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Re: TT acoustic coupling

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  • Robert Greene
    The Moerch arms(DP6 and UP4) have interchangeable arm tubes that enable one to chose the mass one wants and match any cartridge correctly. Cf the reviews on
    Message 1 of 111 , May 31, 2008
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      The Moerch arms(DP6 and UP4) have interchangeable arm tubes that
      enable one to chose the mass one wants and match any cartridge
      correctly. Cf the reviews on www.regonaudio.com
      The one about the DP6 also contains how to calculate resonant
      frequency

      http://www.regonaudio.com/Morch%20UP-4%20Pickup%20Arm.html

      (It would be nice if people read these things! No one here really
      ought to be saying that they are unsure if any low mass arms are
      still available!!)

      REG

      --- In regsaudioforum@yahoogroups.com, "Tom Mallin" <tmallin@...>
      wrote:
      >
      > I believe it is today accepted (based on scanning electron
      microscope photos of vinyl record groove wear--and this was only new
      news back in the 1980s perhaps), that what causes irreparable damage
      is a stylus which loses contact with the groove wall, not a bit more
      downward force. Vinyl is resilient and although initially deformed
      by the passage of the stylus, recovers after a few hours. But if
      the stylus careens off the groove wall due to mistracking, then
      permanent damage can be done. Mistracking occurs more the lower the
      tracking force is. Thus, since the 1980s, the rule of thumb has
      been to operate cartridges at or near the top end of the
      manufacturer's recommended tracking force range, while keeping your
      records and stylus as clean as possible, and adjusting tracking
      geometry and antiskating force as well as possible, and using line
      contact (rather than the old spherical or elliptical) stylus
      shapes. The idea that low tracking force creates less record wear
      is just nonsense, or at least has been regarded so for decades now
      among vinyl afficionados.
      >
      > Again, the resonant frequency of the arm cartridge combination is
      governed primarily by the cartridge's cantilever compliance and the
      tone arm/cartridge effective mass. If you are using a high
      compliance cartridge, then you should use a low mass arm to keep the
      resonance in the ideal 10 to 13 Hz region. Most modern cartridges
      are moving coils and are not really high compliance. Thus, most
      modern tone arms do not have low effective mass. One alternative is
      to use a well damped tone arm, such as the Townshend models. The
      damping reduces or eliminates the effect of the resonance. My
      experience with damping at the cartridge, a la the brushes on later
      model Shure V15s, was not positive since the brush produced severe
      groove echo effects.
      >
      > When there were a lot of low mass tone arms, some of the best were
      the Mayware Formula 4, the Grace 707, the Infinity Black Widow.
      There may well be modern low mass arms, but if there are, I can't
      think of any offhand. Those using modern moving magnet cartridges
      with relatively high compliance in modern medium to high mass arms
      probably are not going to be getting resonances in the ideal range.
      >
      > Much of this is today a "black art" since you rarely see
      specifications for effective moving mass in a tone arm these days,
      much less test report measurements. I think that most folks,
      including tone arm and cartridge manufacturers, really aren't aware
      of the mechanical resonance issues which all serious vinylphiles
      knew as common sense back in pre-CD days.
      >
      > >>> rooknrol@... 5/30/2008 4:53 PM >>>
      > Tom and Fred, (I'm continuing this under the new thread, not
      ignoring your message Fred)
      > this is about the usefulness of soft suspension and the usefulness
      of spectrum analyzers it
      > isn't a "please help me" thread OK, I don't have your expectations
      of vinyl Tom 40Hz is fine
      > for me, as I say there's nothing below that anyway so subwoofers
      (if I used them) could only
      > be excited by warp and rumble which is not something I want.
      >
      > My interest in tracking force arises this way. If you want low
      tracking force you have to use
      > high compliance, the two are joined, it is physics at work. On the
      other hand if you accept
      > higher tracking force you can use lower compliance. The primary
      variable is tracking force,
      > complaince is the way to get it, high compliance = soft mounting =
      low tracking weight. The
      > resonance is a secondary effect, having secondary importance. I am
      interested to know what
      > weights were or are in use by people that are using your bomb
      proof suspensions. That tells
      > me how they rank record wear as a factor, and I put record wear
      reduction ahead of
      > resonance suppression, that's a choice we are all free to make, I
      want minimum tracking
      > weight for minimum wear and if it costs me some of the empty 20Hz-
      40Hz octave that's a
