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Nautilus-style midrange cab



 
 
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  #1 (permalink)  
Old February 25th 04, 10:47 PM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

I've been giving some further thought to The Great Speaker Rebuild Fantasy
and I'm presently looking into a Nautilus-style enclosure for the KEF B110
bass/mid drivers. To be clear as to what I mean, this would be a straight
pipe with a reducing internal diameter, the reduction being non-linear. My
current sketch has a start diameter of 180mm, 40mm at the small end, and is
400mm long.

I calculate the volume of this to be about 2.85 litres. This is a bit
small - KEF suggest a volume of 5-10 litres (4 for a midrange enclosure) for
a fully enclosed box. What would be the likely effect of leaving the small
end of the Nautilus-style enclosure open? I'd expect less acoustic damping,
but would there be any sonic nasties?

I'd like the B110 to handle lower bass than it does in the present setup
(DN12 crossover - 400Hz) since I'm interested in moving the bass drivers
into separate cabs that are off-axis and out of the way. Ideally, I'd like
the B110 to roll off naturally at the low end rather than use LC
components - I assume that less capacitance or inductance in the circuit is
a good thing.


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


  #2 (permalink)  
Old February 25th 04, 10:57 PM posted to uk.rec.audio
Kalman Rubinson
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Posts: 214
Default Nautilus-style midrange cab

Does anyone else recall a similar design from WirelessWorld in the
70s? Nixon? I'll look through my archives but I seem to remember such
along with crossover considerations.

Kal


On Wed, 25 Feb 2004 22:47:12 -0000, "Wally"
wrote:

I've been giving some further thought to The Great Speaker Rebuild Fantasy
and I'm presently looking into a Nautilus-style enclosure for the KEF B110
bass/mid drivers. To be clear as to what I mean, this would be a straight
pipe with a reducing internal diameter, the reduction being non-linear. My
current sketch has a start diameter of 180mm, 40mm at the small end, and is
400mm long.

I calculate the volume of this to be about 2.85 litres. This is a bit
small - KEF suggest a volume of 5-10 litres (4 for a midrange enclosure) for
a fully enclosed box. What would be the likely effect of leaving the small
end of the Nautilus-style enclosure open? I'd expect less acoustic damping,
but would there be any sonic nasties?

I'd like the B110 to handle lower bass than it does in the present setup
(DN12 crossover - 400Hz) since I'm interested in moving the bass drivers
into separate cabs that are off-axis and out of the way. Ideally, I'd like
the B110 to roll off naturally at the low end rather than use LC
components - I assume that less capacitance or inductance in the circuit is
a good thing.


  #3 (permalink)  
Old February 25th 04, 11:06 PM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

Kalman Rubinson wrote:

Does anyone else recall a similar design from WirelessWorld in the
70s? Nixon? I'll look through my archives but I seem to remember such
along with crossover considerations.


I'd be interested in some background info on how they work - I dare say the
damping effects could be altered by changing the diameter of the opening and
the length of the tube, but I don't know what the effects would be in terms
of real-world numbers.


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


  #4 (permalink)  
Old February 25th 04, 11:27 PM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

Wally wrote:

My current sketch has a start diameter of
180mm, 40mm at the small end, and is 400mm long.


I've put a screen-grab of the sketch on my web site...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-01.jpg


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


  #5 (permalink)  
Old February 26th 04, 11:01 AM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

Here's an image showing a pair of the tubular cabs on stands, now with
tweeters mounted on top...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-02.jpg

The CD case gives an idea of scale. Here's another view, showing the full
stand, along with a version with the unit mounted on a bass enclosure...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-03.jpg


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


  #6 (permalink)  
Old February 26th 04, 11:10 AM posted to uk.rec.audio
Keith G
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Posts: 7,388
Default Nautilus-style midrange cab


"Wally" wrote in message
...
Here's an image showing a pair of the tubular cabs on stands, now with
tweeters mounted on top...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-02.jpg

The CD case gives an idea of scale. Here's another view, showing the full
stand, along with a version with the unit mounted on a bass enclosure...

http://www.wally.myby.co.uk/audio/sp...ExpoCab-03.jpg




Nice 'Show N Tell' Wally - keep it comin'

( A picture tells a 1000 words and all that.....)

:-)





  #7 (permalink)  
Old February 26th 04, 11:39 AM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

Keith G wrote:

Nice 'Show N Tell' Wally - keep it comin'

( A picture tells a 1000 words and all that.....)


Cheers, Keith. I think the fantasy is starting to settle down to a basic
design concept. Still not sure what to do with the bass cabs, though...

If I mount the tubular cabs on top, I don't have to mess with the crossover
frequency, making it easier to use a small-volume midrange cab. If I want to
go for the space-age spindly stands, then the mid enclosure becomes a
bass/mid enclosure and I have to get the dynamics right. (If I consider an
open-ended tube as a transmission line, the 400mm length I have at present
equates to something like 200Hz. Quite what significance that has with
regard to whether the bass cabs have to be on axis, I'm not sure yet.)

I like both designs. The main idea is to reduce the sheer space and bulk
that the present speakers take up - their positioning isn't ideal, and
they're a total pain to move around for when I want to optimise the
soundstage stereoferised imaging malarkey. So much so, that they simply
don't get moved. The little stand-mounted cabs would be much easier to move.
That said, the integrated units might not be so bad if they had handles
and/or some sort of glide pad feet.

A third possibility is to make the mid/top units detachable - mount them on
the bass cabs for casual listening, and shift them to the stands for serious
listening. The bass cabs would sit where the current speakers are - they'd
have a smaller footprint and would present the narrow face towards the
listener, making them dominate less.

The bass cab is just a rectangular box at the moment, but I'm going to look
into something a bit more swishy - I'd like to get rid of the parallel faces
to minimise the possibility of in-cab resonances, so the end result might be
an integrated setup that is easy to move, looks good, and doesn't visually
or physically dominate. More design-jockey CAD games to come... :-)


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


  #8 (permalink)  
Old February 26th 04, 07:39 PM posted to uk.rec.audio
Old Fart at Play
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Posts: 185
Default Nautilus-style midrange cab

Wally wrote:

I've been giving some further thought to The Great Speaker Rebuild Fantasy
and I'm presently looking into a Nautilus-style enclosure for the KEF B110
bass/mid drivers. To be clear as to what I mean, this would be a straight
pipe with a reducing internal diameter, the reduction being non-linear. My
current sketch has a start diameter of 180mm, 40mm at the small end, and is
400mm long.


Your transmission line should be about 1.5 m long for a B110.
It has a surprisingly low resonance.

--
Roger.

  #9 (permalink)  
Old February 26th 04, 07:52 PM posted to uk.rec.audio
Wally
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Posts: 395
Default Nautilus-style midrange cab

Old Fart at Play wrote:

Your transmission line should be about 1.5 m long for a B110.
It has a surprisingly low resonance.


Doesn't that depend on the required frequency response?


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music


 




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