Thanks for the replies, I'm wondering what is considered "medium to low" compliance? |
Alun, here's some reasonably concise information from the SME web site about the ranges for high, medium and low compliance, and why it all matters: With one compliance unit (lcu) equivalent to l x l0-6 cm.dyne, a low-to-moderate compliance design has a relatively stiff stylus cantilever suspension in the 8-15cu range. The medium compliance range runs approximately from 15 to 25cu, while very softly suspended cantilevers fit in the high compliance range, from 25 to 50cu. In the bad old days when low frequency trackability was just about the only well-regarded performance parameter, cartridge compliances over 60cu were achieved, the Empire ZX1000, for example...
Some readers may be wondering why the arm mass needs to be matched to the cartridge compliance. It's a long story, but was thoroughly researched by Shure. Briefly, the total moving mass, made up of the cartridge and that of the arm seen by the cartridge - the effective mass' or moment of inertia - in combination with the spring of the cartridge cantilever suspension results in a mechanical resonance, capable of oscillating or vibrating as the groove is dragged past the stylus. Such a resonance will result in an undesirable, non-musical low frequency output from the cartridge, and worse still, it can impair the stability and the tracking behaviour of the pickup. The worst effects can be ameliorated by some form of arm damping, perhaps by means of a viscous fluid filled dashpot, which reduces the amplitude of the rise in output at resonance, but the alternative, of applying damping to the cartridge suspension, results in even worse tracking on difficult recorded passages.
If the arm/cartridge resonance is on the high side, above 15Hz, say, it will begin to affect sound quality in the bass. Conversely, the tracking is secure and recovers quickly from vibration or shock. If this resonance is too low, lower than 8Hz, the cartridge wobbles alarmingly and is unduly excited by minor warps - Shure's work showed that this has a maximum content around 6Hz. Close examination at such a condition will show the pickup perpetually vibrating at its resonance frequency. A further problem arises with the best-sounding turntables, which generally employ a floating, spring-suspended subchassis. These chassis systems have their own resonances in the 2.5Hz to 5Hz region. For arm/cartridge resonances below 8Hz, the proximity is too great and unwanted energy coupling often occurs, worsening stability and increasing the overall turntable flutter, an unpleasant rapid variation in musical pitch.
Thus 10-12Hz is the ideal region in which to place the arm/cartridge resonance, requiring matching of the arm mass with the cartridge compliance; arm damping will help to extend the range of compatibility, but only so far. Arm damping should be used at a sensibly low level, just enough to take the edge off the resonance magnification factor or 'Q', reducing it from 15 to 4-8, say. Excessive damping adds additional loading to the stylus tip, unbalancing the left and right groove contact forces and disturbing the channel balance as the damping attempts to prevent the cartridge from following minor warps and related disc eccentricities.
http://www.sme.ltd.uk/html/revv.html And Galen Carol Audio also has a good explanation at their web site: www.gcaudio.com/resources/howtos/tonearmcartridge.html. |
Thank you Rushton,those were good reads, however I'm a little confused as the effective mass for the ET tonearm is given in two planes, vetical (7gram) and horizontal (25-35 grams). If the vertical is the mass I use to help, it goes against the low compliance figures that Bruce Thigpen has recommended.
Confusing huh! |
Alun, confusing is right! The horizontal mass is what creates the challenge for cartridge matching and why a medium-to-lower compliance cartridge works best in the arm. And, with respect to our more mathmetically inclined forum members, I think it's easy to get *too* caught up in the compliance calculations. There's a lot more going on in the cartridge/arm interactions, and a lot more going on with the cartridge itself, than is reflected just in the compliance/mass calculation data. My philosophy has always been to use this piece of information to make sure I don't have a major mis-match, but not to obsess over it. The only real test is going to be how a given cartridge actually sounds in the arm, to the point of the original question you posed.
To echo Thom's comment on his experience, I expect that any medium-to-fairly low compliance cartridge will work just fine in the ET arm, choose based on the sonic characteristics important to you and the rest of your system.
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Yep! Your right, I would really love to hear a bunch of different cartridges on my setup, but I have to depend a little on reviewers opinion. A nice idea in a store would be to have cartridges already setup on armwands to interchange semi rapidly! |
