Tonearm resonance?

Discussion in 'Audio Hardware' started by Soopahmahn, Aug 13, 2019.

  1. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Good morning experienced Hoffmanites,

    I'm new around here but I've been lurking and reading for quite a while. I've recently made an upgrade to my phono preamp and believe I've learned a few things about my setup, but I'm curious if you all think I have correctly identified a "new" rumble!

    I was using the integrated phono stage in the RC-1070 preamp (not bad, not great) with my Pioneer PL-516 table and AT155LC cart. I have 2-way bookshelf speakers that perform well down to about 45Hz, and a Velodyne FSR12 sub that is crossed over at about 50Hz just to gently fill in the lower octave.

    Everything was great with the bass until I switched to a Rega Fono MM mkIII preamp. Now, out of the subwoofer, I am hearing a non-musical (constant) very low frequency that is somewhat distracting. I would have to say it is <10Hz.

    So my initial assumption is that the Rotel pre must have an infrasonic filter (or uses IEC curve) and that this rumble was previously there, but has only been exposed by moving to the new preamp with no infrasonic filter.

    Whence the rumble?

    I don't believe it to be turntable related as the sound was not there previously (not noticable...) Therefore I looked into the cartridge and tonearm specifications and here is what I have gathered:
    • AT155LC: Dynamic Compliance = 16 × 10-6 cm/dyne @ 100 Hz
    I've read that I should multiply by 1.7 or so to estimate compliance at 10 Hz, which yields 27 × 10-6 cm/dyne. Pretty high!
    Mass = 8.3 g
    Tracking force is set to middle of recommended range and tracks well.​
    • Pioneer PL-516 tonearm: no mass information. Anecdotally "medium mass".
      Effective length 221mm = 8.7". S-shape, hollow arm.
    • Denon headshell. Don't know mass but I'd assume it's nominal.
    So if all the above rings true, I may very well be picking up a resonance around 5-7 Hz, and this is now making it through to my subwoofer. I should try it with several different records to see if there is a difference.

    When I turn the sub off, I don't hear any bass distortion or artifacts (it actually sounds pretty fantastic!)

    So, long-winded first post, but I am an engineer and I like to describe the problem fully.

    If anyone has alternative theories, or a method of weighing the tonearm and headshell that they recommend, then I'm all ears!

    Cheers,
    Soop
     
  2. muskrat

    muskrat Well-Known Member

    Location:
    l.b.,ca
    Did you check Vinyl Engine? They have a lot data on tonearm mass.
     
  3. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Yes, I did check their database, nada.
    I learned there that even if I weigh the arm, that's not actually "effective mass," which instead is a moment of inertia and needs to be calculated based on shape and other factors. :-/
     
  4. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    There are ways to measure the tonearm resonance with a test record or by playing actual music. If you have the ability to do a needledrop, myself or someone here can probably help you analyze the resonance of your tonearm and work backwards to the approximate effective mass. My hunch is you have a compliance mismatch and that is causing the problem. At some point you'll likely need to choose a different, less compliant cartridge or get a rumble filter of some sort for your phono preamp. If the PL-516 is the model I think it is, the tonearm is too heavy to give an optimal compliance match with that cart.
     
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  5. Ripblade

    Ripblade Forum Resident

    Location:
    The Six
    You can estimate the Fs by recording a few seconds of lead out then observing the spectrum. Without a high pass filter, the resonance will be the highest peak frequency; with the HP filter it will be the highest peak below the knee.

    Or you can get a test record with sweeps to trigger resonance. I have CBS STR-100 so I use it on occasion. It only drops to 10 hz but even then it's possible to project the peak frequency empirically by the shape and angle of the rising slope.

    The two methods yield similar numbers, though not exactly the same.

    Either way is only ballpark as there are vertical and horizontal compliances and effective masses all happening at once.
     
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  6. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Thanks for the input guys!

    So... I took my own advice and referenced a half dozen more records of various vintages and styles. Turns out, I am only hearing the "rumble" at appreciable levels on my Miles Davis Sketches of Spain (Columbia, 1977). It's in pretty good shape, nice and flat. Other records, sometimes I can hear it if I get close to the sub, but it's not as distracting.

