T-line boxes

[Moble Enclosurs 10+ year member]

it's ok, that is one of the best ways to get a discussion going. That is of course when the 2 people talking can actually understand each other and no one ends up talking to a brick wall. I will see if I can find the paper I had on t lines. One of the few not based around home theater.

It is a good way to get a discussion going, but more on how to get an argument going, which is less efficient. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif As far as papers on designs, these actually have a lot to do with generalization in some cases and tests that are not repetitive. In scientific theory, it is best to get a trial and error going that consists on at least 3 consecutive similar results. A lot of papers do not do that. They model, then say, "oh, this must be a constant". Which is why so many papers exist, and the technological advances in audio have been slowed down from the beginning. It's not bias, but not enough for one paper to conclude in some cases. So, I would like to see which one that is, myself.

 

[RAM_Designs 5,000+ posts]

I would have to check if you like. I do not have it up right now. But yes, wenn, it is actually a constant area compression Tline, not a bass reflex.

I was just curious, as it seemed kinda short. No need to look it up.

 

[wenn_du_weinst 10+ year member]

I don't agree with many ways people argue ''is the way to do it''

Really it all has to be learned on your own. You never know what variables have been changed from one build to another. I know pete even went and designed his one modeling software to meat his designing requirements. I would like to see how it compares to real world but unfortunately it is unavailable.

 

[Moble Enclosurs 10+ year member]

I'm confused how it is acting as a tline with a chamber larger than the line width and length. Are you certain it is acting as a line? the whole point of a tline is to unload the driver and a chamber that large should be loading it quite a bit

That is actually one of the reasons why the post from surreal existed, lol. It does have a similar response to a bass-reflex, if one were to calculate the design as such. But tlines do not have to have a small compression chamber compared to the line. The concept of the design is constant, but the requested response is what gives it similar characteristics of the bass-reflex, but the designing of the compression area with the line was done of that from my tline calculations. This is why I mentioned in my rebuttle post that it would be easy to argue the fact that they are similar. Because, without showing you the actual and exact way that I design them, it would be tough to form an arugment against others known knowledge of them.

The unloading of the driver is not a characteristic of the tline-but the coupling of it to the environment is, but so happens that it becomes popular with larger area lines. It is still loaded, but yes in this design, much more than what is "popular" and noticed around the world. So, to bunk this, yes, this design alone, has many visual characteristics of a bass-reflex and gives similar frequency response curves, but the other factors are different, as far as mechanical and thermal control of the driver. When dealing with physics and acoustics, as mentioned in the rebuttle post, limitations will cause this to occur(the similarities).

Now, since coupling is important in tlines, it also depends on the vehicle characteristics, which in this case, in order to give a lower response from the center of the vehicle, where losses are evident, than a smaller area is requested by the driver. But again, the calculations are the same. There is not direct rule of the relation to the area with the compression area or surface area of the driver, other than the ones needed to figure for the entire designs characteristics. In other words, unlike quarterwave, and simple ports, the line is based from all other characteristics as well as the others are around it. So, the line area will always vary, and there is no minimal area, other than that considered for "port mach" calculations. That is the main similarity of the designs, is the need for minimizing noise. Other than that, they are in fact quite different-to a point. And again, tough to argue without showing you "how" I do it. That, I will not do, as it took me a long time and a lot of work and money to get where I am.

 

[Moble Enclosurs 10+ year member]

I was just curious, as it seemed kinda short. No need to look it up.

No problem, it seems short because it is not based on quarter-wave like most general ones are. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

it will always be a tough argument for us to explain the reasons for our discussions and differences without evidence. But, this is not something that any of us are usually willing to give out. Mainly for me, because my business is legal and operating actively. It's not a patent or anything, but jsut a lot of information put together that make it work, and give each design the ability for flexibility in its own response for full control of the design output, other than exact spl, which relates more towards environmental factors. That is the one thing that is still tough to design for, unless you have the environment available to test as well, would be SPL output, so for that, I usually use the standard 2.83V output response. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[wenn_du_weinst 10+ year member]

You mean you don't use the, cone area and fs rule? lmao

I always get irritated when a ''box designer'' simply uses max dimensions to design some one an enclosure. I mean I have moved my box 5'' to the side in my car and it changed the response greatly. Now you have some one taking a wild guess on what works best in your car with out any measurements or freq response data.

