Experiments with M2 horns.

[Don C]

This weeks update. I had to get the back finished before moving to the front, because it won't be so simple to lay them down with the back up once the moldings are on the front. I did a test fit on the removable panel, and that was fine until I tried to remove it, and found that it was too tigt of a fit, and it didn't want to come out. It was OK, because I could stand it up and push it back out from the front. Of course that won't work later once the horns are installed. I needed to enlarge the opening a little bit. And I decided I need a handle. I routed out a hole half way through, then moved in a quarter inch in height, and routed all the way through. Those pencil lines are where I clamped boards to fence in the router, for the horizontal cuts. I ended up freehanding the vertical cuts, then cleaned up the holes a bit with a wood chisel. The wide part goes on the inside, to make the place to grip. I need to glue a piece of wood inside to close up the hole, but it's a no cost method to add a handle.



Then I laid out and drilled holes to fasten that back section and put in hurricane nuts. I want a little overboard with the number of screws. Half this number might be enough.



On to the front. I added the moldings along the edges of the front. These are just made from walnut boards cut to size on the table saw. Then the fronts were sawed at a slight angle. This is supposed to match the curvature of the horn at the edge. It should minimize any diffraction there, the grill frame will match the same profile. It wasn't easy to install these, the boards weren't very flat or straight when I started with them, and so the resulting moldings are not very flat or straight either. But with some struggle, they are securely glued into place, with some variation from flush along the sides. I may round the edges on these, they are sharp for now.



I made the length the same as the plan for the outside dimension of the grille cloth frames.



Next was a strip of veneer that covers the bottom where the grille cloth ends. You can see here that I wanted to toughen up the bottom of the cabinets as I'm not veneering there. I painted it with a thin coat of wood glue.

[Don C]

Then it was time for masking tape and paper.



Then black paint. This is semi-gloss Rustoleum from home depot. The label says you don't need primer with this. Its not as good as the Krylon, the finish gloss varies a lot across the surface. Much of it will be hidden behind the horn anyway, and the rest will be behind the grille almost always. They are starting to look a lot like the artwork, quite a transformation.



Next up, maybe the hardest part, grille cloth frames. I'm not too worried though, the advantage of working on them, they are loose parts, and it's not too much trouble to throw them away and start over if the plan doesn't work out.
Then lots of small jobs, wiring, fiberglass, light sanding, Watco danish oil, maybe some feet, etc.

[JeffW]

Getting close now for sure, can't wait to see them finished.

How are you going to mount the grills?

[Don C]

At the top of the plastic horn there is a reverse 45 degree angle molded in. I'll show pictures later. I will cut a wedge of wood there to match that angle, and glue it to the inside of the frame. The frame should just hang nicely there with the wedge and gravity pulling the frame flat to the baffle. At the bottom I can just mill a small recess in the frame to accept some Velcro. Or I could get fancy and glue a magnet or two there.
Edit: Pictures added

[Don C]

Here's the last set of updates for now, as I'm pretty much finished.

Picking up from where I left off before, I started cutting out parts for the grille frame. I cut curved bows for the front by tracing the correct line from the front of a horn. Then I cut the parts out on the band saw, leaving a little extra material. I had to borrow that saw because I don't own one. I clamped several of the bows together and sanded them on the belt sander to get the profiles exactly the same and right to the lines. All of the wood is all about 7/16 of an inch thick. I allowed about a half inch for the grilles in the design, with extra room left for the thickness of the cloth. This is probably not enough thickness for a good robust design. Oak was used for the side rails, because I happened to have some. I think that the wood for the top and bottom bow sections is Douglas Fir. Again, I happened to have some. The front of the side rails is cut at the same angle as the moldings. 8.5 degrees from square.







I made rabbet joints at the corners to maximize the glue surface area. I clamped everything together on the table and glued them up. I used two bows stacked and glued together at the bottom. The center bow is made of 3/4 inch plywood for more strength. It's smaller front to back because it has to sit on top of the higher baffle section. There wasn't room for that at the top, but that's where piece that goes behind the front edge of the horn is located. The wood there is angled at the bottom to match the profile of the plastic behind the top of the horn. During test fitting I trimmed that area with a wood chisel until the frames sat at the right height, flush with the top of the cabinet, after the cloth was considered.

