# Benefit of a T-Line box versus ported or sealed?



## JAX (Jun 2, 2006)

is there a benefit of a T-line design versus the other 2 ?


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## diy.phil (May 23, 2011)

Yeah you can put a small speaker in a long box and make it sound big.
And then sell millions of them like Bose


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## Patrick Bateman (Sep 11, 2006)

Sealed has low efficiency, very small box, good phase response.
Vented has moderate efficiency, moderately sized box, terrible phase response.
Tapped horn has moderately high efficiency, moderately large box, good phase response.
Front loaded horn has highest efficiency, highest box size, good phase response.
Transmission line has moderate efficiency, moderately sized box, good phase response.

The main difference between the various alignments, IMHO, is the phase shift at low frequency. Vented boxes have the most phase shift : 180 degrees. Transmission lines, front loaded horns and tapped horns have 90 degrees.

Where things get INCREDIBLY confusing is that it's possible to bend the rules. For instance, if you know what you're doing, you can make a horn that has close to ZERO degrees of phase shift. IE, it's possible to make a horn with better phase response than a sealed box. And it is also possible to make a vented box with fairly good phase response.

The trick to all of this is the hideously complex relationship between frequency and phase. And if that wasn't confusing enough, the room itself will also effect the frequency and phase.

All box types have their merits. In my home theater I have a FLH, a bandpass box and a vented box. In my car I have a tapped horn.


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## RVA_LVER (Apr 28, 2016)

What does a tapped horn box look like and how do you know if a driver would work well in one? 


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## DC/Hertz (Nov 27, 2011)

If you google PWK boxes he did a lot of horns. I designed one for my old DD 9512 but I never got to build it. 

T-lines also have really good bandwidth. They do tend to be a bit large.


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## MrGreen83 (Jun 11, 2015)

Glad this came up, I LITERALLY was researching T-Line enclosures yesterday and wanted to know all the differences. Good post 


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## DC/Hertz (Nov 27, 2011)

MrGreen83 said:


> Glad this came up, I LITERALLY was researching T-Line enclosures yesterday and wanted to know all the differences. Good post
> 
> 
> Sent from my iPhone using Tapatalk


Most will say you have to match the port tuning to the FS of the sub. You don't. 
FS changes over time as the driver loosens up. It's not a concrete spec.


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## MrGreen83 (Jun 11, 2015)

This guy was very informative. 

https://youtu.be/mq247-OCQg0



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## Patrick Bateman (Sep 11, 2006)

RVA_LVER said:


> What does a tapped horn box look like and how do you know if a driver would work well in one?
> 
> 
> Sent from my iPhone using Tapatalk


Just about any driver that will work in a ported box will work in these boxes:

tapped horns
back loaded horns
single reflex bandpass
transmission lines

For more info, check out the threads over at diyaudio


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## Boostedrex (Apr 4, 2007)

This thread is a great thing. And in the next couple of months I'll have something practical to add in to it. I'm going to build a dual 6.5" T-Line sub for one of my cars. It should be very interesting and I'm hoping that it turns out to be as effective as I'm hoping.

Patrick, I may well pick your brain a bit as the final tuning/math is being accomplished if you wouldn't mind. I believe I have the math solved, but I won't know until I do my test build of a small chamber and some tubing equal to the final line length.


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## rob feature (Nov 15, 2015)

DC/Hertz said:


> FS changes over time as the driver loosens up. It's not a concrete spec.


Lower after some wear?


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## DC/Hertz (Nov 27, 2011)

Yes. A suspension continues to loosen up for months. 
Looser the suspension, lower the Fs


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## Patrick Bateman (Sep 11, 2006)

Boostedrex said:


> This thread is a great thing. And in the next couple of months I'll have something practical to add in to it. I'm going to build a dual 6.5" T-Line sub for one of my cars. It should be very interesting and I'm hoping that it turns out to be as effective as I'm hoping.
> 
> Patrick, I may well pick your brain a bit as the final tuning/math is being accomplished if you wouldn't mind. I believe I have the math solved, but I won't know until I do my test build of a small chamber and some tubing equal to the final line length.


