Zaph ZA5.3 MTM in a Steel Tube?

[---k---]

Crazy idea time. I'm stealing this from a post at the PE Forum by Spasticteapot. He wondered about using steel tube for enclosures. I'm not sure if he did anything with it, because he had problems getting tube steel. I'm a structural engineer - I don't have problems getting tube steel. So, today I picked up a kick back from a contractor. Here in my possession is two pieces of structural tube steel. The pieces are 16"x8"x1/2"-12"long. My math shows that to be approximately a 20L enclosure.

My plan is to epoxy a front and rear baffle on the tube (likely front removable). Line the inside with maybe some roofing membrane and Sonic Barrier and there you go. I'm thinking it is going to be a pretty stiff and non-resonant box. It might ring with the knuckle test, but it should take a lot of energy to move 1/2" thick steel. Only 75# per tube.

CJD raised a concern about the thick tub steel causing induction problems with the drivers, so I pulled an UNsheilded RS180 out of my In-Khan and tested the impedance in and out of the enclosure. I ran 4 impedance sweeps with my WT3 (yeah Thomas is right, lots of problems...another thread). Two sweeps in, two sweeps out of the tube. The steel tube doesn't seem to affect the driver impedance - the peek got a little higher, but the overall shape the same (could just be the WT3). There might also be problems with the crossover inductors, but I'm can put them in the bottom of the speaker stands. So I think I'm in the clear.

Zaph's ZA MTM seems to fit well enough inside. So, what am I missing? Should be a fun experiment. Or, is it just a bad idea?

[chrismercurio]

what kind of sound does the tube make when you hit it???

you can pick what and how hard you smack it.

[JonMarsh]

Should be fun, and you might be surprised, but I think that getting the front panel stiff is quite important. I think the "ring frequency" is well above what would be excited by the midwoofers. Some Whispermat appropriately glued on should take care of any of that. Prep to avoid corrosion might be an issue.

Me, I'm an ex-aerospace guy, so I'm looking at aluminum tube. :W Expect something by April- the tubing is in house already. Time for lamp speakers!

[---k---]

Jon,

You think I'll be surprised? By What?

I was hoping I could get the thumbs up from you. I figured if anyone would find fault in my plan, it would be you or Thomas. It doesn't sound like you see a problem in this plan. You're thoughts about ring, corrosion and aluminum are ones that I got kicking around in my head too. I would love to use Aluminum instead, but steel tubes are free.

My current plan is to attempt to remove the shop primer from the exterior. Sand and polish it up to a shiny metal, then paint it with several coats of clear from a rattle can. It won't be a mirror finish, but should look cool. The interior should be good protection from corrosion with the current shop primer. I'll probably give it a coat or two of clear also for good measure. Then I would cover it with contact paper and epoxy the baffle on.

For the front and rear, I'm leaning towards picking up a piece of 1.5"-thick dark exotic hardwood that will only need a few coats of clear poly to look great. I worry a bit about expansion and contraction, but I think I'll just roll the dice and see what happens.

I debated a removable baffle. I want a good baffle to tie the sides of the tube together, but I also think these will be cool boxes that I may want to reuse. Almost a shame not to put something fancier in them. I guess if I want to do another project I can always get more tubes - not a big issue.

I'm also debating whether I should epoxy wood strips along the inside edge of the tube to give the baffle more surface area to glue to. 1/2" thick wall isn't much. But, I would think epoxy wouldn't need that much surface area. I guess I can experiment on the back without the blocking and install it afterwords...

I got a stockpile of 1" PE Sonic Barrier without the vinyl layer. http://www.parts-express.com/pe/show...number=260-525 The Zaph kit comes with some other foam lining. You think these would be enough? I'm debating the need for stepping up to Wispermat. Like you said, I'm expecting the ring frequency to be beyond what a mid could resonate. I guess that is something I'll have to experiment with a little too. Just once the baffle is glued on it gets tougher.

I guess I should get ordering the kit....

[1Michael]

Those wood strips sound like a good idea. You could also line the inside with say 1/4 ply and then attach some whispermat or whatever to the ply. It might help deaden the ringing...