    So... I kind of feel like a doofus, but it seems that while there is indeed a stylus compliance/tonearm weight issue, I am hearing actual very low frequency hall noise from the recording session that I never picked up on previously (I'm still thinking Rotel didn't extend down as low), or there is something about this particular disc, perhaps how it was treated in a former life, that is exacerbating the resonance.

    I'll keep my eye on the phenomenon, but regardless I do think that when the time comes to replace this lovely stylus, I'll snag a VMN40ML or VMN50SH as they are about 40% lower in dynamic compliance. Should help.
     
    Last edited: Aug 13, 2019
  7. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    Just be aware that AT now lists their compliance specs according to 100hz Japanese standards, NOT 10hz Western standards. That means the numbers are pretty much useless for compliance calculators and the like. Some folks use a guesstimation multiplier to convert them, but IME this isn't very accurate and can lead to wrong info.

    Short answer is the VM500 series is higher compliance by today's standards and ideally meant for a lightweight, e.g. less than 10g effective mass tonearm.

    Your Pioneer probably has a medium to medium heavy mass tonearm and would be better suited for a match with the VM95 series of AT cartridges.
     
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  8. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Hey patient_ot, point taken on the conversion.
    The compliance spec for the AT155LC from the early 80's was listed the same way as the modern VMN carts, dynamic compliance @ 100Hz. So at least we are comparing apples to apples.
    The new VMN series suspensions have been stiffened up by comparison; the compliance spec is reduced from 16 to 10.

    Correct me if I'm wrong here: when replacing a stylus on a cartridge like these Audio-Technicas, you are also replacing the cantilever's suspension, and ergo the compliance spec is really for the stylus system and would be changed by changing the stylus.
     
  9. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    Forget the numbers @ 100hz, they are useless to you as I said. What you really need to do is a get a resonance MEASUREMENT of your current cart/tonearm combo as described above. You only need about 30 seconds of audio recorded into a computer.

    That will give you a baseline.

    FWIW, the VM500 series has been measured by other folks on arms that are likely lighter than yours and the resonance was a little low, e.g. 7-8hz. That is still technically in the safe zone but not a preferred place to be if you are having subsonic problems like you described.

    That is why I suggested the VM95 series. I run one of these myself on a late 70s JVC table that has a medium heavy effective mass tonearm and I get a 9-9.5hz resonance as measured.
     
  10. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Thanks. I do see that the VM series compliance specs are also the same as the VMN series - but the cartridge bodies weigh substantially less than the VMN7xx series (or my current engine). So that would help. :thumbsup:
     
  11. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    VMN is the designation for the replacement stylus for the VM series. The 95 line compliance is different and a better match with a medium mass arm if you want to move that resonant frequency up a little.

    AT VM95E Dynamic Compliance 7 x 10 – 6 cm / dyne (100 Hz)
     
  12. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    ^ thank you. I meant to refer to the 95 line. I saw a different spec somewhere for hte VM95SH. A-T's USA website doesn't have it, I had to go to the European site.

    I see that the VM95E is lower compliance, but the VM95SH is still a value of 10. It must have something to do with the diamond cut and the way it interfaces the groove. I didn't realize that was an effect on compliance.

    I am learning a lot!
     
  13. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    I have measured the resonance of both the VM95C and the VM95ML. Compliance is about the same on each. I don't see why the VM95SH would be any different than those two as it appears to be consistent across the line. Again, ignore AT's specs, they're sometimes wrong and the 100hz values won't help. Again, if you have an arm on the heavier side of medium mass you are better off choosing a VM95 series rather than a VM500/700 series cartridge for your tonearm.
     
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  14. Soopahmahn

    Soopahmahn Well-Known Member Thread Starter

    Location:
    Pittsburgh
    Your point is taken and the specs of the two lines are clearly different. Also it is perhaps possible that 100 Hz compliance is tip dependent, while 10 Hz compliance is not (or less so).

