# Cylinder subwoofers



## Howard Ferstler (Sep 27, 2007)

Some time back, I wrote a construction piece on two “cylinder-style” subwoofers that are now installed in my main music room. The article can be found at:

http://www.woodworkingtalk.com/f13/different-kind-audio-subwoofer-31884/

These units work very well, but even after I finished them I swapped out the 12-inch Dayton Titanic drivers for Dayton Reference drivers. The Titanics were not quite right when it came to handling very low bass (pipe organ) and the Reference versions, although less potent in terms of maximum output, were cleaner down in the 20-25 Hz range. That room is strictly for music, with no home-theater abilities. Ironically, the Reference units cost a bit less than the Titanics, but weigh more: 25 pounds vs 20 pounds each.

The question now was: what would I do with the two Titanic drivers? Solution, make two more, slightly smaller subs for use in my home-theater in another part of the house. The Titanics are better at head-banging action-movie sound than much of the competition, anyway, and there is no need in there to go below 25 Hz. The result can be seen here, with each unit located in a room corner, flanking three bookcases I built recently out of a mix of redwood and mdf. A piece about the building of the bookcases can be found at:

http://www.woodworkingtalk.com/f13/redwood-mdf-bookcases-41842/

The redwood was obtained from an old, retired friend of mine who had been using it for shelving purchased way back in 1980. (He is selling off his fabulous model train collection.) He sold me 260 feet, at a buck a foot, and he still has another 600 feet that I may buy into down the line. The wood did need planing to remove old varnish, and that did make it a bit thinner that when new.

Note that the spacing between the two taller bookcases is more than wide enough to handle that 56-inch TV monitor, because down the line I hope to replace it with a 70 incher. The wife will have to agree with this first, of course.

Anyway, the new subs are 57 inches tall (the earlier ones in the music room were 68 inches), with the main functioning body made of a Sonotube concrete post mold 14 inches in diameter and 48 inches long. This adds up to about 4 cubic feet and the 4-inch diameter port tube at the bottom is sized to give the subs tuning at 22-23 Hz. (The bigger subs in the main room, with an interior displacement of 5 cubic feet, tune at about 18 Hz.) While the sizes are different, the main difference is that with these new units I used that recycled redwood for the top and bottom sections instead of mdf.

This required more work, because the redwood boards were only 5.5 inches wide, and so I had to join them edge to edge to give me the diameters (16 inches) needed for the visible sections. For the joining work I used Kreg pocket screws, obviously located so that they would not interfere with the need to cut holes in the tops for the woofers and in the bottoms for the long port tubes and electrical binding post clips. 

The end of each Sonotube contains an mdf “plug” inserted into the opening with the top and bottom redwood caps glued (Elmer’s carpenter glue) and screwed to them. The plugs are secured in place at the tops and bottoms by screws and PL constructive adlhesive. The bottom plates attached to the Sonotubes are held away from the bottom plates by three 2-inch dowel sections with drilled out centers and screwed in place by bolts threaded from below into t-nuts fitted between the stacked redwood bottom plates. There has to be spacing down there for the downward-aimed port tube to “breathe.”

On top, a thin redwood, driver-protecting plate is held off from the top Sonotube plate and mdf plug by three 2.75-inch dowels also drilled out, with machine screws tapped into t-nuts and with brass cap nuts on the very top. The upward-facing Titanic driver does not have interaction problems with that protective plate, because the spacing is not close enough to matter. The driver covers the range between about 90 Hz and about 35 Hz, with the port at the bottom gradually taking over from 35 Hz on down to below 25 Hz.

The cylinder interior is completely covered with .75-inch thick fiberglass batting (furnace-wrap) held in place with Scotch photo-mount spray-on glue.

Redwood has a natural red look (of course!), but to goose that a bit I stained the surfaces with Minwax red-oak stain (applied and removed quickly to keep things from getting too dark), and then the plates were given five coats of Minwax spray lacquer. The first three were high gloss, with the last two satin. Actually, I may go back and give the protective top plate a sixth coat, again with high gloss, which in this case may be better than satin. The plate is easy to remove and reinstall.

Each tube was painted flat black, and each is wrapped in conventional speaker grill cloth material. To cover up the ragged edges of the cloth at the top and bottom, a heavy felt band was wrapped around and secured in back with Gorilla tape. The backs of these subwoofers are not meant to be seen.

Sonotube is actually dense cardboard, 3/8-inch thick, and one would think that it was not particularly strong enough to make a subwoofer enclosure. However, remember that box-shaped subwoofers have walls that are trying to flex into a circular shape when strong bass notes happen. Sonotube is already circular and because it is obviously strong enough to hold a mass of wet concrete it is obviously not going to stretch when put under stress. The bottom plate, with the double redwood and mdf interior plug is 2 inches thick and the top plate is mostly filled up with a woofer driver, and so there is not much flexing going on with them. The result is an enclosure that is surprisingly inert. Companies like Hsu Research and SVS have used Sonotube material successfully in their subwoofer designs for years.

