# Turning a Boxster BOSE enclosure into a real sub



## NotA911 (Aug 21, 2012)

Greetings!

Just joined this forum at age 52 after being away from car audio for a while. Used to compete back in the 90s but then found myself in cars with pretty good factory systems and never had time to keep the interest alive.

But now I have bought myself a 2003 Porsche Boxster S and the stock Bose audio is so pathetic that I need to take action.

Besides replacing head unit, amp and front stage speakers I need to add some bass. The car has a ported speaker enclosure behind the seats with a 5" woofer/3" midrange pair in what is believed a wave guide configuration. Link here to a thread on DIY Audio where the enclosure is discussed. 

Because of the limited options for subs in the Boxster I am going to gut the Bose enclosure and turn it into a proper sub. I am pretty handy with GRP so I can do whatever I have to do to the interior but the exterior needs to be unmodified.

I need to keep costs in check so I have to use a pair of Kicker 10cvt65-2 Ohm 6 1/2" drivers I have already. These are really intended for sealed box applications so the Bose box needs to be modified. To begin with, I will remove the Bose midtweeters and seal their grill openings.

The problem is, as you can see in the other thread, that the Bose drivers fire downwards straight into the deck the enclosure sits on. Which creates a problem if I seal the port, obviously.

One option is to disregard Kicker's recommendations and keep the port, then attempt to tune the enclosure as best I can. Even if that ends up a complete kludge, it will be an improvement on the awful current sound. 

There really are no alternatives to the placement of the drivers, as the bottom is the only flat surface and I do not want to mod the exterior. Adding port(s) or small grills to the top could be possible but since there already is a front port that is likely no help.

I'd love to hear your ideas about what I can do given the restrictions outlined. 

Thanks in advance!

The Kickers will be wired in series for a 4 ohm load and I have 200 watts from a Pioneer class D amp to power it with. Obviosly the enclosure will be stiffened and braced, if necessary. I suspect I will need to remove the entire internal structure and just keep the exterior shell.


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## NotA911 (Aug 21, 2012)

I should have posted the T/S parameters for the Kicker sub, here they are:

Nominal Impedance [Zn], ohm 2 
Resonance Frequency [fs], Hz 53.9
Power Handling Watts, Peak (RMS) 300 (150)
Sensitivity [SPLo], dB @ 1W, 1m 84.6
Total Q-Factor [Qts] .667
Mechanical Q-Factor [Qms] 9.426
Electrical Q-Factor [Qes] .718
Effective Excursion [EXmax™], in. (mm) .17 (4.3)
DC Resistance [Re], ohm 2.05
Equivalent Volume [Vas], ft^3 (L) .328 (9.28)


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

That Blows system is a bandpass box of sorts.. 4th-5th order, not sure.. but the fact that there is an enclosure in front of and behind the 5", says bandpass to me... 

Not something you throw a woofer into and it works... 

I personally think you should toss the Blows in the trash and start over... I know there's not a lot of room, but if you have any gray hair, you'll have a lot more if you think you will ever get anything "decent" out of that...(in the end)

There are LOT of ways to get some bass out of almost no space... don't jump in feet first, look around and things will pop out at you... 

I wonder if the car is IB'able (infinite baffle) through the front firwall somehow.. lol.. maybe an 8 or 10" under the dash.. 

Bass shakers are another alternitive, maybe your stock system with some added..?? One will provide the "sound" the other, the "woomp"


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## NotA911 (Aug 21, 2012)

I haven't actually opened it up yet and no one seems to have posted any conclusive information. Whether there really are separate chambers inside, I guess I'll find out when I have figured out how to remove it from the car.

Simply dropping the Kickers in w/o modding the enclosure is certainly a gamble.
Most likely you are right and it will sound like crap. A few times, though, I have done something similar and it turned out great because it was so far outside the manufacturer's design envelope that it had not even been considered. 

Anyway I can always use the Blows enclosure as a mold. One possible is to mount the woofers in the top surface of the enclosure, firing upwards, creating two sealed enclosures in one. Easily done with some GRP.

