It's not the length. It's how you use it.... if that's what she said.
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I remember reading somewhere that mistakes in setting up a 12 inch arm as compared to a 9 inch arm will be more "severe". I forget where I read it but it seems to make sense. A 12 inch arm is less tolerant of poor setup than a 9 inch. It started from Bob Graham's white paper originally posted in his website. Now it's gone in the Graham's current website but you can still read in this archive. __________excerpt_begins__________
QUESTION: Which is better - a 9" arm or an 11" arm? Doesn't the longer arm reduce tracking error?
Occasionally we've been asked to produce a longer version of our tonearm (for special applications) and proceeded to do extensive research into the matter. The "standard" 9.0 or 9.5-inch length, which is optimized for the vast majority of reasonably-sized turntables, has proven itself to have the best balance of geometric accuracy combined with optimal performance in the areas of inertial forces which, if too high, will adversely affect the performance of the cartridge. In the 1940's and part of the 50's, 16" transcription records required the use of the longer tonearm. You could hammer nails with some of those tonearms. They were massive and rugged but they didn't sound that good. Today's needs are totally different.
To begin with, a longer tonearm has at least two built-in disadvantages: First, its moment of inertia must be higher, since the cartridge is that much further away from the pivot. This extra force has to be counterbalanced, and this requires a larger balancing system. Even if the counterweight is near the pivot, it still must be larger than the equivalent member of a shorter arm. Remember that the moment of inertia is equal to the mass times the distance squared; therefore, increasing the length of a tonearm will also increase the moment of inertia significantly. With a higher moment of inertia, the arm, which must follow the laws of physics, will become more sluggish in responding to changes of direction and this can become a problem with warped or off-center records. If this problem were severe enough, and with certain delicate cartridge suspension systems, this could even become a strain sufficient to cause early cantilever failure.
There's another area where clarification and a discussion of proper arm length is definitely in order, and leads us to the second important difficulty with a longer tonearm and another question:
QUESTION: Cartridge installation is usually a fussy job and I don't like to do it. How have you addressed this?
In addition to being a tedious, eye-straining chore, normal cartridge installations are usually in error, often to a significant degree. This guarantees that, no matter how elegant the system is otherwise, proper reproduction of LPs is being compromised by geometrical errors. It simply is not sufficient to use a protractor to adjust the cartridge body. Often, cartridges don't have parallel sides and this makes it extra difficult to judge the coincidence with a pattern of lines printed on cardboard or mirrored plastic templates. And most important of all, many cartridges don't have the cantilever truly lined up with the cartridge body. In this case the installation misalignment is sent further awry by this additional cantilever error. It is important to note that even straight-line tonearm designs are not immune to this problem. It is just as easy to mis-align a cartridge in an air-bearing design as it is in a pivoted arm. In that case, the cartridge is traveling in a straight line, to be sure, but now it is in error across the entire surface of the record.
The patented Graham Engineering system solves this problem by providing a two-step process for precise cartridge alignment. We developed a system which ignores the cartridge body and the manufacturers alignment accuracy of the cantilever within the cartridge. Our method allows the user precise and repeatable accuracy in aligning the cartridge properly in the headshell, yielding virtually no significant tracking error. This is obtained first by locating the tonearm correctly on the turntable relative to the turntable spindle. A simple alignment fixture accomplishes this and assures correct overhang, one of the three interrelated dimensions that must be properly observed. The second step is to position the stylus tip exactly at the right place and at the right angle; this is accomplished with our removable arm wand plus a second installation fixture which uses the cantilever itself as a reference and totally ignores the cartridge body or other variables. Correct overhang is now locked in, as is the second important variable, the offset angle. (The third, effective length, is a combination of precise manufacturing tolerances and correct cartridge installation. Our tonearm parts are built to within 0.001" tolerances). This feature also is patented. As a result, and simply stated, greater tracking accuracy will consistently be achieved in the Graham Engineering tonearms than in any other pivoted design, regardless of length. If you think about it for a moment, you can see also that the likelihood of installation error in a tangential air-bearing arm is as great as standard pivoted arms.
But there's more: Only a precisely set up pivoted arm will have it's null (zero tracking error) points correctly located at a radius of 2.6" and 4.76". In achieving this, the tracking error over the entire surface of the record will be extremely small, the remaining error being of little or no actual consequence. On the other hand, an incorrectly installed cartridge will not only give rise to the null points being in error, but also will cause increased tracking error elsewhere on the record surface. The concept of a longer arm having a somewhat lower tracing error is only true if the cartridge is precisely aligned in the tonearm. If the cartridge is off at all in either the overhang dimension or the offset angle, then the longer arm will actually exhibit a larger tracking error than the shorter arm with the very same cartridge installation error. To help illustrate the point, here's a simple example: A 200-mm arm with a cartridge installation error of 0.4 degrees will have it's null points shifted by -2.707mm and +5.159mm. The same installation error in a 300mm arm will increase the error to -4.17mm and +8.14mm, a significant increase in misalignment . (An installation error of only 3-degrees - the same angle as 1/2 of a second or minute when you look at a wall clock - in a 300 mm arm will push the null points completely off the record. Good-bye, accuracy)!!
I'm stressing this point because there must be no doubt about this: there are no free lunches in physics (or other places, either, unless you're in politics). There is an interrelated and unalterable relationship between the various angles and dimensions in any pivoted tonearm. Merely making the arm longer or providing tangential tracking will not guarantee optimum geometric performance without some method of precisely setting up the cantilever and stylus on the phono cartridge. As we have seen, the longer the tonearm the more proper alignment becomes increasingly critical. Using the cartridge body as a reference is simply not accurate enough; the misalignment of cantilevers in the cartridge body is often several degrees, not to mention the inherent crudeness and inaccuracy in trying to view a paper or plastic protractor from above the headshell. Maybe Superman could get it right with his X-Ray vision; he could look at the cantilever right through the cartridge body. The rest of us can't see that way and we're left with a serious compromise. The patented Graham Engineering alignment system gives you back Superman's powers. No, you won't be able to leap over tall buildings, but you will always be able to have virtual X-ray vision when it comes to getting your cartridge aligned properly.
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