curved or straight tonearm?
On Mon, 26 Sep 2011 07:06:39 -0700, Dick Pierce wrote
(in article ):
Audio Empire wrote:
On Sun, 25 Sep 2011 13:46:02 -0700, Rich Teer wrote
(in article ):
On Sun, 25 Sep 2011, Edward wrote:
i'm looking at seriously upgrading the turntable situation for my "at
home" stereo set up. serious in the sense of quality and that i would
like this to be the last turntable i buy. maybe...
so my question is this: do i go with a curved or straight tonearm??
remember, this is for my home set up and not for taking out of the
house and DJ'ing with.
I don't think the shape of the arm is important per se, provided the
offset angle ends up being correct. That said, all the better arms
I can think of off the top of my head are straight, so I guess there's
your answer!
What TT are you planning to use, and what's your budget? (What cartridge
too?)
The shape is not important, PER SE. What is important is the position of
the
stylus on the record with relation to the arm pivot point. Curved arms
allow
for a more ideal tracking angle with a shorter distance from stylus tip to
pivot point, I.E., a physically shorter arm tube.
This is a common myth, but a myth, nonetheless.
Consider the following gedanken: Take ANY curved arm
shape you can imagine providing a "more ideal tracking
angle." Now, without changing the orientation of the
cartridge/stylus at all, draw a straight line between
the mounting point of the cartridge and the main
pivot of the tone arm, and replace the curved tone
arm with a straight tube follwiong that line. You
now have two different toen arms: one curved,
one straight, and BOTH provide the IDENTICAL "ideal
tracking angle."
Basically, what this tells us is tracking geometry
is not intrinsically linked to the shape of the tone
arm.
Which is what I said.
Beyond that, shape IS important for a number of
reasons.
All other things being equal, a straight tone arm
will have lower mass and higher mechanical stability
than a curved tone arm, and lower mass can be argued
as being a good thing.
Except when low-mass arms are combined with low compliance cartridges, and
make no mistake, there are plenty of high-end cartridges which are low
compliance.
Even for those that might claim
that for a given cartridge, a higher moving mass is
required, that is trivially achieved by adding mass to
the mounting of the cartridge. It's MUCH more difficult
(read: it's pretty much impossible) to remove mass from
an arm whose mass is too high for a given cartridge.
That's why matching arm to cartridge is so important. The best way I know to
render a large portion of a real-world record collection unplayable is to
afix a fairly low mass arm with a really high-compliance cartridge. The best
way I know to make one's records sound bass-heavy and muddy is to couple a
low mass tone arm with low compliance cartridge. And the result is FAR from
trivial in either case.
One of the legitimate reasons for a curved arm is to
facilitate the design and implementation of a removable
headshell, along the lines of the original SME arm.
Here, a small machining facility (Small Model Engineering,
to be precise), had limited resources available. It used
a an existing 4-pin connector designed for another purpose
and used it to come up with a workable removable headshell.
Because the connector had to be straight-on, that dictated
the requirement of a curved tone arm in order to achieve the
offset angle required for proper tracking. Then, the use
of the size, material and wall thickness for the tone
arm tube put severe constraints on the amount and radius of
the bend in the tube before the tube ran the risk of collapse.
Finally, the the connector's mechanical requirements dictated
where thebend could occur.
True enough.
The net result was that the shape of the old SME 3009 arm
tube was a compromise forced on the designers by the available
matericals and techniques on hand at the time (1950's).
It did, howver, establish a significant precedent for further
high-end arm design, a precedent whose origins were largely
lost in the usual high-end mythology and hype.
Subsequent justifications for curved tone arms, principally
by a number of Japanese manufactures in the 1970's, was that
a curved arm of the right profile could be statically
balanced by distributing the mass equally on either side
of the "imaginary" straight line connecting the pivot to
the stylus. But that same balance can be achieved, if it
is important, but simply using a straight tube along that
same imaginary straight line.
Yep.
And, it's also interesting to note that for those arms where
this rtype of balance is crucial, i.e., unipivot arms, two
of the more pupoular unipivot arms, the A&D/Monks and the
Decca, BOTH used straight arm tubes with offset angles
implemented right at the headshell/mounting. The A&D "solved"
the quick interchangeability issue by allowing, through
its unique use of mercury-bath contacts, completely removable
arms, while the Decca solved it by simply not having quick
interchangeability.
Bottom line:
* Correct tracking angle idoes NOT require curved tone
arms.
That's correct.
* Any profile other than a straight line MUST have more
moving mass, all other things being equal.
Also correct. But to say that low-mass in a tone arm is always desireable is
overly simplistic and not correct. The arm and cartridge must work together
as a synergistic system. Record players are mechanical systems and mechanical
systems have a number of criteria to meet before they can be considered a
successful solution.
Tone arm shape IS important, but the reasons often given
are irreleventa or just plain wrong.
Mostly they're irrelevant as there are, in engineering, usually more than one
path to a satisfactory solution.
Which is better: depends upon your requirements. Do
you need a commonly-available removable headshell
scheme (i.e. SME-type)? If yes, you're almost certainly
stuck with a curved tone arm? Do you require the absolute
minimum moving mass for your high-compliance cartridge?
Of yes, seek out straight tone arms with non-removable
headshells? Is achieving the correct tracking angle
important? If yes, arm shape is irrelevant. If no,
arm shape is still irrelevant.
Can't argue with your last statement.
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