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Old 7th March 2012, 03:01 AM   #281
John L is offline John L  United States
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Quote:
Originally Posted by Greg B View Post
Very cool project. It'd be a good idea to gouge a couple key holes into the side of the mold if your intention is to make a two piece mold. That's the usual trick for alignment.

You probably could have gotten away without using the silicone rubber compound for this, since the shape doesn't have fine detail, but it certainly won't hurt.
If you scroll up a few posts and look at the silicone that is pulled back from the lens, look to the bottom outer edge of the lens. There you can see that I have marked the outer edge of the blank where it will match the seam of the sliced silicone.

Once I finish pouring the last half of the plaster portion of the mold, I'll also notch the plaster with the silicone so as to ensure the silicone is exactly lined up with everything.

But you are right, it really is important to have everything matched, because nothing is perfectly round, or even.

Last edited by John L; 7th March 2012 at 03:04 AM.
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Old 7th March 2012, 01:35 PM   #282
Carlp is offline Carlp  United States
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What an experience, John. I've worked with that plaster and yes, it does set up quickly. You can change that a little with the amount of water you add, but not much. 15 minutes or so will usually be your MAX working time. Doing multiple pours isn't a bad idea as the plaster will heat up quite a lot when mixed in large batches and can take a LONG time to fully cure. I think so long as the plaster hasn't fully cured, multiple batches should bond properly, but I don't know for sure.
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Old 7th March 2012, 11:47 PM   #283
John L is offline John L  United States
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Originally Posted by Carlp View Post
What an experience, John. I've worked with that plaster and yes, it does set up quickly. You can change that a little with the amount of water you add, but not much. 15 minutes or so will usually be your MAX working time. Doing multiple pours isn't a bad idea as the plaster will heat up quite a lot when mixed in large batches and can take a LONG time to fully cure. I think so long as the plaster hasn't fully cured, multiple batches should bond properly, but I don't know for sure.
Carl, this is my first experience with plaster since my childhood. And I have forgotten almost all of my experiences with it. Fortunately, I've been doing a lot of research before hand. But I still have to learn the hard way.

I checked out the left half of that mold this morning, and it is still very wet. I also read somewhere that it will take up to two weeks for the plaster to cure thoroughly. This is time consuming, and not to mention that it is getting expensive. And I'm just talking about the lens horns. That initial investment is always costly. But once I have some ready to use molds, they can be used a good many times.

Maybe I can entice some others to do this too, in order to defray the initial costs of those darn lenses. And the cabinets don't have to be hexagonal either. The latest one from Duevel, the Sirius, is squared. Aren't they beautiful?

Click the image to open in full size.

You know, I could take the bottom lens, and just make two of them, turn one upside down, and fuse the two together. Then make a box for the top, where I could use a high compression horn to radiate downward on a separate lens. And it would work nicely with a hexagon, or a square box base.

Can you just imagine finishing something like that and having guests check them out? Those Sirius above are going for $35,000 a pair. Can you believe that? And I'll bet you the overwhelming majority are in the cabinets.

Anyway, I'm going down stairs tonight and set up the larger bottom part, getting it ready to pour tomorrow. Only this time I'm just going to set the blank in the box and just fill in the cracks along the edge of the blank since the plaster sets up so quickly. It won't have a chance to start seeping under things before it begins setting up.
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Old 8th March 2012, 12:24 AM   #284
mightym is offline mightym  United States
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Default Duevel cloning

John,

neat find on the new Duevel. I think they make beautiful speakers, but don't have a clue where they can be auditioned in the states....

Regarding your spitballing on turning the diffusers, you could use something like this:Dayton Audio H10RW 10" Round Waveguide 1" Threaded 270-310 Or one of it's siblings, as the waveguide part under the top box, and it wouldn't even be visible.

Just a little more spitballin' here....

John
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Old 8th March 2012, 01:52 AM   #285
John L is offline John L  United States
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Originally Posted by mightym View Post
John,

neat find on the new Duevel. I think they make beautiful speakers, but don't have a clue where they can be auditioned in the states....

Regarding your spitballing on turning the diffusers, you could use something like this:Dayton Audio H10RW 10" Round Waveguide 1" Threaded 270-310 Or one of it's siblings, as the waveguide part under the top box, and it wouldn't even be visible.

Just a little more spitballin' here....

John
As for auditioning them, they are not the kind to show up in a lot of places. The $35000 price tag puts them way up there in the 'blueblood' range. But there have been a few high dollar writers who have listened to them. Reviews on all the Duevel gear are quite positive. But there is one cavet here. Due to their openness and 360 degree dispersion, they have to be placed in just the right location to obtain the maximum advantage. That is the only real serious drawback. But if they are set up in a large enough room, such as living room or den, and moved about three feet from the back and side walls, they should do a great job of making a large room become suddenly a much larger one. The depth should be considerable, and you just can't obtain that from a regular pair of speakers, even the EconoWaves.



The funny thing is that I had looked at this waveguide you show here, and didn't come up with the solution for using it with the upper box, for the high frequency horn, until I read your post.

I'll show you what I mean. Let me bring up a picture on how the Sirius is supposed to work. Its a partial cutaway drawing, and explains a lot on the mechanics of that speaker.

Here it is:

Click the image to open in full size.

