The smallest of which I'm aware from Rythmik are 8" drivers, and the last I knew they're not selling them separately. You can get a pair of them in the FM8, with amp and enclosure.
GR Research reportedly has an 8" OB version returning, along with the OB-tuned version of the corresponding Rythmik amp, but you never know when they'll actually get something to market. I don't pay attention to other servo technologies.
Without desiring to hijack my own thread, I found a link to Peter's series crossover design.
https://web.archive.org/web/20110902214134/http:/arhifi.dk/store/product.php?id_product=22
I can confirm that my speakers have no capacitor in their crossovers.
Separately... I could swear that the new tower build sounds a tiny bit better than they did as standmounts. I'm guessing the stiffer enclosure with a bunch of sand that collectively couples the drivers better to the room and floor is making a small improvement to the sound quality.
I'm also going to experiment with stuffing the ports to see if the transition to the new sub improves, but I have to say... they already blend remarkably well and those ScanSpeak Revelator midwoofs still sound phenomenal, plus the XT25 tweet in this implementation remains extremely listenable every day. Not the latest, but shockingly good.
Backed by a servo sub with the rapid settling capability--very enjoyable without any glaring weakness. With better upstream everything and better room control they'd be even more delightful.
This is as far as I got -- one tubular ~2' enclosure. That's a SBA 12" woofer. I felt the enclosure needed rings & ribs for internal support and built it that way. The tube doesn't stay circular tho -- it gets a little oblong, then the stiff plywood ring you cut doesn't want to slide in and you fight just to get it into place. And how to get the glued in there??! All the circular cutting was hard & tedious. It took a lot of time & effort & at the end, I still had to figure out how to get a flat plate amp in there. I abandoned it there.
But I shouldn't talk. I also built 2 pairs of hexagon towers using mitre joinery and hexagon inner support rings, one from MDF one from BB ply. The idea being no standing waves within. They were insanely hard to build. I don't have the woodworking precision to keep the additive angle errors from getting problematic. More swearing with all of these builds than... If I build hexagon enclosures again, I'll go to CNC.
Thanks for sharing, and honestly it explains a lot. Cylinders are incredibly good at holding pressure, so none of that internal support was necessary--and made it a lot harder at the same time. That's how we all learn, though, and at a certain point one needs to get away from the keyboard, get the hands dirty and learn from it. I love all the speakers in the background of your pictures!
With my sub build I gave myself a tiny bit of play when I made the baffles. Not much, maybe 1/16" or 1.5 mm, but enough to make them slide in and out relatively easily.
To bond them into place, I marked off the zones where I wanted the baffles to sit, painted them with straight epoxy (quite runny) with a cheap brush, and let it soak into the cardboard wall for a couple of minutes. Then, to keep the rest of the epoxy from flowing too fast and to better fill the gaps, I mixed in some ground fiberglass fiber and glass balloons until it was like super soft peanut butter. (This comes from boat-building kinds of activities).
After putting a very liberal coat of this mix on the zones I took a baffle and slid it into place, moved it axially back and forth a little bit, then rotated it a touch to get the epoxy distributed, using the brush to add more epoxy where it was looking thin. Next, I aligned the baffle to be plumb and shot in 8-10 15 gauge finish nails with my Milwaukee nailer (could have been by hand as well, of course) to both fit it into place and to add mechanical tie-in to the cardboard wall. Then I painted in some extra epoxy at a spot or two, followed by chasing around the ring with my finger or tongue depressor to make a nice fillet on both sides of the baffle.
It sounds like a lot but goes quite fast once you've done it a time or two. The results aren't the most perfect of all round cylinders, but so close (for me at least) not to care and the baffles weren't going anywhere.
As for cutting the circles, when I started I didn't have a circle jig, so hacked one myself. It was easier after I picked up a jig. After that it's mostly just taking the time to make the passes and let the router bits do their work... for me it felt no different than cutting all the box panels and braces and hoping your machinery is precise enough and you don't wobble a the wrong moment in time. 🙂
Next year I'll probably build a simple HT sub for downstairs and I'll 100% use concrete form for it--might not take longer than a weekend if I don't get too ambitious with the design!
Now, those pentagonal speakers were indeed an incredibly challenging project. Very cool looking, but even just imagining trying to get all of those parts accurately cut by hand makes me want to check into an asylum! Wow, props to you. Did you consider making them cylindrical? 😉
That's smart but still pretty messy & involved. If I revive this project or build a second tubular enclosure, I'll try gouging grooves into the edges of the internal rings and use expanding gorilla glue -- but you think they're not needed at all? No internal bracing is the approach sonotube enclosure subwoofer makers have used all along?
