Baffle Question/MTM Build

[bikedave]

I searched around and didn't find a definite answer to my question so I will pose it before the experts who can answer it easily. I am copying an MTM design which I like but modifying the enclosure from a standard rectalinear box to cylindrical. I understand that the baffle size and shape must stay the same, which is fine. The quick sketchup picture below will give an idea of what I am building. Don't worry, the driver/tweeter spacing does not represent what will actually be built. My baffle must be 20" x 6.5". If I cut my baffle to these dimensions, as shown in the drawing below, and then place top and bottom plates above and below that baffle which protrude a 1/4 or 1/2" in front of the baffle, does that change the baffle characteristics? Do I need to cut my baffle down to 18.5" and make the top and bottom plates flush to achieve 20"? Not sure if I am communicating, but would appreciate input.

[---k---]

Changing from even a 3/4" roundover to a 1/4" roundover can have a measurable effect. Changing from a roundover to having something overhang will definitely have a measurable effect.

Whether it can be heard in room depends on the design and who you ask. The people around here go through great pains to measure the exact cabinet and baffle diffraction results. Therefore, their designs are optimized for the exact layout they used. Other people have less optimized designs, so it may not matter as much.

I would try and match the original as best as possible. Several people have built round cabs. A search may turn up some examples.

[bikedave]

Thanks Ryan, I see what you are saying. You also answered the question which I forgot to ask and that was the effect of roundovers on baffle diffraction. Thanks again for the sound card as well, I have really been enjoying it, paired with a CleanBox to finally get my signal up to snuff.
Its no problem for me to maintain the baffle dimensions, just wanted to gain a little more understanding. I've already begun construction/planning as the two are usually not separated.
If they aren't too embarrassing I'll post some pictures once completed :P

[---k---]

Just FYI, here are some recent simulations so you can see the effect of the roundover. An overhang would be waaaaay worse than no roundover.

[JonP]

I searched around and didn't find a definite answer to my question so I will pose it before the experts who can answer it easily. I am copying an MTM design which I like but modifying the enclosure from a standard rectalinear box to cylindrical. I understand that the baffle size and shape must stay the same, which is fine. The quick sketchup picture below will give an idea of what I am building. Don't worry, the driver/tweeter spacing does not represent what will actually be built. My baffle must be 20" x 6.5". If I cut my baffle to these dimensions, as shown in the drawing below, and then place top and bottom plates above and below that baffle which protrude a 1/4 or 1/2" in front of the baffle, does that change the baffle characteristics? Do I need to cut my baffle down to 18.5" and make the top and bottom plates flush to achieve 20"? Not sure if I am communicating, but would appreciate input.

Cool idea... And yes, you would make the tops and bottoms flush to be the full baffle length dimension.

As has been said, a square edge is worse than a roundovered one, and a bit of lip like your drawing shows would be a bit worse than the square.

For the top and bottom edges, round them over. The sides, you could also roundover... Not sure how you're attaching the tube, maybe do a saw kerf cut on the back of the baffle? If you make that close to the edge, you could smooth Bondo or such over it to make a smooth transition. Tada.. no sharp edges anywhere!

Take a lot of pictures... I want to see how this one comes out...

[bikedave]

Thanks for the visual ---k---, that give me a little perspective, really does make a difference in the upper ranges. In that case I will certainly not put a lip on the plates! I'm gonna have to go with putting as much of a roundover on them as is physically an aesthetically possible.
JonP, I'll be posting pictures as I go hopefully to draw from the knowledge base here and get advice as I will be joining some dissimilar materials...

Thanks guys.

[bikedave]

Beginning Pictures

As promised, here are some pictures from some mock-up work last night. I've got the PVC enclosures cut down to size (18.5") as can be seen in that first photo. I am using some 8" Pipe which has 1/4" walls, and unless I am completely mistaken, it should be fairly inert. If not I have though of using a butyl deadener to line the inside before stuffing it.
The second picture illustrates my test baffle set up. I cut a V-Groove with my high-end router table (as can be seen in exhibit 3) in the lower half of both sides of the MDF baffle. Then, per the recommendations of others I put a 3/8" roundover on the upper half. Then all that was to be done was pry open the pipe and slip in the baffle. The beauty of PVC is that even though I cut a 6.5" strip out of the pipe and put a 6.5" wide baffle in the gap, it is still very tight as PVC is in constant tension apparently. I'm quite please with how well it went together considering my rudimentary tools and tiny little workspace. I might get brave one day and post a picture of my "workshop". Thanks again to all who have assisted and please feel free to make comments and suggestions.

