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Old 27th April 2012, 02:11 PM   #321
John L is offline John L  United States
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Location: Cary NC
Ivan, I had attempted to use all the plaster I had accumulated earlier. It was dental plaster from Plaster Supply, and supplemented by some regular plaster from Lowes. The dental plaster was indeed a slightly better product. But even using plywood as a filler for the frames I had constructed, it was unusually heavy, and the expansion rate had caused the rounded piece to crack in several places. The clay was never fired, and is just 'green ware', so I had to be very careful.

Price wise, the plaster would have been more affordable, but it didn't work out for me very well. That is the reason for going with double the amount of silicone and all the different urethane ingredients.

Had I known that the ground poly filler would be in such short supply, I may have wanted to go another slightly different way. But everything is here already, with the exception of that one item. So having spent the necessary funds already, I am committed to the urethane mold making process.

And in truth, I really think I am going the best route, because ceramics weighs a whole lot more than resin. Besides, if this works out right, I will have a good set to use for casting, should others want to go with this approach.

What is interesting is that I originally thought that making the six sided cabinet would be the most difficult part, but boy was I ever wrong. And of course, I have tried every which way but the right way. But I am learning and will eventually get everything down for the next pair.

And speaking of the next pair, this omni-directional approach really doesn't have to have a six-sided cabinet: a four sided cabinet will do nicely, as the previous pictures of the Sirius show. That would certainly make construction much simpler. So, the lenses will continue to be the real specialty item.

I'll let you all know when the filler arrives. It should be soon, and I suspect it will be essential because it will cut down on the overall weight of the lense. Urethane is a very thin resin when mixed together, and it is going to need something to make it a little thicker when I add it to the silicone mold.

As for weight, if the lense gets too heavy, it will make the speakers a little too top heavy. I'd hate to go to all this trouble only to have one accidentally fall over and ruin one of the lenses.

And again, sorry for the delay, but once I get everything, I'll start experimenting and keep everyone up to date on my progress.
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Old 27th April 2012, 02:34 PM   #322
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It's unfortunate that the plaster didnt work out.

Plaster does have a limited lifespan before its effectiveness is compromised, this may have contributed.

Another fun thing to do with plaster, is to mix in some cellulose (paper pulp basically) for maybe 5% of the total weight. it makes the plaster much less dense, so you don't need nearly as much and the end product is much lighter.

It might be worth looking at my dad's thread here, and his blog Wood Be Creative: A Shop Journal for Red River Canoe & Paddle: Clairtone Project G
the end goal is different, but much of the process is the same. He built an octagon enclosure, and will be making a spherical enclosure with composites.

If you are concerned with it being top heavy, you could always make a concrete base. that would keep it planted in place
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Old 27th April 2012, 08:57 PM   #323
John L is offline John L  United States
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That's really a nice pair of octagons. After the fact, I am discovering that an eight sided enclosure has certain advantages over a six sided one. And the one that affects me most is the angle of cut for each panel.

Its easy to find a router bit that will make a 22 1/2 degree cut. But try to find one that will make a 30 degree cut. You just have to improvise.

Oh, and I have many fond memories with time spent in a canoe. I used to live in Alaska, a long time ago, when I was a kid. Every summer I usually went to at least three weekly camps. Two of them always had a huge lake, where I would check out a canoe and practice my strokes.

There is nothing more relaxing as to glide over a tranquil lake, and listen to one or more loons calling each other. A wonderful experience.
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Old 4th May 2012, 06:02 PM   #324
soren5 is offline soren5  Denmark
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Hi John,

Recently I've been toying with the idea of making omni-directional speakers myself and in my search for information on the subject I stumbled over this thread. I've have now finished reading through all the posts and just want say that I think this is a fantastic thread, one of best written and most illustrative I've come across on this site. I really admire your work and dedication to this project - it's very inspiring! And your attention to detail just amazes me! I've now subscribed to the thread, and if it makes any difference at all, I have my fingers crossed that your grandson will get a set of great looking speakers for his birthday . In other words and as already said:
Quote:
Originally Posted by kctess5 View Post
We're all sitting firmly on the edges of our seats for this one (or at least I am)
One thing came to mind though when reading your 2012 posts . In post #294 you propose the idea of making additional hexagonal top enclosures to hold down-firing compression drivers (the left drawing). Considering the extra hight this approach would give, you then mention that perhaps you had made the cabinets slightly too tall, and that you now thought about shortening them. Now please excuse me if I've overlooking something, but couldn't you kill two birds with one stone here? If you shorten the cabinets wouldn't you be able to you use the cut-offs for such top enclosures?

Anyway, it was just a thought. Keep up the good work!
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