plywood, pictures and good bass

Hi Folks,
I just joined because I was very impressed with the plans, especially cubo cabs which seem very intelligent design to me (with my dusty old MSc in acoustics). I am building up a small rig after being out of sound amplification for 38 years and decided to build a pair of Cubo 18s to perform the bass duties (Tannoy VX12s do the mid & high with a bit of help from a pair of 60 degree horn loaded B&C DE250s to extend the distance of propagation above 2kHz: I intend to cross over at ~150Hz and 1.6kHz.

I am not very good at reading the plans, though. I think the "under construction" photos here freespeakerplans.com/kunena/16-bass/21333-cubo18 are very helpful. If people who have built cubo 18s are willing to post informative photos of their construction here, it would be really great. I am interested in details such as the kind of screws and glue you use as well.

Significantly, I went to two timber specialists here in the Belfast area and both told me that Baltic plywood was now "impossible to get hold of". They offered me alterntive "good quality" 18mm ply, but would not commit to it being void-free, which I explained was essential. Any ideas on good plywood welcome.

Finally, of course, drivers. I have not chosen yet, but I want a fairly smooth response, so the V18-1000 I was thinking of is out because of the pronounced peak around 125Hz and drop below it. Any suggestions for around 1kW ?

Thanks all.

Keith.

On drivers, I just had a quick look and wonder what folk think of using RCF L18P300 - with cubo 18. Other suggestions welcome!

I would suggest RCF LF18N401. Slightly rising Response, no Dips, some extra Hz extension compared to other drivers i have measured. I can't say anything about the L18P300.

BTW i would not "support" your fully balanced PA speaker by a known brand with some other horn. You will get a lot of interferences without any advantage.

great suggestion!
That looks like a truly excellent driver, thanks.

Regarding your other comment - yes it is somthing that has heads shaking, but convention is just that, the proof is in the physical realisation and this one seems to work, though of course it is a compromise for someone on a very limited budget (by industry standards) and has quite a few VX12s around. For some reason the Tannoys seem very happy used as broad mids and I should add that their main weakness in my experience is hf drivers blowing under stress - they seem a bit underpowered, so taking some of the workload off them is part of my rational. They also loose HF at > 20m, especially >30º off axis, so the wee horns help fill in at longer range. You are right about interference though, but that is inevitable whenever there is more than one point source at the same frequency - Olson's array concept only works under rather restricted conditions, but given the whole spectrum and a room full of reflections, it seems not to matter in practice. Well, it is debatable. Thanks for you advice, though.
All the best,

Keith.

Well it's your decision but i highly doubt any advantages. You won't get over 20m with a direct radiating 12" anyway. The extra HF driver won't go more far either unless it's louder (which leads to more hf to the front row and not good sound) or it extends near field by quite a bit (so that the inverse square law doesn't apply), which is VERY unlikely too. When you already have quite a few VX12s around, just go with a delayline or even 2 delaylines.

Interference isn't inevitable as you can see with the VX 12, which can really minimize that effect.

Best Regards Nugget

I am mainly looking for "in constuction" photos and tips for making the CUBO 18.
Thanks,

Keith.

I would cross the Cubo 18 near 100 Hz to the Tannoy's.

Wow! That is really great. Everything I was needing and more. Thank you very much -- excellent training video (and even using same tools as I do). The time-lapse video is very effective.
I like the attention to details around the handle as well. OK, I will make a pair with and see how they complement the rest of the rig. I might post pictures at some point. 
Thanks again,
Keith. 

I see a search for Cubo 18 Bass yields good results. Found this 
www.instructables.com/id/Building-a-Cubo...and-Modified-Cubo-8/
for example. 

When they are made, I will experiment with crossover frequencies; if I can, in different venues. I might well end up as low as 100Hz. 

Thanks and all the best,
Keith.