[bikedave]

and one more thought on finishing...
The Sketchup rendering above shows an "aluminum" material on rounded back. I am thinking about using either a silver vinyl laminate on that or even picking up a sheet of really thin sheet metal of acceptable finish to bend around that. I would consider using a silver paint, like Zaph did on his Slimline Wallmount Speakers . However, I am not convinced that any paint would durably adhere to PVC. Anybody had any luck with painting PVC??



Then going with a black baffle and plates.

[Bent]

I'm drawing something up along these lines too, but with 10" PVC sewer pipe.
I'm trying to emulate the NatalieP baffle, and for conveniance sake, my baffle width is 8 - 11/16" as opposed to the required 9".



50 inches tall is giving me approx 1.8 ft^ internal volume prior to driver, port and bracing.

There is a paint by Duplicolor specific for coating plastics.

[Curt C]

Looks like you will have an award winning design when you get done Dave I don't see the design change causing any audible diffraction differences, so there should be no worries there.

Looking around, I found a site that sells .024" stainless steel sheet metal with a price that's fairly cost effective. Perhaps this would provide the 'look' you are striving for. Certainly it would be easy to maintain. Stainless bends quite easily, but is also fairly soft and dents easily, so care must be taken until you have it laminated onto your pvc.

http://www.quickshipmetals.com/stainless-steel-stainless-steel-sheet-stainless-steel-sheet---alloy-304---matte-finish----024--thick.html

Or you could use conventional wood veneer, or for the really cheap and easy finish, PE's stick on plastic laminate. 8O

C

[Bill Schneider]

I had excellent results painting PVC after I rolled on Zinsser BIN primer/sealer. I used a lime wash faux finish from Lowes for the final appearance. I was after the textured look on my Linkwitz Plutos (lots of PVC parts) and the subwoofers I built for them which also employ PVC.

I believe the Zinsser BIN primer also comes in a spray can if you want a smoother finish. The roller worked fine for my purposes.

Here's a close-up of one woofer enclosure with the textured surface:



And here are the materials used in the finishing of it:



I can point you to more information about the construction/finishing if you are interested.

Bill Schneider

[bikedave]

Bent, that looks good. It is actually working better for me than I had hoped. THere is enough tension in the PVC that it is a really nice fit. Using the 10" PVC for the NatP variant ought to be interesting for sure, quite a bit lighter I would think... since I really don't think you would need bracing.

[bikedave]

Curt, thanks again for all your help. On the stainless sheet metal: I was walking through my local Atwoods (farm and ranch store) the other night and saw they had sheets like you are describing. It could be interesting, the only downside would be finding a way to get a nice straight cut, keeping it from getting bent and dented before installation, and then afterwards keeping all the fingerprints off of it, you know? I'll works something out though, try a few things.

Bill, thanks for that option. What is that BIN stuff? Is it like KILZ? Have you had any issues with the wash wanting to peel off? Thanks for letting me in to this option.

[Bill Schneider]

Bill, thanks for that option. What is that BIN stuff? Is it like KILZ? Have you had any issues with the wash wanting to peel off? Thanks for letting me in to this option.

The lime wash finish (when overcoated with a clear latex glaze) appears very durable. For example, I dropped one 12" PVC section about a foot onto the basement floor and it bounced against a broom handle that was nearby. The lime wash took the paint off the broom handle instead of the other way around. I was sold on its toughness at that point.

I believe that KILZ, like BIN, is also made by Zinsser. They have a number of products that are alcohol-based.

On my project, I primered with BIN (using a small roller), then rolled on a stone-colored latex wall paint undercolor, then brushed on the lime wash using diagonal strokes, and followed it up with a clear glaze latex for protection and durability. When the textured lime wash is contrasted against another smooth-finished part of the speaker, it looks very classical and upscale.

It's a different kind of finish to consider while you work out construction details.

I like what I see of your project so far!

