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Quarter Wave / T-Line tutorial-UPDATED


Forevrbumpn

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you can post pics.... upload to an image hosting site such as imgur, photobucket, etc... and then copy the IMG code and past it here

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  • 5 months later...

I'm actually very interested in building a T-line setup for one 12" sub for my F150 truck.... But posted a new totitle called, "Its been a very long time".... as I saw that this thread had not been visited in over 5 months.

Does anybody know what happened to Foreverbumpn ?

Any new T-line pros here nowadays ?

I could ask ? / and discuss T-lines here.... Or within my new thread.. whatever is appropriate....

Much thanks in advance.

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Thank you Triticum. So I'm considering an NVX VCW 124.... But open to other suggestions for a 12" SQL kind of sub, in the $200 or less range. Would an Alpine Type R be any better ? I can pretty easily give this 12" sub about 100 sq inches of port area, and a 9 1/2ft transmission line (for about a 30 hz tuning) but the NVX VCW actually has an FS of 26hz. I might be able to get another 1 1/2ft of t-line length, for a tuning closer to 26hz, but it would be a lot more work, and I would only do it if the pros here thought it would make a big difference ??? I was thinking about going with a 30 hz tuning, and maybe using some dampening, to get it down a bit deeper, plus help to flatten out the response a bit too ?

I can give this sub 935wts RMS from my RF Power 1000, into 1ohm.... But I hear that I might need less power in a T-line enclosure (which is really like a free air enclosure, in many ways) and so if I run it at 2 ohms, I can get about 500 wts RMS.... Hmmm. Is more always better ? I mean I will already be going from 2 15"s to 1 12"..... Still want to rattle my internal organs a bit :) lol

What other questions do I need to be asking ?

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11 hours ago, fishchris1 said:

Thank you Triticum. So I'm considering an NVX VCW 124.... But open to other suggestions for a 12" SQL kind of sub, in the $200 or less range. Would an Alpine Type R be any better ? I can pretty easily give this 12" sub about 100 sq inches of port area, and a 9 1/2ft transmission line (for about a 30 hz tuning) but the NVX VCW actually has an FS of 26hz. I might be able to get another 1 1/2ft of t-line length, for a tuning closer to 26hz, but it would be a lot more work, and I would only do it if the pros here thought it would make a big difference ??? I was thinking about going with a 30 hz tuning, and maybe using some dampening, to get it down a bit deeper, plus help to flatten out the response a bit too ?

I can give this sub 935wts RMS from my RF Power 1000, into 1ohm.... But I hear that I might need less power in a T-line enclosure (which is really like a free air enclosure, in many ways) and so if I run it at 2 ohms, I can get about 500 wts RMS.... Hmmm. Is more always better ? I mean I will already be going from 2 15"s to 1 12"..... Still want to rattle my internal organs a bit :) lol

What other questions do I need to be asking ?

So first off, T-lines really are NOT like a free-air enclosure, at all.  They are actually very similar to ported box.  Both ported boxes and t-lines are a resonant system, they both accomplish the same thing, they just do it in a different way.  

Like a ported box, t-lines are very flexible and there isn't one way to design them that is going to be right in all situations.  As you know, changing the length of the line changes it tuning frequency much like changing port dimensions on a ported box changes its tuning frequency.  Changing the line area of a t-line has a similar effect to changing the net volume of a ported box, it changes how much output you are going to get around the tuning frequency.  The reason t-lines are power efficient is because when you make the line area equal to cone area you end up with a huge box for whatever size sub you have.  If you were to put that same sub in a similarly sized and similarly tuned ported box you will get similar results.  Just like with a huge ported box, with these large t-lines you don't end up with much excursion control so power handling goes down quite a bit.  So here's the thing, you don't HAVE to make the line area equal to cone area, and depending on what you are doing making it smaller can be better.  

With MANY (but not all) subs, when you make the line area equal to cone area you are going to end up with a BIG boost in output around the tuning frequency, this is good for getting a lot of output on little power, but you usually have a big peak in the frequency response.  If flat (or at least flatter) frequency response is what you are after, that big peak is a bad thing.  Making the line area smaller will reduce the peak, at the expense of some max output capability.  Another thing to know is you don't have to put the sub at the closed end of the line, putting the sub about 1/3 of the way from the closed end will also help smooth frequency response, but also at the expense of some max output.  One unique thing about t-lines is if you end up with frequency response that is too peaky, you can stuff the line with poly fill to reduce output around tuning and very effectively tame the peak.  

If you want to get an idea of how various subs will perform in a t-line you can use software called HornResp.  Its like WinISD, but for t-lines (and other box styles).  Its free, and very powerful, but not the easiest thing to learn to use.  If you are interested I can help you with it, or model things for you.  For example, here is the NVX VCW124 modeled in two different T-lines:

QcSRIXQ.png

The light grey line is a t-line with the line area = cone area and the sub placed at the closed end of the line. 

The black line is is a t-line with the line area = 1/2 cone area and the sub placed 1/3 from the closed end of the line. Less output, but smoother frequency response. 
Both lines are tuned to 30 Hz.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Triticum, wow, that's a lot of stuff to consider. Read this post like 3 X's before I was brave enough to respond ?

