# Firing 8's through 6x9 holes



## michaellone (Nov 4, 2010)

Getting back into the hobby after taking 20 years off, so forgive me if I am a little rusty.

I have a 2009 Pontiac G5 and wanting to add a pair of 8's to give it some more bottom end. Not wanting to sacrifice a lot of trunk space or the ability to drop the seats, I thought of mounting the sub boxes below the factory 6x9 hole and use a sheet of dense foam rubber to act as a gasket to seat the subs to the cabin. Will the 6x9 hole provide enough area for decent air travel for the subs? Does anyone see any problems using the foam rubber as a gasket?

Thanks for any help you guys can give.

Mike Lone
Duncan, SC


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## Bayboy (Dec 29, 2010)

There's a few 6x9" subs on the market that may be easier to integrate. I wouldn't expect heavy bass like that of a larger one in an enclosure, but filling out the bottom end is very possible. Have you checked any of those out?


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## michaellone (Nov 4, 2010)

Good suggestion, but I have never heard a 6x9 that I ever liked. I listen to alot of rock and 80's Hair Metal. The punch that you get from a good 8 in a proper sealed enclosure has always pleased my ears. That is the reason that I am trying to find a way to make it work.


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## traceywatts (Jun 2, 2008)

the cone area of a 6x9 is roughly that of an 8. they should have similar bass response if you purchase a 6x9 sub and install it in it's proper enclosure.


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## Bayboy (Dec 29, 2010)

It could work if you make sure to heavily damp the rear deck. I'm not to keen on the difference in the opening and the 8" sub. Shouldn't be too limiting down at those frequencies (if at all), but I'm just funny bout that stuff. I'd be worried about some sort of band pass effect. Could be a minimal problem though.


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## dragonrage (Feb 14, 2007)

If you really want to lose as little trunk room as possible, throw some Peerless SLS 8" in the deck itself. Use a lot of RAAMMat or whatever. on it.


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## Patrick Bateman (Sep 11, 2006)

michaellone said:


> Getting back into the hobby after taking 20 years off, so forgive me if I am a little rusty.
> 
> I have a 2009 Pontiac G5 and wanting to add a pair of 8's to give it some more bottom end. Not wanting to sacrifice a lot of trunk space or the ability to drop the seats, I thought of mounting the sub boxes below the factory 6x9 hole and use a sheet of dense foam rubber to act as a gasket to seat the subs to the cabin. Will the 6x9 hole provide enough area for decent air travel for the subs? Does anyone see any problems using the foam rubber as a gasket?
> 
> ...


You could easily fire an eight through the hole designed for a 6x9. Hell, you could fire a fifteen through the hole designed for a 6x9. In pro audio it's done all the time, and those guys are running a lot more power than we are. (Google "horn compression ratio")

Here's what you want to watch out for:


You'll want a sturdy solid baffle - the sheet metal on the rear deck is kind of flimsy
If you mount your woofer beneath the deck, a cavity of air will be created in front of the cone. That cavity of air will roll off the highs, kind of like the front chamber in bandpass box. Keep this in mind when you make your baffle. You'll probably want to keep that cavity as small as possible.
Alternatively, you could size the cavity to intentionally roll off the highs. That will take some trial and error though.
You might consider mounting two woofers vertically underneath each hole. It's probably the easiest way to mount them. For instance, dual eights under each 6x9 hole, with a slot port running up to the rear deck.


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## michaellone (Nov 4, 2010)

Patrick Bateman said:


> [*]If you mount your woofer beneath the deck, a cavity of air will be created in front of the cone. That cavity of air will roll off the highs, kind of like the front chamber in bandpass box. Keep this in mind when you make your baffle. You'll probably want to keep that cavity as small as possible.



That was my thought. Mount the enclosure so that the 8 is facing the 6x9 hole, leaving enough space for excursion + 1". The edges of the enclosure would extend to mount flush with the deck, using bolts to secure it in place, and provide more structural strength to the metal. Separate enclosures per side. Then use the foam rubber to seal it to the 6x9 hole.


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## t3sn4f2 (Jan 3, 2007)

http://www.g5club.net/showthread.php/9114-HOW-TO-relocate-back-seat-Release-Poper

Is your car like this? If so....

I'd put a pair of infinite baffle 10" or 12" on the underside of the rear deck, firing through the 6x9 openings. Some JBL GTO's maybe. Bolt and seal a baffle onto the bottom side and also seal off the trunk from the cabin in the same manner (as best you can).