[Biff]

Heres some neat surface material

I have seen some of the copper sheeting used in a bar project and it is gorgeous and seems very durable. And it sticks!

http://www.alsacorp.com/products/fxsheeting2/fxsheeting_price.htm

[JonP]

However, I am not convinced that any paint would durably adhere to PVC. Anybody had any luck with painting PVC??

Wow... lots of cool stuff developing! First of all, looks like you have a very good method of attaching that baffle to the big PVC pipe. For some reason, I was thinking Sonotube as your pipe material, you've lucked into some heavy duty stuff. Not cheap, if you're buying it outright...

I'd suggest scuffing the PVC up with coarse sandpaper, and wipe the surface down with alcohol to degrease it. Then, good ol' 2 part epoxy would be your best bet for gluing. On a clean surface with some "texture" to grab on to, it makes a good solid bond. Take it from a High Power Model Rocketeer... :T

I like the faux surface... it's a great and different look for a speaker box. Good to know that you can get that primer to evenly coat for base... I'm going to have to try that sometime. I veneered a pair of 3" PVC pipes in matching wood for stands, and used contact cement for the first time. Messy stuff. Putting down the Zinnser primer might provide a surface that glue would attach to, and the iron on technique I use on boxes might work for that as well. Sounds like it could be the starting base for lots of things...

[dawaro]

I have had good luck painting PVC by sanding with 220 grit and then wiping down with a wax and enamel remover that I bought at the local auto parts store. I cant remember the name of the product right off hand but it is the same thing they use to prep the plastic parts on a car before they paint them. Once everything is sanded and wiped down spray paint sticks very well.

There are also several brands of spray paint for plastics now like Krylon Fusion that would probably work.

[bikedave]

Guys, just wanted to give you a quick update on the progress of the weekend. The MDF dust was flying as I learned about routering. These are my first baffles ever and I'd say they turned out pretty well all things considered. Thanks to everyone for your suggestions, I'll comment more a little later once I get caught up. Let me know what you think!

[bikedave]

Update

Well, progress has been slow recently but I have done a little bit. As you can seen in the picture, I built my crossovers and tested them. Everything sounds as good as it should all wired up with alligator clips and sitting on the floor. I also cut all the rest of my MDF caps except for one, so now I need to sand them to shape, round, them over, and glue it all up. I have also found a great solution to painting the PVC. I went to an auto parts store and found this can of BullDog adhesion promoter. Its made to help paint stick to bumpers and whatnot. You just spray that on, wait a minute or two then paint. I am using a silvery auto paint, then going on with a clear coat wheel protector after that. I end up with a really hard scratch and chip proof finish. For the black parts of the speaker I am thinking about using truckbed liner if I can get it to satisfactorily stick to MDF. Any suggestions?

[ThomasW]

Bed-liner sticks well to MDF. Most prime first with a cheap flat black paint since MDF is so absorbent.

It will be interesting to see how well the PVC painting goes.

[bikedave]

From my test piece it looks like the only thing I will have to be careful about is getting rid of all the scratches on the PVC. Have to do more sanding and possibly getting a higher-build primer so I have room to sand. But the color/adhesion/gloss on my test piece of PVC came out wonderfully.

Edit: I've attached a picture of the adhesion promoter I am using. It seems to soften up the surface of the PVC so that a chemical bond with it is possible.

[Bent]

Wow, your enclosure looks exactly like a rattle-can of spray paint.
:T :rofl:

kidding, I am, however, very interested in how this goes.

[Dennis H]

Edit: I've attached a picture of the adhesion promoter I am using. It seems to soften up the surface of the PVC so that a chemical bond with it is possible.

I've never had a problem getting paint to stick to PVC pipe. Soft plastics are another story.

[bikedave]

Wow, your enclosure looks exactly like a rattle-can of spray paint.
:T :rofl:

kidding, I am, however, very interested in how this goes.

Ha ha, ya, well you have to choose a theme and stick with it you know?!

I've never had a problem getting paint to stick to PVC pipe. Soft plastics are another story.

Well, I may just be paranoid, because of other projects where I had to glue it to different kinds of plastics and had minimal success. I think putting a clear coat on it will give it a kind of skin to hold everything together even if the paint doesn't totally adhere. On another note, has anyone ever put a clear coat on bedliner? Or is does it have too much petroleum/oils in it?

