# School me on T-Line



## GotaCC (Sep 13, 2013)

So I have always wanted to experiment with building a T-line box but really don't know much about them other than they can be loud. I have this ID8v3 D4 I'd like to experiment with. In someones post they were building to the speakers Fs and people chimed in to note that it wasn't the parameter to go off of. Is there a really good calculator out there? If someone could educate me on the science behind this it would be very appreciated.


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## SkizeR (Apr 19, 2011)

heres a little something. i think this is from Brandon Buck




> DESIGNING YOUR T-LINE
> This will be a quick and simple primer on how to design a consistent dimension ¼ wave t-line. There are a variety of different ways to build t-lines but this will be an explanation of what has been, for me, the easiest method. For the example, we'll use a single, hypothetical 15' driver.
> First thing we need from our sub is Sd or, usable piston area. To find that we need the diameter of the driver, which is measured from the apex (center) of the surround on one side of the driver to the same point on the opposite side. For most car audio 15s, that measurement is 12.75".
> Then we take that measurement and half it: 12.75 ÷ 2 = 6.375
> ...


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## Lycancatt (Apr 11, 2010)

that's a very consice and accurate way of building a t line, I like that write up


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## SHAGGS (Apr 24, 2011)

Yeah, that's waaaay too easy, and concise, to understand. 
Thanks SkizeR!

I remember trying to build one, when I was about 16.
There was literally no math involved. :blush:
I just tried to copy a picture of one, I saw.
I had a pair of Fosgate 8's, and figured "it can't be that hard"....
It sounded absolutely terrible.

Oh well, it was fun, and all I wasted was a sheet of particle board. So about 10 bucks.:laugh:


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## smgreen20 (Oct 13, 2006)

This thread needs stickied!!!!!

A point that was not touched on about the Fs, you don't want to tune below that is what I was told but that it is also the optimum tuning point for sq and output.


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## r0llinlacs (Oct 8, 2015)

I have a feeling you're talking about my thread. Those guys were FOS, so I stopped replying to them. As the person above me said, tuning to the Fs is the optimal tune for a T-line regarding SQ and output.

It's not all that hard, I can summarize that long winded post above:

T-line = quarter wave transmission line box

The "line" has the same area as the subwoofer's Sd and the same length as 1/4 the wavelength of the Fs or tuning frequency.

At the bare minimum you will need to know the woofer's Sd and Fs.

To figure out the length of the line, you will need to divide the speed of sound by the Fs. The speed of sound is 1128feet per second, so for 28hz, 1128/28 = a 40foot wavelength. Divide that by 1/4, so one quarter of 40feet is 10feet, so a 28hz 1/4wavelength line will have to be 10feet long, and have the same area of the Sd of the speaker. 

Once you know the line length and area, simply all that's left is designing the box how you want. It's pretty simple and the outcome is more than worth it.



This is the giant 25hz T-line I'd have to build for my Eclipses. Might have to build it since everybody wants to recommend box design instead of driver selection like I asked... sheesh.


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## craiggus365 (Apr 5, 2009)

r0llin were you asking for lowest output or SQ, in the other thread?


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## GotaCC (Sep 13, 2013)

I actually found that to be a good read. It got a bit muddy at the end though. Where is the 9" tall line measurement come from? If the chamber is 14" x 9" that's more area than the calculated 127 in2. How do you determine the depth of the speaker compared to the start of the line? Why would the measurement be 9.75" if using .75" build material. Shouldn't it still maintain its 9" measurement? Why not save space with 1/8 wave? (not sure its possible but just asking) 

There was no talk about the tapered line or horn or what ever its called when you increase the width of the line till exit. 

Yes, Rollin I was referencing your thread but didn't want to jack it with my curiosity. I like your simplified explanation though.


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## r0llinlacs (Oct 8, 2015)

craiggus365 said:


> r0llin were you asking for lowest output or SQ, in the other thread?


I wasn't asking for either. I was asking for recommendations on a driver with a low Fs, and I want it tuned to the Fs because I *do* care about SQ.



> Essentially, _the goal of the transmission line is to minimize acoustical or mechanical impedance at frequencies_ _*corresponding to the driver's fundamental free air resonance*_. _This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity._




That is the whole point of tuning a T-line to the Fs of the driver.


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## hurrication (Dec 19, 2011)

Here is a document with everything you will ever want to know about designing a T-line.
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

Better yet, here's a link to a T-line modeling program. Enter the specs of your driver, and see first hand how all the variables contribute to its response.
Download | Leonard Audio

In summary, don't listen to anyone who says you *must* tune a TL to the driver's FS to get the best results. They are simply regurgitating a loosely created "one size fits all" rule of thumb that has spread around the internet long enough that it's become lore.


