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Cubo Sub / Cubo 21

The largest cabinet from the Cubo series stands upon the edge of portabilty; To big to be compact, to compact to be big.

Like it's predecessors Cubo 12, Cubo 15 and Cubo 18 it's a stand-alone bass bin. It will equal or out run an 18" reflex cabinet from 30 Hz and up in terms of sensitivty*. Like all Cubo-designs it excels on the KISS-principle, with a single angled cut and a cut list from 1 and a 1/2 sheets of 244 x 122 cm / 8' x 4'.

Development

Based on Cubo 15 and Cubo 18, Cubo Sub is the 3rd prototype in a series of cabinets aiming at good reproduction down to 30 Hz. Mount the driver with the magnet in the horn for best low frequency reproduction from 30 Hz up to 100 Hz. With the magnet in the chamber for maximum output from 35 Hz up to 110 Hz.

Versions

Cubo Sub is optimized for single 15"/ 18" drivers**, and single 21" drivers, nicknamed Cubo 21. 

All 21" drivers will fit in the standard Cubo Sub but in that case care must be taken when pre-drilling the bolt pattern. Plans for Cubo 21 are available through e-mail (questionsaboutcubo at gmail dot com).

*        Measurement against BR18a tuned to 37 Hz

**      Due to reproducing sub frequencies 18" drivers with an Xmax of 7 mm or more are favoured. On average a 15" needs 1.5 times the excursion capabilities to produce the same output as an 18" driver or 2 times that of a 21" driver.

Acknowledgements

The designer likes to thank Xoc1 for his aid in the development process.

 

 

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Preliminary measurements can be found here: http://www.freespeakerplans.com/index.php?option=com_jfusion&Itemid=64&jfile=viewtopic.php&p=11555#p11555



space141's Avatar
space141 replied the topic: #24353 3 months 2 weeks ago
Hello Cubo,

There seems to be very little discussion on this thread about the 21" version of this design - mostly people asking about 18" drivers and construction.

Perhaps I am one of the few to have made one, so this New Year (just passed) we decided to put two of them through their paces. They seemed to be doing pretty well for a good few hours and then....panic...everyone's coming up to me like....there's no bass....oh dear!

Had a look at the drivers after the event - burnt voice coil...no surprise. Admittedly we were using 21" drivers from Bishopsound which rather suspiciously were missing a few key parameters i.e. voice coil size etc. and you had warned us in a previous post that it might be a little risky putting a bridged CA12 amp (2800W into 4Ohm) to power this 2000W driver. Anyhow, we live and learn eh...!

So, got a couple of questions for ya:

i.) Do you think the fact that we built handle boxes into the chamber (see image, green & purple) might have meant that the reduced volume of the chamber was providing too much resistance to the movement of the cone (this resistance is necessary right - to ensure that the cone doesn't suffer from over-excursion..but it needs to be a cone (and voice coil) that can handle this right..?)

ii.) The fact that the handles are placed in slightly different positions within the chamber meant that the two drivers were slightly out of phase and therefore not vibrating in unison i.e. slightly working against each other (I imagine your answer to this will probably be "it's negligible")

iii.) Considering the considerable expense of purchasing new (half decent) drivers, might it be worth considering making another baffle which could accomodate an 18" driver & screwing it onto the existing baffle? Would this cabinet still perform well in that case or would it not be able to move enough air for such a large enclosure...

iii.) Finally - I had been in touch a while ago about building an extension to our two cubo subs - problem is when you put them both together mouth-to-mouth, the horn section suddenly expands due to the heavy bracing on the bottom panel - I am aware that any sudden expansion in the horn should be avoided. Do yo think that making a triangular brace (see image, orange) might help to alleviate this problem...would it make any difference?

Many thanks for your advice in advance - know that is a lot of questions and you are a busy man.

We are quite keen to keep using these cabinets rather than make something like a Super Bass Horn (Startec) just a question of finding what works best.

P.S. if we were going to load them with 18" drivers we would look at the Fane Colossus 18XB or replacement 21" drivers, the RCF LF21X451.

