Looking at this, is the idea somewhat a reverse horn? As sound goes in/thru it is minimized by the shrinking space. Not sure about the Nautilus but it seems like it would need to be vented to encourage the action... get the most out of it.
Your question got me thinking. I want to experiment with a 4” mid on this. Not tubular but “stepped” openings of sorts ending with a minimal size vent. With the idea of minimizing sound along the way. Vs-same vol box with vent.
That thing still looks cool. 90’s batman . great marketing... make something so stunning looking... don’t really need to sell any. All eyes on you.
Your question got me thinking. I want to experiment with a 4” mid on this. Not tubular but “stepped” openings of sorts ending with a minimal size vent. With the idea of minimizing sound along the way. Vs-same vol box with vent.
That thing still looks cool. 90’s batman . great marketing... make something so stunning looking... don’t really need to sell any. All eyes on you.
If you put a hole in it, it becomes a quarter wave resonator.
The idea is that the sound from the back of the cone travels thru a sufficient distance to completely absorb the wave. The necessary length is relate dto the wavelength of the sound and the absorbtion coefficient of the damping at that frequency.
Tapering such that the passage gets narrower allows the line to be shorter.
We regularily use quarter-wave aperiodic TLs for midTweeters in our WAWs.
dave
Nautilus is not a reverse horn for the simple reason that both ends are closed.
The obvious next question then becomes, what if we vent the other (small) end?
The result is going to be terrible if we analyze it as a horn. A compression driver creates high pressure sound waves forced through a small throat, and then horn loading gradually decreases that pressure until it acoustic-impedance-matches the ambient listening environment. This is how a horn-loaded compression driver works. If we apply this backwards, take an ordinary direct radiating bass driver to begin with, and back-load it with a horn so that the backwave pressure increases, this is okay so long as this backwave does not need to interact with the outside world (closed end). But if we vent the other (small) end then this high pressure sound wave suddenly gets dumped into the low-pressure ambient listening environment.
If we analyze this as a TL we may arrive at a different conclusion but your question was whether this is horn-loading in reverse and IMO it is not and cannot be.
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Sorry but really it is just that the seashell shape being leagues better than a rectangular box in resonance suppression.
If it really has anything to do with dissipating the rear wave, all the members here who have built a TL will be able to attest it is the right thing to do and tell us about the great sound and the reasons why it is so.
It is just that the two do not appear to be related.
(Edit: let me be more specific. "Exponential" is the keyword. If the tapering is not exponential the magic is gone. Of course Nautilus still needs to dissipate that backwave like any stuffed enclosure, TL or otherwise.)
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Well maybe but other drivers in the Nautilus does use a tapered enclosure without the seashell shape (more like a closed tl) and this seems to have an effect too.
Iirc x971 used to great effect what he calls a 'dagger' sub chamber in one of his built to load a full ranger in one of his foam built and this work along the same principle of a tapered closed tl.
Please note i don t advocate for B&W as i never been impressed by most of their high end loudspeakers i ve heard (principally 800 series with one 15" or two 10" as they were fashionable amongst mastering engineer i worked with 10 years ago). In fact the only model i liked from them was a small bookshelf i don t remember the ref and i never heard a Nautilus by the way...
From what i ve heard a Tl can be great sounding (to my taste) as some PMC i ve heard. But they have some drawbacks, main one being you need a huge room for make them justice and placement is critical if not in wall mounted (soffit). This is true for all speakers but seems to be of even greater importance for the PMC i ve heard.
Well it seems there is no definitive unique answer for issues and multiple technical answer can work. But we all know that no?
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There is zero mystery about the Nautilus. It is a 4-way loudspeaker employing a sealed tapered transmission line for each driver, the LF leg of which happens to be coiled up purely for reasons of space, aesthetics & marketing. Sealed TLs are hardly new, they've existed for decades in various forms, the Nautilus is just one of the better known examples for fairly obvious reasons.
