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Curved and Straight Tonearms

Over the last 40 years I have owned 3 turntables. An entry level Dual from the '70's, a Denon DP-52F (which I still use in my office system) and a Rega P3-24 which I currently use in my main system. All of these turntables have had straight tonearms. I am planning on upgrading my Rega in the near future. Having started my research, I have noticed that some well reviewed turntables have curved 'arms. My question: What are the advantages/disadvantages of each, sonic or otherwise? Thanks for any input. 
ericsch
dover
2,262 posts
 
lewm
5,479 posts
07-04-2017 1:34pm
Thank you for that input, Raul.
And thanks for your response too, Nandric.
I don't have the FR64S owners manual. So I assumed that the lateral weight had to stay mounted on its post; I therefore have shoved it up against the pivot as far as it will go, on the assumption that my turntable is level AND that even in the extreme position, the lateral weight is doing something greater than zero to compensate for the J-shape, assuming that is a good thing to do.
Lewm,
Please read my previous post to addressed Raul.
Like Raul you clearly do not understand how to set up the FR64S correctly. The neutral position for the Lateral Balance weight is 5mm in from the end of the shaft. By "shoving the lateral weight up against the pivot as far as it will go" you are running the arm out of balance and your set up is compromised. In a good quality system this should be clearly audible. I would suggest you review the set up of your FR64S again to ensure that you are hearing the FR64S is it was intended to be used.  


nandric's avatar
nandric
4,086 posts
 

Dear Dover, ''there are many ways to skin a cat'' but this philosophy

does not apply for the lateral balance by FR-64. I have no idea why

this distance of 5mm is mentioned in the user manual. By using the

expression ''Apprrox 5 mm'' the manual is as ''exact'' as this

prescription. Not as curious as Raul's ''leveling the TT'' with the

lateral balance but it is difficult to judge which ''advice'' is worst.

BTW why should anyone use ''approximation'' when the correct

method is describd in the same manual? The possible exception

is our ''exceptional Lew'' because his plinths are exceptional qua

weight. Those can't be lifted (grin).

''The less the better or the heavier the better'' are both curious

rules. Those are probably ''deduced'' from Aristotelian ''essences''.

There is this principle called ''reduction of the complexity'' but this

has nothing to do with Aristotelian ''essences'' because he was

proven wrong by Galileo reg. physics and  by Frege reg. logic.

I also missed your opinion about shape. I like Lew very much but

I think that he and, more in partucular Raul, are/is wrong with

their ''J'' guess. Compare the (old) SME arms with FR-64 so

even blind people will see the difference. Looking at the back

side tube by FR-64 one can see the (slight) deviation to the

right seeing from above. To get the innicial balance between

the bearings the ''S'' shape is needed. The ''J'' kinds always

need lateral weight for this purpose. The later Ikeda arms can

obviously do without.  This to me means ''S'' shape,

helomech
1,722 posts
 
Wow.....
nandric's avatar
nandric
4,086 posts
 

helomech, You are sportmanlike if your comment is meant as I would like to understand it (grin).

dover
2,262 posts
 
Nandric,
There is a lot of myth in audio. The most common theory is that S shaped arms evolved from J shape to place the horizontal centre of mass of the arm tube/cartridge perpendicular to the 2 horizontal bearing points at the arm pivot closer to the centre. If you look at the J shape it places a high mass further to the inside and loads up the inside vertical bearing relative to the outside vertical bearing. As you lower the cartridge onto the record with a J shaped arm it will try and lift the inside bearing. With knife edge bearings such as the early J shaped SME's this means the inside bearing is unstable. Lateral balances are provided in some vintage arms to help correct the offset centre of mass of the arm tube/cartridge.  

Straight arm tube arms are more common now, but a key point is that along with straight arm tubes most modern gimbal bearing arms now have offset bearings; that is, the vertical bearings at the tonearm pivot have an offset angle that matches the optimum offset angle of the cartridge determined by the pivot to stylus distance.

Most vintage arms including the FR64S do not have offset bearings.
The disadvantage of non offset bearings is that when the arm goes up and down a rotational force ( twisting ) is applied to the cantilever - the use of a lateral balance never eliminates this effect, but it can reduce it somewhat.

The lateral balance on the FR64S has multiple implications, because apart from providing adjustability to the inside cancelling force, the distribution of mass around the bearing housing alters the loads on the bearings, and ultimately the forces, both rotational and lateral, on the cantilever as the arm moves up and down and back and forth on eccentric records.

For this reason rather than second guess ALL the engineering considerations that have gone into the design of the arm, one should set an arm up as per the manual in the first instance. We have a saying "a bad workman blames his tools" - this is so very true of poor tonearm and/or cartridge set up that all too often leads to indifferent results. 

     
     
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