      > good trade off because I'll still be listening to these discs many
      years hence with the benefit
      > of low wear. My reading leads me believe 1 gram is the target for
      zero wear and I'm currently
      > using 1.25.
      >
      > Tom you said also
      >
      > "and the large cone excursions caused by tracking LP warps with a
      tonearm/cartridge
      > resonance which is down too low and thus in the LP warp/wow
      frequency range."
      >
      > The resonance is vertical mode at about 20Hz this is higher than
      the lateral and well above
      > the warp/wow range in fact it is rejecting warp/wow better for
      being up at 20.
      >
      > I'm curious what you did with your vinyl collection, did you sell
      it?
      >
      > Ted
      >
      >
      > On 30 May 2008 at 15:50, Tom Mallin wrote:
      >
      > >
      > > P.S.: With warp/wow resonance down at 5 Hz and the tonearm/cart
      resonance down at 10 to 13
      > > Hz, that's why the turntable's spring suspension needs to be
      tuned way below the audio band.
      > > The spring suspension acts as a low-pass filter.You don't want
      the spring suspension resonance
      > > interacting with audio signals, the tonearm/cartridge resonance,
      or the warp/wow region. The only
      > > place left to tune the suspension is very low, well below 5 Hz.
      Count the bobbles per second as
      > > you excite the springs with a push. They should be at 3 Hz or
      below.
      > >
      > > >>> tmallin@... 5/30/2008 3:37 PM >>>
      > > Varying thetracking force has absolutely no effect on acoustic
      feedback sensitivity of a
      > > turntable/arm/cartridge set up.
      > >
      > > Varying the tracking force also does not significantly effect
      the arm/cartridge resonance in a
      > > dynamically balanced arm where tracking force is applied by way
      of a spring force without moving
      > > the counterweight.
      > >
      > > Even with a statically balanced arm, where you apply tracking
      force bymoving the counterweight
      > > a bit fore or aft, this usually has only a very small effect on
      the resonant frequency since the
      > > usually small movement of the counterweight fore and aft
      required to vary the tracking force from
      > > the low to high end of a given cartridge's range of tracking
      forceoperation only slightly affects
      > > thetonearm's effective mass or moment of inertia. Similarly, the
      small movements of the
      > > cartridge in the headshell necessary to precisely align it for
      min/max tracking errorby whatever
      > > formula you choose doesn't vary the effective mass of the system
      very much.
      > >
      > > The tonearm's basic construction and the compliance of the
      cartridge's cantilever are the
      > > important factors in determining the resonant frequency of the
      tonearm/cartridge system. Most
      > > expertssay the ideal resonant frequency is 10 to 13 Hz, whichis
      about midway between the20
      > > Hz bottom of the audio spectrum and the5 Hz warp/wow region.
      > >
      > > But, in any case, at the time I think I was using Shure V15III
      orIVor Grace F9E cartridges in a
      > > Grace 707 Mk II tonearm (a dynamically balanced arm, as I
      recall) on the Denon 2550 table.
      > > Tracking forces would have been 1.25 to 1.5 grams for the Shure
      and about 1.75 or a bit more for
      > > the Grace cartridge.
      > >
      > >
      > > >>> rooknrol@... 5/30/2008 1:38 PM >>>
      > > There are two parts to acoustic coupling, the path of the energy
      from speaker to pickup and
      > > the response of the pickup system. The discussion of suspensions
      is all about the path for
      > > the energy only and overlooks the pickup part of the loop, all
      pickups have an LF resonance
      > > it is just a question of the tuned frequency that varies with
      the arm+cart combinations.
      > >
      > > It would be interesting to the know the range of tracking
      weights in use for these examples
      > > you give Tom.
      > >
      > > On 30 May 2008 at 11:01, Tom Mallin wrote:
      > >
      > > >
      > > > Fun to touch, but probably not wobbly enough. Audioquest, for
      one, markets rings of such
      > > > material as their SorboGel Q Feet.
      > > >
      > > > In marginal situations, a little cush under the table, or mass
      damping with dead putty can make
      > > > the difference between grossly resonant turntable sound and
      acceptability. In the day, I once
      > > had
      > > > a Denon 2550 directd
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
    • Fred
      Ted, if 40+ years is longer, well, perhaps yes and my HFN69 test disc has been well used since 1969 (and superseded of course). I also use HFS81 and Ortofon
      Message 111 of 111 , Jun 2, 2008
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        Ted, if 40+ years is longer, well, perhaps yes and my
        HFN69 test disc has been well used since 1969 (and
        superseded of course). I also use HFS81 and Ortofon
        Pick Up Test Record 0002. I've personally needed few
        test discs but am aware that the norm is to include
        those V/H tracks.