[CraigJ]

Me, I'm an ex-aerospace guy, so I'm looking at aluminum tube. :W Expect something by April- the tubing is in house already. Time for lamp speakers!

Man, you sure are hard to keep up with. I suppose your not thinking about a clone of the RAAL Requisite, but perhaps something smaller like this:



Aluminum huh, I'm more of a gardener and was thinking 4" PVC tube painted silver.

[JonMarsh]

Jon,

You think I'll be surprised? By What?


I got a stockpile of 1" PE Sonic Barrier without the vinyl layer. http://www.parts-express.com/pe/show...number=260-525 The Zaph kit comes with some other foam lining. You think these would be enough? I'm debating the need for stepping up to Wispermat. Like you said, I'm expecting the ring frequency to be beyond what a mid could resonate. I guess that is something I'll have to experiment with a little too. Just once the baffle is glued on it gets tougher.

I guess I should get ordering the kit....

I think you might be surprised by how well it works-

Why not use the sonic barrier with the vinyl layer, glued to the steel? It might give the steel some damping, but then with 1/2" walls, it's probably not an issue.

Man, you sure are hard to keep up with. I suppose your not thinking about a clone of the RAAL Requisite, but perhaps something smaller like this:



Aluminum huh, I'm more of a gardener and was thinking 4" PVC tube painted silver.

There are many paths to Rome... some paved with steel, some with PVC, and perhaps some with Aluminum. Now, just what exactly do I do with the 3" and 5" aluminum tube I've got sitting around here now? Better be something interesting, or folks will think I'm falling down on the job...

of course, there will have to be some LBL in there somewhere...

I think the small Raals were incredibly cute, but I'm going for something a little, shall we say, more robust? Bigger stones? Anyway, danger, several weird ideas at work, if it even turns out listenable, that may be an achievement. It will probably look more like Wall*e than a normal speaker.

[---k---]

I think you might be surprised by how well it works-

Why not use the sonic barrier with the vinyl layer, glued to the steel? It might give the steel some damping, but then with 1/2" walls, it's probably not an issue.

Thanks for the clarification. That is what I thought you meant. But, just wanted to make sure.

As for the sonic barrier with vinyl. Well, I probably need to subconsciously sabotage these so they don't sound better than my Khans in any manner.

I'm also trying to be somewhat cost conscious, because I'm not sure where they will end up and how much they will get used.

[CraigJ]

Anyway, danger, several weird ideas at work, if it even turns out listenable, that may be an achievement. It will probably look more like Wall*e than a normal speaker.

Sorry for the hijack Ryan. Jon, same deal a usual, you dream and design, I'll build and enjoy!

[---k---]

Craig, it is all good. The wondering threads are part of what makes this place fun to hang out.

[---k---]

Well, the Madisound order is in. Should be here next week.

Going to have to get working on removing the paint and shining up the steel. I hoping I can do it with sandpaper and an orbital sander and then metal polish. If I have to store it overnight (weeks) before the clear paint goes on I'm figuring a mist of WD40 should keep the corrosion at bay till I can finish. Suggestions are welcome.

[cjd]

You want to wet-sand that. Start with 200 grit if you can, but if it's badly scratched may need to start out with 100. Work up to 600 grit, 1200 grit, then attack it with a medium-hard felt buff wheel and a rough buff compound.

[BretH]

Can you run threaded rods through the corners and thus clamp the back and baffle between the steel at the same time?

[DoubleTap]

Just take it to a metal shop and have them media blast it, then weld some threaded tabs in the corners and maybe a pair mid-way ... to bolt a removable baffle to. Then powder coat the whole shebang.

Edit - cha ching! This place is right up the street from me. http://www.tubularsteel.com/ I have a feeling that this tubular steel would work extremely well. And they have up to 20"x8" rectangle.

[villastrangiato]

Looks like an interesting experiment. I'd try welding a cross brace in both directioins (Jesus cross) in the center using 1/2 inch round stock. Before you do it, try the knuckle test - sampling and recording it with a microphone. It would be cool to see how that compares with the same knuckle test measurement after the braces are welded in. Baffles welded on either end are definitely going to improve the rigidity and shift cabinet resonances - presumably up in frequency - but I don't see how a couple of internal braces being installed beforehand could hurt. There's another European "high end" company that's been around for a while that uses "steel grounding" rods in their designs. The claim - which seems to fall in the "flux capacitor" category, suggests that system resonant energy modes are absorbed by the steel mass........

