Hello,
I designed an experimental TL enclosure, but I can't physically make it. It's a 6-inch PVC pipe bent into a uniform 540 degree spiral over the course of 54-inches (see plan attached below), so that it looks like a spring, not a nautilus. The problem is very simple: I can't figure out a way to bend six inch PVC. Nothing I've tried (and I almost died trying) does the job. It doesn't behave like I anticipated.
Here are the two theories behind the design. One is practical, the other is, well, not.
1) TL enclosures are huge when it comes to size/performance. I figure by spiraling it the volume is the same, but the space it takes up is more manageable. I was hoping, eventually, to build a box around a reasonably-sized curly-Q of PVC pipe.
2) TL enclosure-building is a battle against unwanted resonances.
Part A) In spiral theory, when you send a substance down a spiral, gravity causes the g-force to increase, and components of the substance separate. The same is theoretically true concerning waves, except gravity doesn't cause the centrifugal force, the driver does. I saw another horn-loaded enclosure that had a spiral ( http://www3.ocn.ne.jp/~hanbei/eng-inside.html ), but I have no idea what the theory is behind it. I'm thinking it's horse manure. Not that mine isn't, but still...
I think that the resonances will be more manageable since the frequencies will have separated somehow. I'll try to explain if you'd like me to make a fool of myself further.
Part B) I still think any "uniform" enclosure has the problem of standing waves, even a perfectly cylindrical enclosure. I like the idea of a tetrahedron, but that design is a nightmare once you try to measure the volume of a non-equilateral tetrahedron. It, too, is huge, in the long run. I believe that a spiraling tube creates a perpetual oblong, egg-shaped enclosure. If you look inside a tube that spirals down from the horizontal, you'll see what I'm theorizing. What is that shape at the "back" of the pipe on the plane you're standing on?
At any rate, I don't have the equipment to bend PVC pipe of this diameter (I wasn't even using the stronger schedule 40). I'll be building a variation that doesn't involve bending, but I was wondering if any kind and able soul wanted to test the design theory.
The diagram below is eventually based on a 1:1 Sd pipe for simplicity's sake. It is also two-dimensional, so I didn't bother trying to draw a real spiral. You'll have to bend it in your brain. The calculations are not ideal because a 6.5" woofer has its bass swallowed by the narrow volume at its throat. BTW, a 6.5" woofer fits PERFECTLY onto a standard PVC tee or 90. You can also surmise that this is easy to experiment with. It takes about 5 minutes to saw sewer-grade PVC with a hacksaw, so you can literally place the Tee anywhere you want with only a little work.
Thanks,
Dave
PS--anyone know where I can get 6" 90s for under $10/per in the US?
I designed an experimental TL enclosure, but I can't physically make it. It's a 6-inch PVC pipe bent into a uniform 540 degree spiral over the course of 54-inches (see plan attached below), so that it looks like a spring, not a nautilus. The problem is very simple: I can't figure out a way to bend six inch PVC. Nothing I've tried (and I almost died trying) does the job. It doesn't behave like I anticipated.
Here are the two theories behind the design. One is practical, the other is, well, not.
1) TL enclosures are huge when it comes to size/performance. I figure by spiraling it the volume is the same, but the space it takes up is more manageable. I was hoping, eventually, to build a box around a reasonably-sized curly-Q of PVC pipe.
2) TL enclosure-building is a battle against unwanted resonances.
Part A) In spiral theory, when you send a substance down a spiral, gravity causes the g-force to increase, and components of the substance separate. The same is theoretically true concerning waves, except gravity doesn't cause the centrifugal force, the driver does. I saw another horn-loaded enclosure that had a spiral ( http://www3.ocn.ne.jp/~hanbei/eng-inside.html ), but I have no idea what the theory is behind it. I'm thinking it's horse manure. Not that mine isn't, but still...
I think that the resonances will be more manageable since the frequencies will have separated somehow. I'll try to explain if you'd like me to make a fool of myself further.
Part B) I still think any "uniform" enclosure has the problem of standing waves, even a perfectly cylindrical enclosure. I like the idea of a tetrahedron, but that design is a nightmare once you try to measure the volume of a non-equilateral tetrahedron. It, too, is huge, in the long run. I believe that a spiraling tube creates a perpetual oblong, egg-shaped enclosure. If you look inside a tube that spirals down from the horizontal, you'll see what I'm theorizing. What is that shape at the "back" of the pipe on the plane you're standing on?
