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Old 10th January 2008, 03:06 PM   #111
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Hi John,

I can't believe I missed this project. You appear to be a kindrid spirit. I have worked on 4 omni projects over the past year and a half or so. I thought I would offer some links for you detailing these projects, in case there is something you can learn from my expereince. I was pretty much a noob when I started the first project and they all tended to morph from one concept to another as I learned the limitiations, so most of the good stuff is typically a bit later in these threads. The projects often looked quite different than the initial concepts. Perhaps you are much further in this hobby than I and there is little to learn from my expereinces. If so, please ignore his post!

The first link is my most recently completed project and where it is posted on this forum:

New Omnidirectional Project Complete

Here is a link to a bit more detailed thread on this project over at HTguide. It is a hybrib omnidirectional speaker that uses a front firing tweeter.

http://htguide.com/forum/showthread....mnidirectional

Of more intereste to you might be my first two efforts. You might be able to learn something about diffusers and placement, shape, size, etc., from the pitfalls that I ran into. The first one is below and I post it becuase I started with the concept of doing something like the Duevel. I ran into some trouble with off axis roll off, FR and diffusers, etc. much of which is indicated with measurements, etc.

http://htguide.com/forum/showthread....mnidirectional

I did test some Duevel shaped diffusers in this project. the concave cone diffusers offer much more potenial, in my expereince than any ball shape, flat sided cone shape, etc. However, I think you may be disappointed in the results of the downfiring dome tweeter concept as used in the Venus. I tested this and the FR was not good at all. You can see the results buried somewhere in that thread.

I used a combination of diffusers and waveguides in next project I will link to next. It has been referred to as a waveguide omni. This project was not completed and only one prototype was built. This concept just did not surpass what I had achieved in the first project, so it was abandoned. Still, there is a lot of experimentation with measurements of difusers, their shape, size, height and in combination with waveguides to emulate what Duevel does in the Bella Luna. There might be something here that you will find helpful.

http://htguide.com/forum/showthread....mnidirectional

I'm underway with the 4th project now. It will be a passive 3way, designed to fit into the budget category at the IowaDIY (under $300 for crossover parts and drivers). I have a prototype mostly built and I'm tweaking the crossover. It is similar in approach to two of my other projects and is a WMTM configuration, except it uses a slot ported, up firing 8" woofer (f3 around 31hz) PVC tubes for the mids, one firing up and one down and a small neo tweeter firing forward, mounted to the end of a tube. The crossover points are about 450hz and 3600hz or so. I'm extremely happy with it's performance so far. Attached is a paint shop pro mock up of what it will look like. I have a photo of the preliminary prototype, but don't have it with me now and can post it later if you are intetested.

Good Luck!

Click the image to open in full size.
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Old 10th January 2008, 03:56 PM   #112
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Dan,

The casework doesn't look "budget"
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Old 10th January 2008, 04:16 PM   #113
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Quote:
Originally posted by Ed LaFontaine
Dan,

The casework doesn't look "budget"
Hi Ed,

That's your fault! You set the standard higher. This was the concept, before I started building it. It looks a little different due to some reality checks.

Drop me a line. I'd like to hear/see what you are working on.
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Old 10th January 2008, 04:48 PM   #114
John L is offline John L  United States
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Thanks Dan! I have breezed through the links, and can see that I will have to sit down and go through them slowly, when I have the time later.

But I well remember seeing your project before(at the PE board), and greatly admired your use of my favorite material: Santos rosewood/Bolivian rosewood. It is by far the most beautiful material I can think of, with Waterfall Bubinga a close second.

Anyway, thanks for the kind words of encouragement. I will definately seek help from you soon, as I am about to finish the last wall of each cabinet.

Fortunately there will not be much in the crossover department, as this is going to be a Single Driver project, and the additional tweater is to be a suppliment.
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Old 10th January 2008, 06:41 PM   #115
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Default Hexagons

This hexagon reminds me of the old Empire line from the 1960's...

Click the image to open in full size.

http://greensboro.craigslist.org/ele/532350640.html

Lookin good
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Old 10th January 2008, 07:42 PM   #116
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Quote:
Originally posted by John L
Thanks Dan! I have breezed through the links, and can see that I will have to sit down and go through them slowly, when I have the time later.

But I well remember seeing your project before(at the PE board), and greatly admired your use of my favorite material: Santos rosewood/Bolivian rosewood. It is by far the most beautiful material I can think of, with Waterfall Bubinga a close second.