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## ChrisB (Jul 3, 2008)

All I know is that t-lines used to be hard to implement in the automobile since the older modeling software assumed a near anechoic environment with regards to their response plots. Now factor in the cabin gain typically common in the automobile and there is a large margin for error when designing and implementing a t-line in the car.

OTOH, I'd use a t-line inside my home or for PA in a heartbeat. I just think the trial and error aspect for the mobile environment isn't worth it, nor is the size tradeoff typically required for a t-line. Then again, that is just me. With regards to car audio, I'm all about taking the easy path these days because I just don't have the will or the time to dedicate to perfection in an imperfect audio reproduction environment.


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## peenemunde (Aug 31, 2013)

Sub'd 

I want to build a t-line woofer for home audio use. Figured this thread would give me a good basis to build from


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## GotaCC (Sep 13, 2013)

*!*



hurrication said:


> Here is a document with everything you will ever want to know about designing a T-line.
> http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
> 
> Better yet, here's a link to a T-line modeling program. Enter the specs of your driver, and see first hand how all the variables contribute to its response.
> ...


Thank you for the links. That was easy to get lost in the info.  I was playing with the software but got stuck when trying to generate a model with the speakers parameters. I'll have to contact the group to see if someone can help me along. Maybe I'm viewing the software wrong? The impression I had was I could input the speakers pararmeters and a design model would be displayed with theoretical performance data.


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## GotaCC (Sep 13, 2013)

ChrisB said:


> All I know is that t-lines used to be hard to implement in the automobile since the older modeling software assumed a near anechoic environment with regards to their response plots. Now factor in the cabin gain typically common in the automobile and there is a large margin for error when designing and implementing a t-line in the car.
> 
> OTOH, I'd use a t-line inside my home or for PA in a heartbeat. I just think the trial and error aspect for the mobile environment isn't worth it, nor is the size tradeoff typically required for a t-line. Then again, that is just me. With regards to car audio, I'm all about taking the easy path these days because I just don't have the will or the time to dedicate to perfection in an imperfect audio reproduction environment.


I value my cars cargo space so T-line is certainly not going to be permanent but more of a fun experiment. Sure I have enough projects, but one more isn't going to kill me. Once I gain the knowledge and feel confident I know what I'm doing I would like to make some house speakers. That's really the motivation to this project. I been using a Philips 5.1 in the house for the past 10-12 years and always wish I had something good.


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## stills (Apr 13, 2008)

I've done two different versions over the years. 
1st was a two 10" version about the size of a washing machine in a Toyota 4 runner. Finally settled on some 10w6v1's. Thing got seriously loud with relatively little power. @ 450 watts. Folks were shocked to hear 2 10's that loud. Of course this was the late 90's. 

2nd one was a single 8" sundown. A long narrow one. Again with about 400w. Think I tuned it to @ 35hz. Pretty loud, but didn't do much above @ 60hz. This was in my impala SS. 

If you have the room they are a lot of fun. With power being cheap nowadays, and small encolosure subs the norm, they are kinda outdated. The two ten inch box I had could of easily been replaced with a modern duel 15" encolosure with a class d amp.


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## Patrick Bateman (Sep 11, 2006)

I built a transmission line with a couple of those Adire Shiva clones that Parts Express sells. (I think they're called "DVC 12s?")

I wasn't real thrilled with the box - here's why:

Hoffman's Iron Law is going to dictate how much output your box generates. IE, you might be able to increase the efficiency of a box by a few dB by building a transmission line, but *you can also increase the efficiency by simply using more boxes.*

So it boils down to one question:
*Do you want to buy four subs or do you want to buy one?*

If you're cheap, you CAN raise the efficiency, but keep in mind that an array of sealed boxes will always win because they have more voice coils, more power handling, and more displacement.

Basically a TL is a way to squeeze more output out of a single woofer, but an array will win.

Here's some examples of what I mean:









Here's the output of four sealed twelves in a box that's 87.9 liters. (3.1 cubic feet) The woofers are diyma twelves.









Here's the output of TWO diyma twelves in a transmission line that's 87.9 liters. (Same size as the sealed box, but with half as many woofers.)









Here's the output of the two boxes overlaid. You can see that the response curve is very very close. This is Hoffman's Iron Law - the box size is going to dictate your output, not the alignment.

