Hexagon Pioneer B20FU20 Enclosure
As I had mentioned before I have decided to construct a Hexagon(six sided Enclosure) in which to mount the Pioneer B20FU20, along with the Parts Express ND20FA Dome Tweater.
I first got this idea from two places. First from here with the discovery of the Chang horn enclosure, in which the Pioneer and a slightly different dome tweater from Parts Express. However, I wanted to do something a little bit different.
About that time someone, either here or over at the Parts Express forum, started a thread on the Duevel Venus. It was so different and downright beautiful that I decided then and there to make my enclosure like that one, and a slightly modified dispersion horn on top.
There are several different pictures showing this Duevel Venus, but the one above, with the Santos Rosewood, is the best looking to me. Santos is my favorite veneer material, and the surrounding sap wood contrasting with the heart wood really set off the veneer.
Unfortunately I could not find any examples of Santos like that, but did find a nice bit of walnut, along with sap wood, so I decided to use it instead.
The first thing I did was practice on the table saw in order to ensure a 30% cut with each piece of plywood, and have them come out exact. My Craftsman saw did not cut exactly on the mark for 30%, but was one graduation below that number. Then I finally got the right angle, and after several attempts came up with the sample below.
Each side is exactly 8 inches across.
Following this, yesterday I cut the pieces to size and set up my Dado blade combination, which I had just purchased for this job. I have always used my router to make rabbets and dado cuts, but never cared to pay in excess of $100 for a Dado blade set, not that I could not afford it. I just never thought it worth the money.
However, I was at Harbor Freight, looking at their 10 inch, 80 tooth carbide blade, which was less than $15, and happened to see the dado set in the blade bin. I asked a worker how much it was selling for just out of curiosity. When he came back with a $26 price tag, I finally decided that the price was more then right. I practically ran to the counter with it before they had a chance to change the price.
Naturally my blade guard would not work with a dado blade set up, so I had to fabricate one to go on the Craftsman saw. I did this by using a piece of 1/4" plywood, and removing the belt clip from an old, worn out, tape measure. The clip was for holding down the back end, and a hole drilled in the front end to secure it and I was ready to go.
I have a vacuum system attached to the saw, so I turned it on, along with the saw, and slowly raised the blade until it had cut through the homemade blade guard, to the point I wanted it to go, and that way there would be no saw dust flying around. The dust would be collected in the system and larger debris would not get sucked into the machine through any rough holes. I tried it out and Voila!, perfection.
Here are the cut pieces for one of the enclosures. As you can see on one of the top pieces, the knot hole makes the plywood a reject, but the fact that it is cabinet grade is what I was looking for.
To figure out the braces, I took the origional test case above, set it down on some craft paper, traced the inside dimensions on to the paper, and then added 1/4" to the sides. I figure that if it is slighely smaller than the dado cuts, it will still be fine, as I will be glueing it and also using heavy duty staples to secure the pieces.
Once I had cut the pieces on the table saw, I cut 9" holes in three of the braces with my plunge router and the Jasper jig, which was pretty straight forward.
So, this is where I have gotten tonight. I had earlier taken two cutout pieces from OSB and lightly brad nailed the pieces together with the OSB inside the cut out pieces, as a preliminary test, and they seemed to work alright. Tomorrow I will try to put the one cabinet together, using the three braces with 9" holes, by glueing, using finishing brads, and also staples, and see if I can get it all together and look somewhere professional in the process.
If I can get it to work, I will use it, and make the second one the same way. If not, and things have this strange habit of meeting Mr Murphy, I will use it as a test and apply what I have learned with two new sets of cabinet material.
As a note, I chose to go with cabinet grade plywood in this case, rather than MDF, because I found a special at Home Depot, where Birch plywood seconds were acquired on special sale. They were going for $26 and I purchased four of them for use in my business and with this project. The plywood is a bit lighter and once glued and fastened together tightly, there should be no worry about resonance whatsoever. that is one of the real advantages of a Hexagon. the sides are not wide and the brace and support each other. With the added inner bracing, they should be rock solid.
Anyway, here is the project. I will be adding on as I go along. If you have any suggestions, question, or comments, please feel free to give us the benefit of your extensive knowlege. I have never made a six sided speaker enclosure before, and to me this is brand new ground. It looks quite daunting, and indeed it may well be. And on that I can see two real problems.