Or I put the Kickers in the doors as midbass drivers, and put a 10" or 2 8"s in a more radically modified ex-Bose enclosure. 

Mounting something on the firewall probably won't work, not enough space.


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## 94VG30DE (Nov 28, 2007)

Seems like the folks over at diyaudio seem to think there are some "tried and true" methods with the tang band subs? Any reason you didn't want to go that route?


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## NotA911 (Aug 21, 2012)

94VG30DE said:


> Seems like the folks over at diyaudio seem to think there are some "tried and true" methods with the tang band subs? Any reason you didn't want to go that route?


I once tried a pair of Tang Band drivers in a home theater application and they failed after a short time so I was not impressed with their quality. And there is no longer anyone selling them locally so I would have to get them from Germany. 

And again I have the Kickers already so I prefer to use them if possible. 

There really isn't anywhere good to put a sub in the Boxster other than the rear shelf if I want to keep it looking 100% stock. Passenger footwell, behind the seat back are other possibilities but they both steal valuable space.

I saw someone had made an englosure that fit between the seats and fired forward, but that certainly did not look stock.

I think I may put the Kickers in the front doors and find one or two other subs which will work in the Bose enclosure. Let's say I gut it, stiffen it but keep the forward facing port and create a vented box. Which drivers would you recommend that will play nice and tight in a simple vented enclosure?


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## 94VG30DE (Nov 28, 2007)

hmmm. How much speaker mounting depth does that enclosure have? If it's only 4", that will be the limiting factor in driver selection


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## NotA911 (Aug 21, 2012)

Not even that much, I have not found the exact figure anywhere on the net and I haven't yet opened up the box because of job travel. But I have approximated a max of 90 mm at the current mounting point of the woofers.

The box tapers off in height towards the rear of the car and it is also thinner at the center where the horn-like vent is.

Without any modification, I would say two 6 1/2" drivers of max 90 mm height will fit. Hence my idea of using the Kickers. 

There is very little room for increasing the height of the box because part of the top rests against it when it is down. Possibly half an inch to an inch. 

But I think it may be possible to create a vented or even a bandpass enclosure if the interior is completely gutted with all existing internal structure removed, including the port, then new bracing and internal walls added together with one small port at each end where the midtweeter grills are now.

The box can then be enlarged, removing the contours across the top surface and raising the height as much as possible. I think that would allow for a couple of 8"s. But they would still have to be firing down since almost the entire upper surface is blocked by the top in its lowered position. To me this rules out a sealed box - sound has nowhere to go but straight into the deck. 

I also doubt there is room for making it into a bandpass, that would require extremely thin woofers. 

So I think vented is the only option. I was thinking maybe a curved port through the deck, opening up between the seats. But under the deck is the engine...


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## Fast Hot Rod (Apr 19, 2007)

I found a picture on the web of how the box fits in the car, in case anyone else got curious like I did:










It doesn't appear to be the _exact_ box from the other thread, but I'd bet it's close.

With 3.5" of total height (90mm) you might be able to run a shallow-mount Pioneer 10" driver in a custom box, provided you have the depth front/rear. The way that the Bose box 'throat' extends out between the seats might allow you to have a custom box that has a 10" sub centered and firing upward, that extends out slightly between the seats.

Can you give us the dimensions of the box? I'm curious if you have the required depth, specifically in the area in red below:










Pioneer makes 8" and 10" shallow subs... the 8" is only 2.5" deep, and the 10" is 3" deep. Depending on the box dimensions, you might be able to make a shallow box that fits in that location and leaves enough of a gap at the top to allow the bass to reach into the cabin. 

Let me know what you think.


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## 94VG30DE (Nov 28, 2007)

Do you know how much internal airspace you have available in that enclosure? Ideally we should be modelling some subs in the space allotted, and see what fits dimensionally and acoustically


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## NotA911 (Aug 21, 2012)

Thanks all for helping out! 

