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On some T line designs I see that people have the woofer firing into a chamber and then it goes into the line/port. On most T line designs, the woofer just fires directly into the line/port and that snakes around. I grasp and understand the math to figure out the line/port length. I have never seen anywhere how someone comes up with the chamber size that the woofer fires into before the line/port. How would you figure this out and why is is necessary? What do they do if a T line is really nothing but a long port?
If it is done just to fit a larger driver, how do you figure out the size and how does it affect performance?
 

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With a chamber before the port it would become more of a "horn" design, I'm just getting into these myself. You'd need some software like hornresp to model (lot harder to get my head round than BBpro). diyaudio.com has more users doing these types of design and has some tuitorials for hornresp.
 

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On some T line designs I see that people have the woofer firing into a chamber and then it goes into the line/port. On most T line designs, the woofer just fires directly into the line/port and that snakes around. I grasp and understand the math to figure out the line/port length. I have never seen anywhere how someone comes up with the chamber size that the woofer fires into before the line/port. How would you figure this out and why is is necessary? What do they do if a T line is really nothing but a long port?
If it is done just to fit a larger driver, how do you figure out the size and how does it affect performance?
In a conventional ported box the air in the box interacts with the woofer, and the port is tuned to the Helmholtz resonance.

This worked dandy until 1990 or so. In the past 21 years the box size required by woofers has grown smaller and smaller and smaller and smaller.

Ironically, as box size gets smaller, the port size gets bigger!

This may seem completely counter-intuitive, but it's absolutely true. You can model it with boxmodel, hornresp, whatever you want. If you reduce the size of the box, you need a bigger port to achieve the same tuning frequency.

Somewhere along the way, someone figured out that you really don't need a back or front chamber whatsoever. If you juggle the numbers, and you're using the right woofer, you can completely eliminate it.

And that's how you end up with all kinds of exotic boxes, everything from transmission lines to tapped horns.

In reality, tapped horns are really just a variation on a vented box, but don't tell the patent office.

I've never even heard of a "T Line Design", but I'm guessing it's some type of transmission line.

I am not a big fan of transmission lines, mostly because you lose a lot of efficiency due to the stuffing, and if you know what you're doing, you can smooth out the response using geometry, not stuffing. I have a transmission line sitting here in my bedroom with a couple of Titanic Twelves I'll sell ya cheap if you'll come pick it up. I like my tapped horns a whole lot more.
 

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So basically it's a transmission line with a helmholtz resonator in it? In other forums I've seen horns described as band pass enclosures too, forget what order.

Bass box pro will "model" TL's, create a gross box volume, put a huge port in it and then you'll get some graphs like below, just include the "port resonance peaks". This box has a gross volume of 6cf, but to model it I made the net volume of the woofer enclosure 0.005cf and the port takes up the remaining volume 15"Hx4"Wx160"L
 

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