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In Reply to: RE: Heads Up! posted by John Elison on June 06, 2017 at 08:24:38
I too have a Fidelity Research FR-54 arm on my turntable (Sony 2251). It's a very light arm with great bearings. Chicks dig it. It would seem to be incongruous to use an approximately 1/2 ounce headshell on such a nimble arm. Then, there's the issue of the counterweight position. The result is that a great, light arm is turned into a heavy, slow-moving arm reminscent of 1950s/60s console systems, and contributing to faster record groove wear.
Maybe it's just me.
The Fr-54 is a medium mass arm at 16gms.
I think your theory is wrong!
> It's a very light arm with great bearings.
You might be right about its bearings but you are dead wrong about its mass. It has medium/high effective mass. Therefore, it's a heavy arm with regard to effective mass.
The SME III and the Infinity Black Widow are examples of light arms or low mass arms. The SME 300 Series are considered medium mass tonearms. In other words, tonearms with effective mass in-between 9-grams and 14-grams are considered medium mass tonearms. The FR 54 has effective mass of 16-grams and is therefore verging on high effective mass. It is not a light arm.
Do you know how much the FR 54 headshell weighs? If you have a digital scale perhaps you can weigh it. I doubt the new headshell is more than 6 or 7-grams heavier than the original FR 54 headshell. At any rate, AudioSoul is using his FR 54 with a low-compliance Denon DL-103 cartridge. Many inmates here believe that the DL-103 sounds best in high-mass tonearms so it should be a good match for the FR 54 and the new headshell.
As far as I can tell, reality and theory always agree with each other as long as you use the correct theory.
John, what was the source for your break down of the three categories by mass? I'm not disagreeing, but this is something I've wondered about.
For example, to say that 9-14 effective mass is medium seems to be a fairly narrow range. Particularly if 15 and above is then high mass, given that range can cover up to 25 grams or perhaps higher.
Common headshells can weigh at least 9-10 grams which must have an affect.
"The piano ain't got no wrong notes." Thelonious Monk
My source is basically common sense. The lowest mass arm that I know of is the Infinity Black Widow with effective mass of 3-grams. Another low-mass tonearm that everyone accepts to be low-mass is the SME III with effective mass of 5-grams.
The SME V, the Technics tonearm and Rega tonearms are all accepted to be medium mass tonearms. These have effective mass in the range of 10 to 12-grams. Therefore, the division between low-mass and medium-mass is somewhere in-between 5-grams and 10-grams.
I think most people would consider a tonearm with effective mass of 20-grams to be a high-mass tonearm. Therefore, the division between medium mass and high mass must be somewhere in-between 12-grams and 20-grams. I chose 15-grams.
However, regardless of how you choose the divisions, a tonearm like the FR 54 with effective mass of 16-grams would never be considered a light arm or low-mass tonearm when 12-grams is clearly defined as medium-mass.
> Common headshells can weigh at least 9-10 grams which must have an affect.
I'm not sure what you're getting at. The headshell is always included in the effective mass of the tonearm. For example, the weight of the Technics headshell is 7.0-grams without cartridge wires and between 7.5 and 8.0-grams with cartridge wires, depending on the specific cartridge wires being used. I just weighed a Technics headshell and several different types of cartridge wires.
The effective mass of a headshell is actually slightly less than its total mass because effective mass is the headshell's moment-of-inertia about the tonearm pivot divided by the square of the tonearm's effective length. Therefore, a 7.5-gram headshell might have effective mass of only 5.75-grams, depending on its mass distribution. Consequently, a Technics tonearm might have effective mass without its headshell of about 6.25-grams.
Do you know the weight of the FR 54 headshell? Whatever it weighs, the tonearm's effective mass of 16-grams includes the headshell.
If a common headshell weighs 9-10 grams that would be a major part of a medium mass arm range of 9-13 grams. Of course I understand there are many lighter headshells.
The whole subject of tonearm mass is more complicated than what I remember from HS physics. :^(
"The piano ain't got no wrong notes." Thelonious Monk
The effective mass of any tonearm is simply its moment-of-inertia about its pivot point divided by the square of its effective length. The difficult part is determining a tonearm's moment-of-inertia because its mass distribution is so nonuniform. The only accurate way to determine its moment-of-inertia is to measure it.
The advantage of effective mass is that it allows us to compare the inertia of different length tonearms directly whereas their moments-of-inertia are not directly comparable. Two different length tonearms having the same effective mass will react identically with cartridges of the same mass and compliance; however, their moments-of-inertia will be different. The longer tonearm will always have a larger moment-of-inertia than the shorter tonearm even though their arm/cartridge resonance frequencies will be identical when using the same cartridge.
Well, heck, if it's that damn heavy, I'm gonna throw it in the trash.
I think it's light, and that's what counts. ;) Yeah, I know there's weightless arms out there for a premium price. But I picked up this gently-used TT/arm combo back in 1977/78 for something like $50, and I'm still happy with it. All's I know is that, if I look at it cross-eyed, it'll skip a groove, and if I don't have a decent grip on the fingerlift thingy, it'll bounce right out of my hand and go skipping across the record and I'll have to get my spare stylus.
Still, a half-ounce headshell?!
Anyway, a moment ago I had some inertia. Now I'm in a stationary orbit. (That's a physics joke. Made it up all by myself.)
Edit: Btw, I have a digital scale. It says I weigh 178. Fortunately, the digital scale at my doctor's office says I weigh 174. I'm going to the post office today, and might take my headshell with me.
In or out of orbit, we all have inertia. It's the Law.
Not exactly sure how fast I'm going, but when I'm sleeping or watching "the news", I feel like I'm stationary.
Maybe I should investigate further.
Watching astronauts float around in the ISS, you'd never think that they're going 18,000 miles an hour.
'Course, you'd also never think that the Russians are their only way to get home (with a valid passport).
you and I are traveling at around 600 to 800 mph all the time. Speaking for myself, I'm exhausted.
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