Cheers.

CZoch's Avatar
CZoch replied the topic: #24352 4 months 7 hours ago
Thank you, then I'll give it a try :)
Cubo15's Avatar
Cubo15 replied the topic: #24344 4 months 4 days ago
The RCF LF18N405 is a pretty all round driver, T/S-parameter wise but it's definitely designed for use in sub bass enclosures, excursion wise. In that last regard, it makes most sense to put it in something like Cubo Sub, so that it can utilize it's excursion capabilities by focusing on the bottom octave of music. It's not to efficient so I expect it to be pretty flat in it's working range.

Cubo
CZoch's Avatar
CZoch replied the topic: #24339 4 months 1 week ago
Dear Cubo Sub friends,

has anyone an idea of how good or bad the new RCF LF18N405 reproduce low & flat frequency response in Cubo Sub?


Best regards, Christian :)
Cubo15's Avatar
Cubo15 replied the topic: #24290 9 months 4 weeks ago
Cubo 18 will typically have a bit more output between 50 - 80 Hz than Cubo Sub, likewise Cubo Sub will have more output below 50 Hz.
The 18TBW100 and the LF18X401 are similar drivers, from different brands.
The RCF is a bit more towards the Sigma Pro (Qes/ Vas wise) so that
would be my first choice. If you're able to feed each driver, twice what
you're giving a single Sigma Pro, you should get close to similar
output. Some of the best drivers out there are simply a single step up from here, drivers like the B&C 18DS115 and 18SW115
for example.

Best regards Cubo
Tetris's Avatar
Tetris replied the topic: #24289 10 months 2 days ago
2 years, a wedding and a new flat later, and I'm finally ready to replace my 3 cubo 18's with 2 Cubo Subs! My question really is driver choice... I'd previously asked about the RCF LF18X401 which seemed like a good choice, but what I'm curious about is what are some of the 'best' driver options, for maximum SPL and lowest Hz. I've seen the B & C 18TBW100 has been recommended, I play mostly Dub/Dubstep and hoping I can replace my 3 Cubo 18's (eminence Sigma Pro 2 loaded) with 2 Cubo subs that will outperform them in Hz, and at least equal them in 'volume'.
Thanks as always for your time!
space141's Avatar
space141 replied the topic: #24203 1 year 3 months ago
And a few pics of our first build and our (very basic) system in the early days:

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Loaded with PD ET211S (750W RMS, 4ohm - no other specs available as PD seemed to have incinerated any of the specs for speakers that were manufactured prior to when the company changed hands several years ago.)

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space141's Avatar
space141 replied the topic: #24202 1 year 3 months ago
Hello again & thanks for your in-depth reply.

I hear what you are saying about the Bishopsounds driver - I might call them later to see if I can get these figures. What sort of figures should I be looking for in a decent quality driver?

We have had the magnets in the horn for a fair while now and have tried the drivers the other way around a while back but might go back to that configuration now that we have two of them. Only thing I was thinking might also be a possibility is that these cones are just a little tired (not as rigid as they once were) and struggle to obtain the output that they would have been capable of when new - I have occasionally heard the drivers pop (I assume this is when the voice coil jumps out of the magnet gap...?) at levels which don't seem that loud.

Is there more compression acting on the cone when pumping air into the chamber than if it were with the magnet inside...

So, I have drawn up another sketch of what it might look like with two 21" cubos with 1m horn extensions when put together (They will definitely need more bracing but again, this is just a sketch.)

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Cubo15's Avatar
Cubo15 replied the topic: #24198 1 year 3 months ago
To get the maximum out of your current drivers, your best bet would be to get the T/S-parameters for the ET211S drivers and/or get the biggest horn cabinet you can find for them. To get the T/S-parameters you could perhaps measure them?

As for Cubo Sub, have you tried the ET211S with the magnet in the chamber (so front of the cone visible)? There's quite a difference to be noted between mounting the magnet inside the chamber and inside the horn, both in how it sounds and output-wise.

