I got my hands on a 12' stick of 12" sch 40 PVC tubing the other day. I was going to use published numbers to calculate volume since this particular stick was at the bottom of the pile and not perfectly round. It will be round once I get the ends put in it, but right now its hard to measure.
I've seen published PVC nominal IDs anywhere from 11.75" up to 11.9xx". Mine appears to be slightly less than 11.75". Are they all different? This one is spec'd by ASTM-D3034
I came up with a simple design that I would like you to help with... critique it
The tube is 12" nominal sch 40 green PVC. The endcaps are 3/4" MDF cut for a zero fit, one end obviously cut to hold an 10" driver. Overall length will be 16-18 depending on the final volume I choose. End caps of MDF will be put in place with sealant (what kind should I use?) and then screwed in place around the circumference.
I was concerned about the lack of gussets and supports, but the tubing walls are 3/8" thick (and naturally resistant to flex given their circular design). Problems with the MDF on the ends? Will I need to add braces or supports?
I've seen published PVC nominal IDs anywhere from 11.75" up to 11.9xx". Mine appears to be slightly less than 11.75". Are they all different? This one is spec'd by ASTM-D3034
I came up with a simple design that I would like you to help with... critique it
The tube is 12" nominal sch 40 green PVC. The endcaps are 3/4" MDF cut for a zero fit, one end obviously cut to hold an 10" driver. Overall length will be 16-18 depending on the final volume I choose. End caps of MDF will be put in place with sealant (what kind should I use?) and then screwed in place around the circumference.
I was concerned about the lack of gussets and supports, but the tubing walls are 3/8" thick (and naturally resistant to flex given their circular design). Problems with the MDF on the ends? Will I need to add braces or supports?
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I would consider using more than just sealant to hold the ends. I put a sub in a small tube and ran 4 .75X.75 pieces of oak the length of the tube, mounted inside, equally spaced apart(every 90 degrees). I used small screws through the enclosure to hold them in place. This gave me something with which I could secure the baffles very rigidly. It might be overkill, but it presented no disadvantages.
Just my 2 cents...
Mike
Just my 2 cents...
Mike
What do you mean "it will be round once I get ends on it"? Don't see how you can easily 'persuade' it to go back to a perfect round shape.
Mine was out-of-round too, so I just cut the end caps too large and trimmed them flush with the router. I then used course threaded screws and screwed the end caps directly into the PVC. I also used a liberal amount of that Parts Express speaker gasket caulk to ensure an airtight seal.
Not sure that will work for you since your walls are only 3/8" thick. My stuff was nearly 3/4", so no problem having enough material for the screws to grab.
Greg
Mine was out-of-round too, so I just cut the end caps too large and trimmed them flush with the router. I then used course threaded screws and screwed the end caps directly into the PVC. I also used a liberal amount of that Parts Express speaker gasket caulk to ensure an airtight seal.
Not sure that will work for you since your walls are only 3/8" thick. My stuff was nearly 3/4", so no problem having enough material for the screws to grab.
Greg
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Because the MDF I'm cutting will go inside the tube. By cutting a circular MDF panel and putting it IN the tube it will make it round.
I would cut the end pieces to fit inside the tube. Caulk the edge of each end piece, and and fasten them with screws thru the outside ends of the tube.
I would also laminate a second layer on each end, sized to extend past the outside surface of the tube, and rout it flush to the outside of the tube. It would help to do the laminating before installing the end caps. That way, the outer laminations could hold the inner end pieces in alignment for screwing in place.
Further, if you can get a hold of a larger tube, such a a Sonotube or the like, you can extend the outside laminations of the end caps to be sized to the inside of the outer tube. Then fill the space between the tubes with sand, or inject a rigid spray urethane foam to damp.
I would also laminate a second layer on each end, sized to extend past the outside surface of the tube, and rout it flush to the outside of the tube. It would help to do the laminating before installing the end caps. That way, the outer laminations could hold the inner end pieces in alignment for screwing in place.
Further, if you can get a hold of a larger tube, such a a Sonotube or the like, you can extend the outside laminations of the end caps to be sized to the inside of the outer tube. Then fill the space between the tubes with sand, or inject a rigid spray urethane foam to damp.
Like I said in the original post, " End caps of MDF will be put in place with sealant (what kind should I use?) and then screwed in place around the circumference." Like this:
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That was my exact idea, but I must not have adequately conveyed that 🙂
I thought about doing that, but also thought that the laminated exterior piece wouldn't bring much to the table other than adding rigidity to the panel itself... which is good, but I don't know how much that would be necessary.
That sounds like a nice addition. I like it. At this point, I'm not going crazy with driver or amp. Driver is a 10" Kicker CV-R DVC with a total of 450w (225 per VC). I can understand upgrading in the future, but at what point would I need that extra rigidity/damping?
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3/4 inch is not much of a panel for a subwoofer.
Be that as it may, try keeping that end cap in alignment for screwing without it. I don't think so.
It would also create a greater sealing surface for the adhesive.
Agreed about the 3/4". End cap alignment won't be a problem. The ends of the PVC are square. Lay the MDF on a table, drop the PVC down over it, reach through and hold the MDF flat on the table and drive in the screws.
I also agree with the greater sealing surface, but it would only add the small lip of the PVC's thickness. A definite increase, but necessary?
Please know I'm not challenging your ideas... just seeking clarity.
Right, I get that you want to put the end cap inside, but have you tried pressing the PVC in at all yet to see if it gives enough to wedge that MDF in there. I know that 3/8 is a lot less than 3/4" stuff I got, but it seems awfully rigid. Might want to experiment a little bit before committing to this inset design.
