I thought we answered the OP's original question and moved on to an interesting discussion of the semantics of "waveguide", then to another interesting discussion of the merits of the Karlson. I didn't realize these discussions weren't allowed to segue.
By the way, I'm a push-pull triode guy, myself.
My real objection to the Karlson was that they made unfounded claims about it (that it had the design and performance of a proper bass horn), and fooled the public by adding appendages that had an exponential arc to them. It is not a horn, nor does it have the performance of a horn, yet through marketing the company was able to prey on the gullible. That is why I called it snake oil.
A horn is a bounded surface of expanding area that grows at a particular rate to a mouth size large enough to support acoustic radiation. The slot does not control area growth. With the Karlson, the reflex vent is at the beginning of this exponential slot. The wavelengths from the reflex port are way too long to even see the Karlson slot. The woofer is at the bottom of the broad end of the slot and sees no area growth, just an undamped cavity.
Note that I'm not commenting on the tweeter Karlson variants. I haven't measured one or seen any measurements. It does look closer to the microwave device (although a tweeter needs to work over a broader frequency range than a microwave device).
An experienced engineer can evaluate the merits of an enclosure by seeing a number of response and impedance curves, especially if they consistently reveal the same flaws: serious front cavity resonances added to what is otherwise standard bass reflex performance. The fact that there was never a technical paper modeling and analyzing the Karlson enclosure is a good clue that it had no technical merit.
You can show us those impedance curves? I'd like to see them.
You have a nice day too!
Yes, but I am not aware of any that measure badly and sound good.
By the way, I'm a push-pull triode guy, myself.
And the Karlson cabinet is one of those components. I maintain it is a reflex cabinet with significant additional resonances added via an unfortunate cavity and wings added in front of the driver. The impedance curves consistently show that it is a reflex cabinet, with a tuning frequency and double humps (plus additional wiggles from the front cavity resonance, never a good sign).
My real objection to the Karlson was that they made unfounded claims about it (that it had the design and performance of a proper bass horn), and fooled the public by adding appendages that had an exponential arc to them. It is not a horn, nor does it have the performance of a horn, yet through marketing the company was able to prey on the gullible. That is why I called it snake oil.
A horn is a bounded surface of expanding area that grows at a particular rate to a mouth size large enough to support acoustic radiation. The slot does not control area growth. With the Karlson, the reflex vent is at the beginning of this exponential slot. The wavelengths from the reflex port are way too long to even see the Karlson slot. The woofer is at the bottom of the broad end of the slot and sees no area growth, just an undamped cavity.
Note that I'm not commenting on the tweeter Karlson variants. I haven't measured one or seen any measurements. It does look closer to the microwave device (although a tweeter needs to work over a broader frequency range than a microwave device).
An experienced engineer can evaluate the merits of an enclosure by seeing a number of response and impedance curves, especially if they consistently reveal the same flaws: serious front cavity resonances added to what is otherwise standard bass reflex performance. The fact that there was never a technical paper modeling and analyzing the Karlson enclosure is a good clue that it had no technical merit.
You can show us those impedance curves? I'd like to see them.
You have a nice day too!
Did you read Metro's discussion of their T15? It's pretty much a Karlson except folded back from the top of the coupler. It was designed by modern engineers that make no unfounded claims.
http://www.metroaudiosystems.gr/pages/manuals/E_Array_Manual_en.pdf
An externally hosted image should be here but it was not working when we last tested it.
The Metro T-15 subwoofer
The loading method is an original and highly evolved hybrid of resonating cavities, labyrinth damping, and an acoustic transformation interface. The method is critically tuned and took much painstaking R&D time. Its called THL ™ (Thalis Hybrid Loading). Its name is derived from the E-Array & T-15 sub originator and designer Mr. Thalis Menexelis.
In short, this loading achieves +3 dB sensitivity over woofer driver specs for the low frequencies, it squeezes distortion and cone travel, and it continues to do so under the system’s resonance frequency.
Design goals for this subwoofer design have been set to be small size, and over 100 dB SPL / 2,83V / 1m sensitivity, 40 Hz to 180 Hz bandwidth, and musical power handling in the 1000 W order with no mechanical problems even in the lowest octave. Also no aerodynamic or other noises would be acceptable. Low distortion and even response with controlled output over 150 Hz with gradual weakening from there on without peaks were other goals, so even low order crossovers slopes could be used without resulting to annoying peaks in their upper part of low pass slopes.
The frequency response chart of T-15 sub at 1 meter and with 2,83V input can be seen in the next capture:
An externally hosted image should be here but it was not working when we last tested it.
The T-15 sub has a complex low frequency loading architecture comprised by three types of topologies: Bass Reflex, Transmission Line, and in the end an acoustic coupler that stems from John E. Karlson’s work in the early 50’s, and it is by principle a broadband resonator and an acoustic transformer together.
In the T-15, the back output of its woofer loads a typical bass reflex chamber with a slot reflex mouth. The slot tuning does not follow the classic calculation model since its propagation resistance is not set by open space but by the transmission line and the acoustic transformer that follow, with system resonance definition demanding very complex calculations and many practical tests so to be ideally set.