These two units are powered by the same-brand stereo amp that I use to power the subwoofers in the main system: a 350-watt-per-channel Crown XLS1000 that I got from Parts Express for 300 bucks. A Hsu “Optimizer” equalizer adds some electronic bass boost below 35 Hz (subs like this, even commercially built versions, begin to gradually roll off below that frequency), and the sub-EQ section of a Rane THX-44 equalizer is used to flatten some room modes between 90 and 30 Hz. The result is very good acoustic performance.

Howard Ferstler


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## aardvark (Sep 29, 2011)

Hi Howard. Thanks for revisiting this project and I was unaware of the Daytons low end freq response capability. 20-25hz is excellent for a 12"
Again, beautiful shots of a unique project that I want to visit in the future. We are currently prepping for a move so many personal projects are on hold.

The only concerns I have in Sonnetube construction is the ability for sound to escape through the thin walls (3/8"). From a strength standpoint, I agree totally, and I've been an Architect for 30+ years, so I am aware of the density and strength. Knowing your reputation in these matters, it would seem you determined this sound leak through a non issue, and that is respected.

Mind you I would never steal someone else's design, out of respect for the designer.
The only change I would make in design is wall thickness and this can be done with double layered Sonnetubes. One 12" and one 15"(or the next step up). The wall cavity can then be filled with spray foam or batt insulation. The foam would make them rock solid from a structural standpoint (which isn't needed) and a sound standpoint. Yes they then are a little massive in size, but only 3" wider...not really too bad.

I do wonder if you are lining your cavity with any form of insulation. That hasn't been addressed, and may make my point mute.

I was invited to a speaker builder 'get together' in Grand Rapids Mich., but can't attend this trip. It is a passion of quite a few on this site, and they have been kind enough to contact me about the Michigan event and will again for future events.

Thanks again for posting this up.

My site:
http://gnarlywooddesigns.weebly.com/


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## Howard Ferstler (Sep 27, 2007)

aardvark said:


> Hi Howard. Thanks for revisiting this project and I was unaware of the Daytons low end freq response capability. 20-25hz is excellent for a 12"
> Again, beautiful shots of a unique project that I want to visit in the future. We are currently prepping for a move so many personal projects are on hold.
> 
> The only concerns I have in Sonnetube construction is the ability for sound to escape through the thin walls (3/8"). From a strength standpoint, I agree totally, and I've been an Architect for 30+ years, so I am aware of the density and strength. Knowing your reputation in these matters, it would seem you determined this sound leak through a non issue, and that is respected.
> ...


Hi, aardvark,

It is pretty easy to check the wall integrity of a Sonotube speaker enclosure. Just put on some music (or an action/adventure DVD) and feel the exterior as the bass rumbles. I have done this before with other units (those made by Hsu and SVS that I reviewed for magazine reports), and also have done it with both these new ones of mine and the ones I made earlier for another room in the house. There simply is no significant degree of vibration exciting the cylinder walls. On the other hand, if such a design were used in a full-range systems it is possible that middle and higher frequencies could excite ripple resonances in the cylinder walls. Sonotubes should be used for subwoofers and not regular speakers.

In any case, double-layering as you note certainly cannot hurt. The next size up from a 14 incher is a 16 incher, and one commentator has suggested filling the gap with loose sand. Heck, even cat litter would work. The weight would go up aplenty, though. One could also opt for a 12-inch cylinder and use a 14 incher for the outer wall. Even a 12-inch driver can be used with a 12-inch Sonotube (the Hsu TN1220 used a 12 incher in a 12-inch Sonotube, but the mounting boss on top was thin, and if a 14-inch outer sleeve was also used the result could look like what I built.

The interior of this new unit is lined with 0.75 inch thick fiberglass batting, normally used as furnace-pipe wrap. The earlier one I built used 2-inch stuff (also pipe wrap), and this time I wanted to keep the interior a bit less crowded. If I had to do the first units over again I would have used 0.75 inch stuff in there, too. I think that two inches might actually reduce the thermal interior volume rather than increase it. You can fill acoustic-suspension (sealed) enclosures really full of loose fiberglass, but I think that reflex designs need to be able to breathe a little.

I also think that for all intents and purposes the new units, which are eleven inches shorter (4 cubic feet vs 5 cubic feet), are subjectively and perhaps even measureably equal to the bigger earlier versions, driver differences taken into consideration. Maybe it is the amount of fiberglass, I do not know. In any case, there is no removing the fiberglass from the earlier one now. I will note that the interior of a 16 inch diameter, 48 inch tall SVS subwoofer I reviewed a few years back had 3.5-inch fiberglass lining the walls, and so it was even more "packed" with the stuff than my earlier units. The designers at SVS are utterly competent, so maybe I should not be all that concerned.

