I'd to like to build 2 reflex subs to sit on top of my 2 th18's. I found this build http://www.forum.poweraudio.ro/viewtopic.php?f=92&t=9643 but was wondering how i would calculate how big i need the 4 ports in that plan to be for the B&C SW115 driver?

I'd like my TH18's to run as sub bass, 60hz and below and these reflex subs between 60-125hz for more of a punch...

thanks for any help!

sal

download WinISD, a piece of software designed for creating reflex speakers. You'll be able to play with the sizes of the ports and see what changes that makes to the response, and decide what will suit yout driver best. 

K

That's designed to play sub frequencies as well, so it won't be much punchier than what you have already.

Hemispere, you got any recommendations for a cab to suit my needs?

Edit: What's your budget for woofers? B&C SW115 is 400 quid @ BlueAran.. 400 pounds will buy you a pair of very high quality 12's. A pair of BMS 12N620perhaps : http://www.bluearan.co.uk/index.php?id=BMS12N620L&browsemode=manufacturer

That's only about 10% less cone area than 1x18"

The drivers are still available too, even the 8" horn mounted speakers I believe were available the last time I checked (I was going to build these)

Edit: The mid driver is still available, but the H6000 horn flare is not.

The blue aran 8" phase plug horn & driver combo works in the same frequency band though 

was actually looking at the BMS driver and then also had a look at the Faital pro 12RS1066...http://www.bluearan.co.uk/index.php?id=FTP12RS1066AP&browsemode=manufacturer

They can do it, but we're talking about somewhere around 1250w per driver to reach 125dB @ 75Hz, 130dB at 125Hz.

BMS do a ferrite 12 with incredible excursion capacity for 147 quid,  11mm xmax by conservative calculations, probably 15mm actual. (url= http://www.bluearan.co.uk/index.php?id=BMS12S305L&browsemode=manufacturer%5d" rel="nofollow - http://www.bluearan.co.uk/index.php?id=BMS12S305L&browsemode=manufacturer] http://www.bluearan.co.uk/index.php?id=BMS12S305L&browsemode=manufacturer%5b" rel="nofollow - http://www.bluearan.co.uk/index.php?id=BMS12S305L&browsemode=manufacturer[ /url])

Two of them in a vented box of 60 litres with 3000w of amp power gets up to 131.2dB, flat to 65Hz, or in a sealed box it's more like 125.5 at 75Hz and 128dB at 125Hz.

I think sealed would sound better but you could reach 128dB in a vented arrangement with 1500w, which would be safer on the drivers and cheaper. With 3000w you would need to carefully limit the RMS and peak levels.

The Faital drivers probably aren't efficient enough. In a sealed arrangement, two of them are only 89dB/watt at 80Hz. The BMS are only 2 or 3dB more efficient, but you can see it's already a struggle to get the SPL to meet the output of the TH18.

You could vent the Faital's to enhance their low end efficiency, but it would still barely exceed the efficiency of the BMS drivers in sealed, and if you can get away with a sealed design, that would be preferable.

Reflex is easiest, BPH kick harder and louder, 15" Straight horns kick very well, but are just stupidly long

dual 15's will be simply to big for my needs. I need to compromise on size unfortunately.

EDIT: sorry just saw your faital comments :)

If we use the Faital calculation on the BMS driver, then it has not 11, but 14.33mm xmax, which for a 12" driver is insane, and for the price is a bargain imo. Yes, the weight is high, but only 4kg more than the SW115 you were looking at, and the size and weight of the enclosure itself would be at least 10kg lighter.

If you could justify the amp power to get them moving close to their excursion capacity, a pair of them in a compact vented or sealed box would kick as hard as anything imo. A Behringer iNuke 6000 would probably do it.