[Don C]

After test fitting the assemblies to the speaker I decided that they were to flimsy. I added some reinforcement along the sides of the woofers to provide more strength. The shape looks funny because I used the wood scraps left over from cutting the bows. I had to trim aound the port openings. The frame is strong enough now, but only if I am careful handling it. I painted the finished frames with flat black primer. It looks a lot better than the semi-gloss Rustoleum does, I should have used this for the baffles.





I epoxied magnets to the back of the grille frame to hold the bottom of the frame, and put a screw into the matching location of the baffle to hold the magnet. You can adjust the amount of grab from the magnets by turning the screw. All of that was proven un-necessary later on.
This mounting scheme looks right, but it has occurred to me that if anyone but me ever removes the grilles, they will probably break them. You have to pull out at the bottom just a little, then lift. Pulling out the bottom more than a couple of inches would instantly break these frames. Lets hope that never happens.

[Don C]

After the frames were ready, I started on the cloth. This tan cloth is from Huntley audio. It arrived in the mail with a few snags already in the cloth. I don't think that they will show up in the photos, and you cant see it in person from more than a few feet away. Still, Huntley loses my recommendation here.
I copied the the installation method exactly from this older thread here. So I'm not going to repeat everything.
http://www.audioheritage.org/vbulletin/showthread.php?26984-Grille-Cloth-Installation

As per the instructions there I used a hot iron on dried Weldwood contact cement. This method works great.
The installation looks good. I keep having second thoughts about this color though. The finished grille assembly fits into place with a tight friction fit between the moldings. No catches or magnets are really needed. It's just right.

[Don C]

Then it was time to start finishing the wood. I sanded lightly with 220 grit on the orbital sander. I managed not to sand through the wood anywhere. I then applied the Watco Danish oil finish. This is medium Walnut. It's oil mixed with stain. The oil dries after a while, leaving a wax finish behind. I applied it with a paintbrush then buffed it off with clean cloth. I'm happy with the result. The stain shows that there are a few spots where I was careless and allowed glue residue to remain on the wood for too long, mostly on and near the sides of the moldings. It shows up as light spots. I'll try to touch these up later.

[Don C]

After admiring that work for a while, I installed the fiberglass. It's Johns Manville B777. I ended up using five packages of this. Five dollars a roll at the local home improvement store. Half of what I bought is white, the rest brown. It seems to be the same stuff regardless of the color. I used 3M spray adhesive to stick it to the walls. Afterwards I sprayed the fiberglass lightly with Deft clear finish to cut down on the shedding.



Then the ports went in. These are just fastened into the collars with two small dabs of RTV, in case I want to alter the tuning. The ports are 10 inches long counting the baffle thickness. That should give me about 26 HZ port tuning. Initial listening shows this to be fine. I'll probably go back later and glue these with lots more RTV.

I put the tweeter protection networks on the rib of the middle cabinet brace. Both drivers are wired with Monster XP 14 gauge.

[Don C]

Then the speakers had to brought into the house for final assembly. There are three steps up into the house from the garage, and I don't think I can do it with the drivers installed. Fully assembled they weigh 145 pounds.
The horn went right back on with the #10-14 Plastite screws and fender washers. The woofer screwed down with 10-32 Allen screws. And the back went on with more 10-32 screws, this time flat head. The flat head screws look nice with finishing washers. All of the back hardware should be black, but for now it's silver.

[Don C]

This is what they look like now. Sorry that the indoor pictures are not good.







I'm very happy that this is all finished and paying off. They sound fantastic. Just the same as before really, but compared to the LE14s I'm noticing a little more sub-bass in the room. The tweeters are right at ear height. I'll do some measuring and check the port frequency later, but for now I'm just listening. Very happily.

[srm51555]

Nice work Don, thanks for taking us through the building process.

[Mr. Widget]

Nice work Don, thanks for taking us through the building process.

+1

Nicely done! The grilles look great, I'm surprised you didn't need to use a layer of perf to prevent the ribs from showing. I think I'd go with s darker fabric, but they look very nice.


Widget

[JeffW]

Those look great! Why the 1501FE instead of 2216? And it looks like your port tube ends are right up against the stuffing?

[grumpy]

...but for now I'm just listening. Very happily.