New DIY 1x15 cab, advice on plywood.

[parapentep70]

Hello,

I want to build 2 cabs for my new equipment, they will be 15's, one of them with a powerfull, high efficiency horn that I should be able to cross-over relatively low (at 1200 Hz), the other without.

My goal is "medium size for 15's, relatively low weight".

My drivers, Kappalites 3015 (NON LF). My main reason not to go LF: slightly higher efficiency, and I will put "only" 350W per fifteen. With proper tuning I will not run out of excursion: I will be close only if I put all my watts at the worst frequency, but not exceeding Xmax limits.

By the way I received them this morning

I found good trade-offs with an effective internal volume of 85...95 liters. I can get good lows without being limited by over-excursion at any side of the box tuning frequency (about 43 Hz), at least down to B0. Larger could provide les than an extra dB below 45 or 50 Hz, but I could start being limited by excursion. And larger could be... too large anyway.

The horn starts providing decent H and V directivity at only 1200 Hz, this means the horn is relatively large in the V direction, 202mm. Larger than most similar horns I've seen. I plan to use a slot port in the bottom side. Then the whole thing must be almost as tall as a fEARful 15/6. But at only 85...95 liters, it will be shallower and narrower. External dimensions could end up like 69x47x37 cm (I cannot remember by heart my calculations yesterday, but they should be very close).

I prefer the 2 cabs to have the same size, then I will be sure they play in phase, and they are easier to stack.

Then I'd say size (and to certain extent overall solution) is similar to Barefaced Compact and fEARful 15/6 cabs. Like a thinner fEARful or a longish Barefaced. I know this is not ideal from the point of view of standing waves, but at least I will avoid really bad ratios among internal dimensions (like 2:1 or 3:2). To me this is a compromise solution.

I plan to build 2 cabs for me. I will take my time. It means I can (and I will) provide complex bracing. I can interate. Total power is limited (less than 600W peak per cab). I plan to use good phenolic birch plywood.

Then the million dollar question (well, in this case the ~4 pound question ) is... 9mm or 12 mm thick?

For the front bafle I plan to use 15mm (or perhaps 18), at the end I'll get rid of 1/3 of the area. For the rest of pieces my idea is to use the same thickness, 9 or 12mm (I don't have access to anything in the middle).

I understand thicker means better rigidity at certain bracing level and heavier. And thinner the option to use more advanced bracing while still saving weight.

Then, what would you do?

Thanks a lot!

[will33]

The 12mm (1/2" for us americans) works well and comes in pretty light with adequate but not overly complicated bracing schemes. You can do the 9mm with more involved, carefully thought out bracing schemes but it's up to you to consider if all the extra work is worth a little more weight loss. The key is killing resonances in the panels. Regular old butt joints work fine with 12mm, I'd want to put some re-enforcement in the corners with 9mm.

[parapentep70]

I forgot to mention, I am planing to glue / screw wood laths (is this the proper word for those wood square prisms?) along all joints, even if I go with the 12mm-1/2 inch option.

Will33, thanks for the response. Perhaps I should get a carboard box and put some books inside to get an idea of the "real world difference" between say 16 and 18 Kg.

Anybody who built with 9mm (I think the closest is 3/8'') ?

[will33]

Couple guys here have done 9mm, can't remember who. The bracing schemes can get pretty laborious. If you want to go really light, search up "zaclite", "nidacore", "foamcore" and "fiberglass". Should produce a few build threads. Basically a fiberglass sandwich around various foam cores, very light and rigid. That combined with a neo driver seems to be about as light as one can practically get unless you got a pile of money to burn on carbon fiber or the keys to the materials warehouse at NASA or something.

One of those guys, again can't remember who, did identical 112's, one fiberglass, one wood for comparison.

[billfitzmaurice]

Originally Posted by parapentep70

I forgot to mention, I am planing to glue / screw wood laths (is this the proper word for those wood square prisms?) along all joints?

That's a total waste of wood, glue, screws, weight and time. The corner joints are the strongest part of the cab, they do not require cleats. 9mm is OK only if you are extremely well skilled in cabinet design. Even 12mm must be well braced, far more so than any commercial cab I've ever seen.