Actually, how good a subwoofer seems to sound depends a lot upon the room acoustics, and the smaller ones are in a room that maybe works better than the room housing the bigger ones, and maybe the standing waves in there are more favorable at the primary listening locations. Also, I use the smaller ones for home theater almost exclusively, whereas the bigger ones are in a music system, and the latter does not get the kind of punchy workout the former one does. I guess if I REALLY wanted to know the facts I would haul the new ones out into the main room, rig up an A/B facility, and do some comparing. However, I am fully satisfied with both, so why bother?

I will say that the Dayton Reference drivers are a little less mechanically noisy down below 25 Hz than the Dayton Titanics, so I guess for music work what I have in the big room is fine. The Titanics are excellent for home theater, where punchy explosions and music rumbling are the primary focus. Theoretically, given the xmax ratings of each, the Titanics should be able to play louder, but those Reference units can play plenty loud enough to satisfy me.

Photos of the interiors of both the earlier and latest versions are attached.

Howard


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## Itchytoe (Dec 17, 2011)

If you're going to build a large enclosure, why fill it with material that will absorb the sound instead of reflecting it back. Put enough insulation around that speaker and you won't hear it at all.


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## aardvark (Sep 29, 2011)

Itchytoe
The concept is to dampen sound from the inside to the outside, since the sound wave is totally opposite and they cancel each other. You are out to hear the sound from the outside speaker surface. Inner resonances interfere....
But you also have to design the cabinets sq.ft. area volume to the speakers specifications. Then (as shown in Howards pix) porting can be added but that is a tuning issue that needs designed right as well, and there is a differing boominess of ported vs non. Both have attributes.

Howard.
I see the insulation and think the new is a better idea and doesn't effect cabinet volume as bad. It exempts the need for a 2nd sonnetube.
I Like!
Also I've never been a fan of loose fill batt insul, and usually opt for the white stuff with 3M adhesive. Here, however what you did works excellent.
I get Parts Express catalog and they of course push Dayton speakers.

Thanks again for the info/pix.


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## Howard Ferstler (Sep 27, 2007)

Itchytoe said:


> If you're going to build a large enclosure, why fill it with material that will absorb the sound instead of reflecting it back. Put enough insulation around that speaker and you won't hear it at all.


Actually, this is absolutely not the case at all. First, there is no "reflecting back" in any properly designed speaker enclosure, including the reflex design I built. 

Indeed, the original Acoustic Research patent put forth by Edgar Villchur back in 1954 for the sealed-box, acoustic suspension design has the enclosure completely stuffed with fiberglass, right up to the magnet assembly of the woofer. Classics like the original AR-1 (designed by Henry Kloss and Villchur), AR-3 (designed by Villchur), AR-3a (designed by Ed McShane and Roy Allison), KLH-6 and KLH-4 (designed by Henry Kloss), and AR-LST (designed by Allison), as well as many designs by Allison for his own company, Allison Acoustics, employed sealed enclosures that were stuffed full with loose-fill fiberglass batting.

The acoustic/mechanical properties of the batting actually has the woofer seeing a LARGER space in there than if the enclosure were empty behind the woofer. At least with sealed-box, acoustic suspension designs.

However, my situation involves the optimum amount of fiberglass in a ported, reflex enclosure, where some space has to exist for the port resonances to operate. I am currently checking with some notable speaker designers for some info on this. I may have to remove some fiberglass from the earler units I built, but maybe not.

Howard Ferstler


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## Howard Ferstler (Sep 27, 2007)

aardvark said:


> Itchytoe
> The concept is to dampen sound from the inside to the outside, since the sound wave is totally opposite and they cancel each other. You are out to hear the sound from the outside speaker surface. Inner resonances interfere....
> But you also have to design the cabinets sq.ft. area volume to the speakers specifications. Then (as shown in Howards pix) porting can be added but that is a tuning issue that needs designed right as well, and there is a differing boominess of ported vs non. Both have attributes.
> 
> ...


With some of his Allison Acoustics designs Roy Allison used loose-fill fiberglass, but in some cases with his lower-priced models he used a cotton or polyester fill (or blend thereof) of some kind. 

I once asked him about this and he said that fiberglass cost more and was more problematical to work with (itchy, etc.) but that it was superior at generating the kind of thermal damping needed for the enclosure to be "seen" by the woofer as being larger than what would be the case with empty space. With some of his bigger models (like my own IC-20 units, which are tall and have dual woofers at the bottom) he installed fiberglass with it packed more densely at the top and less dense down near the bottom, essentially simulating an acoustic wedge.

