In article ,
Harold and Susan Vordos wrote:

"DoN. Nichols" wrote in message
...

[ ... ]

No---no baffles of any kind. I've had the woofers out of all of the
speakers to be reconed. They have a foam rim that eventually
deteriorates
and must be replaced. Heavy passages can actually tear them apart
completely, although mine have never gone that far.

I've seen that happen. A problem with pretty much *any* foam
rubber over time, and a foam rim does give significantly better
compliance than the tar-soaked paper or cloth ones with multiple pleats.


When I bought our second pair of S8R speakers, which I found listed in the
newspaper, they were being sold because of the foam failure, along with the
cabinets having been thoroughly abused. I wasn't concerned about the
woofers, knowing reconing wasn't a big issue. I was encouraged to know
that they were still the factory original foam, which was completely
different from the replacements, even from JBL. The price asked for the
speakers was a give-away for those that had an understanding of the value of
the components.

Sounds good to me.

What came as a real surprise to me was when I inspected the woofers in the
Paragon. While I've been talking about them as if they have the same
speakers as they S8 system, they are really the next generation of speakers,
so their identifying numbers are different. Instead of the 375 driver for
the midrange, they use a 376. As far as I know, the chief difference is
modern magnet technology as opposed to the old Alnico technology. The 375
drivers use a 28 pound magnet, along with a 4" ribbon wound voice coil.

Hmm ... how much were they able to reduce the weight with more
modern magnet materials?

In
JBL's literature they make reference to the 375 driver's ability to handle
explosive passages in stride. My personal experience in having owned
them since 1966 is they were too modest. Until such time that you've had
the pleasure to play with a set of these giants, I'm not sure you could
understand their capability.

I'd love a chance, but probably won't get it.

[ ... ]

O.K. My comment was because of your mention of watching the
woofer work with heavy passages.


The front cover is easily removed.

O.K. So no grille cloth while you are watching. :-)

They mount with four locating plugs
that are a simple press fit. One of my methods of enjoying the system is
to watch the speakers work on heavy passages. That's more likely to occur
when I'm listening to the system instead of listening to music. You likely
understand that nuts like me enjoy their systems in more than one way.
Sometimes the music is secondary.

I understand. Sort of like sitting there and watching a shaper
cut away. Relaxing in its own right.

[ ... ]

Dolores has no idea how to *use* them -- but she is good at
recognizing them. She finally found a cut-style knurler which did not
go sky high (compared to new price), and which fits my tool holders, so
I can start to experience that capability. (Well ... I do already have
one in the form of a long-armed 3-jaw chuck which works on the turret,
but that has a limited travel.

You'll have to enlighten me here, DoN. I've never used anything but the
roller type that impresses, and the old school stuff, not even a scissor
type.

O.K. Picture the rollers ground flat on the edges without any
bevel. Mount them at an angle to the direction of cut. And mount them
so the edge, not the center, is at the centerline between the workpiece
and the screw on which the cutter rotates.

This causes the edge of the knurl to actually *cut* material away,
as it is rotated by the workpiece, instead of being embossed into the
workpiece. This produces a much sharper feeling knurl -- and does not
increase the diameter with displaced metal. I'm looking forward to
experiencing the difference once it arrives. (We're in the period
between paying and receiving at the moment.)

This requires much less force from the machine's compound, so
there is less wear on the spindle bearings and the cross-feed leadscrew.

Obviously, this kind is useless for increasing a press fit,
since it does not displace metal -- it just removes it.

The other which you mentioned, the scissors style, has the
knurls on two swing arms, with the knurls touching the workpiece at
points 180 degrees apart (typically top and bottom). A bolt with a nut
connects the two arms, either between the pivots and the knurls (as what
I have), or it connects the two arms past the pivot point (more like the
pressure point of scissors, hense the name). This still embosses the
workpiece, but the force is taken by the lever arms and the bolt, not by
the leadscrew and the spindle bearings. Thus the wear on the machine is
much less.

Another variant on that style is offered by Aloris for their
quick-change toolposts. On that one, the upper and lower knurls are
held on arms which travel on a dovetail on the front of the holder. A
leadscrew with a knurled knob at the top, and left-hand threads on one
end, and right hand threads on the other end, moves the arms
symmetrically together or apart, so once you have set the height of the
tool, you can adjust for differing workpiece diameters without having to
change the height of the tool. (The scissors style, thanks to the
pivoted arms, is self centering in use.

You've probably experienced the principle of these latter two
tools if you have a T-bar knurling tool for your lathe's turret. Again,
the force is applied to pinch the workpiece between the knurls, and the
force is all contained within the tool, instead of being applied to the
spindle bearings or the cross-feed leadscrew.

Enjoy,
DoN.
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