Help me w arm/cart resonance please?

Discussion in 'Audio Hardware' started by Mugrug12, Apr 22, 2018.

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  1. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    hi! Been messing w cartridges this weekend. I had a question about arm cart resonance matching maybe you can help:

    I've put an ortofon super om40 on a black widow markI. Tracks the test record easily but one for one thing-
    The resonance test vibrates around 15hz, when everything says it should be between maybe 8-12 I think.

    Should this be a concern or is it not to worry. Also- the om cart has a removable weight in it. Should I remove the weight? I guess that would cause the counterweight
    To need to be closer to the pivot point. That prolly has nothing to do w resonance or?.....
    The tonearm is ultra light mass and the om I think is decently high compliance at 25.
    Thanks for any advice!

    -Dave
     
  2. punkmusick

    punkmusick Amateur drummer

    Location:
    Brazil
  3. chervokas

    chervokas Senior Member

    Well, this famous B&K paper on mechanical resonances in vinyl playback -- http://www.theanalogdept.com/images/spp6_pics/TT_Design/MechanicalResonances.pdf -- argues that circa 13-18 Hz, but well damped particular at frequencies above 20 Hz, is ideal to minimize rumble-like noise from record surfaces
     
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  4. Davey

    Davey NP: Portishead ~ Portishead (1997)

    Location:
    SF Bay Area, USA
    If you are confident in your resonance test results, you would need to add mass to the cartridge to lower the resonant frequency. Is your Black Widow the carbon fiber (graphite) one with 3 gram effective mass? If you can record and analyze the phono output, sometimes it's easier to just do a simple "drop" test to get the resonant frequency instead of trying to pick it out from test tracks.
     
    Last edited: Apr 22, 2018
  5. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    Sorry I should have added this the op:
    -I use the hifi news test lp for resonance test
    -it's the first black widow w no damping trough. I'm not sure what the material is but I think it's the lightest


    The test record resonance test seems
    Pretty accurate, becuause even w out listening you can see which freq makes
    The cart physically vibrate.

    One more question- this cart is new from the box. Might compliance rise a
    Little w use, thus lowering the res freq?

    Edit- what's a drop test?
     
    Last edited: Apr 22, 2018
  6. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Might look around at some of the older ADC carts with that arm.
     
  7. BrentB

    BrentB Urban Angler

    Location:
    Midwestern US
    Try wrapping the arm with teflon tape. You can also include the cart just up to the point where the stylus is. I start there and wok my way back to the pivot overlapping slightly at the seams. It is a cheap, easy, and fully removable if you do not like the results. It worked well on my Sony PUA-7/PS-X50 using an Empire 2000/E II.
     
  8. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    15 Hz sound a bit high compared to calculated values, I get around 10-11 Hz for an OM40 on a 4 g arm. A 3 g arm should give around 11-12 Hz. . If you use the Hifi News record and the voice calls, note that they are not really 100 % correct. That said 15 Hz should fine anyway.
     
  9. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    I've been using an adc xlm 2. Just messing around w some other ones fer a fun time.
     
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  10. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    Ah well if the voice over during the test tones on the record is off, then that would throw off the results, that makes sense.

    For some clarification is this accurate:
    a resonance that's too high could be in the range of low bass notes in the music, and if resonance is too low it could make rumble too loud? Or does it affect other stuff as well?
     
  11. Davey

    Davey NP: Portishead ~ Portishead (1997)

    Location:
    SF Bay Area, USA
    There's a few ways to check the resonance if you can capture the output. One easy method is to put a record on with motor off, manaully cue the tonearm until the stylus is almost touching the record, then let it go. It should bounce a little at the resonant frequency and decay. Then it's a simple matter of getting the frequency from the reciprocal of the period for one cycle, f = 1 / period. I don't have any plots on hand right now, but this is one from John Elison over at vinyl asylum ...

    [​IMG]


    You can also just record the test you are using now and check the frequency where the amplitude gets higher.

    Another easy method if you have a test disc with a fixed frequency tone, like 1KHz though that is kind of high, preferably something lower, is just to start playing and recording that track and then turn off the motor, and you will see a decaying frequency sweep from 1K down to near zero, but depends how fast your platter stops. Then start it up to capture going from 0 to 1KHz. As it crosses the resonant point you should see the amplitude increase. Some people just leave power off and spin the platter by hand, letting it coast down while recording, might have to remove the belt. The resonant frequency should stand out...

    [​IMG]
     
  12. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    Most records do not have info below 40 Hz so 15 Hz will not be so much trouble. In addition most bass is in mono below 100 Ha so you will unlikely excite a 15 Hz resonance.
     
