Working out the tube sizes
I'm not sure how important maintaining a constant cross-sectional area is, however if you wish to pursue it, the following might be of interest.
I built a test port which was made from three concentric tubes. I was hoping to find a new way to fit a long port into a short space. This is similar to what is being discussed here on a larger scale.
Whist the port itself performed poorly, some of the experience might be of use.
The main finding was that expecting the air to make a hard 180 degree turn at each end produced a lot of turbulence. For a TL sonosub, the airspeed would be much lower than this, but it probably wouldn't hurt to do some profile work on the ends to "help" the air around the corners.
The other thing that might be of value is the calculator I developed. It works out the pipe sizes and endgaps to maintain a constant area. Find it, (plus all the maths for the masochistic), at:
http://www.users.bigpond.com/bcolliso/vent-proof-adv.htm
regards
Collo
I'm not sure how important maintaining a constant cross-sectional area is, however if you wish to pursue it, the following might be of interest.
I built a test port which was made from three concentric tubes. I was hoping to find a new way to fit a long port into a short space. This is similar to what is being discussed here on a larger scale.
Whist the port itself performed poorly, some of the experience might be of use.
The main finding was that expecting the air to make a hard 180 degree turn at each end produced a lot of turbulence. For a TL sonosub, the airspeed would be much lower than this, but it probably wouldn't hurt to do some profile work on the ends to "help" the air around the corners.
The other thing that might be of value is the calculator I developed. It works out the pipe sizes and endgaps to maintain a constant area. Find it, (plus all the maths for the masochistic), at:
http://www.users.bigpond.com/bcolliso/vent-proof-adv.htm
regards
Collo
That is most cool!!! Okay.....a few questions. When you talk about adding and removing strips.....you're talking about cutting one cut through the length of PVC sewer pipe, then using a "strip" cut from another tube at the precise width as your calculator computes....to acheive the circumferance of the circle or the required inside diameter of said tube. This is done for ports 1, 2, 3 or 4 and 5 if desired. Abviousely the risk of chuffing is greater with more tube....so, if I'm aiming big with an 18 inch driver....I think I'll stick with the 3 tube calculation.
Can this calculator be done with a 2 tube only design? Height is higher....but chuffing is less of an issue. One must calculate the volume that the smoothed out inner corners would take up....no? Or would it change the "length"....maybe not?
Can this calculator be done with a 2 tube only design? Height is higher....but chuffing is less of an issue. One must calculate the volume that the smoothed out inner corners would take up....no? Or would it change the "length"....maybe not?
Okay....wait a minute.....when making your own tubes, are you actually cutting down 2 tube, to in fact laminate together to make one new tube??????? Taking away from the inner tube to reduce diamter, then adding to a second tube to sandwich around the first one???
I'm dealing in inches, and with the wood/paper fibre sonotubes. How much is not enough difference in the stock diameter to worry about?? 1cm, 2 cm, 5 cm? (width of calculated strip)
C
PS Thanks for your help dude, this is great!
I'm dealing in inches, and with the wood/paper fibre sonotubes. How much is not enough difference in the stock diameter to worry about?? 1cm, 2 cm, 5 cm? (width of calculated strip)
C
PS Thanks for your help dude, this is great!
The way I made a tube of a certain size was to laminate two tubes together. Each tube will either have a strip cut out or inserted, depending on the size you need. You may in fact need 3 lengths - two for the layers and a third one to cut the strips from.
The calculator doesn't do two layer tubes, but if you are having trouble working out the endgap from the maths on the site, or if the demand is there, I'll re-write it.
The relevant equation is:
endgap_small_tube= ( ID_tube1 ^ 2 ) / ( 2 * ( ID_tube1 + OD_tube1))
I worked with PVC / epoxy glue, whereas you will be using sonotube as you said. I've not worked with sonotube, so I dont know if it can be glued. If its plain paper you could use PVA glue, but if it is waxed, I'm not sure how you will go.
If using a laminated tube in the port calculator, you use the thickness of your completed tube as the value for "wall thickness" ie double the wall thickness of a single sonotube
With regard to acceptable differences in pipe sizes, I suspect that a vaiation of 10% in volume (square root of this for diameter) would be fine. Probably best to throw this one open for discussion!
Adding a smooth bend at the ends could look something like the red area in the attched picture. The extra material would not change the calculations, because the endgap is calculated as shown by the brown arrow.
The calculator doesn't do two layer tubes, but if you are having trouble working out the endgap from the maths on the site, or if the demand is there, I'll re-write it.
The relevant equation is:
endgap_small_tube= ( ID_tube1 ^ 2 ) / ( 2 * ( ID_tube1 + OD_tube1))
I worked with PVC / epoxy glue, whereas you will be using sonotube as you said. I've not worked with sonotube, so I dont know if it can be glued. If its plain paper you could use PVA glue, but if it is waxed, I'm not sure how you will go.
If using a laminated tube in the port calculator, you use the thickness of your completed tube as the value for "wall thickness" ie double the wall thickness of a single sonotube
With regard to acceptable differences in pipe sizes, I suspect that a vaiation of 10% in volume (square root of this for diameter) would be fine. Probably best to throw this one open for discussion!
Adding a smooth bend at the ends could look something like the red area in the attched picture. The extra material would not change the calculations, because the endgap is calculated as shown by the brown arrow.
Attachments
Whoops! A couple of errors which could lead to confusion 
should read "The calculator doesn't do two tube ports...."
should read "I suspect that a variation of 10% in cross-sectional area ..."
The one good thing about having to add an edit, is that I get the chance to use some more of these wonderful smilies
Collo said:
should read "The calculator doesn't do two tube ports...."
Collo said:
should read "I suspect that a variation of 10% in cross-sectional area ..."
The one good thing about having to add an edit, is that I get the chance to use some more of these wonderful smilies
True, but remember that in a non-tapered TL, unlike the port of a bass reflex box, air velocity is relatively slow. If the cross sectional area through the "bend" is equal to or greater than that through the line, there's probably more turbulence to worry about around the back of the driver's basket, as air is being pushed through a smaller space there.Clarkcr said:
This thread contains some of my discussion with MJK re: corner reflectors and line geometry:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=46730&highlight=
Here is MJK and Bob Brines talking about TL bends and corner reflectors:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30907&highlight=
I like the idea of a concentric folded TL. Im thinking of using PVC instead of sonotube. Weight isnt an issue for my application, and the rigidity of the tubes allows for a pair of ends to hold the inner tube centered, and then just a bunt-cake style reflector for one end.
Sound good, or just insane?
Sound good, or just insane?
Sounds great but don't discount the sound deadening properties of the wood fibre sonotube. It is easier to cut, glue and comes in more sizes than PVC. I like the idea of slicing out strips in the sonotube to be able to make a custom diameter tube like the one fellow on this thread did.
Also, the bigger diameter sonotube is very strong. I don't think you would have any problem with weight.
C
Also, the bigger diameter sonotube is very strong. I don't think you would have any problem with weight.
C
Turbulance? Remember that the air is oscillating back and forth a very small distance in the TL, as frequency increases I believe the range of motion is going to decrease. There is no "flow" of air. I don't believe that turbulance is an issue in a classical TL, even in the folds. In a vented system with a restricted port it does show up if the system is pushed hard, but in a TL where the cross-sectional area is at least equal to the driver cone area, I have a hard time being concerned about turbulance.
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