Cubo Sub

Hello Cubo,

I wrote on this thread a while ago with a photo of my 21" Precision Devices driver (ET211S - can't get any specs from PD as they say they lost all the paperwork when they were taken over ) with regards to adding an extension on to the front of the cab to increase the horn length.

I have also been wondering whether the output from the cab might be affected by the fact that I put two small boxes where I decided to put the handles - inside the compression chamber therefore reducing the volume and potentially affecting the airflow??? as it exits the chamber.

So, as I was browsing various other 21" designs saw one plan whereby wedges were added in to the corners of the chamber to increase compression so I have done a quick sketch in sketchup for an idea.

Do you think this will make any difference...?

P.S. I've also included a couple of picks of the handle box inside the chamber so you can get an idea of the size (it's probably on 35mm deep.)

Also, last image has the addition of two extra wedges to create a smoother transition to horn throat...

Someone in the Netherlands has made a horn extension for Cubo Sub and was very positive about the results, claiming reduced excursion and more output.. Let me know if you want to know more specifics.

The other 21" designs you've seen must not have been designs that relied on a chamber in series with the horn for getting low. In those cases the effect of the band pass chamber is already at a minimum, thus further decreasing the chamber has a non-significant effect on the low end.

In cases, like the Cubo design, where the design is relying on the band pass chamber, lowering the volume of air inside this chamber will reduce the low end performance. The larger the reduction in volume, the larger the change will be, the less low the design will go.
Those handle bar boxes combined will be roughly 4% of the total chamber volume, so a minor (and usually negligible) change. Those large reflectors seem to be closer to 11%, combined with the handles the difference is now 15%. Hopefully, needless to say I would leave them out of the picture. On the bright side, anything you take away from the low end will be added to the top end (though not in the same proportions).

Also take in consideration that the wavelengths involved for 100 Hz are 3.43 meters large and become larger as frequency decreases. Being so large, how much influence do you think a 3.5 cm smoothing step will have?

Best regards

Cubo

Glad to hear that the handle boxes won't have much of an effect the sound output - especially when we're talking about such huge wavelengths.

Here is a link to the other 21" designs that I was referring to which also looks like it relies on the chamber coupled with the horn for achieving low frequencies - actually looks very similar to cubo design but just with an extra bend in the horn path ( http://speakerplanarchive.com/othorn.php ):



I will be using the cubo sub together with 6 Fane long throw 15" w-bins (see pic below)



Have been talking with someone else on speakerplans (a speaker designer based in Thailand - username 'thawach') and he was saying that if you really want the sub bass to be noticeable, as a general rule of thumb you should look be looking at making an enclosure which has a horn length of roughly twice that of the cabs above it.

I have measured the horn path of the Fane 15" long throw w-bins to be roughly 1.2m (x2) and the horn path of the Cubo 21" Sub is 1.83m.

Below I have made a sketch of what an extension to the cubo sub might look like - this should give an extension to the horn path of + .3m (ideally guess you'd want it to be nearer to .4m but this is just a sketch...)





Would be very interested if you could send me any further information regarding the horn extension experiments of the person who tried it out in the Netherlands.

Thanks again for all your help,

Thomas.

As I was saying, that's one of those designs that doesn't rely on a chamber to get low. Every extra bend (2 x ) you see increases the horn path. In that particular design, as far as simulation-world is concerned, only the volume inside the cone is "chamber-volume", the rest is horn.
Again, that rule of thumb Thawach (legend in my eyes as for the sheer volumes of cabinets he produces) is for cabinets that don't rely on a chamber in series with the horn.

You see, a Cubo is a hybrid between a reflex cabinet and a (tapped) rear loaded horn. A reflex cabinet can achieve serious low end with a port of just i.e. 30 cm long. The larger the chamber, the lower the reflex will go, that 30 cm port could be tuned to about any frequency depending on the chamber volume. A tapped horn on the other hand needs a horn length close to 1/4 wavelength of the desired low cut-off.

I wouldn't build an extension of just 30 cm, I would recommend between 50 and 80 cm, with a constant flare-rate that is equal to, or higher as the angle of the baffle from Cubo Sub.

That someone (probably from Belgium though) has made the extension 77 cm deep by 95 cm wide:

Work in progress:

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

Finished subs:

As this forum and especially Cubo have been really helpful to me when picking, fine tuning and actually building the speakers of our system I though I'd share a picture of the finished result. The extended subs (horn extensions) are loaded with RCF L18x451 drivers powered by having two in parallel per Master Audio SM4000 amp in bridge which comes down to about 3100Watts per driver. The cubo 18 extended are loaded with Beyma 1600Nd hooked up to a QSC PL380. The kicks are loaded with Kappa pro 2 drivers on a Master Audio DL1800.

In the near future 2 more cubo 18's will be added along with two extra kicks, even though they are keeping up fine with the 6 subs for now playing reggae and dub music. If it were techno I'd recommend 1 kick per 2 cabs. One might notice the lack of bracing in the horns, we actually ran out of time and had to do a festival without. Braces are currenly being painted and will be added. On high SPL levels the horns would growl and start to flex.

May I ask what's on top of the kicks for mids and highs?

Sure
A BBC.BR215 cab with two RCF L15P540 drivers for low midrange (up to 380Hz), 4 Fane Sovereign 250 8" drivers and two Beyma 1" CD's.

We were planning on building 4 trapezoid 10"x1" cabs instead but we are keeping this setup for now since it sounds great and for now we aren't struggling to achieve proper SPL.

Hello Cubo,

I am looking for a PA subwoofer with lots of low bass while achieving high SPL.
My only source of drivers is Parts Express, so can I use the www.parts-express.com/dayton-audio-rss46...oofer-4-ohm--295-472
or www.parts-express.com/selenium-18sws800-...w-subwoofer--264-387 or www.parts-express.com/eminence-kilomax-p...rame-driver--290-434

Which would you suggest for strong low bass?


Thanks

Hi Cubo,
Been building one of these Cubo Subs as a test cab before i build 4 of them (guess the booth needs sound to? haha)

Few quick questions:
The measurement of 155 (top back baffle to back of box) comes out as 165 with all other measurements being spot on - is this a mistake in the plans or something im missing?

I have ordered Beyma 18PWB1000FE drivers for the cabinets, after seeing your reccomendation of great sub drivers (currently page 9) i just wanted to ensure there would be no trickyness to installing this particular driver - a friend used eminence omega 18 and had a honk/bark sound coming from the bottom of the box where the throat would fire sound down (what could have caused this)

I will be using 12 gauge wire from the driver to an XLR in on the back the box - no x-ver in the box but possibly a parralel link out, is this ideal or would it be further reccomended to solder up a hi-pass/low-pass xover to the back of the box

I have heaps of build progress pictures, happy to share them if anyone else wants to see thanks Mr Cubo