Using that plastic waveguide as the top most flare of the equation, it could be turned face down and screwed into the bottom of a slightly deeper upper cabinet frame, like what the Sirius has sitting on top. By attaching it to the bottom of the upper frame, there would not be a need for two separate lenses: only one, which would have two of the bottom halves of the lenses I am currently making. One half would be pointed downward, and the other half would be pointed upward, and both fused together, in order to make the bottom assembly as shown on the Sirius drawing. There wouldn't be a separate upper lense, as in the drawing. Rather, there would be the waveguide you show, and it would be screwed into the bottom of the box, and the high frequency driver would be screwed on top of the waveguide.

I'll have to make a drawing and post it here. I really need to learn Sketchup, but don't know how to use a drawing program yet. So I will do it by hand and then scan it into my computer.

But basically, the upper frame housing would have to be a little bit deeper than the one in the Sirius drawing because the height of the waveguide is 5 inches and the high frequency driver(Selenium D220Ti ) is 52mm, which is 2.02 inches. That means we will need 7 inches, plus the thickness of the top board, and the bottom board, of the frame. That would be at least 8.5 inches tall. I don't know if it would look too top heavy, but its a starting point.

I'm going to go to PE and check out some more round horns/guides and see if I can come up with something shallower. I'll be back later.



While I am gone, also look at how Duevel attaches the outer ring to the wooden lens lense horns. Obviously they first form halves of the wooden lens assembly on computer guided lathes as shown on this page. I can't tell if they make the upper and lower portion of the lense in one piece, but I just don't see how they could accomplish this on a lathe. The blanks have to be secured to a plate that is secured to the lathe motor in order to turn the blank accurately.

But however they manage this, once the lense horns are ready to be set up for the Sirius, there is an outer ring built into the lenses which have been shaped by the lathe.

Now look closely at how they attach that outer ring. they use either a saw blade, or a router bit, and make a thin dado cut all around the outer ring of the wooden lense, and then affix it to the assembly. What this means is that the outer ring can be used to hold up the lenses and the dado cuts will allow this ring to hold up the lens assembly. And there does not need to be any holes drilled into the lenses themselves. Very practical method for supporting that load.

And one more thing too. the need for having a tailor made lense for every type of speaker would be eliminated because the outer ring could be expanded or contracted, depending on the size of the cabinet assembly. And too, the entire process of using it all as a lense horn would still be maintained and look very professional.

My only problem with all this is that it suffers from the German tendency to over-engineer everything. The final result is fantastic, but it has so many parts it takes longer to produce, and costs much more in the process. This is why they lost WWII: they couldn't produce enough material(the MG42 being the lone exception) because they just had to make everything perfect and complicated.

Anyway, to my thinking there is no need for that other lense. Its just too much desire for perfection IMO.

Anyway, I'll get a drawing sketched up showing what I mean.
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Old 8th March 2012, 02:44 AM   #286
mightym is offline mightym  United States
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John

I'm glad you got the gist of what I was intending. I've spent ( probably wasted ) a fair amount of time looking at the different iterations of " Omni Directional " loudspeakers on the web. I have an interest at some point of trying to come up with an Omni design of my own.

I got to hear a set of the Mission HT omni's at an acquaintances house recently. I was favorably impressed with the sound, but didn't have the heart to tell him that putting the surround speakers in the corners at the back of the room was kind of defeating the purpose of the design....

Still, if they came available at the right price I would consider them for my LR, for HT use.

I didn't mean to sidetrack the thread, I just saw what you posted and read the text, and the first thing that came to mind were those O.S. waveguides I linked to....

Hope your plaster gets hard soon.

John
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Old 8th March 2012, 07:15 AM   #287
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Some of the 8" full-rangers have a frequency response that keeps rising out to 10khz or so. I'm thinking specifically of the Fostex FE206En, the Visaton b200, and the Seas FA22RCZ. One of those might work pretty well in that sort of enclosure without using a tweeter-if you didn't mind losing a little in the top octave. Your diffuser horn would counteract the beaming in the treble, and it might even out the response pretty nicely.
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Old 8th March 2012, 10:27 AM   #288
UnixMan is offline UnixMan  Europe
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BTW: a super-simple (yet effective) way to build an omni:

www.audiofaidate.org - Diffusori omnidirezionali "Periakusma" (AKA Walkaround)

(English translation of the above by Google)
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Old 8th March 2012, 01:48 PM   #289
John L is offline John L  United States
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Originally Posted by UnixMan View Post
Thanks for the input.

For some reason my Opera browser is having trouble going to all the links. Can you show me an image of the Omnidirectional speaker that was chosen? I was able to see some, but believe I am missing out on the most important ones.
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Old 8th March 2012, 07:04 PM   #290
AmCan is offline AmCan  Canada
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Hi John,
I am silicone and mould making and resin casting expert. I just happened to catch the back end of what you are doing here and could probably help you out significantly but I am trying to catch up on reading back into the thread to see why you are making a 2 piece mould of an object with no undercuts? I think you could have made a one piece mould here. Plus, there are ways to make light weight mother moulds (shells) without using 10lbs of plaster. I am not sure what your objective is here in making the mould but if I better understood the objective I could help you out better.

Last edited by AmCan; 8th March 2012 at 07:21 PM.
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