I'm not considering the faitals anymore...

amp power shouldn't be a prob...i'll get whatever i need to get the best performance!

he wants 12" though

Very low distortion, light carbon fibre cone, 3" voice coil. Seems like it should be fast and punchy. It says 'optimal for compact subwoofers' but I don't think that's intended as a limitation. (it is also called a 'bass midrange speaker')

The lower sensitivity makes it less suitable than the Eighteensound driver in a vented box, but in a sealed box it seems to tick all the, er.. boxes.

Edit: I guess the mms is not that low, but it has the motor strength to back it up. It's definitely not a traditional option, and there are faster drivers, but if you wanted something that hits hard like a bandpass horn or straight horn, without actually using a horn enclosure, this sort of driver in a sealed box would do well I think.

I'm not sure I understand 'no need for huge xmax'. A kick bin that moves as much air as 2x 18" subs with 6.5mm xmax would be quite enjoyable. It's not needed but it's nice.

http://www.eighteensound.com/Products/Articles/Detail/catid/4059/eid/3391/12w750" rel="nofollow - http://www.eighteensound.com/Products/Articles/Detail/catid/4059/eid/3391/12w750

Maybe I'm misunderstanding the science completely, but it seems that when you've got a stack of speakers rhythmically pumping out several litres of air into the atmosphere, even if it quickly disperses, it's going to reach some of the sensory systems of people in the audience and register as something more than just plain air pressure.

So if you can afford the enclosures and the amps necessary to reach your desired SPL output while being as inefficient as possible, that's the best route to high quality sound reproduction. That's why I find the idea of the compact 2x12 kick bin appealing, because it seems to have the capacity to move a huge amount of air (as much as 2x average 18" woofers), in a 60 litre enclosure. It just needs a huge amount of amp power to get there, but I'm increasingly unconcerned about amp power what with these ultra-efficient (and stupidly cheap) new class D amps arriving. In terms of pure energy efficiency the biggest waste these days is in oversized enclosures (building them, and hauling them around to events), and the real elephant in the room, which is the energy people are using to travel to and from music events! It always dwarfs the energy used by the event itself so the only remaining concerns are logistics (can you get enough power from the mains or the generator?) and economics (can you afford the amps and the drivers?)

When you walk enough steps back in your thinking you see that everything counts towards the efficiency of the system, including the applications of the system itself.

Let's say you host an event on an island in the middle of nowhere with 114dB/watt sound system. Is that very efficient? Of course not! It's just efficient on one very limited dimension which is trivial when looking at the bigger picture.

Or coming back down to Earth a little, if you can fit your system in the boot of someone's car and hitch a lift to the gig, and it comprises a couple of ultra-high output full range boxes that play to 130dB down to 50Hz in a 20kg box), and a lightweight class D amp that runs them both, does it matter that the box is 94dB efficient? It's still more efficient than driving a van to take a full size system if all the event actually needed was 125dB to 50Hz? Doesn't matter if that system is 105dB efficient across the full range, it's still the more wasteful option in that case.

So it definitely helps when making a decision, to consider as accurately as you can, what your most likely intended applications are going to be (and what you can reasonably expect them to be). Will you ever have call to run the system on battery power for example? Or will running into that situation where your speakers need 6,000 watts and you can only be afforded 2,000 due to some onsite logistical issues with overloaded generators or ringmains be worth having that extra bit of fidelity and enjoyable experience for the vast bulk of other times when you're set up optimally? 

If you were going to expand your system to be much larger following the same 'money no object' approach to amplifier watts, then you will be guaranteed to run into issues of venues not having the juice available to power your rig to it's full potential.

