Are you talking about the electrical impedance? Certainly not the acoustical impedance. And just what "impedances" are being matched?
Both - the conversion of electrical to acoustic energy involves BOTH. If a resonant cavity that's coupled to a driver resonates at the driver's peak resonance distribution frequency, the electrical impedance is reduced substantially at the resonant frequencies in question and the resistance to the transfer of acoustical energy both in front of and behind said transducer is also reduced. This is what is meant by achieving critical damping. I suggest you read Augspurger or Shutz's published papers for evidence of this phenomenon. I'm not the one who invented or discovered this - many others have documented this most basic and fundamental characteristic of TL's. Improved deep bass response is only one part of the equation. Critical damping allows increased output with less distortion and more linear response to applied signal input. Again, I cannot believe someone with your background is either not familiar with this phenomenon or not willing to acknowledge its existence.
I witnessed this trainwreck at the last site the OP 
barraged.
Any lurkers should pull up a chair, stay tuned, and grab a
...
I forsee bin time.
barraged.Any lurkers should pull up a chair, stay tuned, and grab a
... I forsee bin time.
OK, I notice that Geddes told you that you were wrong, and now I'm going to tell you that you are wrong. I derived a T&S style model for transmission line speakers as a senior (MQP) project (1979-1980) at WPI and I was a teaching assistant for microwave design, including transmission lines while in graduate school. Take the simple case of a 75 ohm video cable. They are source match terminated by being driven with a 75 ohm source and they are far end match terminated also by having a 75 ohm load, both matched to the 75 ohm characteristic impedance of the cable. There are no reflections on the line in this situation and no impedance matching of any kind going on as a result of the transmission line. There is also no resonance when the line is match terminated.
Now, a TL speaker is a completely different animal, the far end is not match terminated and therefore there are reflections and resonance on the line. The behavior around l/4 is much like that of a lumped vented system.
What makes a transmission line is the fact that it is not a lumped parameter system, there are both capacitance and inductance distributed down the line and partial differential equations are required to model such a system.
A horn _IS_ a special case of a transmission line where the characteristic impedance varies down the line due to the taper and it does therefore act as a matching impedance transformer within its passband. But this is not the TL that you are talking about.
You talk like you are an engineer but I have to wonder where the basis for your understanding comes from.
I suggest that you build a TL speaker and probe with a mic down the line. Read up on VSWR in electrical lines that is what you can measure by probing.
The first, and one of the best papers on TL speakers was published in the 1930s, 1936 IIRC, covering the Stromberg Carlson labyrinth speaker. There is also a patent from that time:
http://www.google.com/patents/about?id=uehKAAAAEBAJ&dq=carlson+labyrinth
They knew that it was a TL and probed down the line - they were probably RF engineers and knew what they were doing.
http://en.wikipedia.org/wiki/Stromberg-Carlson
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By 1st harmonic i mean the 1st undesirable line harmonic. Fundemental (1/4 wl), then 1 (3/4), 2 (5/4), 3 (7/4)...
dave
What your modeling is telling you may in fact be very true - if you are modeling an improperly designed transmission line which seems to be the case more often than not these days.
If you read Augspurger's extensive testing results and published papers, and if you build a proper TL with either a 4:1 taper OR an offset design of significantly greater length with a non tapered tube, you will find improved bass response overall. Unfortunately, most of the current TL designs combine offsets with tapers - like the poorly performing Thor design. Augspurger clearly states that this results in designs that are overdamped - worse performing than many bass reflex designs. This is one of the problems I have with King's designs - offset is combined with taper with very little science and engineering to account for negative effects of mixing the taper with the 5th to 9th resonant multiple cancellation that the offset produces. And by science or engineering - I'm not talking about equations with numerous fudge factors applied - I'm talking about putting desensitized microphones in resonant cavities and measuring the results - directly correlating them with changes in structure and configuration and modeling the actual results in equations.
With most of the "new" TL designs, you effectively have an overdamped bass reflex. If you stuff it sufficiently and taper it to ridiculous levels (approaching 20:1) you wind up with a bass reflex that is so overdamped - it's almost the equivalent of an acoustic suspension design.
