Thanks that was very interesting. In my own research I also came to the conclusion that Löfgren A is the best alignment. I have a Rega arm, and they come with Stevenson alignment by default. Inner groove distortion was an important topic for me, as I have some vinyl from the 80s where discs are used right until the label.
Note there is a calculator at
vinylengine that can graph tracking distortion (you need an account for that). I did that for my arm. The UNI graph is just an approximnation as I haven't found any maths/calculator for that (they probably want to sell their protractors), but
Mr. Fermer let it slip that the null points are 63.3mm and 112.5mm so I got close to that with an iterative method.
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Inner groove distortion was a problem for me for a long time, I generally found that the move to better needles (Shibata/Audio Technica Fine Line etc...) gave the most improvement. However there is another thing that really fixed this for me: I made my own protractor using
Conrad Hoffman's Custom arc template generator. I used Lofgren A, but an inner groove radius according to german DIN standard at 57.5mm.
As you can see from the graph, Lofgren A gives the lowest distortion:
- It doesn't start as high as the others
- In the middle section it doesn't rise as much as Stevenson and is still never higher than at the beginning
- And due to the small inner groove value of 57.5mm, by the time the distortion rises, the vinyl is already at it's end
If you had chosen a bigger inner groove radius, Stevenson might be of advantage, but to me these weird alignments don't really do it.
As I said UNI was approximated, so take that with a grain of salt. If I had to choose, UNI would be 2nd choice. Maybe it's better. I can
follow the logic of it all but until there's a free calculator I'm not gonna bother paying money for their custom protractors.
I think inner groove radius plays a much bigger role than people think. Sure modern records often stop very early and come with multiple dics, but when time comes and you have that disc that is used from beginning to the end, the distortion rise at the end doesn't justify the gains IMHO. You see how the distortion just escapes upwards towards the end of the disc.
Another thing to keep in mind. People always want to optimize for the best result under the best circumstances. However, that is not how industrial products are made. They sell you the quality they can most likely guarantee to be consistent. Some products are gonne be better, some are gonne be worse, but what they optimize for is not the best product they can probably make, but the best product they can make under bad circumstances, because that ensures you get most usable products that are "good enough".
What I'm trying to say here. I had to manipulate the calculator at vinylengine in 0.1 increments in both overhang mm and angle ° to get to the UNI graph. I bought a USB microscope (they're really cheap) to optimally align my cartridge
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and as you can see, that needle is not in the middle. Do I care? No. I arrived at this after a lot of tinkering, pushing the cartridge a little, fiddling with these screws that are not really screws (what the hell were they thinking?)
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And this was good enough for me. If you really want to find the optimal alignment, you need something that accounts for human error and just mechanical imperfections. Ideally you'd have a measurement disk and a computer programm, so you can run the whole disc through and then it tells you what to adjust. Do that a couple of times until there are no more improvements. I mean at the end of the day we're trying to minimize the distortion sum under a graph. That is a solved problem. While you're at it, it could create a file that you can put into your convolver so that the turntable has perfect output (at least frequency response). Maybe something like this exists.
Until then, Löfgren A with DIN 45547 inner groove for me, easily best bang for the buck.