[---k---]

You want to wet-sand that. Start with 200 grit if you can, but if it's badly scratched may need to start out with 100. Work up to 600 grit, 1200 grit, then attack it with a medium-hard felt buff wheel and a rough buff compound.

Yeah, that is what I was looking for. I figured you were the guy with actual experience working with this stuff. It sounds like I'm okay using a small orbital sander and then a drill with a buffing wheel should be good. The edges of the tube look decent, I don't think I'm going to need an grinder for them. It was cut at a real fab shop with a band saw, so I'm hoping that the end cuts are pretty plumb and level across.

We'll see how it goes. I got to get the heater installed tomorrow before this can go much further.

[---k---]

It rings like a bell when I thump the sides with my knuckle and my knuckle hurts. I'm predicting that my knuckle is putting a lot more energy into the side than a 5" driver can muster.

Why not use the sonic barrier with the vinyl layer, glued to the steel? It might give the steel some damping, but then with 1/2" walls, it's probably not an issue.

Jon has spoken... I guess we'll see. I'm not going to do anything fancy. No bracing. No roofing membrane. Just 1" Sonic Barrier. If it rings, we'll then I can always retrofit. But at least I'll know.

If this were 1/4" thick tube, my thinking might be a little different. I don't think you can picture how thick and heavy 1/2" tube is until you see it. Like I said, each tube currently weighs 75 pounds, and that is without the baffles. My Khans only weigh like 100 pounds.

[---k---]

I'm making a little progress. The parts came in earlier this week, and I picked up a nice piece of 1-1/4" Lyptus hardwood today. A little more progress should be made this weekend.

I purchased a 3" Precision Port instead of using the tube that Madisound makes. I modeled up Zaph's recommended enclosure and am a little confused. It doesn't look like what I expect from Zaph.




Luckily, the easy fix is to use the "Heavy Fill" option.



But, considering the Madisound kit ships with only a sheet of 5/8" thick foam that doesn't sound like "heavy fill" to me, it left me wondering:

1) Did I screw the model up?
or
2) did Madisound twist Zaph's arm to have a little bit of thumping bass?
or
3) did Madisound twist Zaph to use the standard off the shelf 5.25" long port?

As long as I didn't screw my models up, I'll probably tune to a hair lower and use the heavy fill. This should give me the more traditional bass tuning found around here.

[chupalt]

Not sure if this helps or not, but Zaph recommends doubling up on the foam on the top, back and bottom of the speaker if you use the madisound foam.

[---k---]

You want to wet-sand that. Start with 200 grit if you can, but if it's badly scratched may need to start out with 100. Work up to 600 grit, 1200 grit, then attack it with a medium-hard felt buff wheel and a rough buff compound.

At Lowes I can only find sand paper up to 220 grit for an orbital sander. Woodcraft online looks like they have 320. Do you know of a source for higher grit or do I need to switch back to a regular sander?

I got most of the paint off today using a enviro-safe stripper. It worked better than I expected. But, the steel is pretty pitted and rough. I got a wire wheel, but that needs to wait until tomorrow. I see now that I'm not going to get a mirror finish. But, the rough pitted finish may look cool if I shine it up.

[mtmpenn]

High grit sanding discs for orbital sanders:

Klingspor's Woodworking Supply:

http://www.woodworkingshop.com/

[jkrutke]

But, considering the Madisound kit ships with only a sheet of 5/8" thick foam that doesn't sound like "heavy fill" to me, it left me wondering:

1) Did I screw the model up?
or
2) did Madisound twist Zaph's arm to have a little bit of thumping bass?
or
3) did Madisound twist Zaph to use the standard off the shelf 5.25" long port?

As long as I didn't screw my models up, I'll probably tune to a hair lower and use the heavy fill. This should give me the more traditional bass tuning found around here.

Just saw this thread. Awesome idea putting that system into at steel tube, can't wait to see how it turns out. Could be particularly cool if you do some sort of natural steel finish on it with a clear coat protectant.