[Gir]

I've sprayed PVC before and it sticks well, but it's easy to scratch. If you're not moving it around much you're fine, but one wrong move and it's nicked. I like your idea, Dave.

[bikedave]

small update

Well, here's another small update, I only seem to be able to work at this in 2 hour chunks and that can slow things down a bit...however, it does get worked on and thats the important part!

I got the rest of the caps cut out after dealing with a bout of too much bad fried chicken. Then last night, I glued them all together. I was having trouble figuring out a way to keep the pieces aligned while I clamped them. So, I ended up just aligning the plates with the PVC on them, then carefully pulling it off without moving the plates. Then, holding the plates together I drilled a couple of pilot holes and pinned them together with 8 penny nails as shown. Then I could pull the top plate off and apply glue and realign with the nail holes and clamp it in place. I was having to get creative with my clamps to get all the plates glued up but I got it. Good to have that done, now its on to trimming the overhang off of them, roundover the edges and actually glue the box together.

[bikedave]

....slow....progress...

Alright, another small update! I was able to put in a couple hours last night and worked on the top and bottom caps. Here is one of the caps with the edges rounded over:



Then here are both cabs with all the plates rounded and in place:



Then here we have my crossover mounted. I routered a 1/4" slot into the plate for crossover to slide into. I'll hotglue it in place when the time comes, but it is already pretty secure:



And here is what it looks like assembled with the crossover mounted:



Right now I have a mock up of the baffle/PVC gluing up to see how the epoxy I used will work to hold the two materials together.

[kevinp.]

very impressive build! thanks for the updates

[bikedave]

Finally an update!

Well, after being backburner for a long time and just spending a few minutes here and there on them, I think I am finally ready to say that the finish is complete!
This is my "paint booth" with one cab ready to paint the silver on the PVC:



After painting the silver, i taped off the silver and prepped for the satin black. Here it hanging from a rafter from like a 50lb test line with some tape to keep it from swinging. Works really well actually as fishing line really doesn't obstruct the spray paint. Here it is:



Then peeled off the tape ever so gingerly, did a bit of touch up and sprayed on some clear coat. They are a bit dusty but here is the final product! I have some stands designed in my head which should look pretty awesome with these but will probably have to wait until after I am married. For now they will sit on my monkey coffins as zaph calls the big 3-ways. Finally:

[ThomasW]

Nice work !..... :T :B

[bikedave]

almost there...

Thanks ThomasW, just got to get them stuffed and loaded... so close...

[bikedave]

Finally Done!! ....mostly

Well, I thought the day would never come but I've finally got the enclosures loaded and am listening to these guys now. What a treat! Thank you so much Curt for your help in this endeavour and all you guys and your suggestions, recommendations, encouragement and support!

Here we have the newly installed binding posts:



and the crossover all wired up and getting ready to go into the box. I have sprayed a contact adhesive on the inside walls of the enclosure to help the polyfill stick:



Now with the crossover mounted in its slot in the bottom, all wires hooked up and protruding from their appropriate holes, the polyfill stuffed and in and stuck on the walls:



And finally, with the drivers loaded and sitting next to the TV. Don't worry, its just temporary until my projector comes in. I just got married and moved into my wifes apartment so still transitioning. Hmmm... looks like I've got a lot of fingerprints and smudges on those baffles, need to get that wiped off and get some better pics:



Whew, what a relief, and what fun, not sure I'll do an enclosure with such different materials again... well maybe. My next question is, considering my choice of DIY speakers, what receiver would you guys recommend to power these? I currently have an RCA Pro series receiver rated at 100wpc but as always I'm skeptical and would like a little more headroom. Any recommendations? I can't wait to get these guys paired with my Tempest-X sono:



I grew up in the Philippines, so for now is has a kind of cloth made from dyed grasses wrapped around it. It is blowing my mind even in a large 25x25x9 living room with plaster walls and ceiling and a 3/4" thick hardwood floor, large openings into other rooms, etc....! Especially liking Transformers at this point, I could watch it over and over just for the LFE!

Well, enough rambling, thanks for watching the progress with me boys!

[Hank]

Good job! :T Nice to see something different and let's hear it for non-parallel walls!