  13. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    Cool thanks for the info. It seems they make the test record way more strenuous than music really gets.
     
  14. Doctor Fine

    Doctor Fine "So Hip It Would Blister Your Brain"

    I might suspect poor bass response if your arm is not letting the stylus push against something.
    Too high a resonance implies the arm wiggles when it should be "holding" the cartridge steady and letting the stylus flex for bass notes.
    Adding a headshell weight might be a way to make the arm a bit more "beefy."
    Just a thought.
     
  15. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
  16. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    That was very thoughtful of you thanks. I'll check it out now. At least I don't have to worry about azimuth- the black widow is not adjustable there! (Guess I could shim the cart screws but...)
     
  17. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    Are there many bass notes in music that are 15hz? The cart was good at 16hz and up
     
  18. Benzion

    Benzion "Cogito, ergo sum" Forum Resident

    Location:
    Brooklyn, NY
    If there are - you can't hear 'em, anyway - human hearing starts at 20 Hz.
     
  19. Doctor Fine

    Doctor Fine "So Hip It Would Blister Your Brain"

    When an arm is too light the cartridge just pushes it around.
    When it is the correct mass the stylus has a solid "thing" to push against and can then move in a wider arc for producing bass notes.
    The sound of a too light arm is no bass.
    That is my point.
    Not what fundamental resonance is doing.
    Fundamental resonance considerations are more about tracking warped records or introducing distortion in the lower notes.
    I am talking about NOT HAVING lower notes.
    Different matter altogether.
     
  20. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    Iirc The black widow was purposly designed to be the lightest tonearm I think ever at that point. So you're saying the design itself is flawed? Or you mean the 15hz resonance is a bad number for tracking bass notes. There are no resonances below or above 15hz according to my test lp results. Help me understand, as I know more about music than the engeneering stuff though it interests me a lot. Also FYI the ortofon superOM40 in question has a 25 compliance rating.
    -Dave
     
  21. chervokas

    chervokas Senior Member

    Not too many. Big orchestral bass drums have a fundamental frequency in the 15, 16 Hz range. The lowest notes on tubas and some pipe organs and a Bosendorfer Imperial piano with the extra bass octave can have fundamental frequencies that get down there -- though at those pitches one is probably feeling the low frequency pressure wave and hearing the harmonics. If you're listening to pop and rock and jazz and this kind of stuff, for the most part you're listening to material from 40 Hz up, and if you're listening on vinyl it may be that whoever prepared the master or did the cutting might have rolled off the lowest bass, especially the "subsonic" bass, anyway. (And of course your home hifi speakers are almost certainly not producing anything at 16 Hz.)

    The arm cart resonances in the subsonic range tend to be excited by record warps, footfalls, bearing noise, and, per Poul Ladegaard's famous paper on the audible effects of mechanical resonances in vinyl playback which I linked to above, surface anomalies in the records themselves, which tend to be very low frequency (which is the primary reason Ladegaard argues in favor of using an arm/cart set up with a fundamental resonance considerably higher than 10 Hz, because there will be less record surface excited rumble and noise).

    Mechanical damping via things like a fluid trough which is something some arms have, some don't, can really control the amplitude and duration of that low frequency ringing too, whatever the frequency.
     
  22. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    thanks that is enlightening. I haven't heard any lack of bass yet but the carts only been on since Saturday. I think I should listen to the saint saens organ symphony, that has some low bass notes. I've tried it w a couple bad warps and only one of them produced a tiny thump sound, only audible between tracks.
     
  23. chervokas

    chervokas Senior Member

    It's not so much the sound that you'll hear, it's if you get uncontrolled oscillation and woofer pumping (which may produce a sound or a wow that impacts presentation of pitch), etc and any other kind of knock-on effects from throwing a lot of subsonic energy at the amps and speakers, or the extent to which and excited subsonic resonance modulates single in the sonic spectrum and maybe presents as rumble or surface noise.
     
  24. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    I have a 4 g arm that gives a lot of bass, and it has been compared to a 10 g arm. The 4 g arm may in fact give a bit more bass due to the increasing level due to the resonance. If the moving mass of arm+cart is 9 or 15 g does not matter that much thinking of the moving mass of the stylus is in the order of 0.0003 g.
     
  25. Mugrug12

    Mugrug12 The Jungle Is a Skyscraper Thread Starter

    Location:
    Massachusetts
    So far the coast is clear on that stuff. Don't think I've ever heard woofer pumping in my house but I'm reading that article now. I do hear the slightest faint bearing noise during dead silence but I have w three carts on this same deck so it must be the tt or arm.
     
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