[Gary Eickmeier]

"Barkingspyder" wrote in message
...
Are there any advantages other than a smaller foot print for
cylindrical subwoofers? Do they require damping material in the
same way a box would?

I'm considering a DIY project and would be curious as to the science
on this topic. Are there the same problems with vibrations inside
the enclosure, or does the cylinder reduce or make them a non-issue?

I see a lot of the sonotube desgins have the driver at one end and he
port at the other. Does it make any difference if they are are at
the same end of the tube assuming a large enough diameter?

I am considering a 143 L EBS alignment with both the port and the
driver at the bottom. The tube would be 20" in diameter and a 4"
port. I am not married to these dimensions but I thought there
would be a higher WAF if the thing looked less like a water heater.

Comments please.

Hi Barking -

Some comments from a friend:



"Well, in theory a box-shaped sub enclosure will try to flex its wall inward
or outward as the cone moves in and out, with the idea being that the
pressure is trying to turn the box into a sphere.

A cylinder-enclosure shape, even with the cylinder walls only 3/8 inch
thick, cannot flex inward or outward (assuming the Sonotube fiber material
is decently strong in terms of stretch resistance, and believe me, Sonotube
is strong), because the surface is already curved to a circle. Yes, it is
not a sphere, but the top plate cannot flex outward or inward, because it is
mostly filled with the driver, and the bottom plate cannot flex much,
because it has the port tube in there reinforcing it and the thing is
usually too thick to flex much, anyway. My bottom plates are each 2.25
inches thick, for example, with the bottom plate itself standing on 3-inch
pegs that themselves are screwed to still another bottom plate. (There is a
similar standoff plate on the top that is there simply for cosmetic purposes
and to protect the driver cone.) The inside of the Sonotube should be
layered with a couple of inches of fiberglass (mine is held in place with 3M
spray adhesive, and the fiberglass is actually furnace pipe wrap with the
foil removed), and the idea there is for the heating and cooling of the
fiberglass under pressure (which can occur at any frequency above the port
resonance) to help the driver to "see" a larger interior space than is
actually there. (Acoustic-suspension woofers and subwoofers also have
something like that in their cabinet interiors for the same reason.) The
effect is actually minimal, but in any case the fiberglass is not there to
control resonances or absorb noise. Resonances are minimal with a cylinder
enclosure, actually, due to the lack of glued-together speaker-wall joints.
In any case, in practical terms, a Sonotube enclosure should be the most
resonant-free enclosure possible for a subwoofer, although the light weight
is a theoretical problem - that I have not encountered.

It really does not matter where the port is, although it can if the
woofer/port interface is not quite right.and the driver and port are side by
side The first successful commercial sub Poh Ser Hsu made was a pretty fat
cylinder and both the driver and the port were on the bottom. Later Hsu
models like the TN1220 had the driver at one end and the port at the other,
as did (and do) the SVS cylinder models. Ditto for the units I made for my
main audio system. If the port and driver are on the bottom, the designer
can have an attractive top on the cabinet that will allow it to function as
an end table, or the like. However, the light weight of a sonotube enclosure
will allow the entire unit to vibrate up and down, which might make that
table lamp dance around a bit.

There obviously is an advantage to a smaller footprint with a tall, skinny
design, if floor space is critical, but of course what you gain in in terms
of left-over floor space you lose in terms of space above the unit. No free
lunch there, particularly if the wife does not like to see cylinder-sub
towers rising towards the ceiling. (Fortunately, my wife may actually like
the looks of my units.)

What can matter when it comes to how low the sub can go, in additon to
port-tube length and diameter (and of course driver design), is the interior
space of the enclosure. There are web-sites out there that help the user to
calculate both interior cabinet space with a cylinder (square inches of
circular area can be calculated with one site; times length of Sonotube) as
well as the required tube length and diameter with a given enclosure space
and desired tuning frequency. The calculating can be done in less than a
minute, actually. Once that math work is done, all one need do is order the
parts (the driver, the Sonotube, which comes in 12-foot lengths and
obviously has to be cut down, mdf to make end plugs, port-tube materials,
screws, glue, and grill fabric). You need the grill fabric to wrap around
the finished product to keep it from looking, as the poster noted, like a
black-painted water heater, tall or short. Heck, grill cloth comes in a
variety of colors and one can even go to a fabric store and look through all
sorts of nifty designs. A bright red cylinder sub would look really cool.
Mine are both black, however, in keeping with tradition.

Note that the pair in my main room are now using 12-inch, Dayton Reference
Series drivers instead of the 12-inch, DaytonTitanic drivers I first tried.
They go down to the bottom end a bit smoother than the Titanics (although
theoretically they cannot play as loud, but can play plenty loud enough) and
have less cone-flex noise. The full systems are 68 inches tall and 14 inches
in diameter, although the Sonotubes themselves are only 56 inches tall (the
additonal 12 inches involve end plugs and standoff bottom and top plates),
giving they an interior volume of 5 cubic feet. This allows tuning to 19 Hz,
and to keep things really smooth I equalize the bottom seven 1/3-octave
points with an ART EQ-351 equalizer. The result is the best sub-extension
measurements I have encountered in that room. Power for the two subs, as I
may have noted before, is via a Crown XLS1000 digital D class, 700-watt
power amp. This is not a super-low distortion amp, but it is more than
adequate for sub driving, and has RCA jacks for an easy interface with a
consumer-grade receiver sub-out hookup. Seven hundred watts is way, way more
power than I need (the room is 3400 cubic feet, and the amp/sub pair combo
can give me 115 dB at 30 Hz with ease, and almost as much at 20 Hz), but I
got the amp cheap from Parts Express. The damned amp weighs less than 9
pounds (each cylinder sub weighs in at about 50 pounds, including driver, by
the way, making them featherweights in the super-sub sweepstakes), and it
has a cooling fan that is so silent that you have to put your ear against
the front panel to hear it running.

I plan on building two more for my AV system in the back area, using the now
spare Titanic drivers (which are better for home theater, anyway, than the
Reference units), mounted in same diameter enclosures as what I have in the
main room, but with a height of 58 inches. They will be tuned to about 24
Hz - proper enough for home-theater use. A second Crown XLS1000 will do the
powering work, and I will use an existing Rane THX-44 and outboard Hsu
"Optimizer" equalizer to fine-tune the response smoothness and extension."

End quote.

Gary Eickmeier