The slot port output loads a folded TL that it can be taken as a second port of larger area and different tuning.
With proper mounting of the main slot port and complex calculations based on volume, woofer characteristics, and box tuning, significant bass reflex port output has been achieved spanning even higher frequencies than its resonance frequency towards the folded transmission line (TL) with further augmentation.
The most significant contribution of the second TL chamber (or TL line) for this design –beyond the output augmentation for a fairly wide band- is that it lends a delay line for the lower than first chamber’s system resonance frequencies. Those are finally coming out of the acoustic transformer; with phase characteristics nearer to the woofer’s front output ones.
In contrary to what happens in classic bass reflex alignments where phase is opposite, bringing high cut off slopes and significant group delay, the T-15 design achieves higher than bass reflex output even lower than system resonance, and mainly lower roll off order.
At transmission line’s output stands the coupler, and its contribution is critical.
First of all, it presents a convenient acoustic resistance for the woofer, and mainly controls its behaviour behind box tuning –a quality missing from bass reflex designs- so it does not hit its stops in very difficult circumstances in the lowest frequencies.
The coupler achieves, for a given acoustic output, woofer excursion in the order of 2/5 less than normal. The result is significantly lower distortion given that the woofer works in its linear range for much higher power intake.
At transmission line’s output stands the coupler, and its contribution is critical.
First of all, it presents a convenient acoustic resistance for the woofer, and mainly controls its behaviour behind box tuning –a quality missing from bass reflex designs- so it does not hit its stops in very difficult circumstances in the lowest frequencies.
The coupler achieves, for a given acoustic output, woofer excursion in the order of 2/5 less than normal. The result is significantly lower distortion given that the woofer works in its linear range for much higher power intake.
The above are prominent in the following two distortion measurements for 2.83V input. The first without the coupler, and the second with the coupler added. For such SPL the differences are confined mainly under 50 Hz, but as the power goes higher and the woofer follows longer excursions, the significant lowering of distortion begins from higher frequencies, and spans the whole subwoofer bandwidth for power intake near its electrical limit.
Sonically the T-15 sub is characterized by total transparency of the low frequency program, diction of notes and significant subjective volume for its size, absence of audible resonance and extraneous noise, no strong / weak tones, and excellent dynamics.
The coupler achieves something more and singularly significant:
Dispersion control. Although it is impossible to reproduce low frequencies with total control, the T-15 design lends a usefully controlled dispersion character to low frequencies which is readily audible if someone listens to its side where significant weakening of its output can be witnessed.
The propagation output of T-15 in near field comes close to cylindrical shape in reality.
OT posts removed.
I know very little about TL. I have never tried to build a speaker using one. That said doesn't the TL need to be of significant lenth compared to the wavelength as in 1/4 WL as an example?? That's a open area, no stuffing, that looks to be of insignificant length as far as the bandwidth that the subwoofer covers. Is that correct??
Rob🙂
As this thread turns out to aim after a clarification thread on some "mess of semantics" versus "technical basics":
😉
IMO a TL is best seen as a special kind of a resonator.
"Special kind" because the resonance is related to the reflection and hence "comes along" delayed.
This is a fundamental difference to a "normal" resonance that ideally builds up from time zero.
So quarter wave resonators - relaying on the principle of standing waves - share their pattern with cone break up and horn honk.
Whereas a high Qts resonance for example could be considered as a "normal braid" of resonance.
Actually a TL resonance IMO shouldn't even be considered as a "true resonance" - but this time we do not "have Earl to accuse for" - simple layman's confusion over long time turning into sort of "semantic fact", I'd say.
🙂
Michael
😉
IMO a TL is best seen as a special kind of a resonator.
"Special kind" because the resonance is related to the reflection and hence "comes along" delayed.
This is a fundamental difference to a "normal" resonance that ideally builds up from time zero.
So quarter wave resonators - relaying on the principle of standing waves - share their pattern with cone break up and horn honk.
Whereas a high Qts resonance for example could be considered as a "normal braid" of resonance.
Actually a TL resonance IMO shouldn't even be considered as a "true resonance" - but this time we do not "have Earl to accuse for" - simple layman's confusion over long time turning into sort of "semantic fact", I'd say.
🙂
Michael
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So the distinction is that one has a single resonance and the other a series of resonances, because it stems from delay and wave repetition rather than lumped parameter resonance.
Of course, TLs are another case where an idealized notion (back wave goes of down a long line, never to return) isn't exactly what you have in reality. Due to the multiple resonances, TLs are generally well damped which makes them close to a vented box variant.
I would say the same about the T15. Although they talk about transmission line qualities, the dimensions aren't long enough for that to be an appropriate description. The same with the "Acoustic Coupler" (the Karlson curve) which they call an acoustic resistance but that seems unlikely. Acoustic resistances are usually dense porous materials with viscous drag.
The key to all these alternative cabinet approaches is to, if at all possible, create an equivalent circuit or mathematical model. If that can be done, the performance of the system can be verified and optimized. If elements of the design, such as the Karlson wings, resist modeling you have to wonder if they are valid design aspects or appendages with no particular function.