Greg
1. J-B weld - can find at auto parts store.
2 - Goop....can find that anywhere, drug store, sometimes grocery store.
Load the tube (end) with glue AND put some on the MDF, knock it in there, let dry overnight and clean with belt sander. I would add blue tape on outside of pvc to keep it clean. Now please don't forget to rough up the area you intend to glue with 60 grit sandpaper.
Not sure you have to add screws - loads of glue/epoxy/tight fit is all you need.
The 3/4" is not a problem, can always add brace(s), maybe 1" x 3" oak boards. OR find a friend with a wood lath and cut some kind of gumdrop shape back brace. e.g. [> ]
Cutting the end of the PVC...not as easy as sounds. Need a good line - wrap pvc with poster board and follow with pencil.
Are you going to damping the walls with something dynamat - I've used cork the last few projects, I think it works well.
2 - Goop....can find that anywhere, drug store, sometimes grocery store.
Load the tube (end) with glue AND put some on the MDF, knock it in there, let dry overnight and clean with belt sander. I would add blue tape on outside of pvc to keep it clean. Now please don't forget to rough up the area you intend to glue with 60 grit sandpaper.
Not sure you have to add screws - loads of glue/epoxy/tight fit is all you need.
The 3/4" is not a problem, can always add brace(s), maybe 1" x 3" oak boards. OR find a friend with a wood lath and cut some kind of gumdrop shape back brace. e.g. [> ]
Cutting the end of the PVC...not as easy as sounds. Need a good line - wrap pvc with poster board and follow with pencil.
Are you going to damping the walls with something dynamat - I've used cork the last few projects, I think it works well.
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Good idea! Strips of wood parallel with tube. Might not want to let them rest on the outside walls, they may come back haunt you (rattle). I'd leave a 1/4" air gap; best round em over with router round over bit.
Let us know if you want to go ported, have a few ides how to transition into a square port underneath.
Let us know if you want to go ported, have a few ides how to transition into a square port underneath.
I can sit on this pipe and it deflects very little. I think at my SPLs, rigidity won't be much of an issue. But I had an idea last night that would add strength to both the walls and the ends. I tried drawing it in SketchUp but I'm not that talented so I'll describe it.
In the original drawing, I have the MDF "ring" that fits in the front for the baffle. Let's say I cut two more of those, but only cut out an 8" hole in the middle. Push those into the tube about 4" from each end and tie them into the end pieces with about 6 chunks of MDF. They can be screwed to the baffle and endpiece and also epoxied to the walls.
As far as damping on the inside of the tube, I was hoping not to need it. I was hoping that the tube would be rigid enough that polyfill would be adequate. Suggestions or ideas concerning that thought?
In the original drawing, I have the MDF "ring" that fits in the front for the baffle. Let's say I cut two more of those, but only cut out an 8" hole in the middle. Push those into the tube about 4" from each end and tie them into the end pieces with about 6 chunks of MDF. They can be screwed to the baffle and endpiece and also epoxied to the walls.
As far as damping on the inside of the tube, I was hoping not to need it. I was hoping that the tube would be rigid enough that polyfill would be adequate. Suggestions or ideas concerning that thought?
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Good ideas. I was going to epoxy, but I was concerned about vibes. PVC doesn't like to hold epoxy quite as well as wood. I was thinking about something that would remain just slightly flexible (like one of the liquid nails products) and then going even more aggressive than 60-grit, like actually cutting circumferential grooves. If I were doing that, I would probably sleep better at night using screws to mechanically hold it in place as well.
I would love the clean look of no screws.
Thanks... now I'm hungry for gumdrops 🙂
Yeah... it took several cuts to get my first one right and I'm still not satisfied. I tried a large bandsaw. It was extremely close to perfect. Then I tried a big tubing cutter which worked well but took about 4 hours. I think I might try to find a large lathe or bridgeport and cut it that way.
Woooo too much work. Only need skill saw, remember once the F & R baffle boards are in, you can just beltsand it. (set baffle in 1/8"). You can use a framing square, just keep it lined up with pvc.
One reason to use pcv is that it's a quick build -- but let the glue dry!!!
Screws or nails in the "end grain" of MDF:
it won't help much and do more harm then good.
Now you do need to "bevel" the front and back disks (and sand the pvc) so there is a place for the glue to sit.
I'd line the "plastic walls" with something, not lose fill.
The advantage of the anything round - equal pressure on all the way around i.e. it can't go anywhere.
One reason to use pcv is that it's a quick build -- but let the glue dry!!!
Screws or nails in the "end grain" of MDF:
it won't help much and do more harm then good.Now you do need to "bevel" the front and back disks (and sand the pvc) so there is a place for the glue to sit.
I'd line the "plastic walls" with something, not lose fill.
The advantage of the anything round - equal pressure on all the way around i.e. it can't go anywhere.
Good point. I like the quick build, but I also want a sexy build. Let's test my belt sanding skills 🙂
Screws or nails in the "end grain" of MDF:
Even predrilled? I was thinking, "that's how you build a regular box, so..."
gotcha.
Can do. I have some rammat laying around somewhere
And cheap. If you buy it new its expensive, but I found a guy with about an acre of the stuff for $2/ft.
BTW.... what is the collective's opinion on polyfil in general? Use it? Skip it? Line the walls with something fuzzy instead?
I like that... if I were going ported. For now I'm staying sealed.
... but I am really tempted to "perfect" this design, go buy 10 sticks, and make a bunch of these enclosures to sell. I could even do custom lengths/volumes for different drivers.
... but I am really tempted to "perfect" this design, go buy 10 sticks, and make a bunch of these enclosures to sell. I could even do custom lengths/volumes for different drivers.
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