Edit: I'm not saying people living on islands in the middle of nowhere shouldn't have access to great sound or events either, but the optimally efficient thing to do in that case, even if it was a one off festival from people around the world, would be to bring a system over to be entrusted to someone who lives on the island (possibly to the landowner as part payment for using their land), and left there so that future events that came to that island wouldn't have to lug another massive PA system over by plane. 

https://drive.google.com/open?id=0B_XE8UpzG2cvTlF6a2NKLVB0a00" rel="nofollow - https://drive.google.com/open?id=0B_XE8UpzG2cvTlF6a2NKLVB0a00

https://drive.google.com/open?id=0B_XE8UpzG2cvV29DYWVlc0sxZlE" rel="nofollow - https://drive.google.com/open?id=0B_XE8UpzG2cvV29DYWVlc0sxZlE

With 1500w into the enclosure, a port like you suggested reaches 52m/s. You want it below 30m/s really. Maybe stretch to 35m/s but many would recommend lower than that.

If you wanted to drive 2000 watts into the box, then you would need a vent 30 x 10cm (or equivalent) and 16.7cm long to keep vent velocity below 34m/s.

You're only using 7.5mm of excursion at that level as well, so what Gen0me was saying about wasting money on high xmax drivers is more or less correct if you're using a vented box. You could always make the vent bigger for higher power input, but once you go beyond about 9mm or so then the vent size is probably getting impractically large for a compact box.

You could just make the vent run right underneath the V baffle, since it needs to be longer than the baffle is deep (or it could at least be adjusted so it would be that long).

I still think there's a case to be made for the sealed option on the BMS, for size, simplicity and tightness of impact (or perhaps more accurately, 'body' or weight of impact). (It's 4-5dB less SPL in parts than the vented options but you could design the crossover from the TH18 carefully so that this dip was never apparent). I'm obviously speculating a bit there, so that's the last time I'll mention it I promise :)

Edit: Sorry, I couldn't help myself. 

What I've done is normalised the output levels for a sealed box design (with the BMS 12s305) and a vented box (with the 18sound 12w750), so they're +/- 1dB between 68 and 125Hz (so a negligible difference in the real world), both in 60 litre enclosures.

The BMS takes 1500w per driver to reach this level, the 18Sound just 350w, so you have a lot more available headroom with the vented box, and honestly the sealed box will struggle to keep up with the TH18, especially when it's corner loaded. On the plus side, for the same volume level you're getting about 60% extra air displacement plus the subjectively tighter sound of a sealed arrangement (218% extra - 318% total - displacement from the front side of the cone, but none from the back side).

If you wanted to go to absolute 'pimp my rig' levels of performance, you could actually fit 4x 12s305 into one 80 litre sealed enclosure and still be +/-1dB across the specified frequency range compared to 2x 12w750 in a 60 litre vented enclosure (effectively 70+ once you factor the vent).

So, approximately the same size box, same output level with double the power input, or -3dB with the same power input. (133/130dB). No possible issues then of matching output with the TH18, and an output equivalent to 2x 18" woofers with 13mm xmax, in one relatively compact kick bin. (or 318% of the total air moved by a pair of vented 12's at normalised SPL levels - 636% of the front of the cone, 0% of the back)

Just two major downsides. Looking at an enclosure of about 50kg (but you could split it into two doubles of 28kg each and use one or two depending on the level needed for the gig - that would also offer the added benefit of adjustable stack height), and second is the cost of drivers at about 600 quid. But you should be able to get the price down below 125 each if buying 8. BlueAran have been known to give discounts to SP members ie.

Actually I've got my numbers way out here. It's much better than I suggested. You can see from the excursion graph easily enough. The 60% figure (from which the 318% and 636% were derived) only accounted for the peak excursion. If you include the average excursion across the 65-125Hz range (which we should do if we're representing music), it's  probably closer to to 120%, 636%, 1272%.

The bass end is covered by 4x 10 or 12" on a sealed v-baffle arrangement not unlike what I'm suggesting, although I recall from memory that they mount them on quite a deep baffle so as to leverage a degree of horn loading to that section. About twice as deep as the design you showed, with a sharper angle inwards, and a touch of exponential expansion as well. Can't find any pictures of what they look like under the grille to confirm unfortunately.