Wide radii curves do not significantly affect the attenuation of LF wavelengths in a TL variation (although it may improve the separate issue of structural rigidity), be it a 1/2 wave or 1/4 wave.
Wide radii curves do not significantly affect the attenuation of LF wavelengths in a TL variation (although it may improve the separate issue of structural rigidity), be it a 1/2 wave or 1/4 wave.
How important is the profile of the tapered line? A straight triangular cross-section pyramid would be easy enough to try, but of course far from exponential.
Also, is B&W really after quarter wave transmission line for midrange and tweeters?
Taking for example a midrange playing from 350Hz (such as B&W 800 series), the wavelength is roughly 1 meter, 1/4 is 25cm. That is rather shorter than the B&W 800 series midrange "egg", let alone the taper B&W uses in their tweeters. So maybe they are after more than 1/4 wavelength?
Also, is B&W really after quarter wave transmission line for midrange and tweeters?
Taking for example a midrange playing from 350Hz (such as B&W 800 series), the wavelength is roughly 1 meter, 1/4 is 25cm. That is rather shorter than the B&W 800 series midrange "egg", let alone the taper B&W uses in their tweeters. So maybe they are after more than 1/4 wavelength?
Above a certain frequency, a box like this allows a single mode of propagation. Ringing is wanted at the lowest frequency. In this case, the higher frequencies are taken on the longest journey through the damping material for a given box volume. The question for me is, is it overkill..in other words can I do it in other ways?
"employing a sealed tapered transmission line for each driver,"
Can you describe what is a sealed transmission line? To me transmission line is only used in designs using the sound generated by the side of the cone that is on the inside, and lets a limited freq band out into the room through a port. The Nautilus have no ports I think. But I have been wrong before.
Can you describe what is a sealed transmission line? To me transmission line is only used in designs using the sound generated by the side of the cone that is on the inside, and lets a limited freq band out into the room through a port. The Nautilus have no ports I think. But I have been wrong before.
Lewinsky, from what i understand the egg shape is for a different effect than the tappering TL. It is here to redirect most of the driver backwave to the transmission line ( a geometrical difractor not really different to a geometrical RFZ in acoustical architecture) which appear at the rear part of the egg (this is the reason the back of driver is enclosed into an ogive/egg shaped piece too). Obviously it works with mid high frequency as it will be transparent to long wavelength (low end coontents)).
Xrk971 did exactly what you say about the triangular line hence the name "dagger"... i will try to find the thread and publish the link to it. It must be in the full range subforum as it is a fast or waw or whatever the name...
Slackweather: long article but you should find answer there Transmission Line Theory
Xrk971 did exactly what you say about the triangular line hence the name "dagger"... i will try to find the thread and publish the link to it. It must be in the full range subforum as it is a fast or waw or whatever the name...
Slackweather: long article but you should find answer there Transmission Line Theory
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The dominant factors in any transmission line, be it a sealed 1/2 wave or open 1/4 wave type are acoustical length and volume. Where relevant, driver & terminus tap locations (+ size in the case of the latter) also. These last do not apply to the Nautilus.
Within these broad limits there is the possibility for variation, the most obvious being that the acoustical length of a TL is a function of axial length and taper. However, if you assume a broadly similar Vb, axial length & OA taper ratio, then differences in profile are usually on a detail level and of less significance to a sealed design.
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A sealed TL = a 1/2 wave pipe (i.e. a pipe sealed at both ends). Often used for midrange enclosures as an alternative to a simple sealed box, although sometimes, as in the case of the Nautilus, used for the LF also. Not novel, they've been around & used for decades.
As a broad observation, the term 'transmission line' has become such a catch-all term that it's frequently used by different people to describe pipes that are polar opposites of each other in terms of functionality. We could say the same about most boxes described under the 'aperiodic' banner, or even 'bass reflex' for that matter, but we're never going to get it changed now, so we just have to put up with it.
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