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Discussion Starter #1
Ive been doing home / car audio for a long time now and have lots of experience with ported and sealed enclosures, and as a project want to build a t-line for two 8" drivers, with the aim of getting them to hit as hard and low as possible (30hz).

Ive researched and seen loads of variations, like some that are just folded lines, some that have a chamber before the line, some where the like gets wider, etc.

I know my line needs to be 112.5" long to get the 30hz tuning i want, as im doing 1/4 wavelength. (Let me know if doing 1/2 wavelength will be considerably better).

Just a few things to help me out:
- How wide should the line be? Ive got a feeling its to do with the drivers Q** values?
- Should it be a simple line, or have a primary chamber before the line?
- Should the line widen?
- Is there a 'best side' that the line should exit?

Any help with this would be great, cheers for reading!
Sam
 

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Greets!

OK, since you're experienced you know that a vent has an end correction and since a vent pipe is a small open pipe (1/2 WL) resonator it has an end correction at both ends that makes its acoustic length a bit longer than its physical length.

If we cap it off at one end to make a closed pipe (1/4 WL) resonator (aka TL) it only has one end correction, so from this we see that if we make the pipe a 1/4 WL long of 30 Hz it will be tuned a bit low, especially once damped since this further shortens it for the same reason that stuffing a sealed or vented cab increases its effective net Vb, lowering box Q. Expanding/contracting TLs (horn/TQWT) are 1/2 WL resonators with a 1/4 WL fundamental, so are closed cone resonators.

From this we see that once damped, a closed pipe tuned to 'x' Fp can be viewed as a stuffed vented cab tuned to 'x' Fb that's had its vent area increased (hence length) enough for it to morph into a large/long enough TL. So an acceptable performing TL (by TL standards) can be calculated using a basic vented cab design routine for whatever gain BW you choose, then by simply increasing the vent's area until it's a little short of ~1/4WL long of the desired Fb, we now know the TL's width x depth cross sectional area (CSA) and length.

For a more technically oriented, ~all inclusive tutorial and accurate (though not necessarily an overall superior performing) design, use MJK's Classic TL Alignment Tables Excel SS designer and optimize it if need be using either his MathCad worksheets or AkAbak.

His software can also be used to design/sim mass loaded (vented) variants, i.e. TL (no taper), horn (expanding taper), TQWT (contracting taper), ergo the vented variants, ML-TL, ML-horn, ML-TQWT. Note that some folks don't make these differentiations, lumping them all together as just TLs, so with no dims and/or description you don't know what variant they're referring to.

Then there's the patent applied for tapped variants by Danley Sound Labs which can easily be designed using HornResp's (HR) TH Wizard, i.e. tapped TL (TP), tapped horn (TH), tapped TQWT (TTQWT). These are basically 6th order band-pass (BP) alignments taken to their logical extreme same as the simple reflex/TL conversion, so a basic one can be designed using a 6th order calculator with the same BW Vs efficiency trade-offs to find a good basic design to optimize in HR.

Note that AkAbak can do all these plus much more, so while it has a steep/intimidating learning curve, there's enough samples and a tutorial now on the DIYaudio Subwoofer forum that you can get a useful sim pretty easily. HR's ability to export a design file into it is a big plus.

No, low pass filter chambers aren't used in TLs, though drivers with a small Vas tend to calculate such small CSA pipes that one just large enough to adapt the driver to it is required, so making it a TQWT is a good plan.

Horns are the largest/longest TLs for a given Fp with the TQWT being the smallest/shortest, making the TL the median choice, so which to use is an app driven choice same as choosing a sealed or vented alignment's gain BW.

Not sure what you mean by 'best' side. I mean a properly damped TL will have little/no significant BW output above ~1.414*Fp, so again, whether it's on the front, side, back or bottom is an app driven choice.

GM
 

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Discussion Starter #3 (Edited)
Greets!

OK, since you're experienced you know that a vent has an end correction and....
Thank you, thats helped a great deal!

Thats enabled me to construct a first design of the box - i have doubts about parts of it - but its a start. Tell me what you think and what areas to change for improvement!

(if the photos below dont show, use these links: 1, 2, 3, 4)







As you can see the line starts off at 2" wide and ends up 5" wide.
Some issues i think i have are:
- the chamber is too large
- the box volume is too big
- the expantion of the line is too great

The drivers ill be using to start with probably arent well suited for t-line enclosures; but theyre only temporary untill i can afford some RE8s which look good for this purpose.
Thanks for all your help so far
Sam
 

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You're welcome!

