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Thread: Different length tonearm why ?

  1. #1
    Join Date: Aug 2016

    Location: Kent UK

    Posts: 223
    I'm Paul.

    Default Different length tonearm why ?

    HI all

    Please excuse the silly question but I always wondered what the thinking is behind longer than normal tonearm

    Most are 9 inches but a few I have seen are 10 and 12 inches, what is the reason or thinking behind these longer arms.

    Thanks for any input in clearing up my confusion on this subject.

    Paul
    Current setup Thorens TD-160 Mk1 with Denon DL-110 MC Cartridge, Pioneer PD-8700 CD Player, Yamaha AX-592 Amp, Yamaha CDX-810 CD Player, Yamaha KX-480 Cassette Deck, Yamaha TX-492RDS Tuner, Monitor Audio Bronze 5 speakers, Van-Damme Cables throughout.

  2. #2
    Join Date: Jan 2009

    Location: Essex

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    I'm openingabottleofwine.

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    The 9" length is largely historic. Clearly tonearms must be longer than the nominal radius of the 12" LP, so a length of 1.5 times that distance was somewhat arbitarily chosen.

    There were at the same time 16" diameter LPs, so to play them a 12" long arm was used. (For example, the EMT927 turntable has a large enough platter to play 16" records, and is equipped with a 12" arm (305mm).)

    Obviously longer arms can be used with turntables having a smaller diameter platter, but there are trade-offs: longer arms will display lower tracking distortion, but have higher effective mass, whereas shorter arms will have higher tracking distortion but lower mass.

    Not all arms are 9" long, several 10" and 10.5" arms are available, and some believe this length is close to optimum and thus preferred.
    Last edited by Barry; 24-04-2017 at 10:46.
    Barry

  3. #3
    Join Date: Oct 2012

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    I'm Alan.

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    Good post Barry

  4. #4
    Join Date: Feb 2013

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    I'm Grant.

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    9 inches is enough for anyone
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  5. #5
    Join Date: Jan 2013

    Location: Carlisle - UK

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    I'm Ken.

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    The best path across a record is a straight line, with zero deviation for the stylus contact angle.

    A longer tone arm has a bigger tracking radius than a short one and therefore less deviation from the ideal path.

    Unfortunately going too long also has other purely physical obstacles when trying to achieve a good design, otherwise 3 foot arms would be in use.

    Simplistic explanation I know, but it was a simple question and deserves a simple answer.

  6. #6
    Join Date: Mar 2008

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    I'm inthescottishmafia.

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    Use a parallel tracker instead. :-)
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  7. #7
    Join Date: Jan 2013

    Location: Carlisle - UK

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    I'm Ken.

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    Quote Originally Posted by Ali Tait View Post
    Use a parallel tracker instead. :-)
    Now there's a thought!

  8. #8
    Join Date: Jul 2012

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    I'm Alex.

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    Quote Originally Posted by Qwin View Post
    The best path across a record is a straight line, with zero deviation for the stylus contact angle.

    A longer tone arm has a bigger tracking radius than a short one and therefore less deviation from the ideal path.

    Unfortunately going too long also has other purely physical obstacles when trying to achieve a good design, otherwise 3 foot arms would be in use.

    Simplistic explanation I know, but it was a simple question and deserves a simple answer.
    This 'less deviation from the ideal path' means that a longer arm would be less susceptible to distortion on the inner grooves of a record yes?

  9. #9
    montesquieu Guest

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    Quote Originally Posted by alcarmichael View Post
    This 'less deviation from the ideal path' means that a longer arm would be less susceptible to distortion on the inner grooves of a record yes?
    Yes.

    12 inch arms in general are also well-suited for low compliance cartridges which work better with a high mass arm. (Though to complicate things, not all 12in arms are higher mass than a heavyweight 9 incher like a Fidelity Research FR64S or my own Ikeda IT-345 CR1).

    The OP's question is actually an opener to the whole topic of arm geometry, overhang, mass, cartridge compliance, resonance and so on.
    Last edited by montesquieu; 24-04-2017 at 11:43.

  10. #10
    Join Date: Jan 2013

    Location: Carlisle - UK

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    I'm Ken.

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    Yes, less distortion at the start and end and in the middle.

    The only two positions on the tracking arc where the stylus is exactly parallel (tangential) with the grooves is at the two null points, everywhere else there is a small discrepancy.

    If you consider it as the overhang, before the first(outer) null point the overhang is shorter than ideal.
    Between the outer and inner null points it is longer than ideal and after the inner null point it is again shorter.

    The amount it is out is directly proportional to the length of the arm, longer is less adrift.

    The points about mass etc raised earlier, are valid, so its not all plain sailing by just using a longer arm, so as with most things, you have to decide where you want to compromise.

    I used to have problems with inner groove distortion, that just wouldn't go away, no matter which alignment scheme I used, which is why I now use a linear tracker.
    Last edited by Qwin; 24-04-2017 at 10:45.

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