No need to build a test box, just pop the parameters into Hornresp and go from there. If you don't know how to use it, just post your T/S and I'll post a design. (I don't have time to design the box but I can give you the volume and length.)










I love copying designs that work, and the Bose layout is rock solid. I detailed how it works here: An Improved Transmission Line Alignment. - diyAudio


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## Boostedrex (Apr 4, 2007)

Patrick,

I just shot a PM your way with some thoughts. You're welcome to respond in the PM or in here since it could be for everyone's benefit. I'll go ahead and copy/paste my PM to you in here so that the OP can keep in the loop as well.

Here's where I'm at so far. I'm planning on using a pair of these woofers for my T-Line sub in the car. My biggest question is one I am hoping you can answer. I remember reading papers on using a driver above or below it's Fs. Will the same thinking work in a T-Line? With the driver having a 69Hz Fs I was thinking of running the low pass filter at 70Hz. But with my lack of knowledge in this area of enclosure design I wasn't sure how well that would work out. Any input from you will be greatly appreciated. Below are the T/S specs for a single driver.

Re	3.2 ohms
Fs	69 Hz
Qes	0.90
Qms	3.0
Qts	0.69
Le	0.03 mH
Sd	136.9 cm^2
Vas	5.5 L
Mms	25 g
BL	6.2
Sensitivity (2.83v/1m)	88 db
Xmax	9 mm
Xmech 13 mm


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## Justin Zazzi (May 28, 2012)

If you're looking for transmission line information from theory to modeling and much more, Martin J. King's website Quarter Wavelength Loudspeaker Design is the best I've found. I purchased his Mathcad models a while ago and they were spot-on with the results I measured after building a transmission line for a 10" woofer in my jeep (resonant frequency was just 27hz and the setup was astonishing on only 300w).

From what I remember, below resonance a woofer will unload in a transmission line just like in a ported box. Excursion will be similar to an infinite baffle and you might damage the woofer if you overpower it. Most people will use a subsonic high-pass filter to prevent this, just like a ported enclosure.

You might want to use a woofer with a much lower Fs if this will be for subwoofer duty.


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## sq2k1 (Oct 31, 2015)

good reading material


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## Patrick Bateman (Sep 11, 2006)

Boostedrex said:


> Patrick,
> 
> I just shot a PM your way with some thoughts. You're welcome to respond in the PM or in here since it could be for everyone's benefit. I'll go ahead and copy/paste my PM to you in here so that the OP can keep in the loop as well.
> 
> ...


Due to the high FS and the VERY high QTS, I didn't think this woofer would work very well. But it turned out alright. Make no mistake, if you want sheer SPL, use a twelve or a fifteen. But this woofer makes an interesting unit if you want to do something different.









Here's a comparison of a transmission line versus a vented box. I calculated the vented box using the same methodology I always do, here : Car Audio - Ported Subwoofer Box Design Formulas & Calculator

The vented box is 65.36 liters and the transmission line is 35 liters. I could make the tline bigger if you want, but I figured most people would prefer something small. With horns and tlines you have a lot of leeway to scale the size up or down, depending on how much output you want.

I intentionally used the *exact* same tuning for both, to illustrate the difference between vented and tline. Basically Hoffman's Iron Law dictate a similar F3 and efficiency. Vented boxes are good at producing big narrow peaks, like you see here. Basically they 'burp' out a lot of SPL but need a high QES to reduce that peak.









Since output and displacement are tied together, the excursion curves look similar. Be sure to use a highpass filter here.









The big advantage of transmission lines and horns, IMHO, is better behaved phase response. In this graph you can see the tline is significantly lower than the vented box, because the vented box has 180 degrees of phase rotation while the tline has 90.



Having said all of that, I think there's a better way. I'm going to try another type of box that will work better I think.

