[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

[Dick Pierce[_2_]]

Gary Eickmeier wrote:

"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.

Several things poop into my head when I read this:

"What's the difference between theory and practice?
In theory, theory and practice are the same. In
practice, theory and practice are different."

It's on the Internet, so it must be true.

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.

Oh, be assured, kind people, it most assuredly can and quite
happily does. The assertion that it cannot is based on the
following assumptions:

1. That the wall material is infinitely rigid, has infinite
tensile strength, i.e., it can neither be stretched, compressed
or flexed. The 3/8" cardboard walls of a Sonotube are VERY
VERY far from that ideal,

2. That the internal forces on the walls are the same at every
point along the walls surface. With ANY musical material,
this is simply not the case.

3. That the cylinder is infinitely long, i.e., it has no
boundary conditions to deal with. Again, not the case
"in practice."

Consider two cyclinders of MUCH greater strength than that of a
20" Sonotube: the walls of the SRMs on a shuttle were 1/2" steel.
The ignition transient was predicted and was measured to cause the
walls halfway between the field joints to expand nearly a foot.
But because the field joints used a much heavier, thicker steel
ring, they did not bulge anywhere near that much. The result was
phenomenon called "joint rotation" and was crucial to causing
the failure of the field joints in the Challenger explosion.

Be that as it may, while "in theory" it seems like Sonotube is
an "ideal" way of building a subwoofer, "in practice"m most
of those teoretical advantages simply aren't there.

I had, for a former client, done quite a bit of measurements on
cardboard tube enclosure, most of which were MUCH more substantial
than Sontotube (minimum 3/4" wall thickness, higher density wrap).
Using acceelerometer measurements, wall flexing was NO better and
most of the time WORSE than a rectangular enclosure of the same
corss-sectional are. The unsuported walls of the rectangular
enclosure did no worse under the same conditions, and at the
corners, they behaved MUCH better.

At freuqencies where the wavelengths were smaller than either the
length or cricumerance of the tube, cyclinders tid MUCH worse
in almost every respect. We would see nodal vibration patterns
on the wall that had very high Q'. This is directly attributable
to the very dimensional symmetry of the shape. Siply because the
unsupported area of the "soundboard" was now the length of the
enclosure times its circumference: nodal patterns could be easily
set up and well established at MUCH lower frequencies than in a
similarly dimensioned rectangula enclosu the largest unsupported
surface in a box is substantially smaller than that of the cylinder.

And the argument that

"A cylinder-enclosure shape ... cannot flex inward or outward"

Makes the simplifying and quite incorrect assumption that there's
a single, in phase constant force on every square cm of its curface,
annd thus the wall MUST be compelled to move uniformly radially.
Sorry, but that just doesn't happen in loudspeaker enclosures. TO
get the walls to fles very nicely, all you have to do is get it
going outward at one point atv the same time it's going inward
womehere else along its circumference. And, as far as local
stiffness is concerned, Sonotube ain't so hot, especially 3/8"
Sonotube.

If you want to deal with this issue, consider getting TWO sonotubes,
on loerger in diameter (by maybe 1-2"): place them concentrically
and then fill in the space between the two with something heavy and
mechancially lossy, like dry sand (or, uhm, concrete!).

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.

Wanna bet? The port tube DOES NOT reinforce it: the hole, in fact,
weakens it.

My bottom plates are each 2.25
inches thick,

Okay, so you "cheated." They don't flex because they are round, or
because they have a driver, or becasue they have a port, they
don't flex merely because they are 2 1/4" thick.

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.

Sorry, the very axial and radial symmetry means they have
the ability to suport quite nasty, highQ resonance. Take a
glass pie plate, fill it with water, and put a speaker near
it, driven by an oscillator: you'll find any enclosure with
a circular cross section support standing wave VERY nicely.

Or, for a dramatic acoustical demonstration of the effect,
toss a fire cracker into a cylinfrical storm drain: it
doesn't go bang! it goes Bonnnnnnnggggggg! for a VERY
long time. And, surprise, you find that the pitch of
the bong! it inversely proportional to its diameter.

And a cylinder also supports end-to-end standing waves quite
nicely as well. That's why flute, organ pipes and such are
made, largely, of cylinders.

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.

Sorry, both theory and practice demonstrate otherwise.

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.

And has a problem in calculating what the effective radiation
impedance seen by both the port and the driver a rest assured,
if you assume that it has no effect, you'll get it wrong.

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.

Please, do we have to bust this myth AGAIN (or did we miss the
smiley)?

Assume the mass of the driver cone is, oh 200 grams. Assume
also that the driver, enclosure and lamp together weigh 30
kilograms. By conservation of momentum calculate what the
worst case "bouncing" of the lamp will be. Show your work.
Get back to us when you have an answer.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[Audio Empire]

On Mon, 16 Jul 2012 06:59:04 -0700, Gary Eickmeier wrote
(in article ):

"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



I don't think the subwoofer cares about the shape of the enclosure as long as
it's as inert as possible and the volume is sufficient and you do the port
maths correctly. You don't want the subwoofer enclosure to flex no matter
what shape it is. I once built a subwoofer from a piece of oval ceramic
fireplace chimney flue-liner pipe. I cut two 3/4" pieces of plywood to fit
on each end of the 3 ft flue-liner section. I cut an oval hole in one end to
take the odd-looking British KEF low frequency driver that was popular in
those days, and after measuring the inside dimensions of the "enclosure",
figured the bass reflex port size after Hoge and Bullock, and used four long,
threaded rods to clamp the end pieces onto the pipe after lining the pipe
with fiberglass insulation. The threaded rods extended about three inches
beyond the end with the driver attached and these served as legs to keep the
driver off the floor. I painted the flue liner pipe and the end baffles
black. It worked fine and I used it for many years with good results. I was
getting good bass down into the low thirties from that KEF driver.