Matrix multicell horns - deconstruction and reproduction attempts

gable

Senior Member
Horns and drivers present many limitations. Size is a big one, pardon the pun. The Western Electric 26a that models out to a ~254hZ cut off frequency would not be crossed that low. I don't recall off hand where WE crossed them in the original Mirrophonic II systems. I would like cross no lower than ~400hz. That is a nearly 40" wide horn. Ok, I might try a lower crossover point, depending on the driver, but not too much lower than 400hZ... :D

All loudspeaker systems are compromise collections. Capitulate size for frequency coverage being one of the most dominant ones. There's thousands of other points to compromise on, to varying degrees of 'importance'. To add to it, a lot of them are rather subjective compromises.

My approach is to design/build the best I can given 3-5 main points.

1 - Cost. No reason to bother designing something I can't afford to build/own.
2 - Size. My main system is in the living room, and while my wife is incredibly understanding, she'll beat me in my sleep if I take over the entire living room.
3 - Reasonable aesthetics. I do my best to not put 'shop' grade systems in the house, at least not for very long.
4 - Cost.
5 - Time. My most precious commodity.

Beyond that all I really care about are 2 main points. I endeavor to learn, discover and hopefully grok new things every day, and especially in long term projects. I have to end up with a system/component that rocks, it has to trigger the grin and butt shake from me or it does not stay in the system.
 

gable

Senior Member
I got out to the shop later than I wanted to today, but still had a productive afternoon. I was able to cut ~12 or so horn cell components for the 1505s and the h808s. Now using the correct router bit, and thus cutting them to the proper size. To cut the mouth and throat ends I used my trim router with a flush trim bit. This works, but it's quite fiddly. I'm going to make a second router table for it with some plywood and long bolts, will make cutting those ends much easier.

My plan for tomorrow is to get an assembly jig for the 1505 and h808 made up, and to make the clamping 'donuts'. If all goes well I should get a few cells glued up.
 
I wanted to test the exponential calculations and horn geometry for a horn with a 90 degrees bend. The WE 31A appeared to be a good candidate.
18357

Took a while, but, finally figured out the odd geometry of this horn. About an inch from the throat, it changed from a round shape to a football shape due to the 120 degrees flare horizontally where the throat is still going down before turning horizontal becoming a rectangular shape.
The theoretical cut off frequency from the model is 352 Hz.
18360

18361


I am done with modeling horns for a while. Learned quite a bit. Gained a whole new level of appreciation for all the Western Electric and Altec engineers who accomplished amazing things using their log tables and slide rules.

Got to get back to my VDCH project.
 
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gable

Senior Member
Your VDCH project is truly bold, cheers to you for tackling it!

Back at real job today, which means I was only able to get in the shop for ~30min or so. I was able to prep all the pieces, well, most of the pieces, to make 6 assembly jigs for the 1505 horn cells. I'll post some pics tomorrow when I get a couple jigs made up. I'm going to work on a jig for the H808 horn cells as well. That will basically be a scaled down version of the 1505 jig...

I _feel_ more confident about the template duplication and horn cell component production, and have some ideas to improve my process. I'm hoping to gain enough confidence with the horn cell glue up to get a long weekend planned before the year is over. The tentative plan would be to rough cut the materials to make a pair of 1505s and a pair of h808s in the evenings, then take a 3 day weekend to cut all the components and glue them up in batches.

A lot of things need to come together well in the next few weeks, and it's a stretch goal to be certain. I like putting a bit of pressure on myself, and am perfectly happy if I come up short of the stretch goal, as I know I will learn a ton and make good progress on the overall project.

Famous last words and all.... I know.. :D
 

gable

Senior Member
Fairly productive day in the shop, the pictures don't capture it all unfortunately. I decided to make a bunch of the 'clamps' that slip over the outside of the cell pieces, while the glue sets. I want to be able to glue up at least 6 horn cells at a time, so I will need quite a few. I'm making them from ~25mm baltic birch as I have a lot of ~12mm on hand. I'm making the assembly jig bases from the same material. I was able to get enough cut today to make 4 bases for the 808s, 6 for the flat mouth 1505s, 6 for the curve mouth 1505s, and 6 for the 26A's. I was also able to get enough thin strips to make the 'clamps' for 6-7 sets. I may make a few more sets of the 'clamps', if I really need, but for now, I should be set.

Also, real clamps, one can never have enough.


The assembly 'clamps':

IMG_2228.jpg


Many clamps, gluing a few of the larger pieces for the 26A bases:

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Just some of the ~2.25" wide strips I cut today and now will glue together to make more of the clamps:

IMG_2230.jpg
 

gable

Senior Member
Gable's an a$$hole, but a productive one so far today:

Got the assembly jig bases for 26A, 1505 Flat Mouth, and 1505 Curved Mouth horns cut to size. I'm going to chamfer the edges, then give them a quick sanding, before drilling the center bore that allows me to mount the vertical piece of the jig. I might put a couple quick coats of polyurethane on the bases. In the very least I'll wax them with paste wax, to help keep glue from sticking.

It's lunch break right now, more action later today.. a few pics of what felt like 43456 ~2.25" strips to glue, and nail together............


IMG_2232.jpg

IMG_2231.jpg

The pics don't properly display how many damn strips of plywood I had to glue up.

I swear there were thousands, THOUSANDS of them....
 

gable

Senior Member
The afternoon was productive as well, I got all the strips that I laminated earlier, trimmed down to final width and ready to be cross-cut to the various sizes for the clamps. I was also able to make all the assembly jig bases for the 1505 Flat Mouth, and 1505 Curve Mouth, and the WE 26A. I went ahead and chamfered the top edges, sanded them and put a few coats of polyurethane on them. Tomorrow I'll quickly sand them, lightly, then wax them with paste wax. That should keep the glue from sticking. Hopefully I'll have enough time to make the assembly clamps as well.

I may be picking up 4 Altec a5/a7's. I think they're A7's. They've been modified, with added bracing inside, and the ports were modified, they've also been painted. I'm buying these off a friend to help them out a bit, and will be looking to pass them on, inexpensively. I'll post some pics when I pic them up. They are in nice shape, well modified. I think they could make a great foundation for a system. Fresh port plate, some filler and fresh paint and they would look and perform wonderfully. If anyone is interested, please pm me.


Some pics of today's progress:

IMG_2233.jpg

IMG_2234.jpg

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I'm also starting to think about a storage cart, with a few shelves for the horn cells once they're glued up. I would like to be able to build several sets of horns worth of cells, and have somewhere to keep them safe as I start assembling the actual horns.
 

gable

Senior Member
Over the last few days I've only been able to get all the assembly jig clamps glued, I still need to sand them a bit and drill their inside corners so they don't glue themselves to the horn cells.

I did get to take my calipers to several vintage horns this evening, and will be going back to measure many more and a bunch of throat adapters.

I also picked up 4 Altec 825's, that have been lightly modded. I didn't have time to get pictures, I barely had time to unload them into the garage. Will get a bunch of pictures tomorrow and try to start assembling some details about them.

My oldest daughter is going to come over this weekend and help me for a day in the shop, so hopefully we can make some good progress.
 
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