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Old 25th December 2013, 02:51 PM   #3961
mwmkravchenko is offline mwmkravchenko  Canada
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I think David did this as an simple exercise in studying the concept. He probably did not try to replicate the exact speaker enclosure.
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Old 25th December 2013, 03:37 PM   #3962
soongsc is offline soongsc  Taiwan
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Well, I thought I would see somthing more convincingly show the marketing gimmic. Having seen pictures of the early concept exploration units, the idea seemed quite sound to me although I had not tried the concept. The test device actually showed a closed volume at the end of the sealed transmission line, not sure whether it was implemented in the final design.

At least get the dimensions to tuned to the driver in the sim, please.
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Old 25th December 2013, 03:47 PM   #3963
tb46 is offline tb46  United States
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Default Posts #3955 and #3957

Hi David,

As I'm not a Nautilus speaker owner (I wish, if for no other reason than that a pair of those should come w/ eight power amplifers, and assorted other electronics, and you can never have enough power amplifiers :-)) I cannot but largely agree w/ your assessment, even if B&W's cute little video claims: "...it works pretty well..."; obviously, a refined technical statement from their Technologies section.

I played around w/ similar designs in the early 1970s, and never found quite what I thought I was looking for. One that sounded quite well was an "omnidirectional" sealed column that I packed from the bottom up, first w/ a layer of pressed fiberglass ceiling tile, then fiberglass insulation, and finally some very light pillow stuffing around the driver area.

In those days I had no way of decently measuring the results, and there was no "Hornresp". I definitely don't want to go back to cut-and-try loudspeaker building, it is much more fun (and environmentally friendly) to simulate.

Anyway, the point I'm trying to make is that this highly resonant column sounded better when stuffed as described above, than when just lightly packed w/ an even density of e.g.: fiberglass.

I was wondering if you had any plans to further refine you software, to assign different airflow resistivities to different horn sections? It would indeed be a great feature.

Thank you very much for you efforts, and have a wonderful holiday season.

Regards,
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Old 25th December 2013, 03:48 PM   #3964
mwmkravchenko is offline mwmkravchenko  Canada
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I'm convinced it is a marketing gimmick as well.

As it is only a concept that looks promising, I doubt it is worth going to any concerted effort to achieve it.

The patent websites are absolutely full of ideas that have no practical value in loudspeaker design.
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Old 25th December 2013, 03:57 PM   #3965
tb46 is offline tb46  United States
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Default Post #3962

Hi soongsc,

I found a pdf file that shows the prototype and the finished product reasonably well:

http://www.audiogamma.it/caricamenti...utilus_ctg.pdf

further descriptions are here:

Bowers & Wilkins - Nautilus Tapering Tubes

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Old 25th December 2013, 06:12 PM   #3966
mwmkravchenko is offline mwmkravchenko  Canada
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Nice post tb46.

But other than the openended port for the mid, I don't really think that there is any really revolutionary engineering being accomplished.

Great industrial design and a leading active system sure. That I can really appreciate.

The last speaker design I did is active. An active speaker can do things that nothing else really has a chance of getting accomplished.
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Old 25th December 2013, 11:52 PM   #3967
soongsc is offline soongsc  Taiwan
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So someone is actually going to show a more decent sim on this tapered tube issue? I to recall I tried some MJK sims and differences did show up, but I never tried to seriously tune the design because lack of knowledge at the time.
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Old 26th December 2013, 03:30 AM   #3968
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by mwmkravchenko View Post
I think David did this as an simple exercise in studying the concept. He probably did not try to replicate the exact speaker enclosure.
Correct.
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Old 26th December 2013, 03:47 AM   #3969
David McBean is offline David McBean  Australia
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Hi Oliver,

Quote:
Originally Posted by tb46 View Post
I was wondering if you had any plans to further refine your software, to assign different airflow resistivities to different horn sections?
Great minds think alike :-).

I have already started looking into the possibility...

Quote:
Originally Posted by tb46 View Post
Thank you very much for you efforts, and have a wonderful holiday season.
Many thanks, and best wishes to you and yours also!

Kind regards,

David
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Old 26th December 2013, 05:02 AM   #3970
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by soongsc View Post
Well, I thought I would see somthing more convincingly show the marketing gimmic. Having seen pictures of the early concept exploration units, the idea seemed quite sound to me although I had not tried the concept. The test device actually showed a closed volume at the end of the sealed transmission line, not sure whether it was implemented in the final design.

At least get the dimensions to tuned to the driver in the sim, please.
Hi soongsc,

Because the tapered rear chamber is sealed, and filled with absorbent material, there is nothing to tune :-).

There is no reflected wave - that is the whole purpose of including the absorbent material. The system is not operating as a transmission line loudspeaker, where the output from the lossy line is combined with the output from the front side of the driver. In the Nautilus design, the radiation from the rear side of the diaphragm is simply absorbed in the filling material and dissipated as heat.

The following quote from the Bowers & Wilkins brochure linked by Oliver is relevant:

"The combination of an acoustically transparent magnet and an exponentially tapered horn absorbs virtually all rearward radiation of sound - creating the nearest thing yet to an infinite baffle."

There is another interesting comment on the B&W web page, also linked by Oliver:

"Tapering the tube enables you to make it shorter for the same level of absorption. It acts like a horn in reverse - reducing the sound level instead of increasing it."

This statement is extremely misleading at best. The tapered tube is not acting as a "horn in reverse". Because the mouth is closed, it is acting as a sealed chamber. Also, tapering the chamber reduces the volume of the absorbent material for a given length. I can't see how this would improve the situation, where the B&W stated aim is to absorb the rearward radiation of sound.

The Bowers & Wilkins company makes very good loudspeakers, but I personally believe that the use of tapered exponential rear chambers in the Nautilus is more about achieving a "remarkable piece of audio sculpture" (their words) rather making a meaningful contribution to the sound quality.

This is just an opinion based on my understanding of the physics involved, and the evidence available to me. You are of course entitled to hold a different view :-).

Kind regards,

David
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Last edited by David McBean; 26th December 2013 at 05:20 AM.
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