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Discussion Starter #1
Hello guys. I wanted to run some questions by a knowledgeable crowd concerning subwoofer selection for my BMW 540i. My previous vehicle had a bit of a problem with a water leak after a minor rear-end accident was not completely repaired properly. That destroyed my last sub amp which was an MMATS, and subwoofer. My front stage amp was left intact because it was above the water-line. In the process of building a system for my new car I decided to go with a four channel amp to allow me to bi-amp and properly time-align the front stage, given that kick panel midbase location is not really practical in this vehicle as it was in my old one and it is important to be able to independently align woofer and tweeter delay values. I will now use my old front stage amp to run a sub.

So, here's the deal. The system design goals are strictly sq, and I am not ok with sacrificing much trunk space because I know good sound can be achieved without the sacrifice. The amp in question is an old school US Amps TU-600 tube hybrid 2 channel, which presents a unique difficulty in that it is not bridgeable, therefore I need either a dual voice coil driver, or two of them. To cut off any questions about why I would use an inefficient tube amp to power a sub, the answer is simple. I have never seen an amp with more iron-fisted control over a reactive load in my life. The thing flat out anhillated the McIntosh MC-404 that it replaced, in the same system, despite giving up over a hundred watts in power. I originally made the switch due to concerns that the MAC would overheat in the tight space it was allocated, due to it's monstrous size limiting my options for mounting, and was stunned when instead of giving away something, I was gaining a LOT. Transient response is amazing with this amp. So, I found a used example of the 4 channel version, the TU-4360, to take over the front stage and allow me the flexibility I need.

Because I am not willing to sacrifice much trunk space, and especially usability, things like a JL W7 are out. It's simply too deep, means any box needs to be almost square which makes them difficult to work around when trying to put anything in the trunk, a straight ski-pass mounting would eat half the trunk, even if the box is only a cubic foot internally. The fact that they are single voice coil and I would need two of them also makes their cost a little off-putting.

So, what what would you guys recommend, does anyone have a setup they really like that would fit this bill? Any input on what is the best pure sq DVC sub out there that doesn't require a foot of rear clearance? or does anyone have a suggestion for dual 8s or 10s that would be easy to tuck away in a corner of the trunk or under the shelf? Bottom line is this system needs to be clean, and it can't make it impossible to fit a big cooler in my trunk.

Thanks for any help you guys can offer.
 

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BMWs are notorious for trapping bass in the trunk, id hang some subs from the rear shelf.

probably several of these

http://www.hybrid-audio.com/Imagine I6SW.pdf

PWK Designs

(An interesting side-note to this setup is that it’s also a replacement for a pair of 18″ drivers, and with noticeably better results.)
 

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I would probably avoid hanging a plexi bandpass enclosure with 4 6.5" woofers from my rear deck, especially in a box clearly intended to fire the port through the ski-pass... The BMW's that are "known for trapping bass in the trunk" is due to the rear "fire-wall", basically the entire area behind the back seat is metal, unless you have a ski pass. Its not like the older Merc's with the gas tank between the trunk and the seats.

What generation 5 series?

Do you have a ski-pass?

Are you willing to cut metal?

How much space are you willing to give up, and in what area of the trunk?

Considered IB?
 

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Discussion Starter #4
Thanks for the reponses so far guys. I don't think I would really consider any bandpass enclosure of any kind, I don't like their sound generally, and the same goes for 6.5 inch subs. It may be able to play down to the frequency required, but they simply don't displace enough air without massive excursion, and massive excursion always colors the sound. As the old saying goes, there really is no replacement for displacement. I think ideally a single 12 would be a good solution if it'll fit. A really good 10 or a pair of 8s might also be a solution.

To answer some questions, no it does not have a pass through, but I am willing at able to cut one. Hadn't really considered IB, but if there is a viable high fidelity solution out there I would certainly consider it. I would prefer to keep enclosure near the front of the trunk, up against the backseat. If it were to hang of the rear deck it would need to be very thin. Otherwise tall items like a cooler will not fit.
 

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I would probably avoid hanging a plexi bandpass enclosure with 4 6.5" woofers from my rear deck, especially in a box clearly intended to fire the port through the ski-pass... The BMW's that are "known for trapping bass in the trunk" is due to the rear "fire-wall", basically the entire area behind the back seat is metal, unless you have a ski pass. Its not like the older Merc's with the gas tank between the trunk and the seats.

What generation 5 series?

Do you have a ski-pass?

Are you willing to cut metal?

How much space are you willing to give up, and in what area of the trunk?

Considered IB?
My e36 has split folding rear seats and used to trap all the bass in the trunk even with the rear speakers removed. So even if you dont have the metal you are still screwed because of how tightly sealed the trunk is.

Turns out though there was already four 3x3" holes in the metal of the rear deck so I just perforated the rear deck trim and upholstered over the holes to hide them. Much better now.
 

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Discussion Starter #7
OK, while thinking about this, a strange thought crossed my mind.

Essentially I am dealing with dual mono amplifiers for all intents and purposes, they just happen to live in the same chassis. The two channels cannot be bridged. The crazy thought that crossed my mind is "what happens if you just wire both channels up to one voice coil?" Physically it's pretty much the same as using a dvc woofer, but electrically I am not sure what would happen. Effectively the two amps would be seeing the other's output through the common connection, but I have no idea what that would do.

Anybody have any ideas?
 