To answer your port questions, all three are No. The port is my selection, and I had Madisound bring it into stock for me since they didn't have it prior to the ZA5 kits. All they had was the Precision Ports. When the supplied port is placed into a 20 liter box (which will equal about 9.2 liters per driver after subtracting out everything that takes up space) they will be tuned closer to 52 Hz than the 54 you are coming up with. So while you didn't get your numbers wrong, I know where all typical box models are off - ports of a given length and diameter always tune lower than models predict. I wouldn't bother with a Precision Port, that's somewhat overkill for the requirements of a pair of ZA14's.

Don't forget what the tuning will look like after the series resistance and baffle step are factored in. It will be about 5 or 6 dB down at 50 Hz, a somewhat lean tuning.

I don't think you would even need any mass loaded damping in that system, though it wouldn't hurt.

One idea to consider for fastening the baffle is to bolt the fronts to the backs with 6 threaded rods, 2 on each end and a pair in the middle. A few high end makers do this. Tensioning the baffles would make the whole box that much more rigid. It also eliminates glue cracking due to the effects of thermal expansion being different between side and baffle materials

[Space]

One idea to consider for fastening the baffle is to bolt the fronts to the backs with 6 threaded rods, 2 on each end and a pair in the middle.

This is a good idea, with baffles ahead of the tubes rather than fully inside them. It would mean losing the ability to expose the cut ends of the steel, but gaining the ability to chamfer baffle edges. And for a given amount of steel, the enclosed volume is larger this way. You could rout a perimeter rebate at the back side of the baffles to step inside the tube by 1/4" or so, to keep the baffles centered and assist with sealing.

[cjd]

You really want to wet sand from 220 on, and you probably don't want to do that with an orbital sander...

[Johnloudb]

You really want to wet sand from 220 on, and you probably don't want to do that with an orbital sander...

Is that due to the circular scratches? I guess that might dull the reflective surface.

[cjd]

I'm just nervous having a steel slurry flying around power tools I guess. May be just fine. Need to keep it rather wet for best results though.

[---k---]

Zaph,
Thanks for the bass info. I wish I would have posted this earlier; it would have saved me a few $$ on the precision ports. I like leaner bass compared to others. I'll have to experiment. I was thinking I would end up around 50hz.

Others have posted the threaded rod idea. I agree that it is a really good idea. But, I'm going to do things opposite of the typical overkill methods found around here, just to see what happens. That means, no vinyl layer and epoxy the baffles on. If it rings or cracks, well I guess I'll know the answer.



As for the sanding, we'll see. I'll probably get lazy and just wire wheel it to a shiny surface. The surface is pretty pitted. It is probably impossible to get it all out of. I'll post some photos later today. I left it soaking in paint stripper overnight. Getting the primer out of the pits is difficult.

[cjd]

Polished up except for the pits can still look good.

[---k---]

CJD, yes, that is exactly what I was thinking!



BTW so far, this works great! PE should consider stocking them.

http://www.amazon.com/Dayton-G73-Electric-Garage-Thermostat/dp/B000TK2SWO/ref=sr_1_1?ie=UTF8&s=home-garden&qid=1264949701&sr=8-1

$300 for the heater, and $150 for the new 240V circuit (family discount) - Well worth it!

[---k---]

Well, I took a dozen steps forward today and a dozen backwards. I learned a lot about working with steel. Leaving it soak in a waterbased paint stripper is not a good idea. Also, don't spray WD40 on it to keep the corrosion at bay while you do something else - it instantly darkens the steel. Finally, this project should not be undertaken without a grinder.

After not making good progress, I broke down and picked up a $39 Ryobi grinder. It actually is a really nice grinder. The box came with a wire wheel, sanding disk, cutting wheel, everything. Progress came real quick once I got the right tool. I'm still not sure that the finish will be what I pictured, but I think it will be cool. It all comes down to how much effort I want to put in with the grinder. Where the tube is smooth, I have a nice polished finish after 220 grit. But the sides of the tubes have big bubbly rough areas, that would take tons of effort to grind smooth. I also went though the sanding disk pretty quickly. Might need to pick a few more of them up. Man this project is getting expensive....

Metal working tips would be welcomed.