When I get back home on Monday I will take the enclosure out of the car and post detailed measurements including an estimate of the volume. Will post some pictures also.

I like the idea of the 8 or 10 in the center but there is the issue with what happens with the top down and ho much it would block the bass output.

Most shallow mount subs seem to be intended for sealed boxes. Are there any which work well in vented applications?


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## NotA911 (Aug 21, 2012)

Aaron'z 2.5RS/WRX said:


> That Blows system is a bandpass box of sorts.. 4th-5th order, not sure.. but the fact that there is an enclosure in front of and behind the 5", says bandpass to me...


"of sorts" being the operative word... 

I have disassembled it now. The box itself is a simple vented enclosure. The two woofers share the same chamber and there is the central vent. No channels or passages. 

When placed in the car, the woofers fire straight down into the carpeted deck. I guess the space between the box and the deck could be thought of as the front chamber of a bandpass box, but there is no way it can be completely airtight as the plastic fixtures holding the box to the deck seem to be to stop it from sliding rather than creating an airtight seal against the deck. If Bose intended it to be airtight, and the whole thing therefore a bandpass - anybody's guess.

Anyway: I dug out a pair of Morel CAW538 5" woofers from my secret stash, and played a bit with Bassbox Pro using an approximation of the volume of the box. It might work, it won't play very low (F -3dB at 48Hz) but could be fun to play with. Now this was assuming a standard vented box, so the bandpass-of-sorts factor may very well shoot my experiment to bits but it will be fun to hear how it sounds.

There really is no room for anything larger on the rear deck and the top lies pretty much directly against the box in the down position. A pair of 6.5" shallow drivers can be squeezed in, but forget 8" or 10", not even a single. Theoretically one might seal the vent in the center and replace it with vents at the front corners in order to fit a single 8" at the center of the box, but I have no time to redo the exterior.

Will post pics and results when I am done.


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## NotA911 (Aug 21, 2012)

Here's a piicture of the Morel driver mounted in the Bose box, which turned out to be much sturdier than I expected.

The basket is a little smaller in diameter than the Bose original so of course the screw holes did not align. Unfortunately there is no room to add a mounting ring so I had to use very short screws in order for them not to protrude on the other side. Had no flat head screws so I used what was available - it does not look 100% but no one is ever going to see it.


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## 94VG30DE (Nov 28, 2007)

Great. Often finding something that "kind of fits" is better than trying to "make something fit" into a Bose enclosure. Have you had time to listen to it yet?


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## NotA911 (Aug 21, 2012)

94VG30DE said:


> Great. Often finding something that "kind of fits" is better than trying to "make something fit" into a Bose enclosure. Have you had time to listen to it yet?


Haven't put it back in the car yet; have a plane to catch tonight so it'll have to wait until Sat.
I will report back how it sounds, of course. At any rate, as awful as it sounded before I cannot imagine anything other than an improvement.

I was also wrong about the available mounting height, it really is 75mm max (3") so drivers any larger than the Morel are out.

In the worst case, the whole thing will end up as midbass/midrange rear fill.  The result will also dictate what I do with the door speakers, I can put 8" subs there even, or mid range or full range drivers. So options remain. 

The door subs, as Bose calls them, are currently the only remaining stock component. Now powered by my new amp, they put out a surprising amount of bass, but it is very boomy and indistinct.


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## NotA911 (Aug 21, 2012)

Wow.

Managed to get an early flight home and I have now spent a couple of hours in the car with a big grin on my face. This seems to be one of those rare occasions when a shot in the dark hits the bull's eye.

The plastic, doomed beforehand, Bo$e box has been transformed into a real sub! I wish I had an RTA so I could measure it, but what we have here is a dual 5" equipped enclosure that is both musical and plays LOW.

No rattles, no rumbling, just dry, tight bass that is more than enough for this little car. I put on Avishai Cohen's "Gently Disturbed" and expected one-note bass reproduction, but what came out had my jaw drop.

I think what happened was I had an enclosure that Bose actually spent some time carefully tuning and adapting to the Boxster cabin, then did their usual thing and put in some really crappy low impedance drivers and connected it to their severely underpowered amp.