Now, obviously there are a lot of reason you might want to build a transmission line:
1) Main reason is cost. You can get more output from a single woofer.
2) TLs, FLHs, BLHs and THs allow you to get more output with the same power. This isn't a huge deal in an era of $300 kilowatt amps. But it *can* give you the edge if you're limited by your alternator. A real-world example of this is that every other concert I go to lately has a power outage, because the buildings aren't capable of delivering enough amps to power the amps.
2) The TL is going to reduce excursion, and if you design it real carefully, you can use that to increase output at high power. (The sealed box will still win, due to lower power compression, higher power handling, etc.)
3) One huge factor is that you can use these weird alignments to get F3s that would otherwise be impossible. For instance, I once built a tapped horn that played down to the single digits. It's pretty easy to play a full octave below resonance with a TL, TH, back loaded horn, or bandpass.


















Here's the hornresp model if you want to play with it. Hornresp can model all of these alignments. Note that both boxes get the same wattage, but the *voltage* is different because the sealed box is 4ohm, and the TL is 2ohm, due to the voice coils being wired in parallel for the TL and series-parallel for the sealed. *Bottom line : same wattage, same box size, same output (for the most part.)*


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## Patrick Bateman (Sep 11, 2006)

Over on diyaudio, I updated my thread about my 15hz tapped horn. Makes for an interesting comparison to the TL in this thread.

Read more here : Night of The Living Bassheads - Page 9 - diyAudio

(Read the whole thread if you have the time.)









Being able to hit 110dB at 15hz is quite fun for home theater, and it's even better when you can do it with one 12" and 250 watts.


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## r0llinlacs (Oct 8, 2015)

hurrication said:


> Here is a document with everything you will ever want to know about designing a T-line.
> http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
> 
> Better yet, here's a link to a T-line modeling program. Enter the specs of your driver, and see first hand how all the variables contribute to its response.
> ...


You are FOS bro, where's your back up? It sure isn't in the link you posted.

"Essentially, the goal of the transmission line is to *minimize acoustical or mechanical impedance at frequencies corresponding to the driver's fundamental free air resonance*. This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity."

Do you not understand this? Do you not know what free air resonance is? Or are you simply just ignoring this fact? All I see from you is "don't listen to him" link link link. Where's your proof? It's definitely not in your links. So far it's my word against yours, and my word is backed up by wiki, and experience. Where's your T-line? 

I also never said you MUST tune to the Fs, I said it's BEST to tune to the Fs. The above quote explains why, if you actually read it. The entire point of a T-line is tuning it to the Fs of the sub, if it's not tuned to the Fs, it's not a true T-line, and you lose all benefits mentioned in the quote from wiki. If it's not tuned to the Fs, say hello to mechanical and acoustical distortion at the Fs, and say goodbye to optimal coupling at the Fs. It's really not that hard to understand and it really seems like you just want to argue.


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## GotaCC (Sep 13, 2013)

There is a ton of useful info in this thread and I'd like to keep it going. Please leave the strong opinions out of it.


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## SkizeR (Apr 19, 2011)

r0llinlacs said:


> You are FOS bro, where's your back up? It sure isn't in the link you posted.
> 
> "Essentially, the goal of the transmission line is to *minimize acoustical or mechanical impedance at frequencies corresponding to the driver's fundamental free air resonance*. This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity."
> 
> ...


but hes right though. multiple people who have built transmission lines (including the person who i quoted in my first post) have all said the same thing to me


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## Patrick Bateman (Sep 11, 2006)

His post was blunt, but he makes a good point. A Tline CAN be used to reduce the Q of the enclosure. 

TBH one of the gripes about the Tline that I built was that it was a little too 'polite.' 

But I've learned over the years that distortion can actually sound kinda good, and systems with low distortion often sound too 'polite.'

I never ran any distortion measurements on my Tline so I can only speculate.


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## Patrick Bateman (Sep 11, 2006)

Side note:

Here's a couple of shortcuts that I use when building enclosures that use the back wave to augment the front wave*:

1) tune the enclosure to .707 of the FS
Or
2) model the woofer in a vented box, and use the FB that the computer tells you

Using these rules, you generally find that a 30hz sub wants to use a driver with an FS of about 42.3hz.

* transmission line, back loaded horn, vented box, dual reflex bandpass, tapped horn, etc


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## hurrication (Dec 19, 2011)

r0llinlacs said:


> So far it's my word against yours, and my word is backed up by wiki












Spoken like a true enclosure design expert.


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## r0llinlacs (Oct 8, 2015)

hurrication said:


> Spoken like a true enclosure design expert.



Get out of here troll.

BTW, you've been reported.