BTW, one big question is how big of a box can you tolerate? You can get some fairly ridiculous efficiencies if you're willing to live with a large box.


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## Patrick Bateman (Sep 11, 2006)

The idea that I alluded to in the last post was to try this woofer in a TQWT. But it just didn't work; the QTS is too high. It wouldn't work in a tapped horn either, for the same reasons.

I was able to raise the efficiency of the tline by about 1dB by making the volume larger, but it starts to get 'peaky' as you push the size larger and larger.

Anyways, let me know if the size is about right, or if you want something larger or smaller.


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## Boostedrex (Apr 4, 2007)

Patrick Bateman said:


> The idea that I alluded to in the last post was to try this woofer in a TQWT. But it just didn't work; the QTS is too high. It wouldn't work in a tapped horn either, for the same reasons.
> 
> I was able to raise the efficiency of the tline by about 1dB by making the volume larger, but it starts to get 'peaky' as you push the size larger and larger.
> 
> Anyways, let me know if the size is about right, or if you want something larger or smaller.


Patrick, first thank you for the in depth information you posted. I really appreciate you taking the time. I will get full "maximum" dimensions that I can use for the T-Line and we can modify the enclosure based on the area available. 

From the graphs it seems like this could be a pretty good performing setup since the install will be purely focused sound quality and not sheer output. It's also going in a Chevy Volt which is a hatchback with a very small interior. So cabin gain will be significant.


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## DC/Hertz (Nov 27, 2011)

I'd hope you get enough gain under 30hz. Even for SQ we still need low end extension. 
That's a bad roll off


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## Boostedrex (Apr 4, 2007)

DC/Hertz said:


> I'd hope you get enough gain under 30hz. Even for SQ we still need low end extension.
> That's a bad roll off


I agree that the roll off is incredibly steep. Worst case scenario, I will have to go with option B as far as what drivers I use. I was just really wanting to use this one particular driver. But if the figures don't work out, then they don't work out and I will make the needed changes.


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## DC/Hertz (Nov 27, 2011)

Maybe 4th order? Sealed to cover the top end and play well with the FS and low tune port to give the low end some help? 
It may horse shoe bad but it's worth a try.


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## Patrick Bateman (Sep 11, 2006)

single reflex boxes have a 2nd order roll-off. (Sealed, single reflex bandpass, front loaded horn)

Dual reflex boxes have a 4th order roll-off. (Vented, dual reflex bandpass, back loaded horn, tapped horn)

The only sixth order I'm aware of is the weird triple chamber bandpass that Bose sold in the 90s. (They replaced it with a tline.)

The steep roll-off of this particular enclosure is largely due to the high QTS of the driver.


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## neuspeedescort (Feb 23, 2010)

i know a couple things about t-lines as i have built only one. this is my experience. on the same power, in the same car.

i originally had a singe DD 1000 series 12 in a ported box. 2.1 cu.ft. tuned to 38hz with two 4" round ports. sub back, ports back. i was happy with the over all volume output. 133.5 db. but the range sounded muddy in the 65-80hz range.

so i build one for my DD 1000 10 that i had. it being the same series as the 12 it needed no changes in the amps gain settings. the "port" opening of the t-line was a little over sized once i assembled it and redid some calcs. but! it put out the same db as the 12 did. with a bandwidth that was awesome. no hiccups in the freq range. i can't recall the exact tune it was due to i didn't have the room to get it exact. it was a just a few hz higher than it "should have been". the box ended up being sub up, port up.

if you have the room there is nothing nicer than a t-line IMO.


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## Boostedrex (Apr 4, 2007)

Patrick, 35 litres would not be a problem at all. It could even go up in size by about 15% if needed. But if these drivers are a bad choice just let me know as I do have a 2nd driver in mind that I believe would be a much better candidate. Also, I know you listed the volume of the enclosure, but I didn't see the line length mentioned anywhere. What was the length for the 35 litre enclosure?