If anyone cares to get any background on what to expect...
HTGuide Forum - Issue Versions of Augspurger Tables
HTGuide Forum - Issue Versions of Augspurger Tables
Limited to?
Here the big tube amp is 20 or 40 w (triode/pentode). The others are closer to 5W.
dave
I think the fundamental misunderstanding here is that the acoustical impedance simply coupling to the speaker and affecting the electrical impedance is being mistaken for some kind of "matching". As was pointed out a short acoustic TL is usually terminated with an open or short as far from a match as possible.
IIRC it works out to about 1,274 erg pounds per square furlong (in imperial units, that is - I prefer metric myself)
Popcorn, anyone?
Augpurgers work is parallel to King's.
Shultz's work consisted of running Augspurger's software over & over again to come up with a simplistic formula for creating simple TLs -- essentially the alignement tables that Augspurger never finished. King's simple tables have much more reach.
dave
Not sure what you're barking about - seems like a lot of noise and nothing really being said to dispute the cold, hard facts. Look at any impedance curve for a low frequency driver before being placed in a TL and after. You will find the impedance curve peak shifts upward slightly in frequency and is heavily suppressed. If you dispute this - you are disputing the measured data of King, Augspurger, Shutz, and Natkaniec. Funny, I don't remember seeing anyone from Worcester Polytech publish a transmission line theory paper recently.
As for your discussion about comparing pure electrical resonance to acoustical resonance - no one is claiming that one equals the other. Before you offer a scathing critique, read the person's posts carefully. I said that one is linked to the other - simply because a conversion of electrical to acoustical energy is taking place - they are linked to one another by definition. This doesn't mean acoustical resonance mirrors electrical or atomic resonance in all respects - whether it be microwave or laser. Please don't put false words in my mouth. If you are offering opinion to be argumentative - please refrain. I'm only interested in discussing scientific facts and evidence introduced by others through published work. If you have published work that offers different conclusions than those of professor Natkaniec or George Augspurger, I invite you to produce it.
Published in the April 1937 issue of Electronics, and an easier read than the patent.
The Acoustical Labyrinth (scanned from my original hardcopy)
dave
An ill-formed but academic question...
Okay. What's the difference, from the purely physics-based wave-mechanics perspective, between transmission-line theory and psycho-acoustics (as illustrated in the in the 1920's in Germany when it was developed) as practiced by Dr. Bose's original work.
🙂
[edit]: I am also curious, if we ever get to it, to explore wave-cancellation or non-distributive mechanics and the dynamic limitations of resonant systems - despite their static physics.
Curious about your reply...,
Tom
Okay. What's the difference, from the purely physics-based wave-mechanics perspective, between transmission-line theory and psycho-acoustics (as illustrated in the in the 1920's in Germany when it was developed) as practiced by Dr. Bose's original work.
🙂
[edit]: I am also curious, if we ever get to it, to explore wave-cancellation or non-distributive mechanics and the dynamic limitations of resonant systems - despite their static physics.
Curious about your reply...,
Tom
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most of the current TL designs combine offsets with tapers - like the poorly performing Thor design.
The problem with Thor was that Joe ignored what Augspurger had to say and compounded the mistake by making a silly mistake when a measurement would have conformed the error. It is well documented here http://www.diyaudio.com/forums/multi-way/64799-clarity-seas-thor-kit.html with many very successful rebuilds.
The problem isn;'t using both a taper & an offset, it is not having the analytic power to set the offset in the right place if you have a taper, King's software has this capability, and many offset & tapered designs have been successfully designed & executed, with lots of people thoroughly enjoying the music.
King is an engineer's engineer. The offset is best used to kill the 1st undesirable harmonic, 5th to 9th are easy to kill with damping.
Pretty much the methodology that resulted in the King model. And refinment continues by model, build, test.
That last bit is an oxymoron. A line damped until it is aperiodic can be very useful, and the only TL that could be called a "non-resonant loudspeaker design".
Here is the impedance curve of a non-optimized design in that vein. (non-oprimized because for its use its performance was suffiecient ie stunning)
As i said in my 1st post, King's software has considerably expanded the range of TL loudspeaker designs.
dave
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