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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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Discussion Starter · #22 ·
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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Thats just it, build custom. Keep the hight as it is, but bring the sub forward.
 

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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.
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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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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Discussion Starter · #26 ·

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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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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Discussion Starter · #28 · (Edited)
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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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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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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I'm not looking for a system that makes the dishes rattle in the houses as I drive by. Just want something that is musical and accurate (not Bose). I'm wondering now if I can keep the stock enclosure and upgrade the subs and amp. (I like the idea of the stock look, and the reduced weight) However, the only 5.25" subs I can find are $500 each (Morel/Focal). Not out of the question if I know for sure that they will sound like $1,000 worth of subs. I'm guessing I'm not in uncharted waters here. Does anyone have any advice?
 
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