 

[Moble Enclosurs 10+ year member]

You mean you don't use the, cone area and fs rule? lmao I always get irritated when a ''box designer'' simply uses max dimensions to design some one an enclosure. I mean I have moved my box 5'' to the side in my car and it changed the response greatly. Now you have some one taking a wild guess on what works best in your car with out any measurements or freq response data.

Far from the truth. i use EVERY factor. I do not use it the way others normally do though. Some of what I have put together is of my own, and some is of constants that have to be used. In the case of all my designs, cone area does help figure for line area, moreso the length of the drivers surface area, rather than cone area alone, but fs is not something to go from. This is a free-air measurement and changes when in a restrictive environment of any size, respectively. I assure you that no wild guesses are made on my part, which I am sure I have made clear in a few earlier posts, such as the response comparison post I did using my math, constants, and programs to show it to the public. Now, regarding max dimensions, this is sensitive. They are usually recommended as an entire enclosures area, but compression will obviously change within the enclosure along with the need for tapering and such. The interior of the design is only related to the exterior in the limitations required. i assure you that any max dimensions used in car audio are still acoustically smaller than what SHOULD be used, and even max dimensions are considered a limitation. And as far as moving the enclosure, this is a factor that is important to me and figured for as well, and within the actual design, can be controlled (to a point like any other factor-as best as possible) by the location of the driver and output of the rear wave. EVERYTHING is involved int he design, and thinking of one single limitation will obviously cause confusion.

 

[surreal 10+ year member]

Im not saying youre bad either. Just discussion - and to be kept as such of course.

And duct is something of a general term. Akabak uses this most often.. The creator of LEAP even stated their chambers and all are computed as very complex 'ducts'. Im too lazy to find the post on their forums but I know its there somewhere.

My point was simply because something is modeled or can be labeled a certain way..doesnt mean it cant be another and be the same/very similar. Box names as understood are only words used to give us a basic idea of what were working with. A chambered t-line for example with a larger initial cross-sectional area could be modeled exactly as a vented enclosure.

 

[Moble Enclosurs 10+ year member]

Rant---It is obvious that a discussion of design will ALWAYS be turned into a bunch of different ideas, and rules, etc. It is because of this, that what i do will always be misunderstood in some case. i find it very tough to get a point across to anyone who has their ideas biased, or stuck on specific characteristics that they know of, from some other source. This is why most designers begin to become distanced during the course of their hobby or career, and why some of them are forced to say some mean things and have forceful attitudes, because someone will always be around to question, based on other forms of design that are so well known that people believe them to be correct.

I can relate this to a very sensitive topic of what we all deal with subconsciously everyday.........the governments around the world and the theories around corruption, specifically involving cults and organizations. The people that are on the side of the wealthy and involved, will always be forced to explain something that they cannot without sensitive information being exposed, and corrupting the actual ideas of the purpose of each organization. In a way, designers are the same. All businesses that do not fully expose their secrets will be questioned in some ways. So, for this, the point is, as much as you will question our ability to design correctly, just believe that it is done the best we can with the limitations we have, and it will never be perfect, but we do the best we can. Why is that never good enough for some people, when we bust our asses to get this far, and people try to figure it all out the easy way?

 

[Immacomputer 10+ year member]

I'm confused how it is acting as a tline with a chamber larger than the line width and length. Are you certain it is acting as a line? the whole point of a tline is to unload the driver and a chamber that large should be loading it quite a bit

The actual point of a tline isn't to unload the driver but to couple the driver's rear wave to the environment and reduce the mechanical impedance on the driver near Fs to allow the driver to become critically damped, reducing distortion while still retaining solid output and increasing transient response. The chamber of a tline will go from a high pressure area at one end and when it leaves the enclosure, it will be at a high velocity area with respect to the air molecules. So there will be pressure and loading onto the driver.