I would post photos, but the tubes aren't very photogenic in my garage light.

[cygor98]

is the sanding disk a flap disk or just a flat one? i have had good luck with flap wheels to finish steel before painting, the only problem is gouging is pretty easy so getting it perfectly flat can be somewhat difficult.

[Woodworker_Jon]

After not making good progress, I broke down and picked up a $39 Ryobi grinder. It actually is a really nice grinder. The box came with a wire wheel, sanding disk, cutting wheel, everything. Progress came real quick once I got the right tool. I'm still not sure that the finish will be what I pictured, but I think it will be cool. It all comes down to how much effort I want to put in with the grinder. Where the tube is smooth, I have a nice polished finish after 220 grit. But the sides of the tubes have big bubbly rough areas, that would take tons of effort to grind smooth. I also went though the sanding disk pretty quickly. Might need to pick a few more of them up. Man this project is getting expensive....

Metal working tips would be welcomed.

I just read through your entire post and was going to suggest that you grab a grinder to take care of the rough stuff but I see that you got to it before I posted. :T

Sanding wood and sanding metal are two different things. Although you can use the same tools and abrasives, the two materials really require different abrasives (and tools) to be achieve the best/quickest results. You will find the best assortment of tools and abrasives for this purpose at a business where they specialize in automotive body repair supplies. If you have a buddy that builds cars (body work) he will certainly have an assortment of tools and experience that will help you out. You can probably find a pneumatic grinder/sander for next to nothing on E-Bay if you already own a decent size compressor- that will help speed things up-that is if you insist on doing it yourself.

I do tend to agree with DoubleTap however, take it to someone who can mediablast it. They can remove the primer, any rust and stains and flatten out any small imperfections in the metal too (probably won't get rid of all of the "pits" in the metal but will get you a long way in one step). The cost of doing this will probably come close to rivaling your investment in grinding and sanding disks and will save you a ton of time. Here's a video that shows one application. http://www.youtube.com/watch?v=hWbBCDnZoNg Your local guy might even have some trick to get the pits out (shot blasting????).

Good luck, this sounds like a great project, I cannot wait to see the results.

[Woodworker_Jon]

One more thing to consider is that the coefficient of linear expansion (the expansion due to change in temperature) is dramatically different for wood-type materials and for steel. Steel expands at more than twice the rate and amount of typical wood examples (7-ish compared to 2-3-ish (10^-6 in/in/deg F)). If for no other reason, I would use Zaph's recommended baffle mounting method for this reason. Oversize the front and rear slightly so that the steel never sticks proud of the front and rear. Although the temperature swings in a residential environment are typically within a relatively small window if you end up placing these on an outside wall or near a window this could become a factor. I tend to err on the side of better safe than sorry.

[---k---]

is the sanding disk a flap disk or just a flat one? i have had good luck with flap wheels to finish steel before painting, the only problem is gouging is pretty easy so getting it perfectly flat can be somewhat difficult.

Flap disk is where I ended up. Works quickly and efficiently, but like you said gouges easily.


Yeah, a sandblast would be the best and easiest way to go. I wish I would have picked them up a week earlier. They had the sandblast equipment up and running then. But, it is a little late now.

[HareBrained]

I like leaner bass compared to others.
...

My Monster Dual SS RL-P15 Ported Sub.

Wow, did this ever peg my BS meter. :E

I use a single 8" woofer and I wouldn't make that statement. You have 2 SoundSplitter 15" sub and you say you "like leaner bass compared to others."

BULL!

:rofl:

[---k---]

Yeah, that is what I thought to. But, ask JonW .

Dualzilla is crossed at 50 hz. It is mainly providing the shaking the the room, not the musical bass. I've grown very used to and like the dry understated bass that a low Q sealed system provides.

No progress because last night I did my taxes (had to do them before I voted today ) and tonight had to work. Hopefully I can get back in the garage tomorrow. Though I think I need a few more flap discs.

[---k---]

Well, I think they are going to get a couple of coats of spray lacquer (rattle can) tonight!