As for putting the cabinets with the mouths together, in theory you could leave the divider out entirely. Originally the panel is so thick, because it's the primary panel the driver pushes against. Personally I would leave them as is, you could even use them to bold the extension to it, using t-nuts or threaded inserts.
As for the extension itself, I would keep the same angle as the baffle or larger. If the extension is 77 cm deep, you could have the horn expand at such a rate that the mouth is the entire front area.

Bisshopsounds gets most of it's gear from China, so even if it does look alike, it's no guaranty whatsoever that it is alike.Three key factors in it specs that I miss are:
- Voice coil size
- Gap depth
- Winding depth

Looking at the magnet size, I don't think we're dealing with a 6" voice coil here but rather a 4". So if it doesn't even look the same and has a VC that's 1.5 times smaller, I doubt it is the same. Regardless, it could be a quality unit or it might not be, that's impossible to tell at this point but I would be very hesitant to put a bridged CA12 at a 4 Ohm BWN21.

If you're going to use an other 21" driver, even though the T/S-parameters of the ET211S aren't known at this point, it's safe to assume that to get substantial more output, you're going to need that extra bit of power. So that would amount to a single CA12 per driver. Most of these high power 21" drivers will likely be with a rather heavy cone and generally are not used for the frequency range that attributes to a fast response, typically crossing over between 60 - 80 Hz.

Alternatively, mounting the driver with the magnet inside the chamber and/ or using an extension will also achieve this. You could even do it all.

Best regards Cubo
space141's Avatar
space141 replied the topic: #24195 1 year 3 months ago
Also,

One other thing before I forget. I am aware that the best way to stack them would be to have the two horn mouths next to each other (as hopefully shown in the below image)

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However, this then creates a divide in the middle which is 108mm wide... We were considering making horn extensions for the two cubos (as shown in Tempest's post) but how would we integreate this around such a large divide...? (Hopefully it's not really an issue considering the size of the wavelengths that we are dealing with here...)

Would it be worth considering removing some of this material so it would only be two panels of 18mm instead of 6 at the throat exit which it is currently...

Horn Extension:

i.) Continuing the mouth of the horn out directly in a straight line

ii.) or having two more angles (allowing it to be slightly shorter) like a Martin Audio WSX bin...

Thanks again.
space141's Avatar
space141 replied the topic: #24194 1 year 3 months ago
Hello Cubo,

Interestingly I can find very little info on this page with regards to building the 21" version of this sub which is what the plans are for on this page (mostly it's 18" & 15".)

Anyhow, I am very pleased to inform you that we have now just finished building the second of two of these monsters and are quite pleased with the results but think that they could be improved somewhat.

We are using two identical (vintage) Precision Devices drivers (ET211S) which are rated 750W RMS, 1500W peak - I have tried getting the T/S parameters for these but PD have changed hands since these were made and they can't help me out in that regard. My feeling is that these are more suited to Scoops and don't seem to be suited for this sort of combo chamber/ horn enclosure - the magnet is huge and the cone is probably quite heavy in comparison to most drivers these days with a relatively slow response....?

Anyhow, maybe this is also an issue to do with our compressors limiters as we were kind of expecting a bit more db before the cone starts popping...

So we were maybe thinking about looking to replace them with some more modern drivers - haven't come across any recommendations so far on this thread for 21" drivers...

Have been scouring ebay for ions and have someone who is offering some RCF LF21X451 for around £300 a pop but they are based down in Yorkshire (We are up in Glasgow) and think they have now been sold.

I have just come across this new listing on ebay for a 21" driver which links to a reputable retailer called bishopsound. Their driver looks almost identical to the B&C 21SW152 but at a fraction on the cost...currently on sale for £199....!!!

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This is the jargon from the ebay listing:

"I have made and sold over 1000 of these drivers on my website Amazon and eBay and to date, only 2 have needed a re-cone. I keep my quality high and my prices low because I remove all unnecessary overheads. Read all about Bishopsound on my website and visit uk.trustpilot.com/review/bishopsound.com to read what my customers say."

bishopsound.com/shop/21-replacement-neod...oofer-4%CF%89-bwn21/

What do you reckon...?

