t line box help

[codyvan87]

I have a pair of Rockford Fosgate P3 12s. I want to build a t line box for them. I have no idea where to start. I know I could use Google sketch up to come up with a design. The only problem with that is that I only have Internet on my phone, and the program just won't work on my phone. They are going in an SUV so there is plenty of room. Is there anybody that would be willing to help me with some designs? The box needs to be no more than 48" wide. Height and depth are no issue. I can get the specs on the subs if needed. I will be running a hifonics 1000w amp and would like the box to be tuned anywhere from 30-35hz.. help please?

[byers319]

Height and depth may not be an issue but still need to give limits on how big you want to go exactly..

[codyvan87]

Well being a t line I know it's gonna be big, but the smaller the better. I was thinking like 28" tall, 48" wide and 40" deep roughly. I will take measurements tomorrow to get a better estimate but that should be big enough I'm sure..

[NathanW]

Well given the size of the drivers you're looking at a line with roughly 175 square inches area between height and width. The length will be set by your tuning frequency and that should either be your drivers FS (26-27 hz) or your bass boost frequency (if you are planning on boosting). So if your amp boosts at 30 or 35 hz, you'll be looking at a length of between 8 and 9.5 feet. You can fold the line as many times as needed to fit your installation space, just be sure you round all inside corners and boards to maintain a constant line (45's in corners are better than nothing if you don't round them).

On a side note, you'll want to reduce the amount of power to the subs by half or more. With equal pressure on both sides of the cone, it acts as a free-air loading. So you'll reach the mechanical limits of the drivers well before you reach the thermal limits.

[codyvan87]

Dies anybody have a program to do some designs and would be willing to do up a couple different ones for me?

[codyvan87]

Help please anybody?

[MaxVolume]

I just built my second t-line yesterday so I'll take a shot at designing one for you. The P3 has a Fs of 26.5 hz but I'll design the box for ~35 hz. Keep in mind this thing will be BIG.

[gckless]

http://www.stevemeadedesigns.com/board/topic/1828-quarter-wave-t-line-tutorial-updated/

[bbeljefe]

I don't recommend tuning a transmission line above the Fs of the drivers that will be in it. They do not provide much acoustical suspension and tuning above Fs will cause you to reach their mechanical limits much more quickly. For the subs you have, tuning at 30Hz would be safe but I wouldn't go any higher than that.

You don't need to reduce power, you just have to make sure it's clean and that you don't play them at full tilt boogie below tuning. Surprisingly enough, even low compliance drivers do very well in t-lines, even though one would think they would do worse than a conventional vented enclosure. Personally, I've run two 75 watt subs on an 850 watt amp in a line without them reaching mechmax and, I poured the coals to them. You can see the video on my youtube channel. That said, I wouldn't recommend doing that long term and my test was just that... a test.

As for the box, there is no calculator that I'm aware of so you have to design it by hand. But if someone knows of a competent t-line calculator, I'd love to see it. :-)

In any event, you'll need the full width of 48" in order to make design as easy as possible and you don't have to make the line area exactly the same as the Sd of the subs. You can reduce it by ~10% without affecting tuning and you can reduce it by up to 40% without making any appreciable differences in tuning. Obviously, less line area will allow you to build a smaller box but it will also provide some more internal pressure which will help your subs with power handling so, it's a win win.

As far as rounding the internal corners, that's a lot of work for not a lot of benefit. 45° wave guides are sufficient and easy enough to construct and, I've even heard a line with no wave guides in it that sounded pretty damned good. I wasnt' able to compare it with a similar box having wave guides but the point is that there is no real reason to spend hours making perfect inside corners unless you're just anal, lol.

For design, understanding Pi is a must because you need to be able to measure the effective length of your turns. Find the diameter of a circle that's the same size as your line width and use PiR or, 3.14 X Radius to calculate the circumference of that circle. Once you have that number, the length of a 180° bend is half that number and the length of a 90° bend is ¼ of it.

If you need any more help feel free to ask. I'm not and don't claim to be the end all be all on lines but I have built a lot of them and I love em, lol. I would be happy to do the design for you but I do not do cut sheets so you'd be on your own with calculating those.

EDIT: Adding to the first statement, when you tune a line above Fs you also seriously diminish low end extension.

[Chris Hammer]

Download Sketchup and play with it for a day. You will learn more and knowledge is power. If someone throws you a design and it "doesnt work" then its on them not you. Try try try again and eventually you will be happy with it.