Okay so I trust you, but going all the way back to a few of the first posts by Foreverbumpn, he made it sound like I should have "at least" as much port area, as the cone area of the driver, but that a little more was probably better ? That in mind, when I was doing some of my original 'napkin' sketches, I was shooting for just over 100 Sq in, figuring most 12" subs at about 95 Sq in.... I mean, I'm sure I could easily tighten that up to 95, or even 90 Sq in.... But how about if I just used more dampening insulation ? Again, for my situation, getting the t-line length quite a bit longer, to get the tuning down to the 26Hz FS of the NVX VCW 124, would be quite a bit tougher anyway. Also, would dampening help the sub handle more power ? I'm thinking dampening might help me in several ways.... deeper, flatter, and better power handling too..... true ?

So what do you think about my choice of subs ??? Would an Alpine Type R or S be any better ? Also, considering that T-lines reduce power handling, if it were you, would you run my sub channel at 2 ohms to get it down closer to 450-500 wts rms ..... OR, should I be looking at a different sub which is "normally rated" at 1500-2000 wts, to be sure it can actually handle 935 wts rms in a t-line setup ???

Anyway, the only part of this that's already decided, is my power, as the rest of my system works great for my truck, and I'm simply going to yank out the current box, and put in a new one..... 

What would you do if you had this amount of power, space, and wanted an SQL setup ???

 

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Hey btw, I just did a few quick calculations, and found that I could easily go with two 10" subs, instead of one 12"..... which effectively doubles my power handling, and gives me about 35% more cone area.... They would still have the same t-line length for 30 Hz tuning.... obviously a little more expensive of an option.... but how does this sound with SQL in mind ???

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Don't ever feel like you need to be hesitant to respond or ask questions, there are plenty of people here who are happy to share what they know as long as you are willing to learn.  We all started at the same place, knowing nothing :-)
 
As far as line area goes, there are different schools of thought when it comes to T-line design and this is an area (along with others) that I disagree with Foreverbumpin.  Assuming that the line area should be at least equal to cone area is an oversimplification, and like many other oversimplifications in car audio, it not necessarily wrong, but definitely isn't always right.  The proper amount of line area depends on what you want to do, how much power you are running, what sub you are using, etc.  Compared to other box styles, T-lines in general don't have any less power handling capability, unless they are oversized, which is exactly what you get when you set the line area equal to Sd (cone area). 
 
For tuning frequency, my suggestion would be to not be too worried about the Fs of the sub, and to have more concern about how low you want to have good output to.  Much like ported boxes, once you start playing below the tuning frequency of the line the output drops and cone excursion increases quickly.  I would suggest tuning to the lowest frequency you want to be able to play well, or may a few Hz higher than that.  
 
Most 12" subs have more like 80 sq in of cone area, not 95, this is because the cone is a lot smaller than the nominal diameter of the sub.  When looking at sub specs look for "Sd" which is cone area in square centimeters.  Divide by 6.4516 to get square inches.  If you have room for a T-line with 100 sq in of area I would not be looking at running two 10"s, I'd go for two 12"s.  With 100 sq in of area that would still be on the high side for my tastes.  With two 12"s you are going to get twice the power handling of a single sub, obviously.  There would be no reason not run you amp at 1 ohm, and you would end up with a big increase in output over a single 12". 
 
The Alpine Type-R and Type-S subs are both decent for the money, compared to each other they are very different subs though and will perform noticeably different.  In similar enclosures, the Type-R is going to be fairly similar to the NVX VCW124, but should give a little smoother frequency response.  The Type-S is going to be quite a bit different though, it has a lighter cone but less motor force.  The Type-S is going to have less low end output, but a smoother frequency response.  Everything is a tradeoff.
 
Here is a comparison of the Type-S and Type-R in the same T-line enclosure:
VQH7B36.png
The light grey line is the Type-R, the black line is the Type-S.
The Type-R has more output below about 38Hz, but significantly less above that point compared to the Type-S.  If it were me, I think the Type-S looks pretty good because cabin gain is going to boost the low end output and you will end up with a more gradually rising low frequency response where as the Type-R may end up being pretty peaky.  That's just me though, everyone likes their music to sound different so I can't say what will be right for you.  In either case I'd still plan on stuffing the box somewhat.  
 
 

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Okay, so I'm starting to drive myself crazy... and I don't want that to rub off on you ☺️ lol 

But about the Alpines, both the Type R and S, I had forgotten they have that funky surround... which I have only had one previous experience with, but it was a negative one, so I kind of have that stuck in my head. Also, while I agree with you on the Type S because it has the more even response, its also only good for half the wattage :( 

 

Are their any other 12" subs in the "less than $200 range that you think would be good for my purposes here ?

Also (I hope this makes sense) but will it hurt anything if the subs are positioned in such a way, that one of them is just a little bit closer (12") to the port opening (in-line, instead of side by side) ? I thought I could have them side by side... but then remembered the box will only be about 19" wide.....

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