Anyway, thanks for the kind words of encouragement. I will definately seek help from you soon, as I am about to finish the last wall of each cabinet.

Fortunately there will not be much in the crossover department, as this is going to be a Single Driver project, and the additional tweater is to be a suppliment.
I'm going to mix figured Bubinga veneer for the dark areas of my latest project I posted above with solid maple on the light areas. I've always used backed veneer and contact cement and the bubinga I have is unbacked, so I may have to try the iron on method.

A couple things to note in regards to the drivers and the omni presentation. You may already be aware of these things, but in case your not, I will charge ahead. The manufacturers published frequency response (FR) graph will be in 2pi space, infinite baffle. Understand that with an up firing driver like you plan, the driver never transitions out of playing in 4pi space into 2pi. The upshot of this is that you lose a good 6db of sensitivity on the listening axis as compared to the published graphs. The good news is that you don't have to worry about baffle step, since the driver never transitions from 4pi to 2pi as it goes up in frequency as a normal, front firing speaker does.

Another major consideration is that there will be very significant driver roll off because you are listening essentially 90 off axis. Lets say the Pioneer is acceptably flat to you up to 5khz on axis. It may very well turn out that at 5khz, 90 off axis, it will be 10-15db down, having started to roll off naturally at 3.5khz (just a wild a.. guess). You might find that your tweeter will have to cover a bigger range of frequencies than you had anticipated, It may not be able to be just a "filler" in the omni presentation and bit more crossover attenuation may become necessary on the high pass to the tweeter.

The concave cone diffuser may help in this regard, by extending the useable freuency range a bit.

Also, the same types of performance issues occur with up firing tweeters. Your tweeter will naturally roll off, probably starting up around 6-8khz or so. Again, the diffuser will probably help some, but you might want to consider a tweeter with a rising FR that will end up flatter and more extended as it rolls off in the omni format. The other Dayton neo, the ND20FB, for example has a rising FR up through 20khz, where the ND20FA you are planning to use actually drops a bit from 10-20khz in a standard application and will drop a lot more in an omni application. Using the ND20FB, with a concave diffuser, you might get good extension out to about 17khz or so before it starts to roll off a bit.

I've got some FR plots I can post, if you like, that demonstrate these concepts with real measurements. They are also posted in those threads I linked.

Diffuser position is quite important (height from the drivers) and will have a significant effect on the drivers FR. It may turn out that the two drivers don't work best with the same diffuser height, which could present a challenge for you. The tweeter will generally have it's flattest FR, with the diffuser about as close as you can get it. Depending on the size of your diffuser, it's profile, the depth of the cone, etc. a position very close to the tweeter may not work with the woofer, essentially closing it off too much.

Anyway, this is some food for thought as you move on to the next step. I suggest you be prepared to play around a lot with diffuser size, profile and height, if you want the optimal results. It will be a much easier puzzle to work out if you have measurement gear.

I'll help in any way I can.
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Old 10th January 2008, 08:47 PM   #117
John L is offline John L  United States
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Quote:
Originally posted by dlneubec


I'm going to mix figured Bubinga veneer for the dark areas of my latest project I posted above with solid maple on the light areas. I've always used backed veneer and contact cement and the bubinga I have is unbacked, so I may have to try the iron on method.


Using paper backed veneer makes things go much faster, but you naturally give up a lot in flexibility. I happen to like the raw veneer best. It is far thicker and is more forgiving. Plus, you can do things that you can't do with the former. I think you will like it quite a bit.

As for using the iron, I find it to be pretty easy, provided I am going the one piece per side scenerio. If you need to bookmatch, or put pieces together, perhaps using the glue in the regular fashion is best.

Quote:
Also, the same types of performance issues occur with up firing tweeters. Your tweeter will naturally roll off, probably starting up around 6-8khz or so. Again, the diffuser will probably help some, but you might want to consider a tweeter with a rising FR that will end up flatter and more extended as it rolls off in the omni format. The other Dayton neo, the ND20FB, for example has a rising FR up through 20khz, where the ND20FA you are planning to use actually drops a bit from 10-20khz in a standard application and will drop a lot more in an omni application. Using the ND20FB, with a concave diffuser, you might get good extension out to about 17khz or so before it starts to roll off a bit.
This is good to know. For the tweater, I plan to install a phase plug on the B20 and post the tweat on the end but not have the phase plug come to a point. That should get the tweater right up to the tip of the horn.

Also, I will have to consider changing the cap to get the tweater to step in at a lower frequency. That will be quite easy.