I don't know if he still uses this e-mail but I found the address of Speakerplans member Opus Jody in a search for details about the AT2000. If you're considering the 4x12" sealed arrangement he might be able to confirm one way or another from experience if it's viable or likely to give the sound you're looking for jody@opuspocus.co.uk

The low section in the AT2000 is geared to run all the way up to meet the low end of a community M4 though..so probably not what you're looking for in a kick bin! Depends how low they were meant to cross. All data sheets seemed to have vanished from the Intertubes.

You don't need to drive the sealed enclosures harder than the vented if you have four, they'll just be 3dB quieter if you drive 4x sealed with the same power as you would put into 2x vented, but will still shift prodigious amounts of air (as much as 4x vented 12's in 140 litres), spread across a much broader frequency band. You would only be putting 750w into each driver rather than 1500w though, so the actual difference could be closer to 1.5dB after factoring in power compression.

If you were running them at 750w per driver and that level of SPL was acceptable, you could use a lower excursion driver with a lighter/faster cone. Anything over 9mm xmax or so would do. There's probably even a neo driver out there that fits the bill at a reasonable price, light enough to have a whole 4x12" one box solution closer to 30kg.

Another option to consider if you wanted to go light and tight (but sacrificing some compactness) would be 4x Faital 12FH500 in a 120 litre sealed box. http://www.bluearan.co.uk/index.php?id=FTP12FH500AP&browsemode=manufacturer#

3.9kg per driver with 7.5mm xmax, 21.55m xlim. With 3000w, 4 of these produce 129dB at 75Hz (slightly exceeding rated xmax), about 1.5dB less output than the vented box. If you could keep under 20kg of cabinet materials that could come to around 35kg in a 55cm cubed enclosure.

The 18sound 12nw530 would be an amazing option if you can afford it. They're pretty dear at 188 quid each.

It performs very similarly to the 12FH500 except it doesn't have the same (relatively minor) excursion issue. It reaches it's limit with 3000w, again it's around the 129-132dB range for 4 with 3000w, but to be honest 750 quid on drivers for a kick-bin is getting a bit silly. I would try and get four drivers for less than 500 if possible (then it's easier to relate it to a pair of expensive drivers...but no 12" costs 375 pounds.)

Is your issue with dividing the kick section into two enclosures a practical one or aesthetic? Do you regularly encounter venues where you literally couldn't fit such a tall rig, and in those cases would it be a big problem to use just half of the kick section? If your highs are ending up too much above head height it's possible (if a bit of a hassle) to angle the top boxes a few degrees where necessary.

If you carried a 3000w amp for both sections, driving 750w into each driver, then in the times when you can't use both for whatever reason, you would still have 1500w of headroom left in the amp, so the difference in output between the half or full kick section wouldn't be too substantial....er, that would only apply with the high excursion BMS 12s305 though. Any of these other drivers mentioned are 750w per driver absolute max.

Why the dB Tech mini DVA? It's kind of a mini line-array style module. If you're stacking a TH18 + a kick bin + another enclosure, you probably just want a traditional midtop. 

Something like the Danley SM80 would be optimal. A high quality high output coaxial.

http://www.danleysound.com.au/products/loudspeakers/molded-synergy-horns/sm80" rel="nofollow - http://www.danleysound.com.au/products/loudspeakers/molded-synergy-horns/sm80

The drivers for these aren't cheap but if you can build it yourself it'll compare very favourably to commercial offerings. Coaxials are also compact on the vertical dimension, so that helps. Maybe ask your CNC guy if they can manage the fancy waveguide even (actually designing the waveguide is another matter..unless you can figure out the driver Danley is using (he generally uses off the shelf commercially available speakers) and use his design as a template.

