I also have a 2009 Pontiac G8 GT, but with a very modest system. I'm always looking for upgrade ideas.  Subscribed!


Gotta love the power from these G8s,, especially once you tune it for premium fuel and program the transmission to act right. They are not very stereo friendly though,, and the stock system is terrible. However,,, if you're not a stereo freak,,, there are some things you can do to make huge improvements to the stock system with very little cash.


I've run the power wires and double checked all the amps with a LOC I had. I should be able to have everything mocked up and ready to bolt in the amp "rack",,, once the carpet comes in later in the week. It's not going to be anything special,, bare-bones and simple,, kinda like the T-Bird install.


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## BadSS (Feb 2, 2008)

Well, the carpet finally came in, but I wasn’t able to do as much as I had hoped. However,,, I’ve learned to accept the little nit-picky things that always seem to happen,,, no matter how well you think you’ve planned and just keep chipping away. 

I had ordered some RCA Y-adapters since the Gen X 4-channel amps require them to run one as a bridged 2-channel. They came in Friday, but they were not nearly flexible enough to make the rather tight quarters turn. So, after searching the net a couple hours, it dawned on me that I could use one of the PARA-1 “2-channel” modules with the 4-channel amp and I wouldn’t need the “splitters”. Worked like a charm!










Since I’m going active and running different powered amps, about 125 watts to the tweeters and 200 watts to the mid-bass, I wanted to set the levels on the gains before running through the set-up with the MS-8. I already had a line output converter rigged in for testing the amps,,, and I had a Blaupunkt crossover ,, so,, at worst this was just a waste of time.










It’s been a number of months riding around with the ear grating stock system. With me being so long without a decent system in the car, I was extremely pleased in how the gain setting session went. I was a little weary about engine noise with the LOC and whether or not the SPX-17PRO woofers could handle 200 watts anywhere around 50hz. However, there’s no engine noise and the 17PRO woofers seem to be handling the 200 watts at 50hz well. In fact, if I had never run time-alignment before and know the difference it can make, I’d probably be more than just happy with this “simple” active set up.

Another time consuming deal was I had planned on running a Zeus on the subs, but couldn’t get it to fit without concluding I was going to have to build a false floor,, or false wall. I really wanted to keep this as simple as possible,, so I ended up breaking out the brand new Zed Audio Deuce I had squirreled away. “Wait a minute, Zeus, Deuce. Is there a little similarity? Whoaaa, I think there is!” Well,, at least they’re family,,, so to speak. I’d rather run the Zeus and keep it all Gen X amps,, but the Deuce will simplify things by mounting up top between the subs.










Once I get the subs in the car,, and before mounting the Deuce, I’ll try them both and if I think the Zeus sounds better/hits harder and it’s worth the effort,, I’ll get it to fit!


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## BadSS (Feb 2, 2008)

It’s been a while, but I’ve finally made some progress.

Front Stage and rear-fill amps mounted on amp rack and ready to install









Front stage and rear-fill amps installed and tweaking the gains and crossover points for an easier set up with the MS-8. I rode around a week with it like this to get it to where I thought I was ready to move on to the subs.









Subs ready to install,,, used the cut-out disks and an old fold-up tool case to position the subs within a quarter-inch of the baffle board. Minimal effort required!









Sub through the stock rear deck opening - one down, one more to go.









The subs are in and ready for some power!!









Next is the sub-amp,, should finish getting all the equipment in the car tonight. Probably won’t be able to finish it until Monday or Tuesday night – there are lot of interior pieces and small details still left to wrap-up.


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## BadSS (Feb 2, 2008)

Everything is in and the subs are starting to sound pretty good with about 40-minutes play time. 

I cleaned up the rat nest wiring a bit on the temporary, pre-MS8 crossover. I’m going to ride around with it like this for the rest of the week. I want to get an idea of the gain setting and crossover point for the subs after they fully break in.










Here’s a close-up of the Zed Deuce and old Hifonic Gen X amps. I’ve just got the power and speaker wiring taped up for now on the Deuce,, I didn’t have enough wire loom to wrap that up. I’ll pick up some tomorrow,,, I just didn’t feel like messing with it anymore tonight.










I think I said this before,,, if I didn’t know the difference time alignment made,,, I’d been able to save a bunch of money on the MS-8. This thing with the center channel sounds pretty dang good as it sits!


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## kizz (Jun 22, 2009)

I like the install, just a quick question though, why are you using the blaupunkt crossover with the ms8. The ms8 can do all of that.


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## BadSS (Feb 2, 2008)

kizz said:


> I like the install, just a quick question though, why are you using the blaupunkt crossover with the ms8. The ms8 can do all of that.


Thanks!

I haven't hooked up the MS-8 yet. I wanted to make sure everything was working properly and figure out where I wanted to set the crossover points before hand. I figured it would be a lot easier in the long run.


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## broadz (Jan 20, 2009)

Wow, awesome effort. Is there much parcel shelf rattle?


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## BadSS (Feb 2, 2008)

I spend a lot of time inside the trunk under the rear deck/parcel sealing things off and using dampener material to make sure the trunk wiring and harnesses were secure. Also, I used super duty duct tape to tape over all the wires on top of the rear deck or parcel shelf. The subwoofer baffle is screwed into the 3/4-inch square bar stock I had welded under and to the rear deck/parcel shelf. That stiffens up the area a good bit. As low as the subs go and as hard as they are hitting, I’m pretty sure,,, as thin as the metal is in the rear parcel shelf that it would be flapping around like crazy. 