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OK, while thinking about this, a strange thought crossed my mind.

Essentially I am dealing with dual mono amplifiers for all intents and purposes, they just happen to live in the same chassis. The two channels cannot be bridged. The crazy thought that crossed my mind is "what happens if you just wire both channels up to one voice coil?" Physically it's pretty much the same as using a dvc woofer, but electrically I am not sure what would happen. Effectively the two amps would be seeing the other's output through the common connection, but I have no idea what that would do.

Anybody have any ideas?
It will work just fine unless there is a difference in the bass output between the channels, then one channel you get half the power. Of course most all bass is mono in the recordings anyway. IIRC that is one reason DVC came to be is to mono 2ch amps. There is a way to sum the channels but its really not needed I've run subs that way with no problems, otherwise use two subs the load you need for it.

A single 12 DVC should work well IB long as that is enough output for you. You get a little less output IB so always a good idea to increase cone area or number of subs. You can subsonic and get more output at cost of bottom end reach if you have to. You need to get the right sub however, if you don't you need some EQ power to make it work most box subs don't have a pretty response IB. An AE 15IB would work nicely for you they have 12s too. They are fairly HD but you don't need a huge motor sub for IB. While those tend to have massive xmax and so are very capable and can have a lot of output, the response is typically ugly without significant EQ. So you have to choose what you want, the QTS will show that right away, the FS should give you an idea how low it will go.

While the 15s are ideal because they are more capable to 20Hz, you can run a pair of 12/10s instead. The smaller drivers will have a harder time digging as deep but similar cone area should roughly give similar output. A single 12 is not going to shake the car but really depends on what you want, larger cone also keeps xmax down that is why I run pair of 15s IB. When they start to move much I am louder than what I call SQ use. They will shake the roof if I want and they are only pyles <$50 each. Even cheap subs can sound good at low xmax.

I'm not telling you to go IB. It will lose a little output compared to box, it will reach lower, it depends on what sound you want out of your subs. To me a solid 30Hz is SQ mine roll off around 25Hz or so it seems being that low it is hard to tell. There is output at 20. Response is quite flat I use little EQ on them. But I wanted to get low that is only reason I need pair of 15s. Into the rear seat it didn't really matter what I used far as room taken, I hung carpet down over them so I can still shove stuff into them if I really need the room and they are not seen that way.
 

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Discussion Starter #9
Ok, I think I have a solution figured out. I found out that Image Dynamics website is innacurate, because it does not show some of the products that they make. They actually have an IDQ series with dual voicecoils. This is a well know high quality woofer, often used as a reference woofer when testing components etc by magazines, but their site does not list DVC which I was sure they did have. They do have them in DVC, and they even have it with dual 2 ohm voicecoils which effectively will allow me to run the TU-600 as if it were bridged and optimise the power. :)

It has only a 5.4 inch mounting depth, and needs only about 1 cubic foot. This will allow me to mount it coupled to the ski-passthrough, and leave room to either side for the amplifiers to be flush mounted. Effectively I will not lose much more space than the slope to the back seats at the back of the trunk. :) This is what I was looking for.
 

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Do you have a firewall in the back? There was an option for folding seats with no firewall, but you also might have non folding seats + firewall like I did. I had a single 15" in IB firing through I cutout I made. The hole was not too big either.
 

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Discussion Starter #11
It has the firewall, and I will have to cut a hole. That's a not a problem though, I will just make it the same shape as the pass-through hole. I will design the box with a raised lip around the front, effectively recessing the faceplate of the box enough that the woofer will not contact anything, and I will seal that raised edge to the back of the firewall so that all of the pressure from the woofer enters the passenger compartment. the backplate of the woofer enclosure will double as an amp-rack, with cutouts to display the two amps. I might want to think about mounting some fans in there and venting it, considering the hot-blooded nature of the amps in question. Will tackle that when I get there.
 

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I had good luck with single 15" in IB as I mentioned. I used yoga mats between my baffle and firewall.

I made cut outs in kick panels to house 7" Peerless, had pictures somewhere, but I didn't get to finish it all - sold the car. It would be ideal location for a 3 way like I was planning to do. LMK if you want to see, I'll dig for you.
 

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One more vote for a pair of 15s IB FWIW. Amazing SQ, super power efficient, goes as low as you want it to with a minimum of power, full use of trunk, and tight punchy bass along with deep bass.
 

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It has the firewall, and I will have to cut a hole. That's a not a problem though, I will just make it the same shape as the pass-through hole. I will design the box with a raised lip around the front, effectively recessing the faceplate of the box enough that the woofer will not contact anything, and I will seal that raised edge to the back of the firewall so that all of the pressure from the woofer enters the passenger compartment.
if you were looking at a cross section of your trunk from the side it would look like this?



where the black line is the trunk/rear firewall
brown in the box sealed to the inside of the trunk
and red is the sub?

wouldn't this setup act like a bandpass box? with the skipass acting like a large [extremely short] port?
 

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Discussion Starter #15
You have the essential design correct my friend.

A port is essentially a tuned damping element, with the tuning frequency determined by the diameter and length of the opening. The size of the port in question would yield a tuning frequency somewhere in the vicinity of 1000 Hz or higher, which is well outside the operational range of the system. Any effect it would have would be due to harmonics, which would be negligible. Field interaction due to the car's interior shape and volume would have more of an effect than this "port" by far, so for all intents and purposes, this will behave as a sealed box.
 
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