"Folded" Sonotube TL Sub Complete! - Page 3 - diyAudio
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Old 10th September 2005, 07:45 AM   #21
Collo is offline Collo  Australia
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Default 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/bcollis...-proof-adv.htm

regards
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Old 10th September 2005, 02:08 PM   #22
Clarkcr is offline Clarkcr  United States
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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?
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Old 10th September 2005, 02:13 PM   #23
Clarkcr is offline Clarkcr  United States
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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!
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Old 10th September 2005, 02:20 PM   #24
Clarkcr is offline Clarkcr  United States
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In addition....wall thickness of stock tube in port size calculator must be doubled. Right?

cool
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Old 10th September 2005, 10:30 PM   #25
Collo is offline Collo  Australia
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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.
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Old 11th September 2005, 06:02 AM   #26
Collo is offline Collo  Australia
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Whoops! A couple of errors which could lead to confusion

Quote:
Originally posted by Collo
The calculator doesn't do two layer tubes...
should read "The calculator doesn't do two tube ports...."



Quote:
Originally posted by Collo
I suspect that a vaiation of 10% in volume ...
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
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Old 11th September 2005, 07:54 AM   #27
Tweeker is offline Tweeker  United States
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Approach Im taking is to add pool noodles to maintain reasonably close to same cross section.
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Old 11th September 2005, 02:42 PM   #28
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Also, make sure to model your design in Martin King's MathCad sheets... I was more concerned about the difference in CSA in my different sections until I modeled it. MJK is also of the opinion that smoothing the bends in a TL, especially in the subwoofer TL, makes not a whit of difference.
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Old 12th September 2005, 02:43 AM   #29
Clarkcr is offline Clarkcr  United States
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Quote:
Originally posted by bwbass
Also, make sure to model your design in Martin King's MathCad sheets... I was more concerned about the difference in CSA in my different sections until I modeled it. MJK is also of the opinion that smoothing the bends in a TL, especially in the subwoofer TL, makes not a whit of difference.

Surely there is turbulance that will create a resistance of some sort.
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Old 12th September 2005, 02:46 AM   #30
Clarkcr is offline Clarkcr  United States
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Quote:
Originally posted by Tweeker
Approach Im taking is to add pool noodles to maintain reasonably close to same cross section.

Interesting....how so? I mean, used as dampening material? Cut in quarters lengthwise?
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