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## michaellone (Nov 4, 2010)

Yep, that's the model of my car. I see what your saying, and that's not a bad way to go either. A hell of allot less engineering. 

Ok, if I go this route... who makes a good free-air 10" ? Looking to stay around $100 per speaker.


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## michaellone (Nov 4, 2010)

BTW, Thanks t3sn4f2 for the link. I need to do that mod to my car! That's Awsome!


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## AAAAAAA (Oct 5, 2007)

I will suggest against the peerless SLS series as mentinoed by someone else. they don't work well as a SUB IB... but very well as midbase as per my experimentation.

I personally ended up running a pair of 8inch polk mm840's and with a lot of bass boost (IE more power to compensate for 8inch roll off) they provded satisfying amounts of bass. 8's IB roll off fast so they need to be able to handle power and have good xmax if they aren't an IB optimized design...

If you can fit 10's then that's even better.


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## t3sn4f2 (Jan 3, 2007)

Acoustic Elegance IB 10,12,15 A (highly regarded IB line yet very affordable, might have wait a while after ordering to get them though)

JBL GTO 10,12,15 (people always recommends those whenever a thread like this pops up).

Remember though that it is important to treat the deviation between the cabin and the trunk like a wall of an enclosure. Since the trunk will act like the box in an trunk IB application. Search on IB installation on here and you'll get a good idea on how to do it. You might even skip the deck mounting for a single or pair of 12" or 15" that will go mounted to the very baffle you use to seal off the trunk. That is the more common way of doing it and you don't even have to worry about the seat blocking the bass since that is never the case. It might cost a little more for the bigger drivers but you'll gain tons of efficiency which will save you a lot on amp power (ie you'll only need like 200 watts for a pair of 15"). Plus sealing off the rear deck with a straight panel will be a lot easier then making one with speakers on it also.


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## t3sn4f2 (Jan 3, 2007)

michaellone said:


> BTW, Thanks t3sn4f2 for the link. I need to do that mod to my car! That's Awsome!


Looks like a needed mod for your application as well!


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## t3sn4f2 (Jan 3, 2007)

AAAAAAA said:


> *I will suggest against the peerless SLS series as mentinoed by someone else. they don't work well as a SUB IB... but very well as midbase as per my experimentation.*
> 
> I personally ended up running a pair of 8inch polk mm840's and with a lot of bass boost (IE more power to compensate for 8inch roll off) they provded satisfying amounts of bass. 8's IB roll off fast so they need to be able to handle power and have good xmax if they aren't an IB optimized design...
> 
> If you can fit 10's then that's even better.


x2, that's what I've read. Good IB midbass _when_ you have a sub.


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## michaellone (Nov 4, 2010)

t3sn4f2 said:


> That is the more common way of doing it and you don't even have to worry about the seat blocking the bass since that is never the case. It might cost a little more for the bigger drivers but you'll gain tons of efficiency which will save you a lot on amp power (ie you'll only need like 200 watts for a pair of 15"). Plus sealing off the rear deck with a straight panel will be a lot easier then making one with speakers on it also.


The only problem with mounting the speakers on the baffle behind the seat is that the the seats have steel backs, if I am not mistaken. That would make it a harder path for the sound to travel.

You guys have given me a lot to think about, and that's what I asked for. Thanks for all the suggestions. I will post back soon.

Mike


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## trojan fan (Nov 4, 2007)

michaellone said:


> Getting back into the hobby after taking 20 years off, so forgive me if I am a little rusty.
> 
> I have a 2009 Pontiac G5 and wanting to add a pair of 8's to give it some more bottom end. Not wanting to sacrifice a lot of trunk space or the ability to drop the seats, I thought of mounting the sub boxes below the factory 6x9 hole and use a sheet of dense foam rubber to act as a gasket to seat the subs to the cabin. Will the 6x9 hole provide enough area for decent air travel for the subs? Does anyone see any problems using the foam rubber as a gasket?
> 
> ...



Sounds good, and easy to execute... look at some JBL gto804 8's...$120 a pair on amazon and they work great in .35 cf. keep it simply


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## IBcivic (Jan 6, 2009)

michaellone said:


> Getting back into the hobby after taking 20 years off, so forgive me if I am a little rusty.
> 
> I have a 2009 Pontiac G5 and wanting to add a pair of 8's to give it some more bottom end. Not wanting to sacrifice a lot of trunk space or the ability to drop the seats, I thought of mounting the sub boxes below the factory 6x9 hole and use a sheet of dense foam rubber to act as a gasket to seat the subs to the cabin. Will the 6x9 hole provide enough area for decent air travel for the subs? Does anyone see any problems using the foam rubber as a gasket?
> 
> ...