Something that I have learned after many years of playing with 1/4 wave enclosures is that EVERY box will be affected by 1/4 wave theory, even bandpass enclosures and SEALED enclosures. I've demoed a box that was made like a tapered tline with no open end creating a very large sealed enclosure. I demoed that box right next to the same driver in an enclosure that was the same cubic feet but was constructed differently. The difference in output was almost the same with the tline sealed box playing a tad deeper. The sound quality was definitely noticeable by a much more clear and crisp mid to upper range on the tline enclosure.

The same thing applies to other enclosure types. So that ported enclosure will have a Helmholtz resonance and a 1/4 wave resonance. How well they mingle with each other will determine the response of the system. Simply summing the two output responses won't give you actual FR you're going to get but both are going to affect it. Also, once the enclosure enters into a vehicle, the transmission line continues with the dimensions of the vehicle and this will affect FR. People call it "cabin gain" having no real idea of what it actually is and they then put random values on it and call them default for all cars. This isn't the case and it's just the car acting as a tline extension. I had a mathcad model setup where I could put any type of enclosure into the cabin of my car and predict the response within 1dB across a 10-100hz sweep. All I did was modify a few formulas from MJKing and added a separate section to enter a set of vehicle interior dimensions.

The enclosure pictured in this thread can be modeled as a tline with the "compression chamber" leading to the line actually being part of the line with a much larger line area than the rest. There will be some 1/4 wave effects as well as Helmholtz resonance. If you design an enclosure like this properly, you get what Pete called a "t-box". I found awesome results from these to get a 1/4 wave sound while actually keeping the enclosure size smaller than it would normally be for a tline enclosure. I had an old AE AV12 in an enclosure like this and got excellent FR results from it while sounding amazing, getting very loud, and handling 1.2kw rms with no problems. I could even get hair trick action out of my sunroof at 22hz with that enclosure. The key I found in designing them was to calculate the line area based on Sd, Re, BL, Vas, and a couple other parameters. Once I found the optimal area, I would sync the helmholtz resonance with the 1/4 wave resonance and try to get them to match with the driver (not Fs). I would use the size of the compression chamber size to tweak the Helmholtz resonance and the actual driver resonance (again, not Fs). Once all these came together, the results were pretty awesome. I made a few enclosures like these for friends and everybody was extremely happy. I also made an enclosure design for two Fi SSD 12s that looked like a standard ported box tuned to 42hz but I synced the 1/4 wave resonance with the sub resonance and with the vehicle resonance to make it peak at 157dB at 44hz while still at 155dB at 27hz and 156dB at 60hz at the dash sealed up with a TL.

So all I'm saying is that all enclosures will have a 1/4 aspects to them regardless of what we try say that our design is or what theory it uses. Moble definitely understands what he's talking about so I would take some time if I were the OP and try to understand it.

 

[Moble Enclosurs 10+ year member]

Wow, I remember this thread. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. Thank you for the explanation as well IAC and it was very well written. The basics of tlines are not that basic when you deal with the changes that occur within a given environment, but if you dont have some sort of nominal figure to base the changes from, which we both seem to have working, then the accuracies of this enclosure will always be an issue of discussion.....as we all know, the same enclosure in a different environment will perform differently when loaded at the listening position, but one thing that remains semi constant is the characteristics of the FR from the seperate/calculated enclosure physical construction of the interior.

And great point about the "cabin gain" assumption. If you do model this out cofrrectly, involving all 3 dimensions, you can effectively "load" the driver to the enclosure, and "load" the enclosure to the vehicle seperately and be able to figure for the changes each time a "loading" situation occurs. The idea of an extended tline is the reason why the discussion/argument of a smaller tline performing much like a BR. Because if the factors of cabin gain are not considered, you may have an incorrect, or should I say, incomplete response curve in any situation of car audio design.

Awesome