Sorry this is turning out to be a rather long post... We were looking to drive these with a CREST CA12 AMP which is 1200W into 4Ω Stereo or 2800W into 4Ω Bridged Mono Power.

Would we need one amp per driver if they are rated at 2000W RMS - surely we don't need to crank it that much but then maybe 1200W isn't quite enough...?

Many many thanks for all the help,

Will post up some of the pics from our build soon,

Thomas (TLC Sound-System)
Cubo15's Avatar
Cubo15 replied the topic: #24103 1 year 7 months ago
I would prefer a single stack, one or two cabinets high in the middle, against a solid wall most of the times. However multiple stacks divided over the corners can sometimes also do the trick. Most important is to experiment with placement, sometimes one or two meter to the right or left can do wonders.

Cubo 15 was designed as an all round bass cabinet and in my opinion it's just that for 90% of music out there. I prefer to get the kick from the tops or separate kicks. If you truly need sub there's no substitute for Cubo Sub. Cubo 18 is basically a Cubo 15 on steroids but Cubo Sub is a different animal.

The Fane 18XS will work in both but as per design it was aimed at Cubo Sub.

Best regards

Cubo
NicolaiGrymer's Avatar
NicolaiGrymer replied the topic: #24101 1 year 7 months ago
Hi Cubo.

If using cubos as singles indoor and stacks of 2 per side outside (Maybe just one big stack). And using cornor or wall-loading indoor, what do you reckon I'll get the best result from? A cubo18 or Cubo Sub loaded with a Fane 18XS. People that I've heard talk about the Cubo15 say that their main problem is they don't go high enough to be a kick, nor low enough to be a sub, so I reckoned that building the biggest cab with an 18" would give me a lot more low, thus putting it in the sub category.

What do you think?
Maikolmks's Avatar
Maikolmks replied the topic: #24089 1 year 8 months ago
Thank you very much Mr CUBO, very kind
Cubo15's Avatar
Cubo15 replied the topic: #24088 1 year 8 months ago
Well, in that case I would go for option C.



Option B will also work but if, for whatever reason one driver will stop working, (damage, overpowered, etc.) the output of other driver will be partially absorbed by the one that stopped working. Meaning it might quickly follow the firsts fate.

Having a panel in-between, ensures enough separation between the drivers/ cabinets, so that the single left driver will keep it's full output and health. It also serves as a brace for the horn mouth.

Option A will work just as well but option C, will work good enough,plus it has a cut sheet :woohoo:
(e-mail at questionsaboutcubo at gmail dot com)

Best regards Cubo
Maikolmks's Avatar
Maikolmks replied the topic: #24085 1 year 8 months ago
I have no problem with the size and carrying of the box. I would like to build that in figure B without compromising the sound
Tempest's Avatar
Tempest replied the topic: #24084 1 year 8 months ago
I'd personally go for two seperate cubo's, this gives you a lot more flexibility and a sturdier box. I've built both and the double one if often left behind since the singles are a lot easier to handle (one man lift).
Maikolmks's Avatar
Maikolmks replied the topic: #24083 1 year 8 months ago
Hello Mr. CUBO, thanks for the reply. I follow your advice and build Cubo18 Extended. If I have to build a Cubo218 version, do better A or B?
Cubo15's Avatar
Cubo15 replied the topic: #24081 1 year 8 months ago
Hi Maikol,

The 18W1300 was designed as bass driver so it will work in Cubo Sub but it will work best in Cubo 18 Extended. Cubo Sub will go the lowest, Cubo 18 Extended will go the loudest.

My guess is that it will work best at moderate power (500 - 1000 W amplifier) with a 24 dB/octave (or even 48 dB/octave) high pass at 30 Hz in Cubo Sub because it has a very light moving mass (only 129 gram). It is also very efficient (at 3.9%) meaning it will, by design work better as frequency rises.