At any rate, I don't have the equipment to bend PVC pipe of this diameter (I wasn't even using the stronger schedule 40). I'll be building a variation that doesn't involve bending, but I was wondering if any kind and able soul wanted to test the design theory.
The diagram below is eventually based on a 1:1 Sd pipe for simplicity's sake. It is also two-dimensional, so I didn't bother trying to draw a real spiral. You'll have to bend it in your brain. The calculations are not ideal because a 6.5" woofer has its bass swallowed by the narrow volume at its throat. BTW, a 6.5" woofer fits PERFECTLY onto a standard PVC tee or 90. You can also surmise that this is easy to experiment with. It takes about 5 minutes to saw sewer-grade PVC with a hacksaw, so you can literally place the Tee anywhere you want with only a little work.
Thanks,
Dave
PS--anyone know where I can get 6" 90s for under $10/per in the US?
What an imagination you have.
My quick answer to your plan is to exchange the PVC for 6" stovepipe (and/or elbows), some zip screws and a couple bags of concrete. Build the box first, and pour it up as you assemble the pipe. (zip screws are self-tapping sheet metal screws)
I don't think a 6" corrogated drainage pipe with a 10# crush rating could be bent this tight.
My quick answer to your plan is to exchange the PVC for 6" stovepipe (and/or elbows), some zip screws and a couple bags of concrete. Build the box first, and pour it up as you assemble the pipe. (zip screws are self-tapping sheet metal screws)
I don't think a 6" corrogated drainage pipe with a 10# crush rating could be bent this tight.
My two cents
My feeling is to do away with the PVC and use wood of whatever type you like. If you want to prototype a concept quick and dirty, there's nothing better than sonotube and some industrial adhesive (say PL400).
If you want to reduce the line volume because TL's are big, start the line at 4 * Sd of the driver and taper it to around 0.5 to 0.75 of the driver Sd at the end. This will reduce the line length about 35 to 40%. You box will probably turn out to be a nice 'U' shape which is easy to implement.
Use Martin King's Mathcad sheets to dig deeper into all the influencing parameters.
Good luck!
Brendon
My feeling is to do away with the PVC and use wood of whatever type you like. If you want to prototype a concept quick and dirty, there's nothing better than sonotube and some industrial adhesive (say PL400).
If you want to reduce the line volume because TL's are big, start the line at 4 * Sd of the driver and taper it to around 0.5 to 0.75 of the driver Sd at the end. This will reduce the line length about 35 to 40%. You box will probably turn out to be a nice 'U' shape which is easy to implement.
Use Martin King's Mathcad sheets to dig deeper into all the influencing parameters.
Good luck!
Brendon
Well.....if you got a lotta pipe to burn (hmm that sounds like a euphamism), you could try cutting it into angled sections (as in a mitered joint), then glue (cement/solvent weld/whatever) them together. With some help and luck, you should end up with a perfect spiral, albeit segmented.
Hmm. Dunno how I got that earlier estimate bass-ackwards
but $60 of elbows doesn't seem all that exorbatant to me.
Tim
Hmm. Dunno how I got that earlier estimate bass-ackwards
but $60 of elbows doesn't seem all that exorbatant to me.Tim
kneadle said:
You are definitely being over-apologetic and putting yourself down throughout this thread. There is absolutely nothing crazy about the idea of a spiraling pipe for a Transmission Line, and I doubt that the has been a speaker hobbyist who has not thought of a spiraling pipe behind the speaker. I do believe that at least part of the attraction to Transmission Lines is that image of the back wave whooshing down a pipe to reinforce the front wave.
Somebody had to bring it out into the open. Might as well be you.
I thought of cutting PVC pipe into small sections as soon as I read your opening post. I will make a suggestion as to how you can start figuring out the correct angle. We can finish off the math tomorrow-getting a bit late tonight to do the whole thing.
By the way, I have never built anything like this in this way. This is all speculation on my part. But hear me out-I think this should work.
We are using 6" diameter PVC, (or Sonotube, I'll just refer to PVC throughout this discussion, it will be understood that you can substitute Sonotube or anything else, for that matter). I will give suggestions for how we can make a circle with this. Tomorrow, we can figure out how to make the angle so the circles slope up, thereby making a spiral.