Then I happened to have a pair of high quality drivers lying around which by another stroke of luck happened to fit physically and acoustically. Added some dampening to the box, real amp power and voilá...

Amazing. I could have spent a thousand euros on a custom job with no guarantee of a better result than this.


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## niceguy (Mar 12, 2006)

I bet that is gratifying! I was going to say that if you really could fit 8s in the doors, I wouldn't have even worried about the Bose setup since 8s would get pretty low....As long as you're happy lol...

Jeremy


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## Fast Hot Rod (Apr 19, 2007)

Nice! Glad it all worked out for you!

Mark


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## 94VG30DE (Nov 28, 2007)

Nice, congrats. That's a great feeling isn't it. 

That mirrors my experience as well, in that the Bose enclosure is usually pretty well-suited to the vehicle, but could use some help in the raw driver department. Pick the right speaker for the box, and you have yourself a great result for very little fab work. 

Cheers!


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## NotA911 (Aug 21, 2012)

Occurred to me that the subs firing into the deck is probably creating a bass shaker effect as well. Wonder if that was the original intention. 

There is quite a punch into the seat back.


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## jhmeg2 (Nov 6, 2009)

well, i am glad it worked out for you. But I'm still upset. I was hoping to do some custom fiberglass and fit a no joke 6.5" sub in there. Although its not shallow by anymeans, the DD sw6.5 is nothing short of amazing. It only needs .33 cubic ft vented. I have one in my trailblazer, in a .456 cubic ported enclosure. WOW, if its like this in this big of a cabin, I can only imagine what it could do in a Boxster... Oh well, I'm happy it worked out.


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## NotA911 (Aug 21, 2012)

That woofer is 120 mm high so no way to fit it in the Bose enclosure without modification. 

I have not measured the vertical space between the rear deck and the roof in retracted position but essentially you would need at least an additional 45 mm of height, everything else being equal, if you wanted to increase the height of the Bose box or build a custom one. 

I am pretty sure there is not that much of a gap between the roof and the box.


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## jhmeg2 (Nov 6, 2009)

Thats just it, build custom. Keep the hight as it is, but bring the sub forward.


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## Patrick Bateman (Sep 11, 2006)

NotA911 said:


> Wow.
> 
> Managed to get an early flight home and I have now spent a couple of hours in the car with a big grin on my face. This seems to be one of those rare occasions when a shot in the dark hits the bull's eye.
> 
> ...


Wow I'm surprised that worked. *The Bose enclosure looks VERY complex.* Appears to be some type of a slot-loaded transmission line. Must have been a crazy amount of engineering that went into that.

One thing about horns and transmission lines is that the response of the box tends to swamp the response of the driver. For instance, with Bill Fitzmaurice's horns, you'll notice that changing from one driver to another only makes a difference of a dB or two. *This is because the box dictates the response shape more than the woofer that's driving it.* JLH over at Diyaudio has leveraged this with some odd designs, such as using $5 cone tweeters as midranges. (You would think that a crappy $5 cone tweeter would sound like ass, but it actually has some distinct advantages over a conventional driver IF you work within it's limitations.)

But that last comment is a big part of how the Bose designs work. I think that people look at the quality of the parts that they use, and assume that Bose is a bunch of cheapskates. But the trick is that the enclosures are very complex, and transmission lines and horns often work best with very cheap lightweight drivers. Basically when you put a driver with a heavy cone and suspension on a transmission line or horn, the high frequency output often goes away entirely. So a light cheap driver will often play higher.


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## Patrick Bateman (Sep 11, 2006)

NotA911 said:


> Occurred to me that the subs firing into the deck is probably creating a bass shaker effect as well. Wonder if that was the original intention.
> 
> There is quite a punch into the seat back.


When you slot-load a woofer it does a few things to the woofer. First, it rolls off the highs, the same way that a low-pass xover does. But the nice thing about slot loading is that it reduces distortion, while a low pass xover does not.

