member 'Oracle' Preference: Tonearm Effective Length 12-3/16" (308mm)
found a very interesting old post about TT,
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=18&t=58779&hilit=ar+arm+rega+conversion&sid=38d8985ef898716a0a955d54dcf969f0&start=120 .................................
pg 9, from member 'Oracle' about the preference for Total Effective 308mm (12-3/16") Arms
Re: Some Thoughts on Turntable DesignPost by Oracle_309 » 18 Jun 2013 15:53
"My thoughts:
first thanks to jraudio for his comments. In many ways I couldn’t agree more. Of course in some ways I may disagree, but those are due to personal experiences outside of the normal "audiophile" experience ;)
Regarding the subject of wow and flutter, it has been suggested that the eccentricity or improper location of the spindle hole of a record effects the total W&F more than most motor drive systems (that is, the centre hole location of a record in regard to the grooves of the record). To me this makes sense, but as I do not have the technology available to actually measure this I cannot confirm nor deny this.
Regarding the comparisons of different length tonearms from the same manufacturer, jraudio’s approach is right on (at least in my mind). There is a difference to the effective tonearm mass and that difference can have a profound effect on the calculated resonant frequency. Adding dampening is a stop-gap solution at best. Was it Einstein or Feynman who suggested that (usually) the easiest solution is most likely to provide the best solution to a problem? Ideally
NO dampening should be used, so material selection for tonearm construction must consider dampening
and rigidity properties. Differing geometries of tubing can also have a profound effect (such as single or double butted tubing, tapered tubing, solid beam or shaft, I-beam, etc.) on both of these qualities.
The cartridge/tonearm (materials and bearing), internal wiring, electrical connectors, physical coupling of the stylus to the cartridge body (whether direct as used in most moving coils, or indirectly as used in any customer replaceable stylus types), physical coupling of the tonearm mount to the plinth or sub-chassis (dependant on whether or not the turntable has a suspension or not) and phono pre-amplifier must be considered as a system, not as isolated parts. This is one of the reasons some people end up with something that simply sounds way better than it should (particularly if the complete system is somewhat "budget" or even terribly price matched. Please remember that it is not the amount of money being spent as an indicator of suitability but performance, this cannot be overstated) or conversely. I’ve heard many expensive turntables (for that matter many expensive complete systems) that have failed to thrill, while many much less expensive systems shine.
I make simple (but I think well performing) tonearms (but not commercially) and can attest to differences in the sound of different lengths, but I choose to make tonearms in the 308mm effective length. My reasoning is pretty simple. Here’s a list:
- proper alignment, or rather finer adjustments to the offset angle are easier to perform
- my material of choice has an effective mass of approximately 12 grams in this length
- my material of choice is incredibly stiff
- my material of choice is a simple, non tapered tube
- I use Grado cartridges almost exclusively (whether you like them or not is not the concern here, but most modern ones have a mass of 4.5 grams and a compliance in the 15-20 x10-6cm/Dyne range). The match of 17 grams effective weight (including headshell, wiring and cartridge screws), a compliance of 15-20 x10-6cm/Dyne and the 4.5 gram cartridge mass results in a resonant frequency of approximately 8-9 Hz
I have considerable opinions (again not verified by measurement but by purely subjective experiences) regarding the design of suspension systems, drive systems and the use of plinth materials. Just a preview: I do have a preference for all of the above, but this is not to say that there are not excellent examples that are contrary to my preferences."
linked to user name
http://www.vinylengine.com/turntable_forum/gallery/image/24663?sid=38d8985ef898716a0a955d54dcf969f0