At a guess, it uses the B&C 12CXN88 http://www.bluearan.co.uk/index.php?id=BAC12CXN88&browsemode=category" rel="nofollow - http://www.bluearan.co.uk/index.php?id=BAC12CXN88&browsemode=category

Eye-wateringly expensive but when you consider the price of a quality 12", plus compression driver and a horn to mount it to, it's a little more understandable. If Danley considers it good enough to put into his Synergy line of speakers, in what, at least on the surface appears to be nothing more than a closed box + waveguide design (there are some little 'Synergy horn' style holes in the front but they're so small I'm fairly sure they're not functional - large bolts perhaps? Or tiny tiny ports..?), then that's a serious testament to their quality.

It's not clear from the spec sheet whether the Mini DVA is 126dB for both modules or 126dB for each module, but at best it's 132dB and you can match that with the B&C coax in a comparably compact and lightweight box. The DVA is about 1,300 Euros, so you'd be saving money considerably even after factoring cost of enclosure and amps/processing for the coax.

To be honest considering the power supply is only 400w and it's using 4x 6.5" drivers, there's no way it's 132dB. They're using intentionally misleading specifications. 'unit' means the whole thing, so it's 126dB total, which for 1300 Euros is just ridiculous. You're basically paying for the exotic form factor.

I might look into making some midtops but to be honest i'll probs just buy a good pair. I've seen a mini array (much like the DVA) on top of a dual 18" sub and 1 mid bass driver and it sounded amazingly clear! I guess they are expensive for what you get but compared to other line array type cabs, they're pretty cheap.

Not saying i can't get the same clarity with a good coaxial midtop, by the way :)

I guess I'm just thinking about aesthetics really. Maybe that's not such a big deal, but if you had a 6 or 8 box system, with the TH18, kick bins and coax tops, you could give it all a coherent aesthetic. Matching paint, grilles, cabinet hardware etc. There's something satisfying about a system that looks as well as sounds coherent.

I'm also gonna go the sealed route even if it means a slightly larger cab.

I may be tempted to design a coaxial midtop but i wouldn't know where to start!

I'll upload a couple pics of my th18s

For your original design brief of a kick cab, I think you'd be hard pushed to do much better than a high quality 15" driver in a compact box. Playing 60 Hz up excursion wont be a massive problem, so you'll be able to throw quite a lot of power at it and I think 1 would keep up with 1 tapped horn not too bad. While its great to think about having cabs with 4 12" drivers and such, I think you'd be looking at massive complication and a huge heavy cab that would be less than ideal for transporting. 

However if you were looking to change your tops, you could look at Peter Morris' DIY90 from the SoundForums page. 

http://soundforums.net/forum/low-earth-orbit/diy-audio/11601-new-diy-mid-high" rel="nofollow - https://soundforums.net/forum/low-earth-orbit/diy-audio/11601-new-diy-mid-high

It has some fairly expensive drivers in it, and needs good quality processing to achieve its best, but everyone who hears it pretty much regards it as one of the best speakers they have ever heard, brand name or otherwise. 

K

not the best pic but you can roughly see the shine on it.

yeah you're right, it will be pretty big and heavy but would i get that punch as well as 4 12"s?

One 2x12 sealed can reach 129-132dB across the required range (with the BMS 12s305), and you won't readily exceed that with a smaller/lighter 15" vented box.

Although that BMS has a slightly heavier cone of 95g Mms, it's high BL of 20.14 means it's similar to other 12" drivers with 65-75Mms

Punchier/faster options, with 50-60g Mms require two double 12's to reach SPL in the 130's, but can still manage 125dB with just one double enclosure, and it sounds like that'll be enough in many cases (if the 126dB dB mini line array is considered a serious option).

It's definitely an extra hassle but surely the bottleneck of weight and mobility in this system will always be the TH18, which is like 415 litres external dimensions. We're talking about something like 100-115 litres external for each kick section with 4x12 sealed. (80 litres internal + wood/hardware + the space in front of the v-baffle, which actually adds a little to the performance which we can't readily calculate in WinISD)

My thinking is that if the kick is powerful enough, with plenty of weight to the sound around 65Hz but not too much SPL that it overpowers the TH18, it could effectively stave off the desire for another pair of TH18's, so the potential for keeping the system portable in the long run would be higher.