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## Patrick Bateman (Sep 11, 2006)

Boostedrex said:


> Patrick, 35 litres would not be a problem at all. It could even go up in size by about 15% if needed. But if these drivers are a bad choice just let me know as I do have a 2nd driver in mind that I believe would be a much better candidate. Also, I know you listed the volume of the enclosure, but I didn't see the line length mentioned anywhere. What was the length for the 35 litre enclosure?


For a sub in a tline, I'd look for something with a decent amount of displacement and a fairly low QTS

For the most part, it doesn't matter how you get high displacement. It could be high SD and moderate xmax, or high xmax and moderate SD.

Basically making bass is all about displacement, and that's why fifteen and eighteens tend to dominate when it comes to bang for the buck

One of my favorite ways to figure out what driver to use is to look at the leaderboard at data-bass.com. You can find some real oddballs over there, for instance one of the highest performers is a SEALED box! Now, admittedly it's a sealed box with a 24" woofer, but still...

Last time I looked, the undisputed champion at data-bass.com was a car audio woofer from Rockford Fosgate. Which is kind of interesting, because all the prosound guys stay away from car audio woofers.

The world's most powerful subwoofer, the Danley Matterhorn, also uses car audio woofers from MTX.


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## Boostedrex (Apr 4, 2007)

Patrick,

Here is the other driver I was considering. Again, these are the T/S specs for a single driver and I would be using a pair of them. Does this model up to be a better option for a T-Line sub for the car in your opinion?


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## Patrick Bateman (Sep 11, 2006)

That SB Acoustics driver is lovely.

I have a set, Madisound sent them to me accidentally. It's amazing how good they are, especially at that price.

With it's low QES and QTS, it is suited to all types of enclosures, particularly these:

vented

dual reflex band pass

tapped horn

transmission line

single reflex bandpass

back loaded horn

front loaded horn

I'll throw something together by tomorrow


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## TaylorFade (Nov 9, 2014)

Patrick Bateman said:


> single reflex boxes have a 2nd order roll-off. (Sealed, single reflex bandpass, front loaded horn)
> 
> Dual reflex boxes have a 4th order roll-off. (Vented, dual reflex bandpass, back loaded horn, tapped horn)
> 
> ...


The "4th" and "6th" in single and dual reflex bandpass include the 2nd order top end rolloff. Which can be a concern (depending).

I'm curious how you manipulated the line to get it to 35L in the earlier example.


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## drinkchamp (Sep 20, 2016)

DC/Hertz said:


> If you google PWK boxes he did a lot of horns. I designed one for my old DD 9512 but I never got to build it.
> 
> T-lines also have really good bandwidth. They do tend to be a bit large.


would you be willing to share that?


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## DC/Hertz (Nov 27, 2011)

It was years ago. I actually looked for the email a few weeks ago for someone else. It's gone. 
I'm not sure if he is still designing on the side but if you get a AD Designs woofer you get a free design from him.


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## neuspeedescort (Feb 23, 2010)

i have PWK horn design for a DD12 on my work computer. anyone that wants it PM me and i will send the files.


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## Boostedrex (Apr 4, 2007)

Patrick Bateman said:


> That SB Acoustics driver is lovely.
> 
> I have a set, Madisound sent them to me accidentally. It's amazing how good they are, especially at that price.
> 
> ...


On paper it sure looks to be impressive. Especially for the price, as you mentioned. I do appreciate you throwing something together for me yet again. I tried working with the modeling program you use, and I've got a lot of learning to do before I can use it reliably. Too many variable fields in it that I'm not familiar with.


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## Boostedrex (Apr 4, 2007)

Patrick Bateman said:


> That SB Acoustics driver is lovely.
> 
> I'll throw something together by tomorrow


Hey Patrick. Did you ever get a chance to model a T-Line for a pair of those SB Acoustics drivers that I mentioned earlier in the thread?


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## JohnyJohn (Aug 12, 2020)

just bumped into this thread, thanks for sharing your opinions! really helpful


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