I have contacted three notable speaker designers for opinions on the amount of stuffing in those earlier subs of mine vs the latest versions. I sent them the same photos I have posted here. 

We shall see. It would be possible to remove some batting from the earlier units (pulling the woofers and screwed-in-place port tubes would be required, but that is no big deal) by carefully pulling out small fingerfulls at a time. Itchy, but doable.

Howard Ferstler


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## aardvark (Sep 29, 2011)

The itchiness in household wall fiberglass is a issue for me. I can't handle it or it drives me crazy. Many other densities are made, and are less troublesome in that respect but also have a differing insulation/density factor. Pipe wrap is denser.
I personally like the polyfill (white stuff), since it holds together better and is easier to use, but I don't see it as cheaper. Fiberglass actually breaks up and can be pumped into the air out of the port. Not much but some, and really a non issue for most. Also I like polyfill and the use of 3M spray adhesive for the purpose of attaching to the box, but also a spray over top of it, holds it in place.

Personally, I can't see that it would make a whole lot of difference except in density, and the poly comes in many forms.

How tall is that unit, Howard?
It looks to be about 4ft.

I think I asked this in the past as well, but what is it's crossover circuit? Passive I suspect.


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## Howard Ferstler (Sep 27, 2007)

aardvark said:


> The itchiness in household wall fiberglass is a issue for me. I can't handle it or it drives me crazy. Many other densities are made, and are less troublesome in that respect but also have a differing insulation/density factor. Pipe wrap is denser.
> I personally like the polyfill (white stuff), since it holds together better and is easier to use, but I don't see it as cheaper. Fiberglass actually breaks up and can be pumped into the air out of the port. Not much but some, and really a non issue for most. Also I like polyfill and the use of 3M spray adhesive for the purpose of attaching to the box, but also a spray over top of it, holds it in place.
> 
> Personally, I can't see that it would make a whole lot of difference except in density, and the poly comes in many forms.
> ...


There is no crossover within the subs themselves. The internal electronic crossover in my Yamaha RX-Z1 receiver is at 90 Hz, with 24 dB slopes. It feeds its mono-sub output to the dual-band parametric equalizer section of a Rane THX-44, and from there, via a Y connector to a Hsu "Optimizer" equalizer's (which boosts gradually below 35 Hz on down to 18 Hz) stereo inputs, which then feeds dual outputs to the 350 wpc Crown XLS-1000 stereo amplifier. It powers the subwoofers.

Incidentally, one of my subwoofer correspondent experts (a guy at SVS) got back to me and pretty much indicated that the earlier subs have maybe a tad too much fiberglass in their enclosures. (the latest versions are OK.) 

So, today I pulled the drivers and the port tubes and removed a bit less than half of it. (My arms are now a tad itchy, but the job on each unit took only about 30 minutes, thanks to the way the drivers and port tubes are installed.) I have not measured the results, but probably the only thing that will change will be the amount of EQ required from the ART 351 equalizer that I use in that system to extend and flatten the bass below 90 Hz.

The earlier sub is 68 inches tall (56-inch Sonotube) and the new version is 57 inches tall (48-inch Sonotube). Both Sonotubes are 14 inchers, and the ports on the smaller ones are a tad shorter than the ones on the bigger ones. 

The earlier design is tuned to 18 Hz; the newer one is tuned to 22 Hz, although the EQ extends the reach to 20 Hz with no problems.

Howard Ferstler


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## aardvark (Sep 29, 2011)

Oh, ok...Thanks, on the height dim's.
I don't know why I thought you were using 12" sonne's . It doesn't even make sense, now that I think about it.

I don't run on a subwoofer circuit so my crossovers must be internal. I'm running a HK AVR210. An older unit I just purchased. which is a relatively low powered surround amp. 60w per, but severely underrated. It kicks tail compared to my old Marantz 2270 stereo unit, and out performs the ole beast hands down. The room area is small and I only sit 11 ft from the speakers, so the power is more than I need.

Cool on the insulation removal. Did you scrape off the top layer? I would have had long sleeves and my wrist taped shut, over rubber gloves...Ha!

Lately I was in a pawn shop and picked up a set of Bang&Olefsen RL60.2 's Paid $75.oo. I like em, for their mid spread and evenness , but thy are terrible on hi's and low's. When I tore em apart to replace speaker cloth, I was shocked at the plastic cases and NO insulation except for a area that had a Maxi Pad like piece over an area.
Hey, for $75.00, some clean up and 6 ft of grill cloth, it was a chance. I like em as mids with my towers and sub going all at once. Sounds like overkill, and is, but it smoothed out things.
Still playing with them.


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