BillFitzmaurice.info

SeisTres wrote:Very nice. Didn't know the new plan didn't need airtight tweets. Mhh, this and the no access covers just might win me over instead of ot12's if i get into building again. But then again, ot12's are just a breeze and do everything i need. we'll see

Cheers,
Yes, less to leak
It's an interesting build...

Ok, Day 10.

I did 8 hours today, including cleanup.
I really don't have any pics to show for it!

I cut and assembled the framework for the module on Cab 1. I decided I would dub it scaffolding.
I had everything cut and PL'ed in place in 2 hours.
It is about now I can really see the value in a brad nail and staple gun.

So, what to do while the PL is doing it's thing?
How about doing some little things like gluing up the other array, hot melt gluing ports in cab 1 and cutting the 4" tubes to go in as well.
Then a bit of forward prep work...

I cut all 4 back halves and wrapped some baling twine around them to pre-curve for however long it takes me to get to them.
Fortune (for my cattle) says we got some large square (well really they are rectangular, 8' x 3' x' 3") lucerne bales recently and the twine (it's really more like rope) that wraps them is nice heavy duty "string" for this task.
I pulled them a bit tighter than the radius of the back halves. I figure they will be inclined to spring some, so I gave them a little more hoping they will end up sitting just right.

Since Cab 1 was a little preoccupied,
After measuring, I cut and shaped the module sheaths for Cab 1
I cut, shaped and fitted the side braces for cab 2, ready to be installed after I have done the module for that cab.
As for Cab 1, I also drew up on top and bottom of what it is I expect to do to build the "scaffold" on cab 2. Same as I did for cab 1. Doing this for Cab 1 allowed me to make a template of the braces and they fitted extremely well, with the odd bit of trimming here and there.

I have been cogitating about the nacelles, even prior to commencing the build.

I know it's in the plans, but please bear with me as I'd like to know that you all think.
The "job" of the nacelles is to allow screws to hold the module flush, as well as seal, the driver chamber.
The nacelles rely on a good bond with the module sheath with not much PL, so potentially a weak spot.
It occurred to me the other day that so many plastic bodied items around today have tubes that take a screw, but that tube may be quite deep at times.
The following thought was "why not put a tube through the sheath to the backing plate which the securing screw(s) can be inserted through/within"?
That allows the backing plate of the module to be what is secured to the driver chamber, rather than the sheath and nacelles.
The tube(s) could be cut/shaped flush with the module sheath, and it removes any possibility of nacelle/sheath failure. I say this, as I believe the sheath, at 1/8", will be inclined to flex, regardless of PL and scaffolding.
In my mind, the only critical point would be drilling through the sheath perpendicular to the backing plate, in a repeatable fashion.

So, I'd like to hear thoughts on my idea, or feedback from those who have built based on the latest plans, regarding the nacelles...

Thanks in advance

Grant, I was thinking along the same lines as you, regarding the nacelles, on my DR 280 build, with the latest plans.
I didnt really like them either. But I ran out of time to get them done, so i actually just drilled and screwed right trough the structural elements, the scaffolding as you call them. So only 4 screws each side. I know, this is not the way it should be done, and it doesnt look good right now, since I didnt had time to do it nicely, I just put a washer under each screwhead:P It works though, no leaks at all, and they have done a couple of gigs in the last 2 months:)
However, I dont recommend doing it exactly this way, and I am going to change it, as soon as I have time between gigs:P That the downside with temporary solutions, they tend to get permanent

Oh, and by the way, I almost had the same problem with the throat horn divider and the halfcircle braces as you did, I cutted the divider to the exact measurement in the plans, mounted it flat with the inside of the horn, and got a space between it and the circles, but I looked at in Sketchup by then, and found that it should meet up, and that the throat horn divider is longer in Sketchup than in the plans, angles were the same though. So I think there is a small mistake there in the plans. I had about .5" missing, both in reality and compared between plans and 3D model. Maybe something that should be looked at Bill?

I simply added a 12x12mm strip in there before putting on the halfcircles:)

Oh,and I am extremely pleased with my DR´s fantastic speaker, everyone that I know that knows something about soundreinforcement says that the are just great:)
So gonna have to build more;) Not that I need more SPL right now, usually my Lab 300/1300C combo is set at around -7 to -10db, and last time I did livesound, I peaked at around -3 to 0 on the mixer, and that was veeery loud;)

//Robin

Robin,
Thank you!

Good to know someone else was thinking similarly.
Thanks also for your honesty

I going to cut up some nacelles and see how they look...

Your welcome Grant!

Test the nacelles, they probably work just fine, they are in the plans after all;) But I´m still thinking about some other way to do it, something like your idea with tubes. Perhaps just a sink with a square bottom, or a nacelle over the "ribs" behind the sheath, then it would be very stiff and strong.