First, cut the PVC into 1 inch sections. A straight 90 deg cut. Do this assembly line fashion on your table saw-should maybe take an hour. If we have a 6 ft pipe, we now have 72 one inch sections.
I don't know how big you want the outside circumference of this spiral to be. I will guess 14 inches around. Again, we are just building a ring for tonight, we work on the spiral part tomorrow.
The outside is pi times the diameter, which equals 43.96". So we have to use 44 one inch sections. The outside of the ring will be 43.96" inches-we will have to custom cut one section, (maybe).
The inside section, if this were a perfect circle, would be 2 inches diameter. After all, the ring is 14" across and the PVC pipe is 6" inches around. That only leaves 2 inches for the inside diameter. That means the inside circumference is 3.14 times 2 inches, which equals 6.28".
That 6.28" must be divided among 44 sections, so each section will have to be cut so one side is one inch, and the other side .143". See drawing below.
Now, we must figure out what the angle must be for us to cut a 1 inch section of 6" diameter PVC pipe so the inside secton will equal 0.143".
That angle will be 85.9 degrees. I could go deeper decimal, but the chances of you being able to measure even one tenth of a degree are not good. But at least it will be discernibly different from 90 degrees.
Anyway, cut your 6 inch PVC into 44 one inch sections, then cut each of those at an 85.9 degree angle, each side. They should fit together to form a ring that is 14 inches across. We might have fudge a little on one section to make everything fit perfectly.
Tomorrow, we figure what angle we cut each section again to make it slope slightly upwards, therefore giving the spiral. That will be for another day-it's late.
Attachments
I take it back
With Kelticwizard's help, I CAN build this design. I hadn't considered angular cuts till last night.
I have one comment for Kelticwizard, though. Before I read your post this morning, I had thought of making the spirals a little more angular than this, that is, fewer pieces.
I also have tools that are rather crude. I'll have to call around to see if I can find someone with a saw that can precisely cut these measurements.
Otherwise, what adjustments would I make to the equations for larger, and therefore fewer and less precise, cuts?
That was a wonderful post. Let's see if we can translate it into reality!
Dave
With Kelticwizard's help, I CAN build this design. I hadn't considered angular cuts till last night.
I have one comment for Kelticwizard, though. Before I read your post this morning, I had thought of making the spirals a little more angular than this, that is, fewer pieces.
I also have tools that are rather crude. I'll have to call around to see if I can find someone with a saw that can precisely cut these measurements.
Otherwise, what adjustments would I make to the equations for larger, and therefore fewer and less precise, cuts?
That was a wonderful post. Let's see if we can translate it into reality!
Dave
Sch3mat1c said:Well.....if you got a lotta pipe to burn (hmm that sounds like a euphamism), you could try cutting it into angled sections (as in a mitered joint), then glue (cement/solvent weld/whatever) them together. With some help and luck, you should end up with a perfect spiral, albeit segmented.
Hmm. Dunno how I got that earlier estimate bass-ackwards
Tim
$60 of elbows is not all that exorbitant, but that buys only 5 or 6 6" 90s.
Did you read Kelticwizard? Angled sections indeed!
Thanks,
Dave
One other thing you might consider: sculpt the shape (I like the idea of a spiral that tapers down in ID) out of foam using a hot knife, then use a fiberglass and epoxy layup to cover it. When that's cured, pull out the foam (this is a little like the lost-wax process!), then start damping the exterior. Fiberglass-epoxy can be a GREAT cabinet material if you pay some attention to the tickness and fiber directions.
The angular method brought up is an excellent idea. If you want i could draw up a plan for you with cad giving you all of the required pieces (once i get it running on my computer again), they should all be the same, as long as your spiral has a uniform pitch and diameter.
It would be quite dificult to cut though, requirering compound angles to be cut on a tube, but it is possible. You would definatly need a chop saw or radial arm saw. Chop saws are relativly cheap and would not be a one time tool. You would also need to make a vee-block to hold the pipe. And maybe some jigs to hold the pieces as you glue them. Definaly a tablesaw is out of the question, unless you build a sliding mitre table for it.
