Quick example -apologies that it's not the best: it happens to be an MLTL variation, but it was to hand on the desktop.
The upper is as-designed, for the client who wanted a max-flat alignment (I'm not a fan, but that's what they wanted). The lower is the same drive unit, in a box with the same Vb, with the same vent dimensions and same damping. The difference is that the proportions have been changed to those of a conventional vented box rather than the tall MLTL form factor. If the operating physics were no different, we'd see no shift. But we do. QED -they ain't the same thing. Related, at a distance, since at some level we're dealing with boxes that have holes in, & even a chambered back-loaded bass horn can be called an extreme variation on a vented box / bass reflex if you go down far enough into the background / abstract fundamentals, but those are functionally speaking not very relevant.
Actually, tall MLTLs do have some interesting traits -you can get to the point where the longitudinal starts to provide some damping of the vent around Fb -this is one of those cases. A lot tend to be a bit shorter & more highly forced. I like the tall types as acoustically speaking it's quite an efficient way to go about things and keep the vent proportions reasonable -the price being the damn thing can get quite tall if you don't fold it up. Since I happen to quite like that aesthetic, it doesn't bother me, but that's a matter for personal preference! 😉
The upper is as-designed, for the client who wanted a max-flat alignment (I'm not a fan, but that's what they wanted). The lower is the same drive unit, in a box with the same Vb, with the same vent dimensions and same damping. The difference is that the proportions have been changed to those of a conventional vented box rather than the tall MLTL form factor. If the operating physics were no different, we'd see no shift. But we do. QED -they ain't the same thing. Related, at a distance, since at some level we're dealing with boxes that have holes in, & even a chambered back-loaded bass horn can be called an extreme variation on a vented box / bass reflex if you go down far enough into the background / abstract fundamentals, but those are functionally speaking not very relevant.
Actually, tall MLTLs do have some interesting traits -you can get to the point where the longitudinal starts to provide some damping of the vent around Fb -this is one of those cases. A lot tend to be a bit shorter & more highly forced. I like the tall types as acoustically speaking it's quite an efficient way to go about things and keep the vent proportions reasonable -the price being the damn thing can get quite tall if you don't fold it up. Since I happen to quite like that aesthetic, it doesn't bother me, but that's a matter for personal preference! 😉
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Why are you not a fan of a max-flat alignment? I agree with you when it comes to BP enclosures.
I agree with "a chambered back-loaded bass horn can be called an extreme variation on a vented box / bass reflex "
BR, TL, and BLH or RLH are all the same to me unless you design some type of Scoop enclosure.
Like I said before, there is a TL thread on this forum where the designer removed the "LINE" from the enclosure and the performance increased as a BR enclosure.
I suppose it says 72” (180cm) because ‘woofer’ (48 hz quarter Wavelegth?) But it says the ‘size of the drivers ‘Sd’ which we’ve all found to be a poor generalization once using horn response and the TS parameters to find the ‘ best‘ combo
I think I lost it thru desktop and laptop upgrades and having to reinstall HR.
Let me see if I can recreate it from that Excel pic.
Let me see if I can recreate it from that Excel pic.
Now you're just being disengenuous. That was asking somebody else to clarify a post they made: it wasn't addressed to you, and unrelated to the remark (not 'question' -you'll notice the distinction comes with a lack of question mark) I made to yourself.
Mmm. Unfortunately, the book you are referring to was published by the late (and much missed) David Weems in 1990, and pre-dates by a decade the research performed by George Augspurger, Martin King and others, which massively advanced understanding of quarter-wave enclosures except in terms of some fundamentals that 'should' have been apparent, but frequently weren't (alas). But since we're here, we can go through it. I see you've avoided further reference to to the difference in the resonant physics that was pointed out to you though, which is a pity. If you don't think Hyperphysics a reliable source, you'll find the difference between cavity and air column resonance in most books on basic physics.
