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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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 Download highest quality: Picture below / right click / save as.

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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



Cubo15's Avatar
Cubo15 replied the topic: #24715 3 hours 8 minutes ago

but it never sounded that great due to the heavy cone I think

It would be really nice if you new the T/S-parameters of the PD.

Now it's difficult to say whether you didn't like the driver, the cabinet or the incorporation into the rest of your system slash processing. If you know the T/S-parameters it's easy to compare them to the 21PW1400Fe and say if it's the same or completely different and if it attributed to your experience of the Cubo 21. To answer your question whether this is going to improve things for you without the T/S-parameters, we need to figure out what you didn't like about it exactly. What did (or didn't)  you do to it, processing, amplifier power, what tops did you use (any delay on those), magnet inside the chamber, magnet inside the horn, etc. To me the 18LW1400 in Cubo Sub with the magnet inside the horn or inside the chamber sounded like two different cabinets, one for 'rumble' and the other one rather tight and loud.

It would also help if you have heard the PD's in another enclosure, anything that tells us if it's the driver, Cubo or system settings, or a combination of those.

Typically a 21" driver doesn't perform that much better than an 18" driver, in the same sized enclosure, it just has more potential. You need either a lot of power or quite a bit of EQ to get that potential (air displacement) to fruition. Someone in the Netherlands is building a custom version of it and probably going for the RCF LF21N551 or Lavoce SAN215.30, I assume with a small nuclear reactor to power the amplifiers because they can handle it and need that kind of power to really shine (beyond the scope of an 18" driver).

Best regards Cubo
space141's Avatar
space141 replied the topic: #24714 4 days 15 hours ago
Hello Cubo and fellow community members.

I made a 21" version of the Cubo Sub a few years back now which was fitted with an old-shool Precision Devices driver that was rated 750W rms (ET211S) but it never sounded that great due to the heavy cone I think.

Can anyone shed any light on the following driver and whether it would be suitable for the CUBO SUB - I cannot find any recommeded TS parameters for drivers on the page, neither can I find a post of anyone else making the 21" version to my knowledge.

Any insight would be greatly appreciated - the driver is the Beyma 21PW1400Fe with the following specs:

Thiele-Small Parameters

Resonant Frequency (fs) 30 Hz
Impedance (Re) 5.2 ohms
Coil Inductance (Le) 3.7 mH
Mechanical Q (Qms) 7.44
Electrical Factor (Qes) .36
Total Q (Qts) .34
Comp. Equivalent Vol. (Vas) 14.18 ft3 / 401.5 Liters
Voice Coil Overhang (Xmax) 10.0 mm
Surface Area of Cone (Sd)m2 0.1734m2
Reference Efficiency 2.83%
Displacement Volume (Vd) 1729 cm3

Many thanks in advance,

TLC.
Cubo15's Avatar
Cubo15 replied the topic: #24650 2 months 2 weeks ago
I suppose you mean reducing the inner width to 30 cm, although I would make it as small as possible, so perhaps 28 cm inner width. Also, with a single driver that wouldn't work out all that great, I would fit two 10" drivers (one behind the other) on the baffle. It should just fit, with about 1 cm between the drivers. Only one 10" simply doesn't have the Sd to make it work but two have.
Now, although I'm a big fan of 12V PA systems that drop down low, it isn't the most energy efficient. If output is more important or how long the battery lasts, two Cubo 12 (with reduced inner width) will have more output between 50 - 80 Hz. This is where the most energy in bass is located, it won't sound as low but add a lot of thump.

Cubo
SubMeditation's Avatar
SubMeditation replied the topic: #24648 2 months 2 weeks ago
Greetings Cubo,

do you think i could adjust the inner depth to about 30cm and put thi 10" driver in: www.lautsprechershop.de/pdf/mivoc/awm104.pdf ?
I've builded a tapped horn with this speaker and want to know if the extra wood & weight is really worth it, because i'm planing to build serveral of them for some 5ghz connected 12v bicycle systems.

Cheers
Cubo15's Avatar
Cubo15 replied the topic: #24635 3 months 3 weeks ago
I don't have any of the data anymore, I suggest making a (2D-)model in Sketchup and derive the Hornresp input parameters from there, if you need any pointers let me know.
Cubo
Stefist's Avatar
Stefist replied the topic: #24630 3 months 3 weeks ago
Hello

I would be curious to see the simulationwith a rcf 18X451, A b&c 18DS115 and a bms 18n862.

Can anyone do this ?

cheers
Cubo15's Avatar
Cubo15 replied the topic: #24601 5 months 3 days ago
I have no data.
oksana's Avatar
oksana replied the topic: #24600 5 months 3 days ago
I want to get data for hornresp
Cab calloway's Avatar
Cab calloway replied the topic: #24586 5 months 1 week ago
Amazing thanks very much for the info!
Cubo15's Avatar
Cubo15 replied the topic: #24585 5 months 1 week ago
The Celestion is a very decent 15" driver and although I would normally recommend Cubo 15 Extra Extended as the best match, I've seen lesser 15" drivers used successfully in Cubo Sub. So if those drivers survived, these definitely will. The attachment shows Future Pussy Sound System, 8 x Cubo Sub loaded with the Eminence 3015LF (if I recall correctly).