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## peenemunde (Aug 31, 2013)

Please don't scare off the people who are actually interested in this post.. We gather here to share information, then based on the cumulative we're able to form our own ideals. It doesn't matter if you think you're "more right" than the next guy. Maybe to you, but the rest of us are annoyed by nitpicky argumentative BS


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## r0llinlacs (Oct 8, 2015)

peenemunde said:


> Please don't scare off the people who are actually interested in this post.. We gather here to share information, then based on the cumulative we're able to form our own ideals. It doesn't matter if you think you're "more right" than the next guy. Maybe to you, but the rest of us are annoyed by nitpicky argumentative BS




Really though who are you talking to? I'm trying not to argue with anybody and this kid shows up on all of my threads trying to start sh*t, so I really hope you're not referring to me.


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## SHAGGS (Apr 24, 2011)

r0llinlacs said:


> Get out of here troll.
> 
> BTW, you've been reported.


Really? You've been here for a whopping three days, and then you say something like that....


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## SkizeR (Apr 19, 2011)

r0llinlacs said:


> Get out of here troll.
> 
> BTW, you've been reported.


im just gunna say it.. go back to the forum you came from


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## GotaCC (Sep 13, 2013)

Patrick Bateman said:


> Side note:
> 
> Here's a couple of shortcuts that I use when building enclosures that use the back wave to augment the front wave*:
> 
> ...


So I was using that software you linked yesterday and this is what it came up with. Its not working today for some reason. Are you saying I should change the Fs to .707? What would be the reasoning behind that?

BL 7.698
Sd 0.0231
Qes 0.367
Qms 3.572
Rms 3.1221
Re 1.95
Fs 24.7
Vas 0.04389
Mms 0.0718585328870082
Cms 0.000578
Lvc 0.00148


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## Patrick Bateman (Sep 11, 2006)

GotaCC said:


> So I was using that software you linked yesterday and this is what it came up with. Its not working today for some reason. Are you saying I should change the Fs to .707? What would be the reasoning behind that?
> 
> BL 7.698
> Sd 0.0231
> ...


Hurrication linked to software, not me

I use hornresp but that's a hideously complex program to learn

If you want to give it a try, tune the enclosure length to .707 of the FS. That will get you 'in the ballpark' and you can optimize from there

I don't have any recommendations for building a transmission line, in fact I generally avoid them. Not that they're bad, just that they're more trouble than they're worth IMHO

YMMV


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## Darth SQ (Sep 17, 2010)

r0llinlacs said:


> You are FOS bro, where's your back up? It sure isn't in the link you posted.
> 
> "Essentially, the goal of the transmission line is to *minimize acoustical or mechanical impedance at frequencies corresponding to the driver's fundamental free air resonance*. This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity."
> 
> ...


You blast in here (Oct 2015) and start telling long term members they're "FOS, You're all sh&t" and then expect us to clean up your mess when they respond to you in a way that pisses you off?
I suggest you chill out and play nice or follow Skizer's advice and find another forum.


Bret
PPI-ART COLLECTOR


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## SkizeR (Apr 19, 2011)

PPI-ART COLLECTOR said:


> You blast in here (Oct 2015) and start telling long term members they're "FOS, You're all sh&t" and then expect us to clean up your mess when they respond to you in a way that pisses you off?
> I suggest you chill out and play nice or follow Skizer's advice and find another forum.
> 
> 
> ...


but bret, his argument is backed by wikipedia! we cant win this one!!


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## craiggus365 (Apr 5, 2009)

PPI-ART COLLECTOR said:


> You blast in here (Oct 2015) and start telling long term members they're "FOS, You're all sh&t" and then expect us to clean up your mess when they respond to you in a way that pisses you off?
> I suggest you chill out and play nice or follow Skizer's advice and find another forum.
> 
> 
> ...





SkizeR said:


> but bret, his argument is backed by wikipedia! we cant win this one!!


Glad to see we have each other backs here. 10/15 ego is strong in these Tline threads.
If we all chill, maybe we can all learn something from each other, instead of puffing our chests and filling our E-Peener...:laugh::laugh:


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## hurrication (Dec 19, 2011)

GotaCC said:


> So I was using that software you linked yesterday and this is what it came up with. Its not working today for some reason. Are you saying I should change the Fs to .707? What would be the reasoning behind that?
> 
> BL 7.698
> Sd 0.0231
> ...


Here's a tutorial with pictures on using the software. I had quite a time figuring it out the first time I tried to use it, but the tutorial is good.

http://leonardaudio.co.uk/wp-content/uploads/2013/12/TL-UserGuide.pdf


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## thehatedguy (May 4, 2007)

I would make taped horn before a t-line.