The other idea that was brought up was to use flexible heating duct. The stuff they use to conect clothes dryer to outside vents, it is very well made stuff and is pretty cheap, and i'm almost positive that it could be bent into that tight of a bend. To further reinforce the duct you could fiberglass it and it should be pretty solid.
I hope you go through with this project, it sounds very interesting and has got the wheels in my head turning.
It would be quite dificult to cut though, requirering compound angles to be cut on a tube, but it is possible. You would definatly need a chop saw or radial arm saw. Chop saws are relativly cheap and would not be a one time tool. You would also need to make a vee-block to hold the pipe. And maybe some jigs to hold the pieces as you glue them. Definaly a tablesaw is out of the question, unless you build a sliding mitre table for it.
The other idea that was brought up was to use flexible heating duct. The stuff they use to conect clothes dryer to outside vents, it is very well made stuff and is pretty cheap, and i'm almost positive that it could be bent into that tight of a bend. To further reinforce the duct you could fiberglass it and it should be pretty solid.
I hope you go through with this project, it sounds very interesting and has got the wheels in my head turning.
I have to go grocery shopping
Yes, yes I do want to have measurements from you. That would be great. I don't have any means. If a chopsaw is reasonably priced (I'll look), I'm definitely going to build this with the pipe I have.
The solution for making the circle into the spiral is quite simple, really. When I'm cutting the angles, all I have to do is turn the piece a few degrees. If I do it uniformly, it will gently spiral down and around.
This is just great, everyone. I don't know why I didn't post this idea earlier; I sure could have used this help sooner. I was despairing until last night.
Dave
Yes, yes I do want to have measurements from you. That would be great. I don't have any means. If a chopsaw is reasonably priced (I'll look), I'm definitely going to build this with the pipe I have.
The solution for making the circle into the spiral is quite simple, really. When I'm cutting the angles, all I have to do is turn the piece a few degrees. If I do it uniformly, it will gently spiral down and around.
This is just great, everyone. I don't know why I didn't post this idea earlier; I sure could have used this help sooner. I was despairing until last night.
Dave
Hmm...perhaps you could make a jig for this. (BTW, if you don't forsee you using a chopsaw - get one that can handle 6" pipe! - try renting one!) Clamp a piece of wood to the fence 1" from the blade (for a stop) and set the blade for the angle. Take a slice of the pipe, then rotate the pipe 180° (along its longitudinal (lengthwise) axis) and take another slice. The piece you just cut will now have two angles on it, and be the proper segment that you're looking for.
For alignment, that's a toughie...but I think I know how to get there. Before you cut up the pipe, draw a straight line along one side in black permanent marker, then do the same on the other side(180° away). (If you put a piece of wood on the table, such that it holds the pipe against the fence, and is half the height of the pipe o.d. (what, 6 1/4" o.d.? So 3 1/8" tall piece), you can line up the lines with this and you will be assured a symmetrical segment.
Now, that solves cutting alingment (GRR that's it, I hate the word "align"), but what to do when you have them cut! Well go back in time (you can rent time machines too ) and draw a different color line (or at least different size) either side of each line you drew above on the pipe. The angle of difference on these, I think, will be the angle of your turns, when you line them up on assembly.
Speaking of which, assembly could be tedious. You can't glue PVC too fast, and it would take one heck of a jig to hold it in place while they all set up...hmmm. With 72 pieces, and gluing two a day, it would take a whole month of construction :/
Tim
For alignment, that's a toughie...but I think I know how to get there. Before you cut up the pipe, draw a straight line along one side in black permanent marker, then do the same on the other side(180° away). (If you put a piece of wood on the table, such that it holds the pipe against the fence, and is half the height of the pipe o.d. (what, 6 1/4" o.d.? So 3 1/8" tall piece), you can line up the lines with this and you will be assured a symmetrical segment.
Now, that solves cutting alingment (GRR that's it, I hate the word "align"), but what to do when you have them cut! Well go back in time (you can rent time machines too
) and draw a different color line (or at least different size) either side of each line you drew above on the pipe. The angle of difference on these, I think, will be the angle of your turns, when you line them up on assembly.Speaking of which, assembly could be tedious. You can't glue PVC too fast, and it would take one heck of a jig to hold it in place while they all set up...hmmm. With 72 pieces, and gluing two a day, it would take a whole month of construction :/
Tim
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