With a more lightweight driver (50-60g Mms, 8-9mm xmax), it's generally around 122-127 for 2x12 or 128-132 with a 4x12. (with half the amp power required of the BMS, but no more headroom available)

That's across the 70-125Hz range with a rising response, 20 litres sealed enclosure per driver. You can get an extra dB gain in the low end of the range with 30 litres per driver.

A good idea of how this possible would be to look at the pic Kyle posted of the inside of the Danley cabs on the "how do Danley speakers work" thread. They have a 4 way angled baffle, which in that case obviously makes the walls of the Synergy horn, but the way it goes together may trigger some ideas on how you could do your own design. 

K

It's worth considering that for the 65-125Hz frequency range, the 12" drivers really don't need to be facing anything like straight forwards. The resulting look of a design that works might not look like it will work well at all, so if you can only see one way that they could physically fit within your size requirements, and it doesn't look like it'll work, try it anyway. Hopefully someone can tell just from looking at it.

There are a few other unusual loading types for lots of drivers in a small space like push/pull designs, but don't know how they work exactly or if they would be appropriate.

Looking at the height of your subs, and considering a midtop could easily be designed to be between 35 and 55cm, even if your kick section was 65cm you'd be looking at somewhere between 200 and 225cm overall stack height, depending on whether the kick is in two sections and how tall your midtop is, which is typical, if not optimal, for a system like this. If it's at the high end of that number and the kicks were in two sections you could adjust the height to 190cm for low ceilings, cosy/intimate gigs, or gigs where the system is going to be raised on a stage already, and you could definitely design the midtops to be pole-mountable so there wouldn't be any situations you couldn't work with.

A close commercial equivalent of what you're trying to achieve is the HK Audio Linear 5 system. 'big venue pack'.  http://hkaudio.com/products.php?id=400" rel="nofollow - http://hkaudio.com/products.php?id=400

That's 233cm tall. Their smaller 'rock pack' is 201cm. That's fairly typical. If anything the 'rock pack' is a little shorter than a typical compact ground stack.

Another benefit of designing your own midtops is you could give them that unusual 57.5cm wide form to match the rest of the stack. A set up with the TH18 and then 3 matched dimension boxes, all 57.5 x 34cm from the front (with the midtop box being not quite so deep), could look very neat. You'd get a good visual balance of two sections 'the bass', and 'the rest', each approximately 1 metre tall.

Something like this ie: 

And in 'short stack' mode:

they'd look pretty cool though!

to be honest, not even sure there's enough clearance for the drivers....i think they'll just about fit 

Space in front of the baffle doesn't count towards the enclosure size..but as mentioned it will have some impacts on the sound reproduction which are harder to predict. But will probably be positive in terms of the character of the sound and perceived impact delivered by the box. Appearances are important too and can have a slight placebo effect. It looks loud and punchy.

I actually like the look of the 1 box so i'd prefer to keep it as 1 and just extend the height to 60cm and see what the volume ends up being.

You can also stuff the enclosure with fibre fill to increase the apparent volume of the box. When you factor that in, you can probably get away with 57.5 height which would give you a good neat square.

The mouth of the TH18 is approximately square shaped right? So that would be a good balance. (if it isn't exactly square shape, perhaps work out what ratio it actually is and copy that for the kick bin)

We're talking very, very negligible differences in output though (the difference between 80 and 120 litres is only 1dB). A lot of the practicality of the box rests on the weight of the wood. 4x12" could be 14kg, so watch the volume of wood. Assuming a rule of thumb 1g per CC (I think it's something like that for ply?) a single 60x60x1.8cm panel alone is 6.5kg. 5 of them plus baffle and bracing that's 6 is 53kg with the drivers. If you use well braced 15mm ply and 55cm panels it's 41kg

So think about the fibre stuffing, and consider that even if it's 30 litres undersize it'll only be about 1dB less efficient, and the stuffing will smooth the response. 40kg is viable then. (not suggesting 30 litres undersize is okay though, as mentioned 80 is really low for 4 12's already, but it wouldn't be a disaster if it was 70 or so)

In terms of pure sound quality you'll still be better doing it in halves though. Having 30-35kg or so per half to play with would open up many options. Cheaper/higher quality ferrite drivers, 18mm plywood, better bracing, etc. You really don't want to skimp on the box quality if you can help it. 4 12's running flat out in one box is a lot to handle. Then again you would lose the possible benefits of the exotic angled baffle.

