Yes, that is what I am saying. I am talking about small changes to the tuning and sound, not transforming a poor performing speaker design to a world beater. The trade-offs may have improvements in one area but degradation in another. No magic, no miracles.
Reasons
What are the attempted advantages of a TL speaker cabinet with equal sizes channels all the way to the port, as opposed to each channel being wider than the last?
Also, what is being achieved by a decreasing size horn channel compared to an increasing size channel?
Are there any simple answers to these questions? I probably won’t comprehend a high level answer.
Also, what is being achieved by a decreasing size horn channel compared to an increasing size channel?
Are there any simple answers to these questions? I probably won’t comprehend a high level answer.
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Bob Brines, Jim Salk, and Dennis Murphy to name a few have all used my software (Paul Kittinger did the actual TL design work for the later two) to design the TL portions of their speakers. Bob Brines was a very early supporter of the software and is a very talented designer, his understanding of TLs is excellent. I think there is some adjustment potential with a TL design. Adding internal obstructions and/or a constriction at the open end can always be used to change the tuning frequency and response. Also changes to the stuffing density and location is another tweak that can be used to change the TL's response. |
"Now with the computer design tools available, a TL can be designed on the computer and perform as predicted." I believe you, having been amazed at the performance of speakers by Bob Brines, who I understand licensed your software back when it was available. I'm familiar with some of the wideband drivers he used and would not have expected them to deliver the kind of low-end performance he was getting. One of the things I've found attractive about vented boxes is, adjustable tuning via multiple pluggable ports. Without giving away any trade secrets, are there techniques which would make would a somewhat adjustable transmission line be feasible? Thanks, Duke |
"One thing I learned was, respect for those who had mastered the art of transmission line design." Art is the right word to describe those older designs. By intuitive feel and a lot of trial and error a few people could build very good TLs. But there were more failures than successes. Now with the computer design tools available, a TL can be designed on the computer and perform as predicted. No more myths or snake oil, an understanding of how a TL works and what trade-offs are available is easily accessible. The accuracy of TL design is on par with the bass reflex and sealed box enclosure designs. Measured results correlate with the predicted response. The calculations are more complicated but the rewards/payback are greater. |
"The music was sooooo much better. Big cars, big hair, big LP jackets that I could look for hidden pictures and read without a magnifying glass, big amps and speakers producing huge sound." I miss my big hair. My daughter decorates the wall of her apartment with some of my old LP’s. I’m still in love with the first pair of IMF transmission line speakers I heard, which is what sent me on my DIY quest. One thing I learned was, respect for those who had mastered the art of transmission line design. Never could bring myself to outright copy someone else’s design though... always felt like, for better or for worse, part of the calling of DIY speaker builder was to experiment. Alas, almost invariably it was for worse. |
"back in the 70's" The music was sooooo much better. Big cars, big hair, big LP jackets that I could look for hidden pictures and read without a magnifying glass, big amps and speakers producing huge sound. No earbuds or blue-tooth speakers playing poorly recorded downloaded music. Those were the days. |
(MJK) Some answers. What are the attempted advantages of a TL speaker cabinet with equal sizes channels all the way to the port, as opposed to each channel being wider than the last? (MJK) A constant area TL with need to be L = c / (4 x f) long to produce a fundamental 1/4 wave mode that is tuned near the driver's fs value. There will be higher harmonics generated at 3 x fs, 5 x fs, 7 x fs, and so on. You can mitigate the peaks and dips in the response by offsetting the driver 1/5 to 1/3 of the TL length and by adding stuffing to the first 2/3rds of the length. The worst ripple and most ragged response will be achieved with a TL that expands from the closed end to the open end. The open end will never be large enough to be a horn loading so the standing waves will be very strong. To achieve a fundamental tuning frequency near the driver's fs the length will be much greater than L = c / (4 x fs). The harmonic's (3/4, 5/4, 7/4, ...) standing waves will be closely spaced just above the tuning frequency. This is a very difficult design to tame and get a decent SPL response. I would not recommend this style of TL. Also, what is being achieved by a decreasing size horn channel compared to an increasing size channel? (MJK) My recommendation is to use a severely tapered TL with a closed end to open end area ratio of at least 10:1 if not higher. This will produce a shorter and smaller TL compared to a TL with a constant or expanding area along the length. You can taper the line in steps of decreasing area or a constant slope. A simple single fold TL will work well so all you need is a slanted dividing wall in the enclosure. A decreasing area TL will reduce the required length for a given tuning frequency. The length will be much less than L = c / (4 x fs). It will also push the higher harmonic's (3/4, 5/4, 7/4, ...) standing waves much higher in frequency where the stuffing is better at damping the peaks and reducing the resulting ripple. Mount the driver at 1/5 of the length and stuff the first 2/3rds of the TL with fiber. Are there any simple answers to these questions? I probably won’t comprehend a high level answer. (MJK) No simple answers. TLs are difficult to design and get an optimum result. An accurate computer model to simulate the TL and iterate the design is a requirement to get it right. Rules of thumb and other commonly accepted myths for TL design will produce a hit of or miss result, you would need to be very lucky. |
Of the links mentioned, the Philharmonic Audio page is the only one that accurately describes how a TL works. The first article linked is full of inaccuracies and just plain wrong information, the fact it was written in 2016 is very surprising. There have been four different pieces of software available over the past 20 years that accurately model TLs. 1. Augspurger's TL program which I do not believe is still available. 2. My MathCad worksheets which are no longer available. 3. Hornresp 4. Leonard Audio TL progrma avaialble on DIYaudio. If you want more in depth information on how TLs work and can be designed look at the TL page on my site. www.quarter-wave.com Martin |
This review may be of interest also. http://www.theabsolutesound.com/articles/acoustic-zen-crescendo-loudspeaker/ |
Tapering the transmission line, towards the opposite end from the woofer, lowers the woofer’s F3(the woofer’s 3dB down point, according to Thiel/Small parameters) and(combined with proper damping) reduces ripples, in the back-wave’s response, equivalent to what could be achieved with a longer(straight) line. Reversing the taper raises the woofer's F3. http://audiojudgement.com/transmission-line-speaker-design/ http://www.philharmonicaudio.com/ML-TL.html https://en.wikipedia.org/wiki/Transmission_line_loudspeaker |