Be that as it may: from the top:
...and David is absolutely correct in this. That does not make it a synonym for a reflex enclosure: it means that it shares similar requirements from the drive units. That Land Rover Discovery outside: it requires four tyres for normal operation. So does the toddler push-chair my neighbour has just trundled up to her front door. That doesn't make it a Land Rover Discovery. It means it has something in common with it.
David is correct again here. They are ultimately both 4th order systems and will unload 24dB/octave at some point, in the case of the ported box usually directly below tuning (some exceptions), and with somewhat greater variability in a QW based design depending on the specific type in question. An aperiodic TL (as I've mentioned above) such as one of Augspurger's alignments, has an initial 2nd order rolloff; it will ultimately transition to 4th order at some very low frequency and / or very low amplitude. I note with amusement that David mentioned they share 'one characteristic with the ported box...'
'One'. As mentioned, sharing some characteristics doesn't equate to being the same. Unless you invoke politician's logic, i.e. 'My dog has four legs. My cat has four legs. Therefore my dog is a cat (or a Land Rover Discovery)'.
This was exploded decades ago. There is no direct functional connection between line cross section and cone area. In one sense David was right: it damn well better not be smaller, but that's because it will in almost every practical instance be chronically over-damped even with that used as a minimum. But that wasn't quite what he was meaning. 😉
There are two parts to that. First, the statement is 'a typical minimum'. Which (again) is not a synonym for 'all times and places without exception'. And second -you've forgotten to mention (inadvertently I'm sure) where he got it from. Since I happen to have the 2nd edition of his book open on the desk, I'll save you the trouble. David took that from Cockroft's experiments published in Speaker Builder magazine. I also happen to have a copy of that article. 😉 And why has he used that value? Because that's the length of the pipe John used as a nominal except for high Q drivers. Alas, John didn't publish especially detailed measured data, so we don't find it in David's book either. And if we use the equations he published, per Cockroft, we find some major problems. David himself (and John to give him his due) admitted that you get some weird figures' outside certain limits -he mentions a Qt of 0.6. What he doesn't mention is that the results often contradict his own statements, even when the driver spec. falls within the 'loosely defined' limits. For instance, I've just worked out the values Cockroft's equations provide for the new Markaudio MA200. They provide a line CSA about 25% less than the 1*Sd minimum David sets (despite values falling within the supposed limits), a very long pipe length, and a very light packing density of Acousta-Stuf. The result is catastrophically bad, unless you happen to think the attached is a quality TL alignment. I certainly don't.
None of which is to insult David -I've a huge amount of respect for him and his achievements. But he isn't a great source for theory (insofar as there is any) on transmission line operation or design.
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Depends on the specifics, but mostly because in the majority of practical in-room situations, you'll end up with an LF heavy balance. If you've plenty of space from the boundaries & a fairly dead acoustic, or have some other specific object in mind then it can work. Most people don't have that luxury though, so in general I find a better-damped LF alignment, preferably designed for the intended system & room, is more practical / neutral. Other reasons too, but that's the major one.
Eh? A scoop bin is a back loaded horn.
I'm not sure how I can put this without causing offense, so I'll simply say it and hope they don't take it as a personal insult:
You don't specify how 'performance' is being defined, and alarm-bells are already going off, since a TL is not something that's just tacked on some random box any-old-how. But if 'performance' (however it's defined) shows a dramatic improvement in some unspecified way, then either the TL was incompetently designed, the objectives were mistaken, or some combination of the two. Which rather underlines the point: they aren't the same thing as a bass reflex / vented box. If they were, as you keep repeating in the face of basic high-school level physics, there would be no difference. QED. 😉
In Car Audio. Hence, big subs working in 0.25-0.50ft3 enclosures due to transfer function (cabin gain).
However, the actual tune should have been around 60hz instead of 74hz.
I think my goal at the time (2009) was to make sure the enclosure could handle 2Kwrms @ 16.1mm Xmax.