Second, it reduces excursion; basically the mass of air acts like a 'spring' pushing against the cone.

Third, it raises the QMS of the driver. This is a tricky one. By raising the QMS, it changes the response shape so that the F3 is lower. But you have to be careful with this, because it can also make the box sound 'boomy.' If I had to hazard a guess, this may be yet another reason why Bose drivers tend to look cheap and flimsy. Light cones = low QMS


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## NotA911 (Aug 21, 2012)

Patrick Bateman said:


> Wow I'm surprised that worked. *The Bose enclosure looks VERY complex.* Appears to be some type of a slot-loaded transmission line. Must have been a crazy amount of engineering that went into that.


Actually it is not complex at all. Looking at the pictures I thought so too but now that I have had it open I know it's not. It's just a vented box with the two drivers sharing a single chamber, with a flared rectangular (ish) port.

In the picture below (which only shows half of the box but it is symmetrical) I have marked in red the walls which enclose the single chamber. Everything outside the red line is just an outer shell and has nothing to do with the woofers. When the enclosure is closed up, the bottom/baffle is sealed to the upper section (the one in the picture); there is a rubber gasket running along the entire joint (red line).

So the only thing about it that differs from a simple vented box is the fact that it sits on the deck and the woofers fire straight down into the carpet.


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## Patrick Bateman (Sep 11, 2006)

NotA911 said:


> Actually it is not complex at all. Looking at the pictures I thought so too but now that I have had it open I know it's not. It's just a vented box with the two drivers sharing a single chamber, with a flared rectangular (ish) port.
> 
> In the picture below (which only shows half of the box but it is symmetrical) I have marked in red the walls which enclose the single chamber. Everything outside the red line is just an outer shell and has nothing to do with the woofers. When the enclosure is closed up, the bottom/baffle is sealed to the upper section (the one in the picture); there is a rubber gasket running along the entire joint (red line).
> 
> So the only thing about it that differs from a simple vented box is the fact that it sits on the deck and the woofers fire straight down into the carpet.


But both the woofers and the port fire into a slot right?
You can't really model that with a computer, you have to do it with trial and error. The volume of air in the slot changes the efficiency, frequency response, phase response, impedance curve, power handling, etc.

That's a huge change.


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## NotA911 (Aug 21, 2012)

The port fires into the cabin, not into the deck (slot). I forgot to add a couple of details in the picture; the circular tube to the left is not a port, it is also sealed off from the chamber and is used to fasten the enclosure to the deck (large plastic "screws" go through from the top of the enclosure into bayonet receptacles in the deck). 

And the space between the woofers and the deck (=the slot) is not air tight by any means. Air will escape, I'm sure, both between the edges of the box and the carpet and through a little cut out where the speaker wire passes through the outer shell of the box.










The arrows show the direction of the sound waves through the port. I also indicated the approximate placement and orientation of the woofer(s) - the bottom of the enclosure is facing up in the picture.

But I think your reasoning about trial and error is spot on. Another Boxster owner over on the renntech.org forum had the same box but with two very expensive Focal 13KS woofers in it and he was not happy at all.

I guess I was just lucky.


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## JPStine (Apr 27, 2020)

NotA911 said:


> Here's a piicture of the Morel driver mounted in the Bose box, which turned out to be much sturdier than I expected.
> 
> The basket is a little smaller in diameter than the Bose original so of course the screw holes did not align. Unfortunately there is no room to add a mounting ring so I had to use very short screws in order for them not to protrude on the other side. Had no flat head screws so I used what was available - it does not look 100% but no one is ever going to see it.


I’d like to do the same I don’t see a pic of what you did can you send a pic or give me some ideas ?


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## PerfectlyNormalPerson (Jun 10, 2021)

Since I'm not allowed to send a message despite signing up for that express purpose....

"I signed up just to message you about what you did for speakers for your boxster bose sub. Google showed me your thread when I was searching for specs on the rest of the system, but most of the pictures in it no longer work. Hopefully you're still active and get this message!"


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