[Harp-L] Re: CR vs CM elements (long)

[HTownFess <Spschndr@xxxxxxx>]

As I understand it, the main difference is nomenclature: Shure's two
names refer to two aspects of the same process used to generate
electrical impulses, namely a magnet moving within a wire winding
coil. I'm more familiar with wire coils being spun within magnets to
generate electricity, but either one gets electrons moving thru the
coil.  Reluctance here is defined as "the opposition offered by a
magnetic substance to magnetic flux" where flux means a movement of
energy, and I think the "controlled" part simply refers to the
mechanical arrangement: a pin glued to the center of the mic diaphragm
pushes a right-angle lever armature that's anchored at one side of the
element interior, and the magnet is attached to that armature, whose
movement is only in a controlled direction within the magnetic field,
back & forth to create electrical AC signal.  The sound wave hitting
the diaphragm pushes the works one way for the + part of the AC
signal, the diaphragm springing back pulls it the opposite direction
for the - part of the signal, I think: the "reluctance" of the moving
magnet makes the electrons move in the appropriate direction.  The
magnet doesn't want to change its magnetism's orientation, that's the
reluctance, and pushes the electrons thru the coil instead.  I guess
the whole thing is an electromagnetic field, but the magnet is used to
generate a little electricity, rather than electricity being used to
generate magnetism.  It's the reverse of a permanent magnet speaker,
where a wire [voice] coil attached to the cone moves relative to a
fixed magnet when electricity is applied, and that might be the
easiest way to understand it, if indeed I do.

Incidentally, a crystal element uses the crystal itself as a fixed
lever arm that is pressed by the actuating pin, and under pressure the
crystal itself generates a positive electron flow.  I suspect Shure
switched to "magnetic" in the name for their element to stress that
they were using a magnet instead of a fragile crystal to generate
signal, as by 1958 people would have noticed that crystals do not like
humidity or being dropped, if they hadn't noticed that already during
wartime.  I mean, in addition to reluctance being too technical a
term, even when more people understood practical electronics.  The
downside of the magnet in that regard is that if you leave a CR/CM mic
too close to a big speaker magnet for long periods, say by leaving the
mic in the back of an amp, you can mess up the element's magnetic
field and weaken its output.

Dave Kott says if there is a crucial physical difference between CR
and CM, it may be that there is a small metal disc added where the pin
attaches at the diaphragm center on CRs.  How firmly the pin attaches
to the diaphragm may influence the mechanical actuation of the
armature/magnet combo enough to be audibly perceptible, and because
the pin attachment is glued on both CRs and CMs, deterioration of the
glue over time may be a factor also, one influenced by having that
reinforcing disc there to firm things up (I've seen CRs described as
more consistent than old CMs, though not necessarily better).  One can
also see a phenolic bobbin in pre-1955 CR windings, but 1955-58 CRs
have plastic ones like CMs and it's not a functional difference, apart
from when one is soldering the mic leads (phenolic doesn't melt as
easily).  I suspect that the condition of the actuating pin's
attachment to the diaphragm, its mechanical leverage on the armature,
and the condition/ease of movement of the armature/magnet combo have
the biggest impact on the tonal signature and output of that family of
element.  Working on all that seems best left to a qualified
technician like Chuck Gurney unless you're willing to write off
elements as part of the learning process.

Here's what Dave Kott says at greenbulletmics.com:

<<  I often get asked, "what is the difference between a CR and a CM"?
Well the black labeled CR's have an obvious difference in the material
of the winding bobbin. All the black label CR's have the phenolic
bobbin, and a very few white labeled CR's have them as well. CR's also
have a small cymbal shaped metal disc that Shure used to secure the
foil diaphram to the center pin of the magnetic armature pickup. You
can see it glued to the center of the diaphram of all CR elements. I
have never seen a CM with this disc. I do not believe that there were
ever any CM’s made with the metal disc on the diaphram.
          There is also a slight difference between the two as far as
how the winding wires were ran to connect to the lead wires of the
element. Many people like the tone of the CR's better than the CM's. I
think the two are very close in tone but the CR's have a slightly
grittier tone to them. This is likely attributed to the metal disc on
the center of the diaphram. Other than that, a white label CR and an
early 60's CM are basically identical. >>

I don't know whether I have actually explained the difference
accurately or clearly, or if someone else has posted an explanation
while I was writing this, but I used to wonder about it myself and the
above is how I understand it now.  Harmonica content: Decreasing the
voodoo quotient is ultimately better for learning harmonica.

Stephen Schneider

On Mar 16, 9:37 am, "mike wesolowski" <mwesolow...@xxxxxxxxxxxx> wrote
> Can anyone here clear up the difference between CM elements and CR elements?  
> Mike "Wezo" Wesolowskiwww.bluesworldorder.comwww.myspace.com/harpwezowww.megatoneamps.com
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