Cubo
Cab calloway's Avatar
Cab calloway replied the topic: #24580 5 months 2 weeks ago
Hey Cubo,

Sorry if this has been asked before (couldn't find anything on it) but what do you think of the Celestion FTR15-4080HDX being used in a cubo sub? I can get a pair for reasonably cheap and was thinking of building the subs with these and then upgrading later on to 18s when I can afford them. The subs would be used for mostly house and disco at open airs.

Thanks!
Cubo15's Avatar
Cubo15 replied the topic: #24420 1 year 2 months ago

you're saying a 4 ohm version sub rated 1200watts will sound different as compared to the same model 8 ohm version sub
rated 1200watts

Ideally it does not but power handling is simply a measure of how much (thermal) energy the driver can handle before it burns up. If Qes, Le, etc. are different enough, it can affect the sound, although these differences are least noticeable in bass and sub enclosures.

ss the RCF LF15G400 a good driver for the cubo sub?

As far as 15" drivers go, it's actually a pretty good Cubo Sub driver. For a 15" driver that's a very respectable Mms.

Best regards Cubo
geritas's Avatar
geritas replied the topic: #24417 1 year 2 months ago
Hi,Cubo15. Is the RCF LF15G400 a good driver for the cubo sub? The mms parameter is OK?
Your help will be very appreciate.
thanks in advance my friend.
kasey's Avatar
kasey replied the topic: #24415 1 year 2 months ago

Cubo15 wrote: Personally I've never seen an 8 and 4 Ohm version with the exact same T/S-parameters.

The 4 Ohm version will see 1.414 times as much current for the same power as the 8 Ohm driver, to safely handle this extra current the voice coil wire needs to be different (thicker, shorter). As a rule of thumb the BL (Newton/ Ampere) is 1.414 times as low. The Re of a 4 Ohm driver is usually not exactly half that of the 8 Ohm driver, therefor Qes will also be different. So now you have a different BL, Re, Qes and Qts so that the 4 Ohm driver will behave the same as the 8 Ohm driver. The offset Qes can but doesn't have to be compensated for by a different Vas, etc.

Best regards Cubo

I understand what you are saying now, and I definitely learnt something, but in terms of power, you're saying a 4 ohm version sub rated 1200watts will sound different as compared to the same model 8 ohm version sub rated 1200watts if they are tested in the same enclosure? I mean if two different 1200watt amplifiers are used for each sub (a 1200watt 8ohm amplifier, and a 1200watt 4ohm amplifier). I honestly thought that if you give a speaker its rated power, it will sound the same regardless of its impedance (because you match its impedance to the amplifiers power rating).
Cubo15's Avatar
Cubo15 replied the topic: #24414 1 year 2 months ago
Personally I've never seen an 8 and 4 Ohm version with the exact same T/S-parameters.

The 4 Ohm version will see 1.414 times as much current for the same power as the 8 Ohm driver, to safely handle this extra current the voice coil wire needs to be different (thicker, shorter). As a rule of thumb the BL (Newton/ Ampere) is 1.414 times as low. The Re of a 4 Ohm driver is usually not exactly half that of the 8 Ohm driver, therefor Qes will also be different. So now you have a different BL, Re, Qes and Qts so that the 4 Ohm driver will behave the same as the 8 Ohm driver. The offset Qes can but doesn't have to be compensated for by a different Vas, etc.

Best regards Cubo
kasey's Avatar
kasey replied the topic: #24413 1 year 2 months ago
Oh I see. Your comment was directed to these particular woofers! I didn't know these woofers have different t/s paramaters when it came to their impedances. Thanks for taking the time to clear that up.
Cubo15's Avatar
Cubo15 replied the topic: #24412 1 year 2 months ago

kasey wrote: I see you said that a 4 ohm sub will perform different than a 8 ohm. How is this possible?

This is not actually what I said ;)

If you look at the T/S-parameters of the 8 and 4 Ohm version of the mentioned B&C drivers, you'll see that a lot of the T/S-parameters are actually quite different.  So this is what my previous post suggested. Hope that clears things up.

Best regards Cubo
kasey's Avatar
kasey replied the topic: #24411 1 year 2 months ago
Cubo,
Just a curious question, I see you said that a 4 ohm sub will perform different than a 8 ohm. How is this possible? If I have the same model speaker with the same parameters, driven by the same amount of power from an amp, how would the coil impedance make a difference? Note I know that an 4ohm sub will consume twice the power than an 8ohm sub driven by the same amplifier, but wont the two speakers sound the same if each is driven to its full potential?
Cubo15's Avatar
Cubo15 replied the topic: #24410 1 year 3 months ago
Hi,

Assuming you have the 8 Ohm models I would leave them in that order: (1) 18ds115, (2) 18sw115 and (3) 18nw100
If you have one or several 4 Ohm models that order might change.

Best regards Cubo
geritas's Avatar
geritas replied the topic: #24409 1 year 3 months ago
Hi, Cubo

I have these B&C 18ds115, 18sw115 and 18nw100   drivers.
May you please rate first, 2nd and 3rd. place about cubo sub please?

txs.
space141's Avatar
space141 replied the topic: #24353 1 year 8 months 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 1 year 9 months ago
Thank you, then I'll give it a try :)
Cubo15's Avatar
Cubo15 replied the topic: #24344 1 year 9 months 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 1 year 9 months 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 2 years 3 months 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