We are going to have somekind of grill on ours, so it doesnt matter if the screwarrangement looks good or not.We are still thinking about a grilldesign that leaves the compressionhorn visible, perhaps painted in high gloss purple metallic;) Or maybe use Blue Arans Tuff Cab paint in their Funky Purple, should be easier to get that to look good than high gloss metallic spraypaint. Gonna use Black Tuff Cab on the rest of the cab.
Right now they have foam front, stretched over the whole front, and I´m starting to like the smooth clean discrete look.. So I dont really know how its gonna end up:P

//Robin

Day 11,
Three hours in total, including cleanup.

I cut and installed the scaffold for cab 2. 1 hour.

Then I cut some nacelles, some based on the plan, some not.
I consulted sketchup for the umpteenth time, that didn't help.
I get the concept, I just cannot for the life of me make them work!

So, I'm going the tubes way, well at least I've started to suss that out.
In regards to the plans, this is the only way I will be deviating from them (apart from my mistake)

Pics coming soon, I promise lol...

Grant, have you made the nacelles already? The way I understand the procedure is to drill the screw holes from the back of the module through to the front. Predrill the nacelle. Locate the module into the cab and 'lock'. Drill through previous holes. Now everything is lined up.
Perhaps the sheath might flex, but it won't constantly flex in and out since all the screws are continually adding the steady pressure to keep the module in place. Also, there is such a short span between the uprights that minimizes the flex as well. And, the screws will be right at/near a brace, which, when you think about it, nullifies any fears about flex.

Hi Tom,
Thanks for your thoughts
I understand what you're saying and the theory.

When I physically pick up a nacelle and try to place it, my brain does not compute.

Bit of

Did a few hours today messing around with bits and bobs...

So: Technically lol Day 12, 3 hours including cleanup.

The last 2 pics show my effort in doing some "tubes" on the module.
It would be unfair to call it a solution, as that would suggest a problem.
I just couldn't get my head around the nacelles.
So the tubes are what I'm doing on my cabs.
Please note: this is a variation from the plans.

Cab 2 with the module "scaffold" completed and set, and ready to put sheaths on:
Sheaths installed on second module, removed after PL set:
Middle side braces installed on cab one, with a side view of module 1:
And looking down into the tubes:
Pardon the mess, that's bog (= bondo) over the module face and tubes

These tubes look great. What method did you use to drill these holes in the sheaths ?

mr.lussier wrote:These tubes look great. What method did you use to drill these holes in the sheaths ?

Probably a drill press. I considered this method, briefly, because I doubt that one in ten builders owns a drill press.

Grant Bunter wrote:

Is that the bondo monster looking at me?

Bill Fitzmaurice wrote:

mr.lussier wrote:These tubes look great. What method did you use to drill these holes in the sheaths ?

Probably a drill press. I considered this method, briefly, because I doubt that one in ten builders owns a drill press.

Yeah I had guessed for the drill press... But I never attempted such cross drilling operations with one. Was more wondering about what kind of bit was used. Wood bit ? Forstner bit ? Hole saw ? Grant, can you explain a little more about the process ? Did the plywood went all a mess around the perimeters of the holes ?

I own a large drill press and would probably be interested by this method for a future DR build. Can't wait to see how it looks when finished.

Thanks for the interest!

I considered a drill press. My cheap crappy one moves too much to use it with any precision.

Of course, the first one was the most difficult.

I marked up a line on the very back of the backing plate, 3/8" in from the edge of the plate (rather than 3/8" in from the edge of the ply sheath) and hand drilled through the plate and the sheath to get a centre to work from.

I'm using 5/8" ID conduit (whatever you guys may call it, think electrical plastic pipe), which measures out at 3/4" OD. The reason I chose this size, apart from having it on hand, was to allow for both the screw head (7/16") size, and the socket required to drive the screw in.
Using the hole drilled up as a centre in the sheath, measured a tad over 3/4", ie just over 3/8" either side of centre.
Drilled a half inch hole within the marked out area.
Then used a fine blade on the jigsaw to cut out the sheath..

After minimal experimentation, the pattern to cut that works best:
Think of an old stained glass church window:

Flat at the bottom with perpendicular up rights for about 50% of the height, that then arc to an apex.

The flat matches the top of the backing plate.
The position of the apex determines the position of the tube. So I kept trimming until the tube was centred over the hole in the backing plate.
It turns out that when centred on the hole, the outside edge of the conduit sits just on the lip of the backing plate.

Cut the conduit so it stands tall of the sheath.
Holt melt glue the conduit in everywhere you can reach around each tube, also using the glue as a backing for bondo to fill any voids in the sheath.

The first one I trimmed with a hacksaw blade.
The rest I did with my trusty angle grinder and 1/16" thin cutting disk.
With care, the sheath remained intact lol. Bondo fixed the rest...

In reading what I have typed, this sounds complicated.
It's not!
The very first one took maybe half an hour of head scratching.
The rest of that side took half an hour to all glued in, and 10 minutes to trim with the angle grinder.

I reckon they will pretty mush disappear when sprayed with black paint.

And Yep Bruce, you're looking at 2 of the 5 eyes of the bondo monster

Edit: After doing the first one, a round hole via drill bit and press will leave a large void in the sheath towards the top end of the tube...