Edit: When you say you cut the baffles, do you mean you moved it forwards? It looks like you could move it quite a lot forwards, if you could find a practical way to square off the front of the box.

It doesn't need to be so wide open.

You can also mount the drivers with their magnets facing outwards, and that will work absolutely fine (and if you can find drivers with well designed magnet structures, potentially look amazing). If you modelled them facing inwards then you'll gain about 8-12 litres from doing that.

Something you might want to consider is designing the box so that it can be ported, perhaps even so you could switch it between ported and sealed with a single adaptor mounted to the middle panel. There's always a possibility you would prefer the ported sound, and even if you prefer sealed it would mean if you ever did expand your bass section, you wouldn't need to build new kick bins, you could just open up the port and they would keep up with 2x TH18.

so basically i've positioned the diamond shaped plate further forward thus cutting the baffles from the rear...that gave me more volume to play with.

now i've always wondered whether theres a difference in performance with front vs rear mounted drivers?

cos if i can mount them outwards, that'll save some hassle of making sure they can actually fit inside.

i was thinking about that last night...to make the diamond shaped panel a port panel! I'll need to measure it carefully though as for now it's just a plate.

where can i buy port covers/caps to close them off? do they exist?

Not that I know of. I was thinking a DIY job. A piece of ply with the port built into it, which you mount onto a larger cut-out hole like you would with a speaker driver. It might be a trick to do it optimally but it should be possible.

You could even design it so that the port extended outwards in front of the baffle. With the port, drivers and grilles all sitting in that empty space there would be a lot less waste overall.

Ported is absolute overkill for 4x12 with 1x18" TH though, so it's an unnecessary design risk and you could probably modify the box later on if you ever really needed it.

anyway, i'm not too bothered about weight as my th18s are 100kgs each but size is a little more of a priority although it looks like i'll be compromising on that as well!

I'll defo still to the 1 box 4 drivers idea as i really like the look and i'm sure it'll kick some butt!

I'm gonna forget the ports for now.

unfortunately front mounting might not fit so i'm gonna have to stick with rear mounting and stuff some fibre to compensate on the smaller volume.

just added some drivers for graphical purposes.

It's worth rendering the woofers with some degree of accuracy (approximate dimensional accuracy at least) and actually seeing for sure. My instinct says they will fit fine. 

Tom Danley always renders his components in intricate detail, as you can see from his promotional materials. That's one of the main tricks to fitting lots of drivers in a small space.

The other midtop that was recommended in this thread (I forget the name.. by Peter somebody, with the dual 12" horn loaded low end), even makes sure the bass drivers are rotated to exactly the right angle that the compression driver fits in the gaps between the chassis supports, to within a cm or two of clearance.

Edit: If you're confident enough in the quality of your CNC guy's work to make the shapes you've rendered so far, I think there is a possibility to move the baffle even further forwards, by cutting the space in front of the cutouts like you did the space behind, and squaring off the end, perhaps recessed by a couple of cm from the front so each flat corner works as a mounting point for the grille.

But the kick, must also be used as a simple stand-alone sub from 45/50 Hz up.

The idea of Hemisphere was exactly what I had in mind. My idea was first one (later two)15" kick/sub, probably light cone driver. And a BMS coax on top.

For now I have two front loaded 12/1.4 mid highs, so combining those with a small 15" would be really flexible.