First, getting all these pieces of wood to cooperate and stay in line and even, as I attempt to glue, attach and align them all together, is going to be a real job and probably very frustrating. All the sides are straight, and I can now see the need to obtain a special router bit that will cut an interlocking groove for each surface. I'll have to look around and see what I can come up with, but until then, I will have to settle for smooth angle cuts of 30% with each side. If anyone knows where I can get a bit that will make this cut for me, I would love to know about it.
And Secondly, I am still trying to come up with a way to make the top horn dispersion piece. A member offered to help ne with the job by making them on his lathe, but I have not heard from him lately. I'll have to contact him soon, and see if he is still up to contributing to my project. I have looked into purchasing a wood lathe, but really don't have all that much need for a power tool that will take up added space and not be used to it's potential.
So, here I am just getting started, and only at stage one, with most of the planning complete(I'm certain that I overlooked a great deal already) and the pieces cut to size. Next will be that of trying to get the parts to work with me and allow me to put them all together and have it look respectable. I have a long way to go here, I'm sure. So please look at this as your project too, since my success here also depends on your interest and keeping the thread alive and interesting.
Well, I love B20s, and I love nice walnut like you've got there, even before finishing. Sorry I don't have any advice on the carpentry aspects of things, but I am very interested in your project. What sort of cabinet will this turn out to be? With a cabinet this size, sealed or vented would be viable, though I would vote for sealed. It just sounds better, IMO. Besides, low bass is omnidirectional, just like your intent with these speakers, so a sub to fill out the bottom shouldn't change directivity.
Some things I'd like to note for you . . . stock, the B20 is pretty dull off axis. When I modded mine with phase plugs, that changed dramatically. If you're intending to make reflectors styled after Duevels', possibly you could have the point of the reflector flair back out till it is proper width and length to fill the cavity over the B20s pole piece. Removing the dust cap in order to install a phase plug or my proposed extended reflector also improves the driver's response by removing the airmass under the dust cap which compresses, especially at higher levels which you'll need to compensate for using it as omnipole like this. Another point in favor of phase plugging the B20s is the fact that these small tweeters don't like to be crossed very low, and that far off axis, even with the reflectors, I'm afraid you would have to cross them too low.
I look forward to seeing you work through this project. The potential for a wonderful sound system, not to mention some wonderful looking cabinets, is huge with this.
Would it be possible to make the horn dispersion piece as an extension of the phase plug? Or would that affect the sound of the b20 to much?
Another reason for going with a cabinet of this size is that it would be interchangable with other larger drivers. A 12" could easily fit on the top of the cabinet, and it is conceivable that a good quality High Compression Horn could work with a 12" driver and have a smooth transition in the 1000-1250 hz range. If you look at the higher costing Duevel models, the Bella Luna, and the Jupiter, all three models use a high compression horn. and with the Jupiter, it is used with a 12" driver.
Also something else.If the above scenerio is not doable, in a reasonable alternative, it is also possible to set up the enclosure to accomodate a low frequency driver, firing out of the bottom of the cabinet, and using an 8" on top as a midrange, and a coaxal tweater mounted in front of it, instead of having to come up with a high compression horn siting on top of the array.
I know that using a down firing low end driver is not difficult, because It appeared in the Dunleavy Aletha, which was also a Hexagon unit. Unfortunately the Dunleavy and Duevel are the only ones that I know of which are six sided speakers. It's something that may be a bit daunting to most designers. And that is not really fair for the design, because it is actually the most efficient enclosure for space utalization, other than the Octagon. It's just quite a bit more difficult to make.
Here is what the Aletha looks like.
So what do you think of the 2.5 cu ft size? Incitentially, the Aletha above is 51" high finished. The ones I am making will be somewhere close to that, once the base and the dispersion horn is attached. Currently the body is exactly 40" high in their raw form. Of course I can still cut them down a little bit, since I have not assembled the walls yet. All I would have to do would be to recut a new rabbett joint at the bottom of each piece.
The 2.5 ft^3 volume is perfect for sealed and is very workable for vented for the B20. Shouldn't be any problem designing an alignment to fit your setup since you have so much volume to play with.
Having the tweeter sitting on something (like a length of dowel) that's sitting on the B20's pole piece (yes, with the dust caps removed) with whatever you come up with as reflector suspended above should be a fine design. Just as long as you remove the dust cap and have something acting as a phase plug (plugs don't have to be bullet shaped; cylindrical should be fine for this application), you should get much better off axis performance from the B20.
