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9" Arm = 12" Arm?!


There is much kerfuffle nowadays about having a longer tonearm. Putting the psycho analytics of such audiophile preoccupations to the side, we need to ask ourselves why we would want such a potentially unwieldy thing swinging about our pivot points.

The obvious answer, of course, is a longer tonearm will allow the stylus to get closer to tracing a linear path across the record, decreasing tracing error and its attendant distortions. Read Do You Swing Long and Large? for more on this issue and the trade-off we make by getting "enlarged".

Whether the arm is long or short, it still needs to traverse the distance from the outermost groove to the innermost groove of the record. A shorter arm will result in this distance being covered by a shorter radius - a tighter turn. A longer arm will have a longer, more graceful arc that is "straighter" over that same distance than the tight-turning shorter arm.

But what if that distance from outermost groove to the innermost groove in my record collection is REDUCED? What if the innermost groove on newer pressings has been scooting closer to the outermost groove over the years? With less terrain for the tonearm to traverse, should we not re-calculate the ideal path any pivoted tonearm should follow to achieve optimal alignment?


The International Electrotechnical Commission (IEC) determined standardized values for record geometry - including the innermost and outermost musical grooves a record should have - in the 1950’s and 1960’s. These figures are 146.05mm (outermost) and 60.325mm (innermost). Most tonearm manufacturers design their products for ideal alignment of the stylus/cantilever assembly based upon these standards. However, we have found that recording engineers have been cutting vinyl further and further away from the center of the record for a few decades and that this may offer an opportunity for those with newer record collections to decrease playback distortion.


WAM Engineering has taken well over 1,000 measurements of the innermost groove radius and has found some statistically significant results. The dataset includes classical, rock and jazz records from 1950 to 2018.


Findings: from 1990 and later record productions:

  1. All genres show significant increase in innermost groove radius versus pre-1990 records

  2. Less than 5% of rock music records have innermost groove radius of less than 68mm

  3. Less than 3% of jazz music records have innermost groove radius of less than 68mm

  4. Less than 1% of classical music records have innermost groove radius of less than 68mm

  5. Nearly all 45rpm 12” records of reissued titles have innermost groove radius larger than 68mm



So glad you asked.

If the playing distance (from start to finish of the musical content) has decreased, then we can recalculate our two points of perfect cantilever tangency (the null points) and bring them closer together which results in lower average tracing distortion across the entire playing surface. Yay!


The reasons you might choose the “Newer Record Collection” arcs for your setup over the standard IEC ("Older Record Collection" arcs) are as follows:

  • Your record collection is predominately produced in 1990 or later

  • Your pressings of music recorded before 1990 are predominantly reissues pressed at 45rpm

  • Playback distortions decrease the same as you would get from changing a 9” tonearm for a 12” tonearm and you wish to optimize playback for the majority of your records


Note: the downside of choosing the Newer Record Collection arcs is that ONLY those grooves LESS than 68mm from the center of the record will have higher levels of tracing distortion than you would get if you had aligned to the Older Record Collection arcs. For most people, the percentage of playing time you have that is less than 68mm from the center of the record is likely in the high single digits at most.


If you aren’t sure – stick with the Older Record Collection arcs!


Use the WallyTractor Universal's spindle to pivot ruler and centering jig to measure a record's innermost groove for yourself. Use the little “nipple” on the opposite end of the centering jig to find the spindle hole in your record.


IMPORTANT: We encourage you to experiment between “Older” and “Newer” alignments to listen for the differences but keep in mind your vertical tracking force (VTF) will change when you move the cartridge forward and backward and you will have to compensate for this by adjusting the counterweight.

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