[ptidwell]

FYI, the VAS (compliance Equivalent Volume) for the 3015 is 153 liters. I don't know what you mean by good trade offs at 85-95 liters. Also, I would discourage you about using 9mm what you would have to make up in bracing would make this moot, and btw the corner joints are the strongest area of the cabinet, that's not where you would screw and glue. just my 2 cents but what do I know

[will33]

On 1/2" the corner renforcements are a waste no matter what, on 3/8" you might want a little something in the corners IF you're gonna really round them off on the outside.......mating surface. If you're only going to round them off a little bit, may not need it then either.

[billfitzmaurice]

Originally Posted by ptidwell

FYI, the VAS (compliance Equivalent Volume) for the 3015 is 153 liters. I don't know what you mean by good trade offs at 85-95 liters. :

Vas does not equal Vb. The 3015 is maximally flat in 79L.

[parapentep70]

Wow! What a great forum!!

billfitzmaurice, thanks, what you say goes in line with my WinISD calculations. I feel more confident now. A lot. When running calculations I did not even know there is a clear point of diminishing returns in terms of low frequencies, I realized very recently, and now you come basically with the same number.

OK, no wood on corners. I understand the joints are the stronget area. The reason to consider it is because I thought it could make construction easier, but when calculating volume and weight... Now I am fully convinced. Perhaps some little dice, but never full length.

Finally you all are very clear that going down to 9mm is not free. I prefer to minimize potential issues and simplify things, and I don't need to save the last kg. So 12mm.

What would YOU do for the front panel? I thought 15mm, but it could be 12 or 18.

Thank you all!

[will33]

I use the same 12mm for that too and put little 1x1 squares to make double thick wherever there will be a driver/handle or wheel mounting screw. If you use T-nuts you don't need those either. Maybe still double it up on the wheel mount locations if any.

[parapentep70]

I planned to use T-nuts. In fact I learnt what a T-nut is a few days ago. If simpler is as good as, then I´ll go simpler: 12mm everywhere, only some light, thin wood for the "frame" over the front panel. Thanks again.

[will33]

T-nuts can vibrate loose too, nothings perfect. Use lockwashers or put some silicone caulk/gasket maker stuff like RTV or something on the threads, tighten it, let it dry. Don't use loctite or something that will sieze, just help grip, you might need to take it apart someday. Lockwashers are easiest.

[parapentep70]

I've got the plywood needed for my two 1x15 cabs in the garage. It has been accurately cut direclty from the store, the cost of the many perfect cuts is so low compared with my effort to do the same without adequate tools!

Finally my form factor will be 69x45x36cm external dimensions. The baffle will not be recessed and I´ll use a metal round grille (similar look to Audiokinesis ThunderChild proposal). The "thin and tall" form factor is required to install a relatively big horn in one of the cabs, the horn provides decent directivity in the vertical direction at relatively low freqs... so it is large in the vertical direction, 202 mm. I need the 69cm to fit woofer, horn, port and top & bottom lids plus some extra for round grille, some bracing and so on.

At the end, following your advice, 12mm plywood for everything. I got the leftover ply cut in small long pieces that will be good for bracing.

I also brought home a brand new RH750 from the store, it was a good offer and didn't want to wait more. With bag and footswitch.

I want to finish my working day and start glueing some plywood pieces! or perhaps try the new head with the speakers in my old combo (I can disconnect them from the head section !!).

One question, reading many posts in Talkbass I got to the conclusion that polyurethane wood glues (PL premium or somehing like this) are better than aliphatic resin glues (Titebond).

If I understood well, Titebond requires very strong clamping for good joints, where PL Premium can do the same without strong force or even when surfaces have small gaps. Is this correct?

I cannot get here PL premium, I only found "Imedio PU-MAX" that seems to be similar. Is there any other popular equivalent in Europe that you have used?

I've got some experience with Titebond Original (and I have a bottle), but I don't think it's easy for me to provide very good clamping and no gaps in all joints. On the other hand I am familiar with advantages (water cleaning, easy to sand) and tricks. Any help with PU glues will be appreciated.

[billfitzmaurice]

Originally Posted by parapentep70

I cannot get here PL premium, I only found "Imedio PU-MAX" that seems to be similar. Is there any other popular equivalent in Europe that you have used?
.

Check here, something may be listed:
BillFitzmaurice.info - View topic - Links to everything you need for your BFD-build, in Europe.

PL Premium is the only adhesive I use or recommend.

[parapentep70]

billfitzmaurice, this is THE thread I was always looking for. Now I need to do 5 pages of research. I shoud've asked before and I would've saved time!!
Thanks a lot!