If you decide to put a low frequency driver downfiring,you could still use the B20 as your mid. You would simply design the volume for the sub driver (I could recommend the Dayton SD215 which is a very flexible 8" dual voice coil sub driver that can work well in sealed or vented enclosures), then use the remaining enclosure volume as a sealed enclosure for the B20. The smaller chamber will act as a high pass filter for the B20. Then you would install a sub plate amp with a variable low pass filter for your sub driver, and you'll be able to very easily mate everything up.
I have more than my share of tube receivers and amps, so I have to keep efficiency in mind. I'm into 60s and early 70s vintage units, such as the Sansui 1000A, or 2000/5000 series
As for the mid range, I had been considering the PA 165, but again you are bringing me back to the B20, which has an even better efficiency, and would go along easily with the subwoofer. Amazing how versatile the B20 really is. ;)
I think we may be coming up with a great future project, once this one is complete.
Oh, I have the first enclosure glued, and stapled together. I have all the pictures ready to go into the computer, and I will upload them to Photobucket soon. Then I will post them here.
I was concerned that the entire carcus would not fit well, but it went great. It is not a perfect hexagon, because the precut brace leaves some opening at one end of the carcus. But I can custom cut another piece and make it fit nicely. And it really wasn't all that difficult. However it does help to have a table saw, with dado blade set, and also a compressor for using air tools. :D
Now that I have put together one of the carcuses, I have found that it is not all that difficult as I had anticipated. What I did was start with two of the three internal braces, then glue and line them up with one of the walls. Once that was done, I used my brad gun to nail them in place. Then I did the same with the third internal brace.
Next I turned the carcus over one turn and glued the end of the braces and the first wall. Then I lined up a second wall, and starting from the center brace,shot the aligned walls with brads into both walls, and continued down to the ends of each side.
Here is what it looks like turned face up. I used a pretty good bit of glue, so I needed a wet clothe to wipe off the excess.
Click on pic for larger shot.
And here is the inside shot.
Here is what the seam looks like.
2/3s of the carcus done.
And a closer look at the inside seams.
Here is the carcus put together. Once I completed attaching the six walls, I liberally used the finishing brads and then used my Duo-Fast stapler, and shot the braces in place with 1 1/4" long 1/4" wide staples. Once the carcus dries it will take a lot of force to get the walls loose, because i shot everything full of brads and staples.
Here is an inside shot. And note that I really lucked up and got the cuts to match pretty well. Looks almost professional. I'm not going to count on the next one to look that clean. :)
Next up is to fill in all the small holes and then sand everything down smooth. I found that some of the outside veneer had come off on the corners, so I will have to fill in there too.
As for routing the wiring for the tweeters, you've got some options. Most invasive would be venting the pole piece by drilling through it. That way you could also drill through whatever you end up mounting the tweeter to and the wires would be 100% hidden. I doubt this would have any real effect on the B20, unless you were unlucky enough to get metal shavings into the voice coil. Simpler and safer would be to simply string the wire (which could be 30ga magnet wire, no problem) from the phase plug/tweeter mount to the edge of the basket or beyond, letting it enter the cabinet someway other than through the cone. You won't be able to see that if you orient the wire toward the back of the cabinet, once the reflector is in place, and it won't effect the sound of the B20.
I mentioned the 8" Dayton simply because it seems to sim better than either of its larger siblings in that line. WinISD pro shows it behaving slightly better in BR than the 10" or the 12", even though it needs a 1.6 cu ft enclosure and the 10" and 12" need about twice that. Just a quick look with the B20 in .9 cu ft sealed at the top adn the SD-215 in 1.6 cu ft BR tuned to 29Hz at the bottom, shows that the B20 will start rolling off around 120Hz and you should run the SD-215 on a plate amp that will let you move the crossover point at least down to 50Hz so you'll have enough room to play with it and get them optimized. The plate amp won't have to be too beefy, though since the B20 should peak about 1dB higher than the SD-215 in this configuration. And just for discussion's sake, this sim shows the SD-215's F3 at about 26Hz.
If you like the omnipole sound (which I do, second only to good dipole like OB or planar/electrostat), this should be a good and cheap (well, driver wise, anyway), not to mention almost text book "full range" speaker.
What does "BR" mean? I'll probably slap my forehead when told, but I can't think of it at this moment?:)
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