Jon, some of your points here have been addressed in my response to
Walt. You are correct that the decreased mass at the reproducer could be
replaced by increasing the mass elsewhere in the tonearm. RCA did just that
in their "inertia arm" of the 1930s.
With regard to needle hardness, you must keep in mind the two completely
different principles of playing records with styli: The early acoustic
system REQUIRES the use of heavy tracking force. This was and remains
necessary because the record groove is required to perform WORK on the
needle to move the diaphragm against the mass of the air that it needs to
move in the horn. Significant power must be transferred to the needle which
cannot be accomplished at a light tracking force without gross mistracking.
The only way you can use heavy tracking force with the relatively soft
materials found in records is to spread that force out over a fairly large
area so that the PRESSURE (force per square unit of area) is kept down to a
low enough value that the record material does not permanently yield. This
means that the needle MUST have flatted contact patches with the groove wall
of fairly significant size.
Modern record playing technology, on the diametrically-opposed other
hand, is completely different. The power required to move the air mass to
achieve audible sound is provided by electrons and directed to the
loudspeaker thru the amplifier and its power supply. The amplifier needs
only the "instructions" of how to direct the electronic power. This means
that infinitesimal power (even NONE in the case of tracing the groove wall
with a laser beam) is all that is required from the groove. This allows the
use of a pickup that can track at (almost) arbitrarily low tracking force,
so long as that force is sufficient to transmit the tiny power required to
move the VERY SMALL effective tip mass (ETM) of the modern hifi stylus
assembly. The lower the ETM at the stylus tip, the lower the tracking force
can be with no untoward effects on the signal pickup. This assumes, of
course, that your tonearm is capable of holding the stylus in the groove
properly without a bias against one wall or the other (skating or friction).
Consequently, you can use the hardest material that you can find (diamond)
for the stylus since it presents vanishingly low pressure on the groove
walls, even though it is typically made to present very small contact
patches (necesary to reduce tracing distortion). And doing so means that
the stylus will retain its desired shape for MANY record playings. As you
can see, the physics of the two record playing technologies is VERY
different. You must keep in mind that you can't mix them up.
In case you may be wondering about now, Edison got away with using
diamond styli in his vertical recording systems because the shape of the
groove was rounded at the bottom and that curvature was designed to fit the
curvature of the playback stylus. This, together with infinitesimal,
temporary deformation of the groove bottom during play caused the stylus to
present a fairly large, elongated contact patch, thereby reducing the
pressure on the record groove. The small amount of groove deformation was
below the permanent yield point of the record material so that permanent
record damage was avoided.
As I said in the earlier response, the tip shape of the tungsten wire is
irrelevant. It conforms to the record groove in a matter of seconds when
first used. You just have to be aware that it is gouging the crap out of
your record while this is happening, so you want to use a junk record during
this shaping period. The harder the material used in the needle, the longer
it will take to shape it to the record groove. So modern harder materials
will probably never be a practical solution. And the problem of tonearm
tracking angle error further adds to the likelihood that a super-hard needle
would always be gouging your records even after it develops its flats.
Greg Bogantz
----- Original Message -----
From: "Jon Noring" <[email protected]>
To: "Antique Phonograph List" <[email protected]>
Sent: Saturday, February 09, 2008 12:05 PM
Subject: Re: [Phono-L] Victor versus Columbia big guns
> Walt wrote:
>
>> BUT, Greg made some other points along the way that must be considered
>> and I
>> will try to harness a few of them here for focus' sake. This means that
>> the
>> other not-so-short answer to the question would be, no, decreasing the
>> mass
>> of an acoustic soundbox will not necessarily result in a decrease of
>> lateral
>> inertia. How so? Theoretically, if the reduction in mass is compensated
>> for
>> by way of compliance, and if the tone arm pivot friction (not the tone
>> arm
>> weight) is not a factor (which I believe it would probably be in
>> actuality,
>> and even more so as the soundbox is made lighter and lighter) then the
>> needle movement of the soundbox would not suffer from decreased mass.
>> It's a
>> neat theory.
>
> If I understand the discussion correctly (and I may not!) a decrease
> in mass of the reproducer to reduce the vertical force on the record
> can be compensated for by increasing the mass of the tone arm (rather
> than the friction of its rotational movement). Since the issue deals
> with lateral movement and vibration and not vertical, shouldn't this
> work?
>
> About the tungsten needle issue, Greg, when you take the tungsten wire
> and snip it to lengths, do you finish the tips to have a particular
> shape/radius?
>
> Also, I've always been intrigued by modern materials for needles not
> available in the 1920's. For example, some titanium alloys are
> intriguing for their strength/hardness and *might* confer other
> advantages such as reduction in contact friction.
>
> Also, carbon fiber, even Kevlar, for use as a needle is intriguing.
>
> There is also tipping a steel or tungsten needle with another modern
> material.
>
> All in all, I think modern materials offer a lot of possibilities to
> substantially reduce shellac record wear while maintaining great sound
> reproduction in Orthophonic-like playback of shellac discs.
>
>
>> I would love to hear the "audible mistracking" you mention because I am
>> inclined to think that what you are hearing is something that phonograph
>> makers during the acoustic Victrola days knew would be a problem, and
>> they
>> therefore engineered the mass of soundbox/gooseneck combinations to stay
>> away from it altogether. That 135 to 140 gram figure representing
>> soundbox
>> weight is somewhat of a magic number. We tend to not think of tone arm
>> "skating" in regard to an early acoustic machine. But, as the tracking
>> force
>> is decreased then the issue of skating (among others) arises. Food for
>> thought: As the motor drives the turntable it rotates and develops
>> momentum.
>> When the stylus is in the groove of a record, the momentum will tend to
>> pull
>> the soundbox in the direction of the spindle. On a modern stereo skating
>> problems are pretty easy to hear and compensate for. But once the magic
>> number of 140 is lowered on an acoustic machine, things start to happen.
>> This is why I would have fully anticipated hearing some kind of audible
>> mistracking before I ever left the drawing board. But the mistracking
>> also
>> opens the door for groove damage.
>
> Yes, very interesting.
>
> Of course, one can compensate for skating by applying an anti-skating
> force, but now we are moving away from simply a reproducer change
> on an original phonograph. (Hmmm, calibrated friction of the horn pivot,
> or whatever that is called, may be sufficient. Walt mentioned this.)
>
>
>
>> p.s. I think you will find more than a dozen "of us". We are they who are
>> called "nerds" at MIT <wink>.
>
> An interesting side discussion is if we were to start with a clean
> slate, and were told to design an acoustic/mechanical playback system
> without need to be compatible at all with what's been done before, but
> may apply modern technology (except no electricity or electronics for
> playback; the recorded media though could be produced by any modern
> process and technologies, such as lasers), how would the design look?
> Would it converge to the designs of the early 20th century? Or would it
> be radically different? Obviously other requirements are needed to be
> able to converge to some final design...
>
> (I've been toying with the idea of a "mechanical tape" system as an
> example of something very radically different that as far as I know has
> not been commercially used for serious acoustic audio playback. The wave
> form would be "cut out" along the length of the tape so the edge of the
> tape would not be straight but follow the wave form -- I even see this
> approach being used for modern playback using lasers as a replacement
> for "vinyl" -- we can get stereo by cutting the waveform on both edges
> of the tape. Of course, the tape itself could be a totally different
> material and even different thickness, probably thicker, from magnetic
> tape... There are certainly variations on this general theme, and maybe
> someone here will think of the "killer" variation I haven't thought of
> yet.)
>
> Jon Noring
>
>
>
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