I drove the car a couple days without the rear deck cover and had no rattles in that area. However, after installing the rear deck cover, I ended up with a couple buzzes/rattles. One is coming from one of the factory subwoofer speaker grilles and another area is where the plastic “flow through” ventilation strip meets with the raised metal “strip” under the rear glass. So,, I’m going to have to pull the deck cover back off and silicone the factory grilles to the cover and use some thin adhesive backed, closed-cell foam along that rear window “strip”.

However,,, there were some buzzing and rattling around the fenders/rear bumper area – not just the “flapping” noise from the trunk vents. I had to drop the mufflers, remove the muffler heat shields and used dampener material in a number of places. I also fastened the inner wheel-well cover to a small thin (flexible) plastic extension already connected to the rear bumper cover. There was a hole in the “extension” like there should have been a fastener connecting the two in the first place. I also had to bend a corner of both muffler heat shields to get it off the inner wheel-well. 

On a side note, I had fabricated a long “terminator box” that replaced the factory muffler and the bullet resonators. It sounds great,,, but I was experiencing some VERY annoying drone that began around 53mph,, getting quite loud between 58 – 67 and going away around 72 mph. I was seriously considering dropping over a grand on a “no drone” Corsa exhaust. After dampening the area under and behind the rear seats, with the amp rack and rear deck baffle with the subs in place, the drone was drastically reduced. After securing the inner fender wells to the rear bumper cover and dampening the areas around there that were vibrating/rattling,,, radio off and listening for it,, I can barely hear it coming in about 66mph and goes completely away around 70mph. I don’t notice it at all with the radio barely playing – so I’m as happy about that as I am the sound system!

There are a couple other areas rattling and as soon as I resolve how and what to do about those, I’ll post up.


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## req (Aug 4, 2007)

awesome stuff so far! i have a pair of IDMax12's infinite baffle too... very capable speakers


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## mnoia (Apr 13, 2013)

hi, came accross your posting.
i wanted to ask have you figured out which lead can remote the amps without the key in?
thank you
08-G8 GT owner


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## D-Bass (Apr 27, 2012)

just so you G8 owners are aware, there is a company that makes a small touchscreen to retain HVAC if you replace the radio with a headunit or pad


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## eviling (Apr 14, 2010)

req said:


> awesome stuff so far! i have a pair of IDMax12's infinite baffle too... very capable speakers


still one of my faverate sub setups. i never heard anything so natural.


I love this build, very KISS logical build, that didn't break the bank that'll probobly sound very good  I am a fan.


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## JoshHefnerX (Jun 13, 2008)

I've got a g8 and am trying to get some ideas about what/how to fit things in the trunk. this has been the worst car to mod the stereo... 

Do you have anymore pics of how that rear deck was done?

Josh


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## BadSS (Feb 2, 2008)

JoshHefnerX said:


> I've got a g8 and am trying to get some ideas about what/how to fit things in the trunk. this has been the worst car to mod the stereo...
> 
> Do you have anymore pics of how that rear deck was done?
> 
> Josh


Sorry,, I switched gears and haven't completely finished the install,, so I haven't dropped by in a while. 

I don't have anymore pictures,, don't know if they would help a lot. I used a couple big thick cardboard boxes taped together and stapled to a 6x1 board to make the template for the baffle board - mainly to get the shape right at the rear seat area. I used that to make the first cut across the seat then popped a couple screws in it to draw off the curve at the trunk. I will say I would not hang anything like this from the rear deck without that extra bar stock 3/4" square tubing running from end to end,, terminating at the place where the fenders , body, and trunk all join together. 

Another bit of advice,, I knew I needed to mount a relatively large amp up top and went with the ID-MAX 12s for clearance. 15's will fit,,, and if I had to do it over again, I'd do the 15s and get a smaller amp. 

I've installed stereos for years,, but my last car was a 1997 T-bird - I drive them to the wheels fall off. It was basically introduced in 1989. I've helped friends with newer cars,, but this G8,,, and I think many newer cars are a bear. Super flimsy metal, not much window clearance and the doors pour in water. 

One final thing, I'm not happy with the tune,, or lack of tuning capability of the MS-8. I'm going to try an Alpine unit to see if that'll work for me (I think it will). If not,, I'll have wasted a lot money I could have just put on a HVAC controller and nice head unit.

Good luck with your install.


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## knever3 (Mar 9, 2009)

Did you audition the Hifonics amp on the subs like you had mentioned? Did it sound better or worse than the zed? I would love for you to find some way to mount the Hifonics in there too for sub duty.


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## BadSS (Feb 2, 2008)

knever3 said:


> Did you audition the Hifonics amp on the subs like you had mentioned? Did it sound better or worse than the zed? I would love for you to find some way to mount the Hifonics in there too for sub duty.


Yep,, I really wanted to keep it all Hifonics Gen X also, but I'm still keeping it in the family, so to speak, by running the Deuce. I did do a comparison and thought the Zeus might have been a little "tighter". IF it was,, and not in my head,,, it sure wouldn't have been worth the effort to put the amp somewhere else. Both pushed the subs to their limit in the IB configuration. I'm more than just satisfied with the output of the Zed Deuce and ID-Max combo. Wish I could say the same about the MS-8, lol.


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## Eric B (Mar 20, 2013)

Nice build, but they do not build those rear decks strong at all. I've done police car installs in the Caprice (same thing) and our trays mount to part of the rear deck. Well had one in for service a couple months ago and the spot welds had ripped right off, leaving our tray dangling. Definitely not built like they used too...


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