Well, isn't a big BR enclosure with a big CSA external port the same as a coupling chamber TL?
Yeah, and tapering it to 1/2 Sd instead of creating an actual port transition from a ‘chamber’ seems to remove some of the potential chuff turbulence funk noise ? But a proper double flared ‘port’ shape connected to a long skinny box shape is likely ‘better’ ?
Would a 6-8ft tall home audio ported tower speaker be considered a BR or TL??? Polk Audio power port tower speakers would be a good example.
It’s a long air column and pretty ‘long‘ standing waves…. But then they get ‘mass loaded’ by the port to officially be ‘subwoofer type frequencies at the Fb ?
so almost anything that’s not just a 12” cube /long is sort of a TL??
so almost anything that’s not just a 12” cube /long is sort of a TL??
The point I'm making is that you're presenting your two selections as some kind of universally applicable scenario. I doubt anybody is likely to argue with Josef's contention, since they're running up against fairly basic physics if they do. What I'm saying is that you stated:
But these aren't facts -they're just choices you happen to have applied to them. There's no law of physics that says an inverse taper pipe has to posess a smaller volume than a straight or expanding pipe.
Sure. Although I've never been entirely certain about this 'coupling chamber TL' business. Depends how it's applied; George Augspurger found it provided a somewhat faster acoustic low pass than a straight pipe of the same Vb & Fb, but in other cases, it hasn't worked as well. Either way though, yes, it's one way of creating one, if you feel so-inclined.
As in a chambered line with an inverse taper to the pipe? In theory you'll create more turbulance from the reduced terminus area rather than less, but in practice so long as you don't go too far it's not usually a big deal & it does reduce issue with lateral standing waves. Since most are well damped anyway, again, usually not a big issue. Augspurger didn't find it particularly valuable, considering it slightly reduced LF performance, but he wasn't more specific than that, or precisely what he was comparing it with. Ted Jordan (to a point) used it & most early TLs e.g. Radfords, IMFs etc. followed this approach, as did some of the earlier S-C acoustical labyrinths (which Ted's were more closely related to). Functionally speaking, there isn't much harm in it, if it's designed well.
Yes & no. A conventional vented box assumes Helmholtz operating conditions, i.e. a uniform internal air particle density and no standing waves -they aren't considered as part of the operation / alignment. 'We' tend to consider the transition to start occuring when one dimension of an enclosure is stretched sufficiently relative to the others for the eigenmodes generated to affect the alignment, i.e. change it away from what you would anticipate from that driver, box Vb and vent dimensions when only assuming cavity resonance. So in that sense, many floorstanding boxes are MLTLs, either by design, or more commonly 'accident' / inevitable result of the form-factor, which then needs some kind of compensation such as a ruddy great amount of damping added in the base to absorb the longitudinal. Personally, I'd say the more acoustically efficient solution is to just account for & use them for practical value in the first place, but that can be harder for many to do if they don't have access to software capable of modelling QW behaviour, or the time / money / facilities to do their own empirical testing.
If you set a specific tuning, then the negative taper enclosure will be smaller and less efficient than the positive taper enclosure.
If you set a specific volume, then the positive taper enclosure will be more efficient, but will not play as low as the negative taper enclosure.
Hofmann's Iron Law is still winning.
Yeah, I'm familiar with what they are: I've designed enough of the things -even some commercial examples. I'm just not convinced that many implementations are particularly effective. Some, yes, but a lot? No.
I did you 1 better. Here are 2 coupling chamber TL's, 1 with positive taper and 1 with negative taper. Note, 1 of the enclosures is on this forum!
And once again, I ask: who said it has to be smaller, and what law of physics are they using to dictate that?
Only true if they share the same physical axial length.
I seem to recall saying that myself, above. I even mentioned the fact that nobody is likely to dispute it since they're running up against some fairly fundamental aspects of physics.
All right. These comparisons are getting skewed. Ignore Josef (with respect to him) for a minute. Basic scientific method dictates only changing one physical variable at any given time. So:
Take three different end-loaded QW pipes of identical physical axial length and volume. One is untapered, one expands from the throat to the terminus (horn) and one contracts from the throat to the terminus (inverse taper). Our sole variable is the change in tuning resulting from the different pipe geometry (remembering all three pipes have the same Vb and physical length). What do we see? Nothing profound that isn't very well-known. The untapered pipe lies on the mean, the expanding pipe has a higher Fp, greater efficiency as a result, and a wider gain BW. The inverse tapered pipe, being inherently mass-loaded, has a lower Fp, a reduced efficiency and narrower gain BW as a result. That's a scientifically valid comparison since only one variable changes. Hoffman clearly at work, as you, I and the average lop-eared rabbit are well aware. Using the latter as an example, you can hold Vb static & (say) raise Fp to that of the untapered pipe by shortening the physical length appropriately for the taper ratio, increasing the efficiency in the process, although the gain BW will always be narrower than an untapered pipe or horn due to the characteristics of the pipe geometry. And so on & so forth. But: only one variable at a time for comparisons to be valid, and that, with different QW pipe geometries, usually means you need to account for their specific characteristics -in that last example by altering the physical length while maintaining Fp and Vb, since Fp in a QW is a function of both its physical axial length and geometry, not the physical length alone.
What do you mean by particularly effective?
As long as the enclosure performs the way the designer intended it to, that's all that matters.
'1 better' than what? What's special about either of those? I've designed plenty of coupling chamber lines with straight, inverse and expanding pipe geometries -the latter being better described as horns, as noted, including some as commercial commissions. So (no offense) I'm struggling to understand what your point is?
Those aren't laws of physics: they're design choices or usage requirements. Which of those is a law of physics that says an inverse taper pipe must be smaller than an untapered or expanding pipe?
That's the problem. Those that do, great. But many don't, particularly early examples (the Daline comes to mind). Far too many tend to be based on either mistaken assumptions of how effective the decoupling can be (which as you can see from Augspurger, when done well can be reasonable but not especially startling), or simply little in the way of effective design method. One common example is too low a tuning frequency employed for the driver and / or the available Vb. That also applies to many other types of QW or TL of course -it's not an exclusive to chambered types! 😉
You asked about coupling chamber TL with an inverse taper. I showed you inverse and reverse tapered coupling chambered TL's.
I already said there is nothing special about TL's. They are just fancy BR enclosures.
That's my point.
I didn't ask anything. Quoting, I said 'I've never been entirely certain about this 'coupling chamber TL' business', immediately followed by the sentence 'Depends how it's applied'. That wasn't a request for information about what they are: it was me stating that I'm not convinced many approaches to this geometry work all that well. Sorry for the lack of clarity there.
And as noted, I've already shown that that is contrary to the basic laws of physics. A 'BR' (taking the term as a catch all to include both Thuras and later ducted vent types) is designed and functions as a Hemholtz resonator. The basic operating physics assume a uniform internal air particle density and no standing waves present. Period. A 'TL' (taking the term as a dodgy catch-all for all QW pipes) operates under pipe resonance / air-column resonance principles: the entire purpose of a resonant QW pipe is to generate and use standing waves. No offense (genuine statement -I don't go around trying to cause it), but if you still don't understand how these are fundamentally different modes of operation, you need to read a book on basic physics, or head off to the excellent Hyperphysics site and read their sections on cavity and air column resonance and how they differ:
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/cavh.html
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html
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