The transmission line definition is interesting because an acoustic transmission line doesn’t act like an electric transmission line where all of the information is transmitted over long distances. An acoustic transmission line is a resonant tube with a low pass filter of damping. Does a closed end acoustic transmission line behave any differently? I don’t think it does. It still provides output at resonance and filters out the midrange. Where the Nautilus differs is that the line tapers to close to zero and the taper reduces energy at the middle of the fundamental wave. It’s difficult to set up a standing wave in a cone. It’s like yelling into a trumpet. Not much sound comes out of the mouthpiece. Add to that the wool as damping and the snail coil is an absorber of all the frequencies. It’s a reverse horn that absorbs the high pressure sound with wool. The Nautilus used electronic crossovers and significant bass boost to control the highly damped woofer output.
Is it an acoustic transmission line? Yes. Does it transmit any sound? No.
Is it an acoustic transmission line? Yes. Does it transmit any sound? No.
BTW, as I recall, B&W showed 2 versions of the completed Nautlius sculpture with 2 very different sets of drivers. If my poor memory serves, one was all white, so I think anodized aluminum?
Yes, I've repeatedly said that is the entire purpose of a sealed half-wave transmission line, so I'm slightly mystified why you are claiming anybody has said otherwise. Somebody might, if they were feeling ungenerous, suggest you were deliberately claiming people have said the exact opposite of what was in fact the case.
Because you are announcing that the single definition and sole purpose of a transmission line is a resonant quarter-wave pipe designed to provide low frequency gain. That is not the case, and you steadfastly refuse (now counting 5 times) to provide your documentary evidence showing that is the universally accepted definition. I assume you are refusing because you can't, for the excellent reason that there is no such universal definition, however desperately some try to claim otherwise.
'Transmission Line' in audio is in fact a fairly useless term precisely because there is no fixed definition of what it functionally is, in the same way that in electrical engineering, there isn't a fixed functional definition, beyond (which applies in both cases) it a structure designed to conduct EM or acoustic waves in a controlled fashion. What you do with it & how depends on what purposes you have for using them, since you can do different things with both. Although ironically enough, since one of the most common requirements when working with electrical TLs is impedance matching, the B&W Nautillus & other damped types designed for the purpose of maximally-flat [as far as practical] impedance are actually closer to what many RF engineers would recognise as a common design type / goal than others. That doesn't make them the sole type of acoustical TL any more than, say, a highly resonant QW pipe though, precisely because there is no fixed definition in acoustics beyond them all being pipes of some kind or other.
Yes, it is. That's the entire purpose of it. Who has been claiming otherwise, here or elsewhere? I haven't -I've repeatedly said it's a damped TL designed for the purpose of flat impedance, not LF support. Dave has also pointed out that is the purpose of the B&W & similar types. Perhaps you would like to explain why you are claiming we said the exact opposite?
No help necessary thank you, since I seem to understand them better than you -especially since you're actually asking why a well-damped response objective can benefit from a TL (!).
The simple reason for a using a damped 1/2 wave (sealed) TL rather than, say, a sealed box of the same volume is that it offers greater flexibility for the designer, and if your objective happens to be a well-damped impedance or FR characteristic, they can actually be more effective, providing you can accommodate any relevant extra complexity etc. For example, see the attached. Working from top to bottom, the left column shows a 1/2 wave (sealed) transmission line. Top graph shows the IB and actual system curve with the pipe undamped, the graph immediately below the IB and system impedance. The 3rd & 4th graphs then show the same pipe, damped to a modest level. The right hand column shows a sealed box of identical volume, leakage losses, damping type and quantity, top two graphs undamped, lower two damped to the same quantity as the TL.
What do we see? In the undamped enclosures, the resonant chain from the sealed 1/2 wave pipe is obvious, although the harmonics are low-level & easily damped with a minimal amount of material. The TL is actually tuned lower because I selected a max-flat impedance (aka 'flattest practical') tuning frequency (length) for it. The sealed box of identical Vb is tuned about 8Hz higher, & less in the way of a resonant chain since no dimension is stretched significantly relative to the others for eigenmodes to affect behaviour / tuning in any significant way. Beyond the difference in nominal tunings though, the impedance of the damped enclosures is where we see some further interesting differences, with the TL being a significantly flatter load, despite the identical Vb, damping quantity & type, leakage etc. This is why they can be useful: we have several extra dimensions of tuning & load characteristics that can be exploited. Midrange lines are an obvious example of where they can be useful & are quite commonly used, since the potentially flatter load can be valuable in passive filter design. Beyond that, the potentially more effective suppression of enclosure modes may (may) make for a cleaner response with less in the way of colouration from the enclosure. Whether that is audible, or more than marketing depends on the design. I'm no particular fan of the Nautilus as is, but it's grounded in solid enough physics as far as its design objectives & operation goes.
Attachments
From B&W brocure’’/coffee table book, added emphasis by me. They like using the term inverted horn. Called transmission lines in a numer of places.https://www.bowerswilkins.com/on/demandware.static/-/Sites-master-catalog-soundunited/default/bowers/Files/Nautilus_Brochure.pdf
The above representing the mid+tweeters. But they extend it to the bass, but leave it sealed.
Another quite from B&W:
So B&W say it is a TL, or an invetred horn — just so they couod use the term horn over again and again, eor marketing reasons?
dave
The above representing the mid+tweeters. But they extend it to the bass, but leave it sealed.
Another quite from B&W:
So B&W say it is a TL, or an invetred horn — just so they couod use the term horn over again and again, eor marketing reasons?
dave
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Probably, although there's precedent enough -Prof. Fred Terman got there back in 1940 with his 'Sound Absorbing Apparatus', which was exactly the configuration B&W use[d] with the Nautillus: an inverse damped horn, & he used the term constantly too. Whether B&W knew about Terman's work when they developed the Nautillus or simply hit on the same idea, I don't think we'll ever know for certain. The physics is sound -TLs & horns are tightly related anyway, so aperiodic 1/4 wave or sealed inverse 1/2 wave horns for damping / impedance flattening purposes is certainly an effective way of doing it, if you've got the space.
I have a few of these frmmwhen they cam out, if anyone wants. Netlist already gets one.
dave
Another case of appropiating a term from somehwere and it not really being right.We can probably thank Bailry for that.
dave
Unfortunately. Plenty of analogues / similarities, but in both cases it rather depends what you're actually doing / using them for.