Nut-job in the carpentry asylum. That's me sometimes. 🤣
I did make cylindrical versions out of PVC pipe. The project began as a twist of the Linkwitz LXmini. I didn't care much for the plastic tubing & the plumbing parts of the original. I also think a pentagon shape has intrinsically less standing waves than a cylinder, tho the difference may be moot. The idea of a slim pentagon tower was appealing & initially, seemed simple to achieve. 🙄
IIRC, the miter angle for each of the long edges of the 5 panels was 36 degrees. This proved to be very difficult to do with high precision on 2 sides of five 6" wide 30" long boards. Something in my table saw allowed just enough movement in the cut so the 6" width was never exact from end to end. That meant fighting to make the 5 boards mitre fit without gaps. Plus the internal ribs -- not only ridiculously hard to cut them all the same but necessary to make adjustments to compensate for the 1st problem. Yeah, I spent many days swearing a lot. Probably cut over 30 side panels to get 20 usable ones. And double the number of ribs. But once glued up, the pentagon tower is super strong & rigid.
Did you ever think of drilling a hole through the cylinder and slide/glue a dowel across to hold the baffles?
Smart but messy and involved? 🙂 It's probably a matter of perspective--I think it took longer to type the description than it did to do it in the shop, and there wasn't much mess other than what was intentionally used to fill gaps. The gaps were there since it made it way easier to assemble. But I'm also used to working with epoxy and, as such, it seems normal and efficient to do it that way; and I certainly realize not everyone has gone up that particular learning curve.
But to answer your question, sonotube sub makers don't use internal bracing because it's not necessary. It's part of the beauty of the concept--a relatively light cardboard tube that can hold back hundreds of pounds of concrete with many feet/meters of hydrostatic pressure is already more than capable of handling the air pressure in audio. The only standing wave is down the length, so the walls don't otherwise resonate, and the tube forms 4 out of the six "sides" of a normal box enclosure with amazing efficiency/economy of material. Slap some end caps on and you're done. So to speak. ;-)
I've read of bracing when the end caps are large in diameter and paired with huge excursion drivers driven by multi kW amps, but there the problem is the baffle and not the tube itself--they're more directly connecting the drivers, like in your earlier example.
You nailed it in your description of the pentagon cutting! Very, very difficult to have each width be exactly as you described. You definitely showed amazing tenacity and skill in completing them!
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I'm thinking that instead of sonotube.. perhaps a bunch of #10 cans stacked with a pair of 5 1/2 woofers at either end might work quite well -if not so deep ( in terms of frequency ).
It could easily be build in sections. and adding the internal plates would be trivial. The trick will be covering them up. I don't think a Duct Tape Woofer would be agreeable to most people in domestic situations. Maybe paint them black and wrap them with fake ivy so they look like plants...
I can get a case of #10 cans for not too much money... no need to eat Chili Con Carne for six months... so that makes it doable...
It could easily be build in sections. and adding the internal plates would be trivial. The trick will be covering them up. I don't think a Duct Tape Woofer would be agreeable to most people in domestic situations. Maybe paint them black and wrap them with fake ivy so they look like plants...
I can get a case of #10 cans for not too much money... no need to eat Chili Con Carne for six months... so that makes it doable...
OK, I'll try it this way for the 2nd one.... and since I didn't actually glue the internal ribs on the first one, maybe just pull them out.
I joined 2 circle plates for both top & bottom -- the smaller one to fit inside the tube, a bigger one to overlap it. My wife sewed up a couple double-knit cloths into tubes that fit nicely over the sonotubes. This requires the ends to be tucked into & probably glued between the end caps & the tube. Then I have to sort our what to do about a plate amp. This is another challenge for me. Breaking the continuity of the sonotube feels wrong -- surely its strength is directly tied to the symmetry. Maybe I'll just leave the amp external.
Actually, thinking about this... a 56" long 16" sonotube with woofers on the end caps, mechanically coupled to each other internally, placed atop 16" curved radius stands (maybe 3 with weather-stripping to absorb any vibrations to the floor). Hidden under a simple upside down 3-sided U profile TV "stand" with a top shelf -- and this structure doesn't touch the sonotube at all. Grill cloth on the sides.
I wouldn't cut into the tube if it's in the active airspace of the drivers. Some people put the plate amp in one of the ends, but many run sonosubs externally--replacing a power and signal cable to the sub with just speaker wire in the process.
For your new idea--it basically sounds great. You could skip the cradles and just make the end cap pieces in a D shape, with the flat to the ground and tube slightly above the floor, then stick on felt furniture feet (or your favorite flavor of sorbothane to get fancy). The middle of the tube wouldn't need any support at all... in fact, it would likely be worse than none. Alternatively, recess the baffles slightly like I did and add a couple of feet into them from the outside of the tube.
The end result of this is El Pipo... where the woofer(s) sat in a box and the tuned pipe extended from the top.
https://www.firstwatt.com/wp-content/uploads/2023/12/art_elpipeo.pdf
Note that Nelson had two iterations.... I'm referring to version one. His second version, the single driver, is closer to the one we're discussing here.
Just make sure not to drive the X1000 to excess nor drink too much cabernet. Otherwise you go from Version One to Version Two. ( Nelson's writing is a hoot... ).
Just to say, much thanks to the OP & others for helping to clarify sonotube concepts & execution for me. ✌️🙏👍
Thanks for saying thanks! But no problem, happy to share and learn in kind. It's the best part of this friendly community. I'm certainly no expert, but feel free to post here or DM me if anything else comes up.