Question on T-Line boxes

[pervitizm]

I'm trying to follow the sticky write up on building Quarter Wave enclosures. I've finally gotten the nerves to try one out on a 12 in elemental design sub that I've had sitting around for years now. I did the math on the sub and I came up with these numbers:

T-Line (eD 13Kv.2)

To calculate length of Freq divide 1130 / (Fs freq) = Full wave Length

To calculate Quarter Wave length divide (Full Wave Length / 4)

Take the SD (cone area) if in cm2 (squared centimeters) convert to in2 (squared inches)

1.) 1130 / 21.5Hz = 52.55 ft – rounded to 53 ft

2.) 53 ft / 4 = 13.25 ft Q-wave length

3.) SD =545cm2 which is 84.48in2. The line has to be 84in2

So based off of what I have, I'll need a line that is around 13 feet long with a port area of around 84sq inches, does this sound right to you? Here are the specs based off of that 13Kv.2 sub that want to use:

Qts: .31

Qes: .35

Qms: 3.33

Fs: 21.50Hz

Re: 3.7

Vas: 162L

Mms: 142.0g

Bl: 15.00T*m

SPL: 88.47dB

Sd: 545cm²

Xmax: 15.1mm

Voice Coil: 50.0mm

Magnet Width: 5.700"

Cutout Diameter: 11.000"

Mounting Depth: 5.750"

Weight: 14lb

Total Height: 6.250"

Displacement: .06 ft³

Outside Diameter: 12.375"

I'll want to try and sketchup a design later on this evening when I get home from work. The two main issues that I have when designing one of these is how do you calculate the fold when doing a folded design, and how do you deal with woofer displacement when your woofer displacement is actually bigger than you line? What I mean is this, say my line has a depth of around 8 inches from the front baffle to the line wall, but I need a mounting depth of 8.5 inches for my woofer to fit. How do you deal with getting that extra .5 inches? Doing an inverted install wouldn't work out to well for my enclosure's final location.

Sorry for such a long post but I think I'm on the right path with this I'm just looking for a bit more guidance. And I know if I can figure this out for a 12 then when I'm ready to try it on one of my 18's the design phase will be much much easier.

[liftedranger08]

That looks to be correct. Now for your sub to fit, you could do a a spcaer under the sub. I would say do a 3/4" spacer. That should raise the sub up enough so it wont hit the inside of the box.

[kandiman71874]

That looks to be correct. Now for your sub to fit, you could do a a spcaer under the sub. I would say do a 3/4" spacer. That should raise the sub up enough so it wont hit the inside of the box.

Spacer is the correct idea, but yer only leaving a 1/4" behind the motor doing a single layer of 3/4" mdf. If the sub has a pole vent of any kind I would at least do 1.5 inch spacer to let the motor assembly breathe a little for cooling purposes.

Next thing to address here though is what/where will you be putting this enclosure once it is built. A 1/4 wave with a line length of 159 inches tuned to the FS of that sub is going to be huge...

Edited April 15, 2010 by kandiman71874

[pervitizm]

Spacer is the correct idea, but yer only leaving a 1/4" behind the motor doing a single layer of 3/4" mdf. If the sub has a pole vent of any kind I would at least do 1.5 inch spacer to let the motor assembly breathe a little for cooling purposes.

Next thing to address here though is what/where will you be putting this enclosure once it is built. A 1/4 wave with a line length of 159 inches tuned to the FS of that sub is going to be huge...

This would go either in the living room or the wife's van. So when you guys build these you do the line by the inches instead of by the foot? Is it easier to do the line by inches? And the spacer ideal is good. I kinda thought that would be the way to go. I'm about to do a quick sketup of what I think this should look like. Hopefully some of you guys in here can take a look and let me know if I'm on the right path with this.

[pervitizm]

Ok so I sketched up a drawing in google's sketchup. Now I didn't add the top to this but the box height with the top on is only 12inches high. So if HxWxD then the box is 12 x 45 1/2 x 27 3/4. The three drawings are of the same box just showing different measurments for what I wanted to illistrate. Now to get my 84sq of line I did a HxW of 10.5 x 8 = 84sq. So the lines wide is 8 inches high by 10 1/2 height.

This image here shows how I kept the line a constant 8 inches wide throughtout the line including in the folds with the 45's there.

This next image shows the box outer dimentions along with the 45's as well. The only dim I didn't show what the height, and that was because I didn't draw the top of the box.

This last image is the one I have the queston on. When I did the finial go throught on this box I come out with a final line lenght of only 115 inches or roughtly 9 1/2 ft. Without the 45's I have a box that is 175 inches or 14ft. Why did my 45's take away almost 4ft of area? The only way I could add 45's and keep the line constant thoughtout the folds was to add those size 45's. Can I build the line without the 45's? Would I notice the difference? Or better yet did I calculate the line measurment in this last pic correctly?

Any help and feedback I can get will be greatly appreciated.

[kandiman71874]

Line length is measured down the center of the tunnel for length. average person looking at that is gonna miss the additonal 4 inches on each fold

[pervitizm]

I'm not sure I'm following what your saying. What 4 inches are you referring to?

[pervitizm]

Okay so I played around with it again. This time I think I got the line count right, the bad though is that I'm still around 2ft short of my 13ft line. Take a look below. The first pic shows the cross section lines of the middle of the line. Again my line is 8 inches wide so the middle of the line is 4 inches.

So after taking another look at the sticky I decided to remeasure my line again based off what I read somewhere around page 12 of the sticky. So this is what I came up with

31 1/4 + 27 1/4 + 36 +8 3/4 + 8 3/4 + 22 7/8 = roughly 135inches. Again I'm still not there yet but I think I'm getting closer.

This is just a cleaner picture without the cross section lines, which makes it easier to see.

[STEvil]

using 1/2 circle radius would give you a more correct number for the corners. Flare the mouth if possible, free horn area!

[pervitizm]

Thanks for the suggestion.