Docere MLTL - build thread

[bkeane1259]

I'm doing Jim Griffin's MLTL of Jeff Bagby's Docere. The Docere was the system that Jeff designed and then used in his speaker workshop last December. Pics from the workshop can be seen here - http://tinyurl.com/kyfbrm2.

The bookshelf version (the original Jeff B design) is offered as a kit here at Meniscus - http://meniscusaudio.com/docero-full-pair-p-1408.html

Jim Griffin is a MLTL design master and the Docere MLTL should add some significant low end to an already great woofer, the Meniscus Eclipse W6520R-4.

Just got started on these this weekend so there's not much progress thus far. The plan is to do a 1.25" constrained layer baffle with 0.75" ply and 0.5" MDF sandwiched together with Acry-Tech Acoust-X. http://tinyurl.com/kq58s83

Some initial pics-

The original design:


The MLTL:




In boxycad:


Coating the ply with Acoust-X:







Fabricating lots of bracing in my super duper fancy brace fabrication rig:


Only half done with the braces so far and about to run out to watch the White Sox kick some booty. More later:

[bkeane1259]

Here's a short video on the Acoust-X application - https://www.youtube.com/watch?v=af8LHIldVXg

[jrhollander]

So Bryan what the process for the constrained layer? Let dry and glue together, assemble wet? What I've read so far seems to indicated there needs to be a bond between layers?

[bkeane1259]

I've never used Acoust-X before so the baffle will be a bit experimental. The product isn't a great bonding agent, so I'm going to be using a lot of screws. I thought about screwing the panels together while the Acoust-X was wet, but I didn't want to get a bunch of squeeze-out. So this is what I'm trying. I coated the ply and I’m letting that dry. Then I will coat the MDF panel and screw it onto the ply and let the whole baffle dry. This way I should (hopefully) get a good even layer of damping compound in between the ply and the MDF.

[bkeane1259]

Second set of brace holes cut (slightly smaller hole saw). Cutouts rounded over and all of them sanded. Fingers hurt. I need a sanding sponge for the cutouts.



Here I'm coating the 1/2" MDF panels with Acoust-X. Right after coating, I'm screwing these on to the 3/4" ply which already has a layer of dried damping compound.



Lots. Of. Screws. 67 to be exact in each baffle. Honestly I have no freaking clue if this is going to make a beneficial difference but it's fun to experiment.



A closeup of some minimal squeeze-out. I expected this but my intention with doing one panel dry and one wet was to fill all the textured grooves and ridges created by the roller in the Acoust-X application on the ply panels. Now I'm sure there's a "complete layer" of damping compound in between the ply and MDF. Again, no clue if this is adding any real value to the cabinet. We'll see though.



Starting to rain again, so that's all for today.

[mattsk8]

Can't wait to hear these in Indiana!!

[bkeane1259]

Here's a good link to a variety of volume calculators.

http://www.hometheatershack.com/forums/ ... #undefined

Considering that I'm going to use five 3/4" thick window braces per cabinet I did the calculations to see how much I'd have to alter the depth of the cabinet to maintain the 1.4 ft^3 internal volume. Sure enough, mine will be an extra 1/2" deeper to maintain the proper volume.

In the OP, I posted the Boxycad sheet for the original design. My cabinets will end up being 10.5” deep – An extra ½” for brace volume displacement and an extra ½” for the constrained front baffle.

[bkeane1259]

The rest of the panels are cut, glued, clamped and slightly out of square as usual, but I seem to get a little better with each build. This one is pretty close.

Dry-fitting the cabinets together looked promising........but..... I think part of the problem is I do not have any sort of protocol for gluing and clamping towers. I've absolutely required help from my 19-yr-old any time I've done a large cabinet and this one is no different. Seems as soon as you start spreading the glue and clamping stuff, inevitably a panel is going to shift. Well, this is my experience anyway.



Did I mention that I need more clamps? I do...no joke.

One tower:



The other tower. Notice that in this cabinet, I tossed in a few pieces of scrap to help align things. I did not dado the braces in this build and that definitely made gluing and clamping more challenging.