        Good point about minds but when people expend heavily
        on good gear and become aware of tweaks, a latent
        something strangely akin to engineers mindset can kick
        in.
        The "must" of betterment can drive the once
        non-technical to obsessions and acceptances beloved of
        snake oil merchants and the industry often benefits
        from repeat business and upgrades (and magazine
        readership)!

        A hobby and need perfectly suited to male displacement
        therapy? :-)

        Fred.



        --- Ted Rook <rooknrol@...> wrote:

        > Fred probably you have been doing this longer than I
        > have, it seems our experience of test
        > discs varies, I was pleased recently to discover
        > both types of test on the HFN disc 2 and I
        > stopped searching, was it more common previously?
        > Also perhaps I was speaking rather
        > loosely about vinyl users in general rather than
        > individuals here, don't you think that many are
        > uncurious about technical evaluation? That requires
        > the type of mind which engineers have
        > and that's not everyone.
        >
        > Ted
        >
        > On 2 Jun 2008 at 13:21, Fred wrote:
        >
        > > Ted,
        > >
        > > As a universally documented aspect of tonearm
        > > adjustment with almost every test record including
        > > both lateral and vertical resonance tests, why
        > would
        > > you infer that most people never give thought to
        > > vertical resonance?
        > >
        > > Fred.
        > >
        > >
        > >
        > > --- Ted Rook <rooknrol@...> wrote:
        > >
        > > > Thanks for the low mass arm recos Tom. I have a
        > > > pretty good grasp of tone arm and
        > > > cartridge dynamics but no motivation to put
        > energy
        > > > and money into a low mass unit at
        > > > present there are other priorities that come
        > first.
        > > >
        > > > I have to repeat myself here because I don't
        > think
        > > > the message is getting through. This is all
        > > > about LP records not CD. Tone arm resonance may
        > be
        > > > stimulated using test discs
        > > > specifically cut to activate either lateral or
        > > > vertical resonances. When most people talk about
        >
        > > > resonance they mean horizontal. In my system the
        > > > lateral resonance is fine, if anything a little
        > > > low at about 8Hz but not a problem, it is above
        > > > warp/wow and below the audio band, end of
        > > > story. The vertical resonance, which I supect
        > many
        > > > people may have never measured or
        > > > given any thought to is where the acoustic
        > coupling
        > > > becomes significant in my system. The
        > > > amp and speakers can reproduce everything
        > cleanly
        > > > all the way down to DC, there is no
        > > > problem with speakers or electronics, in fact
        > there
        > > > is no problem and I hope people realise
        > > > this, I am not looking for help here, I have a
        > neat
        > > > way of putting a high pass filter in the
        > > > system that suppresses the vertical resonance at
        > > > about 20Hz and prevents the low end from
        > > > being muddied. People are saying ah but the high
        > > > pass filter introduces phase shift. My
        > > > response is I can't hear it as a problem, it may
        > be
        > > > there but with LP source material I can't
        > > > hear it whereas I can the benefit of the
        > resonance
        > > > being supressed. A good compromise I
        > > > think.
        > > >
        > > > Regarding mistracking I'd like to find a way to
        > > > evaluate your claim about the stylus "bouncing
        > > > around" in the groove, I am persuaded otherwise
        > by
        > > > what I hear and measurements made
        > > > during antiskate adjustments. These measurements
        > > > quite clearly show this to be a linear
        > > > thing, harmonic distortion rises as the
        > antiskate is
        > > > reduced and reducing it further eventually
        > > > results in bursts of gross distortion. It is
        > > > avoidance of the gross bursts that is the aim of
        >
        > > > antiskate and it works. I'm operating in the
        > linear
        > > > controlled region, well away from the gross
        > > > bursts. I can believe that the gross distortion
        > if
        > > > allowed to occur would cause groove damage
        > > > but then I don't allow that to occur so I don't
        > have
        > > > any concerns about uncontrolled stylus
        > > > motion, it is audible and it is not happening in
        > my
        > > > system, there may be some who are new to
        > > > vinyl and would allow that to occur but I'm not
        > one
        > > > of them. So my concern with ordinary wear
        > > > remains the number one priority and at 1.25
        > grams
        > > > I'm at the upper limit of the
        > > > manufacturer's recommendation.
        > > >
        > > > Ted
        > > >
        > > >
        > > >
        > > >
        > > >
        > >
        > >
        > >
        > >
        >
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