Also, I may just get the ND20FBs and give them a try as well. They are dirt cheap and also perform very well. I haven't looked at the specs, but I think they are just a tab more sensitive.

Quote:
I've got some FR plots I can post, if you like, that demonstrate these concepts with real measurements. They are also posted in those threads I linked.
Thanks Dan. I can use all the help I can get.

Quote:
Diffuser position is quite important (height from the drivers) and will have a significant effect on the drivers FR. It may turn out that the two drivers don't work best with the same diffuser height, which could present a challenge for you. The tweeter will generally have it's flattest FR, with the diffuser about as close as you can get it. Depending on the size of your diffuser, it's profile, the depth of the cone, etc. a position very close to the tweeter may not work with the woofer, essentially closing it off too much.
I can see that there will be a lot of tweaking going on here. Perhaps two or more phase plugs of different length, and also anchoring rods for elevating or lowering the diffuser. This is going to be a real study.

Quote:
Anyway, this is some food for thought as you move on to the next step. I suggest you be prepared to play around a lot with diffuser size, profile and height, if you want the optimal results. It will be a much easier puzzle to work out if you have measurement gear.

I'll help in any way I can.
As I mentioned earlier, I have a class this Saturday on wood lathe usage. Not only will I learn a lot on this, but I will also have the opportunity to make my own diffusers too. I expect them to be between 13.5" and 14" in diameter, and of an upper and lower piece. That way I can turn the pieces easier and perhaps custom cut the insides of the diffuser in the future. I'm trying to make an enclosure that is as flexible as possible.

And I don't have any measurement gear. Oh, I do have an older Woofer Tester that I never got around to working with. I bought it at the tail end of one of my speaker interest cycles, where I got tired of it and moved on to other interests. Now that I am back, I will have to call PE and ask for help using it.

But I don't have anything sophisticated. I don't have anything like SoundEasy either. Oh well, we will be able to work it out.
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Old 13th January 2008, 10:56 AM   #118
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verry nice job
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Old 14th January 2008, 05:12 AM   #119
John L is offline John L  United States
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It's been a long weekend of various things, including the continued work on the Hexagon Enclosures.

After finishing the veneering job, and rough sanding, I finally got down to the fine sanding. As I went along, I discovered that the glue I used, the Heat Bond cement, dried a dark dark brown. The problem was that on the lighter sap wood of the walnut, it showed up on the edges, like a sore thumb to me. No matter how carefully I sanded, it still came out.

So another lesson learned was not to rely on this Heat Bond on regular veneer. I will go with Titebond II from now on. I have since learned that Titebond II will do the same thing if ironed on, and it is no different in color or darkness than that of wood carpenters glue. When it dries, it will dry a lighter color and shade.

On this picture, there are two things I wish to show you.

Click the image to open in full size.

First, no matter how hard you try, it is virtually impossible to keep all the corners from showing a chip or two, or more. In this case, it happened to me twice, but I found a piece of walnut of the same shade, and custom cut it to match the chip, where I glued it on and managed to cover up this little problem.

But second, if you look a little further to the right, you can see the dark shade of the glue, where the two veneers overlap each other. I tried filling in with sawdust, but no change. It is just something I will have to live with. And fortunately it is not like there on most of the edges.

After I got all walls sanded and looking as nice as possible, I began the process of applying the Super Blond shellac for sealer and finish. After the first coat on two of the walls, I quickly realized that Super Blond made the dark glue at the corners stand out even more than they did without it.

What was I going to do? I had a choice of sanding it back down, or compromising by using the Orange shellac I had mixed up already. I decided on the Orange shellac.

The first heavy coat (3 pound cut) went well on each cabinet. I would rotate cabinets by doing two walls on one, then the corresponding two walls of the other cabinet. Then I would go back inside and do other things. After about 30 minutes I went back outside and rotated the cabinet two clicks over and repeated the process, until I had all six sides shellaced.

After I completed that, I decided to do this one more time, before letting it set up over night. I had planned on lightly sanding the shellac until everything was even and smooth.

As I started in on the second coating, I noticed that some of the veneer was bubbling up a little bit. Oh G-d!, what next? By the time I completed the second coat, there were about a dozen places on the two cabinets that had veneer loose and bubbling up. All that work for nothing, because the minute I reapplied the hot iron to attach the veneer, the fresh shellac would be ruined. I was right.