The bracing is randomly spaced and the circle cutouts alternate. Does it help break up standing waves? I have heard it does but I've never seen any scientific proof. Of note: One brace will sit between the tweet/woof and one brace was purposely positioned below the woofer to mark the end of the line stuffing. This way I can just stack the required amount of stuffing for the MLTL between the braces, up to the top of the cabinet. BTW - Meniscus sells the perfect product for this. The MLTL calls for stuffing with uniform density of 0.75 lb/ft^3 and their bonded dacron just needs to be cut into sheets that fit the line without compression. How easy is that?

Bonded Dacron - http://meniscusaudio.com/bonded-dacron-p-185.html



These are sitting in the garage curing. Tomorrow I have a lot of sanding to do, or maybe it will just be Duratex to the rescue. Have not decided on a specific finish yet, other than the baffle which will definitely be black Duratex.

[bkeane1259]

Took some time today in between rain storms to unclamp and sand the cabinets. First order of business is to knock down some of the glue squeezeout and high spots with the router and flush trim bit. A while back I picked up a big honkin dual bearing flush/pattern bit from MLCS - http://tinyurl.com/mxy9ltg I think it was $25 at the time but it was well worth the $$ - one of my favorite bits.





After flush trimming - just need to sand away minimal glue now.



Some 80-grit sanding to get the butt-joints perfectly level.



Right on cue.....Mother Nature steps in to ruin the party with yet more rain. Most of the sanding is done....still need to do some prep work before painting/veneering.





My thought right now is to veneer the sides and do black Duratex front, back, top, bottom. However, I'm not 100% sold on that idea. Not even sure if I have enough veneer, which is still in storage with a bunch of other stuff from our move last year. Sadly my tools and hobby stuff remains in a state of chaos as I never got around to organizing everything. Somebody sign me up for "Mission Organization" please.

[bkeane1259]

May 16 - Pissing down rain and 40 degrees in Chicago.

[Wolf]

Yep- I took the day off and wanted to work in the garage myself to put the curves into place for my theme entry. So- I bought some music for the event, and tested some of it out on the 'Tudes....

Interesting,
Wolf

[bkeane1259]

Yup.....almost cold enough for it to snow here but we lit up the fire pit, turned on the grills and popped a couple brews and all was good. Didn't get anything done on the project tho.......

[bkeane1259]

Just out of curiosity, I checked the squareness of the cabinets. Shocked, to say the least.

[bkeane1259]

Worked on the baffles today.

Port cutout. The design calls for a 2.5" x 7" port. Normally, I'd use schedule 40 PVC but 2.5" is an odd I.D. to find around here so I just got the 2.5" flared port that PE carries. It will need to be trimmed a bit. http://www.parts-express.com/speaker-ca ... d--260-478





I wanted to see the Acoust-X layer in between the ply and MDF, so I pried apart the port cutout puck. I actually had to use a hammer and chisel to separate the puck. That Acoust-X bonds a lot better than I thought.



Tweeter cutout:





Since the jasper circle jig only adjusts by 1/16th I had to go a hair bigger than the 104mm cutout. When I Duratex the baffle, it should be nice and snug, but for now there's a tiny gap.



Woofer cutout and the chamfered backside. I use a cove bit and freehand it.

[bkeane1259]

I have enough Cherry veneer left over from when I did the Seas Trym MLTL, so I will be veneering the sides and tops of the Docere MLTL towers and Duratexing the front/rear baffles and the bottoms.

I've tried raw and paper-backed veneer with the iron-on method and got good results, but the process is a bit long and it requires a fair amount of patience (which I lack). For the Seas project I used PSA-backed veneer from VeneerSupplies.com and I found that process to be a quicker and less messy, although the substrate requires some prep work for the PSA to get a really good bond.

Today I brushed on two coats of dewaxed shellac on the panels that will receive the veneer. Tomorrow I’ll lightly sand to make sure I have an even and completely flat, sealed surface to work with.

The veneer is paper-backed cherry flat cut with the PSA option - http://www.veneersupplies.com/products/ ... 2-x-8.html