The sd of an 8 incher is roughly the same as a 6 x 9er. No issue what so ever.
if the foam rubber is dense and not too thick, it will work fine. low frequencies can travel right through foam, so the closer , the better.


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## trojan fan (Nov 4, 2007)

amitaF said:


> The sd of an 8 incher is roughly the same as a 6 x 9er. No issue what so ever.
> if the foam rubber is dense and not too thick, it will work fine. low frequencies can travel right through foam, so the closer , the better.


Leave an 8 inch cut out in the foam


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## IBcivic (Jan 6, 2009)

trojan fan said:


> Leave an 8 inch cut out in the foam


X 2


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## sqshoestring (Jun 19, 2007)

If you want to do IB, you are best off to figure out how large a sub you can fit there over the hole plus the baffle thick enough for xmax at least. Then shop up a good IB sub with a higher qts at least around .5 and low Fs, depending on what kind of bass you like to hear. If you like more lows find a qts of .7. Or you can say screw it and run something massive like a jbl gti and EQ it. I used a 15 pyle plwb155 they are $40 each, because they are so large the output is significant and I don't run them hard at all most of the time. Great IB specs, but they are pretty big. A 10 for example is not going to have as low an Fs as a 15, unless it is really inefficient. The plwb 10" has Fs 40. I got the pyles because they have similar specs to the IB AEs, and are heavy paper cone I prefer, and largely because I could find hardly anything else for less than a load of coin for a pair of 15s. I got lucky and they work pretty nicely.

Note if you do IB; you will want metal backed seats, and if you fold them down the bass will likely cancel and not be as loud. You need to plug any big holes to the cabin, it does not have to be air tight like some say.

Believe me when I say if you want to do it IB, go large as possible and as many subs as possible. I am certain a 12 can run through a 6x9 hole, pretty sure a 15 could though I've never done it. The loose rule is the hole should be half the cone area, the more xmax the sub has the larger it may need to be...that means you could have an issue at very high outputs. But a lot of people have done it and it worked. 

Why not 8s, they just don't have the output down low. They will work like big midbass more or less, they can't move enough air to get low. They will be ok if you don't play the system that loud or don't want low bass. If you want output you will have to SS filter them hard, or buy a massive xmax 8 and there is little point to that. Even a cheap 10 should compare to an expensive 8.


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## south east customz (Jan 17, 2011)

I've made adaptors to fire 10'a thru stock holes pretty easily. Or u can do 3-4 of them across the under part of deck on a baffle Thats about 3 inches from the bottom of the deck all sealed off and I've a quasi-bandpass box
I've used the id's and DLS OA's with great success. Also the oz matrix elites but they are disco


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## trojan fan (Nov 4, 2007)

When you add in transfer function , the 8's in a proper sized enclosure will sound fine, keep it simply, getting into some of this other stuff will just open a can of worms


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## michaellone (Nov 4, 2010)

After thinking about it, I think I will stick with the 8's. You guys have given a lot of good options, but I love the tight punchy sound of 8's.


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## AAAAAAA (Oct 5, 2007)




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## sqshoestring (Jun 19, 2007)

8s can sound fine IB, they just don't go near as loud as a comparable 10....unless you cut the bass out of them. I'd likely use a box if I were going to put 8s in unless you don't need a lot of output.


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## trojan fan (Nov 4, 2007)

michaellone said:


> After thinking about it, I think I will stick with the 8's. You guys have given a lot of good options, but I love the tight punchy sound of 8's.



X2 ....good choice


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## LunchboxCritter (Mar 8, 2011)

Have you ever tried fiberglass? To get the sound in the car through the rear dash I would recommend building a 4th order bandpass box and running the port through the rear dash. There is a write-up done by bobwires on fiberglassforums.com where he builds the type of box and install that I am talking about.


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## michaellone (Nov 4, 2010)

I have never worked with fiberglass... yet. I also own a drag boat and need to do some minor repairs on the hull. Guess sub boxes would be a good starter project before I tackle the boat.


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## michaelsil1 (May 24, 2007)

michaellone said:


> After thinking about it, I think I will stick with the 8's. You guys have given a lot of good options, but I love the tight punchy sound of 8's.


Sealed 8's, I don't think 8's IB is going to give you the punch you desire.


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