This mistake was not a result of the denatured alcohol causing the glue to come loose. What had happened was that I failed to keep the iron over the veneer long enough after turning down the heat, once I realized that the higher heat would cause the veneer to open the pores. By going back to heat level 3, from level 5, I needed to remain longer on the entire veneer surface. All that was needed was for me to reapply the heat to that loose spot. Unfortunately, the shellac was already on and correcting one mistake created another.

After that collosal fiasco, I wanted to cry, but came out of it after about ten minutes and almost losing my religion. But once I decided that I would have to remove all the Orange shellac, I brought the cabinets inside, broke out the fresh pack of 0000# steel wook and a new can of denatured alcohol, along with a pack of new work rags. Then I just started soaking the steel wool with alcohol and rubbing one side, top to bottom, and loosening the shellac.

One nice thing from this was that a good portion of the shellac managed to fill in the grain and add to the buildup of sealer. The rest I began wiping off with the new rags. As the shellac came loose, I would keep wiping, until I managed to get all of it off that wall. Then I turned the cabinet one click over, and repeated the process until I had cleaned off all the Orange shellac from both cabinets. In the process I managed to go through about 1/4 can of alcohol, half a pack of steel wool, and an entire pack of work clothes. Oh, and a great deal of humility as well.

What a Terrible Mistake to learn the hard way!

But I am a true believer that every set-back is another chance to shine in another area. Once I had succeeded in removing ALL the shellac, I noticed that the color and tone of the cabinets were a wonderful combination, AND the dark glue in the corners were greatly marginalized. What a stroke of fortune! All this work removing the Orange shellac had actually resulted in a sealed cabinet, along with just enough tone of the shellac to add enough character to blend in the dark glue. I don't know how I managed to luck up on this, but I will gladly accept it.

Oh, here is a picture of the veneer showing how it bubbled up. I almost forgot that.

Click the image to open in full size.

I had taken several pictures of the bubbling, but they did not show up as good as this. And as you can see, the shellac had dried and come up with a nice shine. All to no avail. And as you can see, the dark glue does not show up as much either.

Last night I had a great deal of time to think about this, and finally decided to take the cabinets back outside today and reapply two thin coats of Super blond shellac, but in very thin coats. I wanted to just get enough on to give it a lustre and not build it up too much. I was not worred about bubbling again because I had ironed down the spots that had come up with the heavy shellac application before.

I applied two quick and thin coats, which dried quickly. Once I finished that, I brought them inside and started finishing the base to both cabinets.

I had not been too happy with my first attempt on a base, so I made some slight changes to the piece already cut out. First thing, I cut down the width of the base, so it would overlap the cabinet by only 1/2 inch instead of an entire inch. Then I used a 1/2" round over bit, set up on the router table which is part of my table saw extension. I rounded the six sides of the base, and bevel cut the stacked smaller piece that fit between the cabinet and the actual base. By cutting them at about a 40 degree angle (getting the blade mechanism cranked to 45 degrees was not worth the agrevation), they will be able to reflect the sound coming out of the cabinet's venting.

Here are the cabinets with the roughed out bases.

Click the image to open in full size.

The bases are roughed because I had to fill in all the holes in the plywood, which will be sanded tomorrow if I have the time.

Also note that what appear to be horizontal blemishes at the bottom of the cabinet are really reflections off the cabinet. Most likely from my plastic ruler that is just outside the picture, but in the last picture.

Also, the two little coats of Super Blond shellac really brings out the shine in the cabinets. When I lightly sand them down with emory cloth, and apply a nice polish to the cabinets, they should really shine. Almost makes me want to apply two more thin coats just to make them shine more.

Here are what the bases look like.

Click the image to open in full size.

For some reason my table saw blade just wouldn't cut the left part of the base without burning the wood. Perhaps I need to get a new blade? I don't know, but the cut was very hard to get to go through the cut and not catch on itself. I will have to check the alignment of the blade and also the rip fence. I haven't done that in some time either. Anyway, I will sand all that off, and it will be painted black when I finish getting it smooth.

If I discover that the beveled portion is not back far enough to accomodate the venting, I can always recut it, and attach it to the cabinet with bolts.

After I have sanded the base pieces, I will seal them with my good old shellac, and then paint them black.

Not sure what I should use. Any suggestions?

After that, it is on to the upper section, where the most skill will be required. All the rest of the work on the cabinet and base is just downhill work. Or as one of my constructions buddies once used to tell us on all our jobs together, "We're all through 'cept the finishin' up". How prophetic that is too. If you are in construction you will know exactly what he meant.
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Old 14th January 2008, 07:39 AM   #120
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Absolutely BEAUTIFUL work!!!
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