After trying multiple techniques I was able to get the smooth areas pretty close to mirror finish. But, this tended to clash with the adjacent rough areas. I ended up liking the look of them wire wheeled and evenly scratched in every direction. 50 grit sand paper on the orbital evens out some of the wire wheel pattern and gouges, but not all. I think they look cool. Very industrial. The perfectionist finishers around here would probably put 10 more hours in on them, but I've already gone through 1 wire wheel and 2 flap discs... good enough.


I need to clean them good tight before I paint. The wire wheel got most of the paint and rust out of the pits. It seemed like the mineral spirits I was using darkened them up - not sure with the poor light. Probably will use alcohol tonight with a nylon scrub brush.

I'm tempted to see if I can find some mild acid for a quick acid wash. But, I'm not sure it would clean any better and if I want to deal with it.

[fbov]

If you're still up for suggestions, go back a few to posts to Double Tap's suggestion to have it blasted and powder coated. I did this for one of my telescope projects (flat black), and for the sundial gnomon I'd just made for our club's observatory (flat white). It was cheap ($$) and the gnomon's been outside about 6 years now with no rust visible, even by the weap holes.

It all depends how long you want them to last; judging by the pics, you'd powder coat all surfaces; it'd last forever!

Then, I second the end cap with threaded rod idea, but also suggest making inserts, plugs if you will. You'd have plenty of glue area and a 3rd one makes a nice window brace. I'm doing something similar on a test box I'm making with removable baffles to allow easy config changes.

And 75 lb. is a nice weight for a speaker... same as my MTMs, but I'm including drivers!

HAve fun,
Frank

[---k---]

I'm finding that these speakers are more an experiment in a lot of wacky ideas. Unfortunately, not all wacky ideas make things easier or better. But, I'm learning a lot.

I got the front baffles cut today. They are ready to be glued to the tubes. I confirmed that one should not attempt to use real wood without a planner. 60 minutes with an orbital sander helped, but I'm not sure the tubes are cut flush either. I'm still being stubborn and just planning on gluing the baffles on. I bought a big tube of 30-minute epoxy, but think I'll probably switch to PL Polyurethane.

I'm waiting for the weather to improve. I'm thinking I'm going to try acid etching the surface - something to try and experiment with.

[cjd]

Seriously. Don't glue them. THreaded rod front to back.

[---k---]

You're usually right. Just extra effort.

Stupid question, can I put the same polyurethane on the steel tube as the wood? It would just make finishing easier.

[cjd]

Yes. Though it might discolor visibly over time on the steel using urethane, depends.

Wood and metal expansion rates are SO different, which is why I recommend bolting the mess together.

[---k---]

Yes. Though it might discolor visibly over time on the steel using urethane, depends.

Wood and metal expansion rates are SO different, which is why I recommend bolting the mess together.

The General Finishes Poly that I have says that it has a UV stabilizer in it. But, who knows about the steel.

Yes, I know that wood and metal expand differently. I'm just stubborn, but I think you've won out.

[cjd]

You can set it up so you don't have to through-bolt the baffle at least, should you wish.

I don't want to dissuade you from trying epoxy, but if you've ever watched how much a hardwood floor shifts with humidity changes you'll understand why I think epoxy is only going to cause trouble.

[frascati]

Image not available

Image not available





The first two are "painted" with oxy/acet torch and described on this page....
http://www.hgtv.com/crafting/steel-s...eat/index.html
Although the heat required to discolor the mass of steel you've got might be outrageous. The last photo is a bluing process.

Really interesting things can be done with steel. One that I've used occasionally is simply cleaning the metal really well and leaving it outdoors to weather for a bit until it gets a somewhat even layer of surface rust. Then apply something called RustFix by Duplicolor

http://www.duplicolor.com/products/rustfix.html

It sprays on clear and reacts with the surface oxides to create a pretty interesting surface of very hard, very black "rust". I've used it for hardware on rustic furniture pieces and really liked the result. It's called hillbilly primer in some locales because you can just paint over body panel rust with it instead of taking the time to clean the surface first. You don't even have to put your beer down.

I was once thinking of speakers made of terra cotta rectangular pipe of similar dimensions to those you've pictured. I saw stacks of it setting on pallets one day and "speaker cabinet" just leapt into my head. I wanted to cap the ends and cut the driver holes out of one face. Probably would have been a nightmare to to work with though.

Love your idea.