    I would like to record the response to my computer but I have unfortunately sold all of my recording equipment. I suppose purchasing an ADC would allow me to rip audio to my iMac. I am mostly curious if I am actually hearing tonearm resonance or something else! Although it seems clear that I have a mismatch going regardless, which I suppose affects ultimate performance somehow.
     
  15. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    You don't need high end equipment for this purpose. You can simply run RCA to 1/8'' from your REC out to computer. Alternatively you can purchase an ADC for $30 that will do the job and run the USB ouput of that into the computer. Record with Audacity, which is a free program.

    I don't think compliance is tip dependent. The cantilever and the rubber suspension are what's going to affect compliance the most.
     
  16. empirelvr

    empirelvr "Give me the chocolate, and nobody gets hurt!"

    Location:
    Virginia, USA
    In all my experience, I have never heard of a compliance mismatch producing rumble or hum. I don't see how it can. Cartridges/styli only respond to the information in the groove or external influences like vibrations from the motor or things like footfalls on springy floors. Compliance mismatches cause different issues. Wow or flutter when the arm gets excited by such a resonance? Absolutely, many times you can even see the arm shaking or vibrating in those cases. Woofer pumping in silent grooves, especially in a ported speaker system, is another big clue of a compliance/resonance mismatch. Mistracking? Yes, it's a known phenomena that a compliance mismatch can cause poor tracking or skipping from a cartridge that otherwise has a sterling reputation for being sure footed in the groove. Bad, unstable or wonky soundstage? Yes.

    Think about it: if such a thing were possible, all of us would have such a hum in our phono sections. It would just be a question of what frequency, because even a properly matched tonearm and cartridge would have a resonance point where the arm will get excited and would generate such a spurious tone. And if this indeed were true, your guesstimation of the tone being at 10Hz would mean your system IS matched because that's the frequency where you want to see a match at.

    If you are hearing various amounts of rumble or hum now on different records my guess is your first thought was correct: the Rotel's phono stage has a rumble filter the Rega doesn't have and you're now hearing either low frequency noise captured at the session, or even rumble from the lathe that was used to cut the lacquer that the disc was made from. (It's not a given that lathes had/have superior rumble specs to a consumer turntable.) Or there is something in the Rega's wall wart power supply (or it's location around other components) causing an issue.

    But, even that I'd find suspect as you have a single subwoofer, right? Since that means all bass below 50Hz is now mono, that usually cancels the effects of turntable or lathe rumble. So my guess is you might be hearing hum "built in" to the discs for all sorts of reasons, or again, an issue with the wall wart. I sincerely doubt it's a compliance mismatch/tonearm resonance issue.
     
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  17. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    With a test record, the resonant freq of cart/arm will be the frequency at which the arm/cart moves the most, correct?
     
  18. patient_ot

    patient_ot Forum Resident

    Location:
    USA
    Depends what test record you are using. Some go down only to 10hz, which means you need software to analyze. You can't just look at the tonearm while the test record is playing.
     
  19. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Yes, assuming the vocal track on the test record is correct.
     
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  20. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Yes, there's confusion about these carts and styli. You'll also find a little lower output spec for the SH and VL. Some of these are for the older cartridge body, and feature bonded styli. The great thing about the new AT95 is that they give you a nice nude stylus for lower tip mass.
     
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  21. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    My test record goes from like 6 to 15 Hz.

    Why can't you watch the tonearm when playing to determine the resonant frequency? It has been my understanding, and it makes sense, that the largest arm/cart movement would correspond with the actual resonant frequency.
     
  22. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    It does, but what you'll find is that it's like a bad party guest—comes in early and stays late. Where is the peak movement? Can be hard to tell. And if the voiceover is not timed well, it can be even less informational.

    A real-time VST plug in or recorded pink noise from LP can show the the frequency bump with a bit more precision.
     
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  23. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    With my test record it's easy to determine which frequency the tonearm is moving the most at. It gives you the frequency via voice first before playing the sine wave, then there is several seconds of that frequency playing to observe the tonearm. The sine wave stops before the next frequency, then the voice again. It's always been very evident visually, with no early/late thing. Your test record is a lot different than what I am using sounds like.
     
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