All your Qs and more will be answered by loading the driver's specs and cab dims into MJK's DBR WS and hit 'calculate Worksheet', then begin tweaking stuffing density and dims as required. ;)

GM
 

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Discussion Starter #5
You're welcome!

All your Qs and more will be answered by loading the driver's specs and cab dims into MJK's DBR WS and hit 'calculate Worksheet', then begin tweaking stuffing density and dims as required. ;)

GM
problem is - i dont know enough of the drivers specs, and some of them i couldnt even make a guess on... though i could use the re8s specs as thats what i hope to replace with anyway :)
Does that look alright as a base design though; will the way ive widened the line along the way work, or should i keep it all the same length?
Sam

ps. theres a 3d view vid of it here -
 

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........though i could use the re8s specs.........
Makes the most sense to me..........

Out of curiosity, what make/model is this mystery driver and what specs do you have?

Cool video BTW, I need to quit posting, so I can learn how to do cool stuff too. ;)

GM
 

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Discussion Starter #7
Out of curiosity, what make/model is this mystery driver and what specs do you have?

GM
All i have is 200Wrms D4 8"
By the looks of it though theyre not gonna have an Fs of under 30hz and theyve got quite a stiff suspention. Ive four, two already L ported @ 30hz - heres a vid of one of them free air


and theres plenty of vids of both of them in the L port.

Theyre strange though... they came with weird huge connectors on the end for connection to their designed system... and the tinsel leads are like proper wires...
 

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Oh well, the only 'D4' I know about is the CV 8D4 which looks nothing like yours. Guess you'll have to measure them. Suspension sure looks non-linear though.

GM
 

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Discussion Starter #9
UPDATE -
I changed the width of the start of the line to 3" instead of 2", which also had the effect of reducing the chamber to 0.4cuft, which may be an improvement:




I was also considering making the end of the line 4" instead of 5". This should reduce the effect of raising the tuning of the line, and making the chamber smaller should let more pressure occur.

Original plan or this one better?

Sam
 

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Where's the RE8's sim data to browse/critique?

GM
 

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I already have them loaded into WinISD, but thanks anyway! I meant where's your MathCad or similar response sim of your design using the RE8's specs? How did you arrive at the design?

GM
 

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Discussion Starter #13 (Edited)
Oh sorry ! To be honest i just worked out the length of the line, and folded it in such a way that it fitted into a reasonably sized box...
As im new to this all the calculators / programs looked very daunting and the project needs to be complete with writeup by the end of september.
This is why i posted up images asking if the design LOOKED alright, as no programs were used in its design.

Im getting the wood cut today, so just one last bit of advice before the build :)

Either,
1) stick with the original plan of 2" start expanding to 5" exit
2) go for 3" start with a smaller chamber (0.4 instead of 0.6 cuft) and 5" exit
3) do a 3 / 3.5" wide line throughout (traditional t-line instead of horn)
4) keep the line starting at 2" wide but only expanding to 4" by the end

Thanks for all your help im learning a lot through this!

Sam
 

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If you are designing TL or a horn enclosure, and just randomly picking widths, then your chances of failing are high. Horns are one of the most difficult enclosures to get right.

Easiest way to get a simple TL is to just pick up some sonotube from home depot (or similar) and then experiment with it. Once you figure out the proper length and amount of stuffing needed for this woofer, then you should build something out of MDF. This way you can prevent wasting money on improperly designed enclosure.
 

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It looks like a well built and executed enclosure design but without simulating the response who knows how it will sound. Why not hold off a bit and try to model it? You may need to make major changes to the design, but if it gets better performance it'd be worth it. It'll also help answer some of thse questions you have.
 

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As im new to this all the calculators / programs looked very daunting and the project needs to be complete with writeup by the end of september.
So, how did it turn out?

GM
 

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hello, can you help me build a plane for a t-line 2 subwoofers 8 "?
Greets!

Build it, no, [or at least not me], though can help design it if I [we] know the driver's specs [preferably measured], desired band-width [BW], any cab size constraints, intended app [stereo, HT, car].

Please start a new thread with your answers and reference the driver make, model in the title.

GM
 
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