The T15 seems to perform fine but I'd ask if you couldn't get the same performance with a conventional vented box of the same volume and tuning?
Yes thats *one* distinction – but not the most interesting one IMO
“Resonance” is per se a time related phenomena.
A normal resonance behaves completely different than a pipe / TL resonance in this respect.
Sadly this usually is not kept clearly separated in audio terminology.
Some even invent more fancy names like “stored energy” to increase the semantic mess and further blur the underlaying technical and sonic principles.
At least for *this* maladity ("stored energy") we luckily "have Siegfried Linkwitz to accuse for"
😀
IMO the confusion about the topic "resonance" stems form the omnipresent FR thinking.
Any wiggle in the FR is labeled a resonance / stored energy - not looking any deeper into time domain behaviour differences of CMP systems.
🙂
Michael
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Waveguide and horn are just different aspects of the samething. 95% of horns are wave guides and 95% of waveguides are horns. If a design is one and not the other it is probably not very well designed.
They are different!
A waveguide has parallel sides, and performs a point to point transmission function. Its mission has nothing to do with altering the density of the energy across a wave front.
A horn, on the other hand, performs a dispersive (with driver) or collective (with microphone) function because of its flare. Here the distribution of energy intensity across an increasing or diminishing wave front is at issue.
The attempt to call one, the other, has to do with the art of marketing flair, not wave mechanics, nor the science of acoustic flare.
If we destroy the meaning of the words we use, then a lie can be transformed into the truth, and what we say, no longer has meaning or veracity.
Regards,
WHG
Wow I forgot i posted this thread..........What a furore! 
I take the view that really the celestion flare, is actually a horn.
I take the view that really the celestion flare, is actually a horn.
That always sort of bothered me too, the adoption of the term waveguide - which is a straight duct - and using it to mean a specific flare shape of horn. Like many of you have said, traditionally, the transmission line (duct) is the waveguide, the antenna (flare) is the horn.
I used to kind of debate the sematics on my forum and various others, but have noticed it's a sinking ship in the loudspeaker market. Kind of a bummer, we've sort of bastardized the language, in my opinion.
Still, I rarely kick that subject around anymore. I tend to stick with the term "horn" when discussing them, even if conical, quadratic or caternary. They're conical horns, quadratic horns and caternary (OS) horns to me. But sometimes, I'll call 'em "waveguide horns" just because that's what most people expect for these kinds of devices now days.
Microwave waveguides can be straight but they offer corners and bends also. Some times their cross sectional area varies large to small or small to large. They even open up (flare out) and terminate, but then they are termed "microwave horns" (always straight sided rather than exponential).
There are certainly acoustical waveguides true to the spirit of the microwave type. Look at the multisection manifolds as used to allign wavefronts in the large pro line arrays. Those are certainly waveguides in every sense of the word.
What we are looking for is a word for an acoustical flaring object that is designed primarily to define directivity rather than to be an acoustic transformer of high efficiency. Is there a better term for that than waveguide?
David S.
p.s. Can we get back to dumping on Karlsons?
There are certainly acoustical waveguides true to the spirit of the microwave type. Look at the multisection manifolds as used to allign wavefronts in the large pro line arrays. Those are certainly waveguides in every sense of the word.
What we are looking for is a word for an acoustical flaring object that is designed primarily to define directivity rather than to be an acoustic transformer of high efficiency. Is there a better term for that than waveguide?
David S.
p.s. Can we get back to dumping on Karlsons?
???
That may be *your* goal resulting from a very limited perspective on sonically relevant issues - but certainly not "what we are looking for"...
Besides that, the term "wave guide" most strictly seen, is by itself an oxymoron - meaning - waves can't be "guided" at all - its only the wave front that can be guided - undergoing reflection and/ or diffraction at any point of non-straight boundary.
🙂
Michael
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Hmmm, Shall we tell the microwave guys that have had it equally wrong for all these decades?
David S.
I still think this is all just silly semantic stuff. I also think this is all about marketing. Waveguides sounds better then horn to most people, its that PA horn stigma that has existed for ever. No one building an audiophile speaker with a shallow waveguide around the tweeter is going to call it a horn that marketing suicide!! 😉
What is important is just educating people. Only purests are going to squabble over the actually differences or get bent out of shape because more people use "Waveguide" now.
I always ask my employees, what really matters. Arguing definitions/semantics or just understanding any terms used (ie. the idea of everyone on the same page) and getting real projects done?? Bottom line is that anyone arguing semantics probably has too much time on their hands.
Blah...Destorying meanings of words used? 🙄 veracity? 🙄
You take the "Horn" and "waveguide" words a little bit to seriously if you really think somehow a lie is created here.
People are not stupid, they can figure out and care about any differences if they do exist. You can keep your strict definitions, the rest of us are too busy just buying, building and enjoying.
Absolutely. The waveguide is the transmission line, the horn is the radiator. The waveguide is usually just a duct or box shaped pipe, the horn is flared. Where the duct is flared, it provides an impedance change, which can be used for impedance matching. Just like acoustic horns, which are also impedance matching devices.
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lol pity one couldnt make an electromagnetic 'waveguide' in the same way that one could with microwaves.......
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