Another OT12 build

[ctmullins]

With the T39s almost done, I'm starting work on four OT12s. I'm making four based on recommendations from other, senior forumites; seems having a pair on each side smooths out response. Sounds good to me! I have enough electronics on hand for two currently, so the other two might be shells for a short time. Melded piezo arrays, 2512 drivers, Arauco ply. I'll use standard top hats, with the bottom cab having them in both bottom and top, so I can join the top cab securely.

All major panels got cut out last weekend. Today I'm beginning the markup on tops and bottoms!



It would be great to have these up and running (at least the first pair) by our March 5 gig, but that may be too ambitious....

[Bruce Weldy]

having them in both bottom and top, so I can join the top cab securely.

That really isn't necessary. Put the locking chevron corners on 'em and they aren't going anywhere.

[ctmullins]

Baffles are cut. I remember this maddening step from my W8s. Only this time I have four of them to do!

So I decided to do two at a time, by stacking, clamping and cutting. Good idea or foolhardy? Inquiring minds...

After each section I tidy up the blade wander with the fearsome Shinto Saw Rasp. It's one of my favorite tools!



First pair nearly done....



And then there were four!



We'll soon find out if this little shortcut causes any problems....

[Tom Smit]

Your process is fine if you don't have a router....cuts the work load in half.

If you have a router (and pattern bit), you could make just one of which you could use as a template for the rest.

[ctmullins]

It would be great to have these up and running (at least the first pair) by our March 5 gig, but that may be too ambitious....

Humph. That's definitely not happening. Too much life stuff lately. Tonight's the first night of progress since writing that...

Putting the shells together. I deviated from the plans again.... But a big "thanks!" to whomever invented those W clamp thingies!

[Tom Smit]

But a big "thanks!" to whomever invented those W clamp thingies!

Bruce Welby posted a few times about them.

[Bruce Weldy]

But a big "thanks!" to whomever invented those W clamp thingies!

Bruce Welby posted a few times about them.

Just something I found in an old woodworking magazine......I've used 'em for tons of stuff outside of speaker building over the years.

[ctmullins]

Small progress today - got eight throat reflectors cut out, with their angle cuts. The long side 45 degree cuts were easy, then I used this makeshift sled on the small tablesaw for the other cuts. First one side:



Then I rotated the sled over to the other side of the blade, flipped the piece over, and did the second side:



I don't think I have the energy to actually glue them tonight, though...

[David Raehn]

http://billfitzmaurice.info/forum/downl ... &mode=view

I've found this to be the best and easiest way to clamp those buggers.....

[ctmullins]

Thanks David, that's easier than what I was going to try! Makes perfect sense!

[ctmullins]

Throat reflectors installed, lots of excess PL trimmed (tedious), and holes cut for top hats. I clamped my little "portable drill press" to the cab and used a 1 9/16" Forstner bit. This way the holes line up just right.





The top hats (the steel Penn-Elcom ones that Leland sells) are a very snug fit. I won't need to use any sealant here.



On the very last one, however, the final layer of ply gave way and separated completely. I'll have to patch that up. I suppose I should have used a sacrificial backer board...

[Bruce Weldy]

Throat reflectors installed, lots of excess PL trimmed (tedious), and holes cut for top hats. I clamped my little "portable drill press" to the cab and used a 1 9/16" Forstner bit. This way the holes line up just right.





The top hats (the steel Penn-Elcom ones that Leland sells) are a very snug fit. I won't need to use any sealant here.



On the very last one, however, the final layer of ply gave way and separated completely. I'll have to patch that up. I suppose I should have used a sacrificial backer board...

Just put a doghouse on all of 'em....you have to seal 'em anyway....

[ctmullins]

Just put a doghouse on all of 'em....you have to seal 'em anyway....

You know, I need to understand this part of the design a little better.

Unlike the Jacks, the space under the throat reflectors is completely isolated from the main chamber. This means that it must not play a part in cabinet tuning, other than serving as part of the horn path.

So why exactly does it need to be sealed off?

[Bruce Weldy]

Just put a doghouse on all of 'em....you have to seal 'em anyway....

You know, I need to understand this part of the design a little better.

Unlike the Jacks, the space under the throat reflectors is completely isolated from the main chamber. This means that it must not play a part in cabinet tuning, other than serving as part of the horn path.

So why exactly does it need to be sealed off?

Well, you made me do some research. I built mine under an older set of plans where the baffle had slots in the top and bottom - only the baffle for the 3012HO was solid. Looks like the newest plans don't show a different baffle for the 3012HO and the other drivers as far as the slots.

I guess you don't need to seal 'em.

Mea Culpa....

[Chris_Allen]

Looks like the newest plans don't show a different baffle for the 3012HO and the other drivers as far as the slots.

Yep, they disappeared in the 2011 set of the plans and aren't present in the JArray version either.