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Concentric Transmission Line Idea
Concentric Transmission Line Idea
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Old 15th August 2001, 05:54 AM   #1
Ignite is offline Ignite  Canada
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I was considering how I might make a powerful and interesting subwoofer out of a 12" long throw subwoofer I have kicking around. The idea of transmission line is intruiging, but generic. I thought perhaps a design in which a speaker was mounted in a transmission line enclosure that was designed such that instead of folding the horn vertically, it would be built concentrically around the driver. Then the end of the line would surround the speaker, and reinforce the forward wave directly around the driver itself. Has anybody tried this? If not, does any transmission line / horn guru have throughts on the viability of such a design?
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Old 15th August 2001, 07:49 PM   #2
GRollins is offline GRollins  United States
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A couple of points to keep in mind:
1) If you're building a transmission line, every time you put a bend in the cabinet, you run the risk of either reflecting the sound back up the TL towards the driver or creating a constriction.
2) If you're planning on a smooth, curving TL, you're going to run into some woodworking headaches. (See the B&W Nautilus for a closed-end TL using this idea.)
3) Whether the port (assuming open-ended) reinforces or cancels will depend on the frequency and amount of stuffing.
4) A well done TL is capable of stunning sound quality, but it's going to be big, no matter how you put it together. I used to build mine rectangular in cross-section, with the driver in the upper, inside corner. The pipe went down, up, down, up, and ported near the driver. I probably would not do it that way today, as I'd rather reduce the number of turns.
5) Given the amount of woodworking involved, it's a good idea to have a table saw (or at least access to one). I shudder to think about the build quality of a TL made with just a circular saw...

Grey
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Old 16th August 2001, 10:22 PM   #3
planet10 is offline planet10  Canada
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Concentric Transmission Line Idea
Default Concentric TL

There is a good article in Speaker Builder that used nested concentric sonotubes with a 15" driver

dave
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Old 24th August 2001, 11:08 PM   #4
Beggar is offline Beggar  United Kingdom
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hey GRollins, this is a little off topic, but I made my TL's with a... Jigsaw, I think you would resonate and subsequently explode if you saw the amount of 'damage' I had to repair on the panels before assembly, although jigsaw considered, they dont sound too bad!
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Old 26th August 2001, 10:23 PM   #5
GRollins is offline GRollins  United States
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Beggar,
Yeah, I made my first speaker cabinet with a coping saw. It was a little box for a 4" driver that I'd taken out of a junked TV. I was, I think, about 8 years old.
My next attempt was with a jigsaw. And the one after that, and the one after that. Then a friend talked me into doing one with a circular saw. That was a disaster.
Tired of bad woodworking, I bought a tablesaw back in about '74 or so. Never looked back since. Now, granted, I've used that saw to build a lot more than speakers over the years, but it's light-years better than any hand-held saw.
(Actually my original table saw--a Craftsman--got replaced with a Delta Unisaw this summer. The poor thing had given its all over the years.)
For those who don't intend to do more than the one project, making cuts with a jigsaw (or circular saw) may be the answer. But what about your next project? And the one after that, and the one after that? And once you've got a table saw on hand, you find *lots* of things that you can do, like good furniture, and such. Wanna DIY? Sure! Just do *everything* DIY. There's a lot of money to be saved. The saw will pay for itself in no time.

Grey
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Old 5th September 2001, 03:01 AM   #6
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Default Saws

Hi,

I do not want to be a part pooper, but one can do quality case work with a circular saw!. First get a crcular saw with a very stable base like a DeWalt, Bosch or porter cable ($150-$180). Make sure that the base of the saw is adjsted dead parallel with the blade. Get a good quality small 2 or 3" machinist square to adjust the blade perpendicular to the base. If you do not have a good small square just use a large one and check the cut by cutting a 2by4 and check the cut for square. If not square adjust. Next you need to make a couple of straight guides out of plywood. (one for square rips and one for 45 degree rips) take a piece of plywood about 12" wide and 8' long srew a 3" wide 8' long strip of very straight plywood on top of it. If you do not have a jointer or other tool to get the strip dead straight have a shop make it for you or you can use a straight aluminium extrusion. It is critical that the strip is straight. Once the strip is fastened. get you best 40 tooth carbide tipped blade adjust it dead square or dead 45, with the base, and rip the guide with the wide section of the base tight against the 3" strip. At this point the base of your guide will mark the exact location where your saw will cut. Now you just have to measure at both ends of the cut. Line up the guide with the marks, clamp and cut. You will need a good quality 4' square (about $50) to get your right angles. With this setup you are ready to make anything that one can make out of MDF or other sheet material.

Working this way is actually easier on your back than hoisting 4x8 sheets of MDF on the tablesaw. I do have a delta with a 50" biesmeyer fence but i use my circular saw get the sheets into manageable sizes, or if i work away from the shop i just do all the cutting with the circular saw and a sliding compound saw. In the shop i use a raial arm saw. It is all matter of convenience.

A word of advice. If you can not adjust the base parallel with the blade, get a circular saw where you can. It is well worth the money.

And for your own sake wear earplugs or earmuffs. After all you want to listen to your creations right?

dee
;-D
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