newbie questions

Hello to all fellow DIYers!

This is my first post and I have a few questions that I hope someone wiser than me (that shouldn´t be a problem);) could answer.

First question: How do I determine the required length for a terminated "transmission" line?

Second question: I´m very interested in constructing a TL. One thing (among many others) pussles me. A general rule of thumb for a TL is that you should make the line 1/4 the wavelength of Fs of particular driver, but for example Jon Risch has this opinion: "The line length should be 1/4 wavelength tuned to the resonant frequency of the chosen speaker IN THE BOX VOLUME CREATED BY THE TOTAL T-LINE CROSS SECTIONAL AREA TIMES LENGTH, and as if the box were a closed box." Where is the catch?

Third question: I´ve downloaded Martin J King´s software, but I don´t know how to use it (how to read the graphs etc) since it doesn´t seem to have any help or readme file. Could someone give me a quick&dirty lesson in how to use this software?

That´s all for now!
Thanks Keld, very informative site.

One thing that caught my attention was "Bob´s" opinion about Classic bass TL´s, that they should be unstuffed (if crossed over before first dip that is). That was new, I always thought that lines(even bass ones) have to be stuffed. Atleast you get a huge bass TL if it´s unstuffed :eek:

Anyone on the first question?


diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
Hi Junkie, Very Good Question!

I decided about 6 months ago to try a pair of terminated TLs as my next project, but finding real, decent, information on the web is very difficult. Just about anyone can find the formuli for building boring old vented boxes, the math for quarter wave TLs is starting to happen, but any sites that deal with terminated lines seem to be proprietry in nature.

I am currently trying to back engineer a theory mainly from product info from the B&W Nautilus designs, but it's not easy!

An old Pro speaker designer told me he once mucked around with Terminated TLs and had some success using lines with the same volume as an ordinary closed box equivalent, but the taper for the line and the length were purely guesswork, and he never had the chance to take the design further!

Stuffing a QWTL does two things, reduces mids radiating from the line,as you know, but if heavily stuffed it can increase the apparent length of the TL to the driver, thus giving you a smaller box size
Hi pinkmouse!

I´m glad to see that someone else is also wrestling with the terminated TL issue.

I wish you good luck in your quest to back engineer the theory, and please do tell if your brainstorming results in some revolutionary ideas!

Thank´s very much for the B&W tip, found it very informative. Among other things I found out that I would have to opt for the sphere/tube design, since my plans are to use a Manger MSW driver. Now just have to figure out that "sphere with particular diameter to the driver diaphragm" and the length of the tapered tube to get an enclosure which "internal resonances are to a large extent eliminated. Any residual effects are readily mopped up by wadding inside the sphere and tube."


2002-08-20 7:06 pm
When designing a T-line enclosure from scratch, how many people simply find a decent speaker, and start doing trial and error?

It's a little harder to do in a "standard" enclosure, but with a T-line, it seems you can remove baffling, change the length, add stuffing, etc, much easier, and trial and error may be the best way to achieve the sound you want. I've found that some speakers that sound good mathematically, or on a graph, don't necessarily sound good in reality.