Read Me First
Me & my site
The T-Line Speakers site is my hobby site. It started out as a question to the basslist with a single page and has grown beyond my wildest dreams. It sort of marks my return to serious interest in HiFi after a 15 year absence (i spent 9 years in the hifi business in the 70s & 80s). It's prime theme is T-Lines but i'll put up anything (hifi related) that i am interested in. I am always way behind getting stuff up on this site, because i just don't have the time i'd like to devote to it... there are many projects and articles sitting in my queue -- enuff to at least double the size of this site.
I built my 1st tline in 1975 inspired by the Radford S90 when i was finishing up an honours degree in Mathematics. After that i went to work in hifi, then computers, now i'm back doing a mix of stuff. I currently support myself recycling hifi on eBay, servicing & selling Macintoshes, doing websites & graphics, and building a few custom speakers.
The Transmission Line
Up until the recent work of Augspurger & King, there were no models that came close to describing the behavior of the TL and it took a lot of cut & try, luck, and refinement to get a good TL. The result of this is that there are a cooresponding range of opinions and assertions about the performance of TLs.
I was present at the AES seminar when Augspurger let the world know what he has found out ... i got pretty excited. George's work can be seen in his original AES paper, the revision of that in a later AES Journal article (my pick if i could only have 1), and in his 3-part audioXpress article. Before i attended this conference, Martin King had contacted me about his work on modeling TLs.
Augspurger's electrical TL model generates lines that are in VERY close agreement with Martin J. King's mechanical model. I find it confidence inspiring that two guys independently, with two different analogs, at the same time come up with software models that generates the same lines under the same conditions.
Rick Schultz (Exolinear) uses Augspurger's software for his designs (the Rhino pre-dates this) and working with Martin King they have shown that Augspuger's model and King's model are in close agreement.
Martin King's & Auspurger's computer models for 1/4 wave speakers have opened up a huge amount of space for exploration. Think of t-lines, horns, & TQWTs (aka TQW or Voigt Pipes) as (some of) the axis for a space of possible designs. Anything along one of these axis can now be modeled fairly accurately, and there is all the space in between that is largely unexplored.
Martin makes versions of his software accessible for the hobbiest. There are a number of very detailed papers with practical examples, and a downloadable MathCad TL model. Martin is also very helpful by email. Martin has also made some quick alignment tables available.
Martin's software can model modestly complex lines from tapered TLs to tapered pipes -- most of the projects on the net* that have their basis in martin's software are actually ML-TQWTs or ML-TLs (ML = mass-loaded). These designs are a rich new breed of QW designs.
*(Bert Doppenburg's BD-Pipes are an example of a successful ML-TQWT developed in a true cut-and-listen path -- an independent validation of the design IMM)
Exolinear is Rick playing around with Augspurger's model in the fringes of this space. He is slowly publishing easy-to-design alignment tables for subsets of QW space -- his 1st is the alphaTL, published in audioXpress, and in the queue for his section here. He is already hard on work on his next article.
Besides this site, there are 2 other web-sites that are required reading for anyone interested in building a TL.
Martin J King's Quarter Wavelength Loudspeaker Design where Martin presents his research, projects, and a gallery of designs built using his software
Bob Brine's Speaker Stuff. Bob has some very important articles which support Martin's Software Model, his own projects, and some commercial designs*
* (Bob pays a license fee to Martin for these -- unlike some less appreciative commercial ventures. The TL world one be an awful lot less rich if it wasn't for Martin's work)
The 1st 35 years or so of TL design was seat of the pants -- many of the projects here are classically designed, and there are articles on historic TL speakers. I would advise anyone building a TL to look at them for inspiration, but use modern methodology to actually design your TL. This site covers off some of the history of the TL and some of the more important historical designs.
John Risch outlines the extent to which classic TL design evolved. This is based solely on cut & try & evolution over the period of 35 years since Bailey 1st published his seminal article. Martin King's model (and George Augspurger's parallel model) have shown that this usually produces less tham optimal TLs.
The IMFs (which are directly descended from the original Bailey line thru Radford) is an evolutionary product that did a good job of approaching what was possible in their day. The geometry of the line achieves the majority of the low-pass function of the TL (they fall into the 1/3 pre-chamber 2/3 line class of TLs most commonly associated with Dalines) and they work well. The Radford S90, the IMF TLS80, and the Fried Hs were some of the best speakers i had the opportunity of hearing in my formative hifi days and they will always have a special place for me.
I think that using modern drivers & tools such as King's software you can build a better TL easier today.
I hope you enjoy this site and get some useful information from it. I am always interested in publishing people's designs and articles (and they don't have to be about TLs :^) as previously noted it sometimes takes me a long while to get things up.
My early projects can be found in the FALL section (Finlayson Arm Loudspeaker Laboratory) and more recent at diyAudio.com. The fall-out from some of what is shown here has culminated in a commercial venture and 2 sister sites frugal-horn.com & frugal-phile.com
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