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Discussion in 'Archived Threads 2001-2004' started by Brett DiMichele, Feb 24, 2003.
Brett, Have fun building that one! If you're going to go for the big ribbon you may as well do a dipole. BTW, really nice rendering... is that 3D Studio Max?
Mike, This isn't something I am designing.. Jon (Thomas W's Bud) is designing a Line Array and when it's complete I am going to build a set for myself from his plans. But I want to make the outside of the cabinents slightly different and that's what this is, a design exercise. The rounded back shouldn't be too bad to do. You can make cuts in MDF 98% of the way through the material and this allows you to curve the material. It will need fiberglassed to make it more stiff after it's curved and then the cavity will be filled with concrete. I am not altering his cabinent design I don't want to get into baffle step issues, I am just going to add on to the back of the cabinent on the outside so it won't affect the inner volume or dimensions. This image was modeled/rendered in Metatools Bryce 3 and thanks
since the rounded back is just for looks, and will be filled with concrete, why not split a sonotube then cover it with bending birch) or a plywood cylinder or mdf cylinder? it'd be tricky though. better yet, maybe something here could fit the bill. a lil more money, but alot less work and ugg, mdf dust.
Jeff, I suppose it could be done numerous ways. I probably could even just use some thin HQ Ply and form it around MDF braces and fill the sections between with concrete. I'll cross that bridge when I get there (and I won't be getting there any time soon)
Your midbasses need to be flush-mounted. If they were flush mounted, they would't be throwing those big shadows.
Running the B&G monopole in that small of an enclosure will affect it's sound considerably, IMO. Jon usually likes to design no-holds-barred, no compromise speakers. I like the design, tho. Pete
Pete, I think Brett will follow Jon's enclosure volume recommendation. I'm actually surprised that Jon won't do his as a dipole to take full advantage of the RD50 ribbons, but HE is the expert, not me. Brett, consider plywood half-rounds from Tape-Ease. An 8" O.D. half-round 5/8" thick Poplar x 96" long is $60: http://www.tapeease.com/2rounds.htm
Instead of making cuts in MDF 98% through you can buy it 98% pre-cut in sheets. That would save on the MDF dust factor also. jay
Hank, Thanks for that link! Yes I will follow Jon's enclosure designs to the T. As for the drivers being flush mounted, this was just a quickie render to experiment with enclosure design, If Jon says the drivers get flush muounted then they will be mounted flush. Any modification I do to the enclosure will merely be for asthetics and I will make sure not to change the actual baffel design or the area where the BG will mount. If Jon changed the design to a Bi Pole then I will built it accordingly! As Hank said, Jon is the expert..
Brett, Few things you'll want to look at. First off as someone mentioned, mids should be countersunk. Second, the farther away the mids are from each other, the more issues you will have with comb filtering and wierd things going on in your response. If you only planned to use them up to say 500Hz and then cross to the ribbon you'd be fine with them further away. Then a few other things that would help too. You'll really want rounded edges on the baffle to help with diffraction effects. Especially on the side closest to the ribbon. A 2" radius tends to work pretty good if you can do it. I'm about to get back into working on our Baby Grande Theater system. The system consists of all line array speakers, including a line center channel. The front speakers use 12 7" mids and 12 smaller ribbon tweeters. The front speakers are a dipole system. On the side closest to the ribbon I actually use a 6" radius roundover. The other side is tapered to help smooth the dipole rolloff. Then it has a 2" raidus roundover on that edge. When finished the 6" radius will actually wrap all the way around and come back behind the tweeters making a column. On the other side, the baffle will go back 12" as well and then curve back in. By extending the baffle back, you can essentially make the baffle appear wider, increasing the low end cutoff frequency. Here's a pic of the first prototype. The small space between the ribbons will be taken out in the next one, and the ends of the faceplates on the ribbons will be shaved also to get the mids even closer together. FYI, our large Grande Theater system will actually use RD75 ribbons and 12 Seas Excel 7" drivers in a similar configuration. John
John, To say those are substantial would be an understatement! WOW they look gorgeous and I bet they sound as beautiful as they look! The Mids I am going to use are MCM Carbon Fiber 6.5" units. They have a semi round basket with flats on each side so they can be butted right against each other. I am guessing the way Jon has it figured out 6 of these 6.5's mate up with the lenght of the BG RD-50.
John, that's what I basically was planning, sketching a dipole design. I was thinking of using 6" O.D. ply half-round on the mid-woof side, tapering the other side and using a smaller O.D. half round. Jon has decided to go with monopole however, and since he's got the knowledge, I'll probably go with his basic design. Brett, you're right, Jon's number of mid-woofs matches well with the B-G RD50 that he'll use. I see you're taking his recommendation on the MCM mid-woofs. They're certainly impressive and unusual for MCM.
Hank, I am taking his word for everything. HE knows this stuff I don't.. I can built it.. But I can't design it I am sure there are great drivers out there that could be used.. Seas,Scan Speak, Vifa etc... But the sheer number of drivers needed isn't very cost affective for DIY and the whole theory of line array's doesn't place much stress on any one particular driver so distorsion figures would be low.. The MCM driver looks like the right driver for the job. A much cheaper (not so visualy pleasing) driver could even work in this setup but the price of the MCM is very reasonable. I was going to do a set of Alpha LS's untill Thomas pointed me to Jon's Modula's.
I am in the middle of CLIO testing the MCM 6.5 CF drivers and they dont look bad. Also they look just like the Audax HM170CO externally, square flange with rounded corners. BTW the picture MCM has on their website is NOT what they look like. If I get a warm day that I can play I will rerun the T/S tests. Right now I am working on a design using the 4" MCM CF.
Mark, I saw your post before where you were CLIO'ing the drivers. What do they look like? You said very similar to the Audax 170CO? (not that it matters)
what would be the cost to make these.
Bryan, Rough estimate (assuming you do all the labor) 2 grand or so... Could be less could be more.. If you went with different drivers you could easily DOUBLE that price.. And you might not gain any better performance. I haven't sat down and figured out driver cost and I have no clue what the XO's are going to cost to build Jon hasn't gotten that far yet..
Here's a link to a thread page with Jon's description and two photos of the 6.5" MCM CF driver: http://www.htguide.com/CFBoards/inde...6&StartRow=106