Best regards Cubo
Maikolmks's Avatar
Maikolmks replied the topic: #24076 1 year 8 months ago
Hi Mr. Cube, i write from Italy. Sorry for my English but I use a translator. I have eight Eighteensound 18W1300 available and would like to build eight of CuboSub but I do not know if this driver works well in there. My Eighteensound seems to have the specifications to work in Cube18 (Footnotes: 18 "drivers preferably with an EBP of 100 or higher, Fs (22-42 Hz), Qts (0.25-0.58), Vas (200-450L). (Eighteensound 18w1300: Ebp 100, Fs 35, Qts 0.33, Vas 336 lt) So can it work in Cubosub too?
Cubo15's Avatar
Cubo15 replied the topic: #24038 1 year 9 months ago
@Lawbadman: Well, I can advise you some drivers for Cubo Sub but the scenario you describe doesn't exactly sound like needing 30 Hz performance at all. Especially for live music and 90% of DJ's I would stop at 40 Hz. There's also some types of hiphop (like lil wayne) and edm (especially trap) that I wouldn't play at home unless I've got 30 Hz performance. That's why I asked for some songs ;)

Cubo 18 Extended; B&C 18PZB100, B&C 18RBX100. Celestion FTR18-4080FD,
B&C 18TBX100

Cubo Sub; B&C 18RBX10, B&C 18TBX100

@Orikei: This also depends on your tops but generally, with the magnet visible doesn't need reversed wiring, however trying them both is quick and easily done. Not sure what you mean with the 25 mm bit but it sounds small enough, not to matter in the overall scheme of things.

@Capicva: I'm sure to use those pics at some point ;)

Best regards Cubo
Orikei's Avatar
Orikei replied the topic: #24036 1 year 9 months ago
Hmm, not sure where ky 165 has come from then xD hopefully the added 10mm doesnt give any noticable effect

The barky box was fine before in tapped horn config, said builder did use ALOT of bog, many short cuts on braces and mighty MDF - i've put it down to that - no one else has had the issue like you say

Using 12 guage from the driver to a speakon seemed the easiest idea - DIY x-overs are shady at best :p
I will also be running a parralel out by bridging the +/- of the in speakon to the +/- of the out

Do i need to be aware of any reverse wiring? I.e negative wire to positive terminal? This was also information aquired from the barky box owner, so not entirelt sure

Ive also added a piece, about 25mm wide just under the triangle bracing as i got a little happy with the router - will this effect the end result at all? I wont be building future boxes in the same manor

No translator here, just have a funny way of wording some things i guess
lawbadman's Avatar
lawbadman replied the topic: #24035 1 year 9 months ago
I will be using the Cubo Sub mainly for live PA and some DJ so a flat frequency response from 100hz down to 30Hz would be needed.
Can you suggest drivers from Parts Express that can deliver that kind of performance?
capicva's Avatar
capicva replied the topic: #24034 1 year 9 months ago
@Cubo15 I'm pretty sure you quoted Orikei there, but I did upload my build pics to a gallery on my own server (to avoid swarming the forum):

photon.colectico.org/index.php?/category/1

Feel free to use those pics.

About the finish, it's two coats of monolayer polyurethane on a weird grey color (that gives a funny green hue under direct sunlight), over two coats of white primer over some nitrocellulose sealant on the okoume plywood. On the pics you'll spot my father in law who is very crafty with a spray gun.
Orikei's Avatar
Orikei replied the topic: #24033 1 year 9 months ago
Hmm, not sure where ky 165 has come from then xD hopefully the added 10mm doesnt give any noticable effect

The barky box was fine before in tapped horn config, said builder did use ALOT of bog, many short cuts on braces and mighty MDF - i've put it down to that - no one else has had the issue like you say

Using 12 guage from the driver to a speakon seemed the easiest idea - DIY x-overs are shady at best :p
I will also be running a parralel out by bridging the +/- of the in speakon to the +/- of the out

Do i need to be aware of any reverse wiring? I.e negative wire to positive terminal? This was also information aquired from the barky box owner, so not entirelt sure

Ive also added a piece, about 25mm wide just under the triangle bracing as i got a little happy with the router - will this effect the end result at all? I wont be building future boxes in the same manor

No translator here, just have a funny way of wording some things i guess