And you can sim either using hornresp...which is a nice free program.


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## SkizeR (Apr 19, 2011)

thehatedguy said:


> I would make taped horn before a t-line.
> 
> And you can sim either using hornresp...which is a nice free program.


and this is where i cant really find much info on. how do you design a taped horn?


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## Patrick Bateman (Sep 11, 2006)

SkizeR said:


> and this is where i cant really find much info on. how do you design a taped horn?


1) Determine how low you want the speaker to play









2) Find a woofer that has an FS that's 1.41 times the frequency from step one. For instance, if you want to play to 25hz, you want a woofer with an FS of 35hz








3) Set the mouth of the horn to twice the SD of the woofer
4) Set the throat of the horn to somewhere between 25% and 100% of the SD. (Tweak the size until you get the size, bandwidth and efficiency you want.)

*And that's all there is to it.* Note that the length of the line is set by adjusting it to .707 of the FS. The tuninq frequency is determined by looking at the trough in the impedance peak, or better yet, the displacement minimum. (You can see that in the displacement graph.)









I literally threw this together in under ten minutes. Back loaded horns and tapped horns are probably two of the most forgiving designs you can build. They're way WAY harder to screw up than a vented box or a bandpass box.









Back loaded horns have fallen out of vogue, but their response is nearly identical to tapped horns, particularly when the woofers are close to the end of the line. Tapped horns still offer some flexibility that back loaded horns *don't* offer, but there's nothing magical about the TH alignment.

The graph above shows the response of the same woofer in a TH and a BLH, with the line length set the same and the volume set the same. You can see the response is virtually identical.









Here's some Bassmax BLHs with the mighty Aurasound 18" woofer loaded


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## GotaCC (Sep 13, 2013)

I thought the tapped horn was a t-line? Basically 3 styles: straight, tapered and expanding. Expanding being the style that resembles your tapped design.


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## thehatedguy (May 4, 2007)

A tapped horn is a cousin of a t-line. Similar, but not the same.


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## SkizeR (Apr 19, 2011)

thehatedguy said:


> A tapped horn is a cousin of a t-line. Similar, but not the same.


pros and cons against each other being?


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## ultimatemj (Jan 15, 2009)

Y'all can find some better than average info here: TL Design Basics

But I have to also add this amusing quote from 2008?



> I'm not even sure that I know what a "tapped horn" is but here is what I do know:
> 
> I've studied LF sound sources my whole life and there are no free lunches. Nothing has ever turned out to be an effective improvement in LF design except the Acoustic Lever and its just plain impractical.
> 
> ...


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## stills (Apr 13, 2008)

Bah! Geddes's a noob


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## Patrick Bateman (Sep 11, 2006)

I think the Geddes statement is accurate.

Here's an example of this:

A few years ago, I built a clone of the Auto Tuba. I loved it. Punchy, dynamic, and clean. But it didn't play low at all.

So I measured it, and noticed that it's efficiency advantage was purely above 60hz.

IE, above sixty Hertz it shined. But below 60hz? It basically behaves like an 8" woofer in a sealed box. 

That's the conundrum with all of the exotic alignments. You can definitely raise output and lower distortion. But there's no getting around Hoffman's iron law. 

I still think they have their place, but I'm not so sure that car subwoofer duty is on the list. Perhaps if you have a lot of space and a small budget. I'm going bandpass for my Mazda.


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## Shush Deeni (Oct 2, 2015)

Does the math of a T-Line change with the use of 2 woofers as opposed to one. Most threads only mention the use of a single woofer, and not the use of 2. This would be useful information for future novices who seek out to build a t-line.


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## hunde (Nov 14, 2008)

Perfect thread! Been wanting to build a t-line (home) for a long time, forgot everything i knew about them, and all these cool new drivers keep hitting the market! 

Would use either Tang Band 8" full range or Dayton 8" full range point source, a small audio research amp to drive them, and I'd expect to greatly enjoy them! Hell i might even go all the way and make 'em look nice - a first for home speaker experiments for me! A tall, narrow cabinet with a single 8" driver looks sick in my head...


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## SkizeR (Apr 19, 2011)

Shush Deeni said:


> Does the math of a T-Line change with the use of 2 woofers as opposed to one. Most threads only mention the use of a single woofer, and not the use of 2. This would be useful information for future novices who seek out to build a t-line.


pretty sure you just do the formula i posted in the second post of this thread, but with the SD of both drivers. not positive though


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