Turntable Physics

Discussion in 'Playback Devices' started by Anthony F., Jul 18, 2003.

  1. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    I was curious if any of the vinylphiles could explain how turntable suspensions work to either keep good sound in or keep bad sound out. Specifically I've seen tables with 3 or 5 point suspensions that seem to couple the arm and platter; tables where the arm and platter were separate but the feet had springs like shock absorbers; and tables with no suspension at all, but just padded feet--all in different price ranges. Curious what works best and why.
     
  2. Jack Briggs

    Jack Briggs Executive Producer

    Joined:
    Jun 3, 1999
    Messages:
    16,738
    Likes Received:
    129
    The best turntable suspension I ever saw was on the old Acoustic Research AR-Xa classic: the belt-driven platter and integral tonearm were mounted on a separate spring suspension from the unit's base. Excellent isolation. And isolation is what you want lots of.
     
  3. Lew Crippen

    Lew Crippen Executive Producer

    Joined:
    May 19, 2002
    Messages:
    12,060
    Likes Received:
    0
    Jack, you have to be of a certain vintage to know this off the top of your head. [​IMG]
     
  4. Philip Hamm

    Philip Hamm Lead Actor

    Joined:
    Jan 23, 1999
    Messages:
    6,873
    Likes Received:
    2
    The best isolation of all is isolation from the floor. Try mounting the table on a shelf on the wall instead of a table on the floor and be amazed at the amount of disturbance that dissapears.
     
  5. Saurav

    Saurav Cinematographer

    Joined:
    Feb 15, 2001
    Messages:
    2,174
    Likes Received:
    0
    I think there are several different schools of thought when it comes to this. And the suspension design is related to the table design as a whole. For instance, a light table might be designed to dissipate vibration into the stand, while a heavy table might be designed to damp/absorb vibrations. I'm sure the two would need different kinds of suspensions to perform at their best.

    And of course, I know next to nothing about any of this.
     
  6. Grant B

    Grant B Producer

    Joined:
    Mar 29, 2000
    Messages:
    3,210
    Likes Received:
    0
    if you have a sub that goes down to 20HZ, it doesn't matter how well it's isolated.....
     
  7. Chu Gai

    Chu Gai Lead Actor

    Joined:
    Jun 29, 2001
    Messages:
    7,270
    Likes Received:
    1
    This should illustrate that Mr. Hamm is quite mistaken about turntable placement...

    [​IMG]
     
  8. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    Thanks so far. My table is of the springy feet variety and is wall mounted. I like the sound a lot, but always curious what separates the LP12s of the world from the rest of the pack. I assume placement can't make a lesser table into something more.
     
  9. Saurav

    Saurav Cinematographer

    Joined:
    Feb 15, 2001
    Messages:
    2,174
    Likes Received:
    0
     
  10. alan halvorson

    alan halvorson Cinematographer

    Joined:
    Oct 2, 1998
    Messages:
    2,009
    Likes Received:
    0
    Anyone here old enough to remember Mitch Cotter products? Mitch Cotter produced a set of excellent electronics, including a moving-coil transformer (probably the best moving-coil transformer ever), a noise filter and a phono section, each in a neat little blue aluminum brick, all plugged into a seperate power supply, all of which I owned at one time. He later produced a control center that I wanted very badly but couldn't afford (and couldn't find, anyway) at the time. He also manufactured a couple of turntable isolation platforms.

    The cheap platform, the one I owned, was simply a thick, heavy rectangular plate mounted on four springs at the corners. The turntable - any turntable - was placed on top. This plate was more than just a plate of some heavy material though. It was a many layered laminate of various materials - I can't remember what they were. There are two problems to be solved in mounting a turntable. One is feedback from mechanical vibration such as footfalls, vibrations through the floor and walls, etc. The other is feedback from acoustic sources - airborne vibrations from your speakers, mainly. The Cotter platform reduced mechanical feedback by its use of a heavy plate mounted on fairly soft springs, and acoustic feedback by making the plate acoustically inert - acoustic vibrations are totally damped so that they could not couple back into the tonearm and stylus.

    Cotter also produced a much more expensive platform specifically designed for the top Denon turntables of the time, and, if I recall correctly, the top Technics turntable also. I never came across this platform but reviews were very positive.

    Systems that use those little feet are a joke. It's just cheap to do it that way and come up with some mumbo-jumbo explanation to justify it.

    So, when looking at turntable mounting systems, look to see how both mechanical and acoustic feedback are handled - give it the old rap and tap test! Do something to produce mechanical feedback, tap the base while the turntable is playing. If you hear any feedback at all, regardless of how expensive the turntable is, you're looking at a hunk of junk.
     
  11. Jack Briggs

    Jack Briggs Executive Producer

    Joined:
    Jun 3, 1999
    Messages:
    16,738
    Likes Received:
    129
    Yes, Lew, I go back with audio equipment: I owned an AR-Xa (to which I mated a Shure V-15 Type II Improved, in 1971). This unit replaced a Garrard SLX-2 changer (which was factory-fitted with a Pickering cartridge).

    From there, I went on to a Thorens TD-125 Mk II, to which I mated an SME 3009S tonearm (to which I attached a Shure V-15 Type III). And then I had a Technics SP-25 direct-drive unit, first sporting the SME arm and then an Infinity Black Widow (remember that arm?). At this time I started a longtime love affair with the cartridges coming out of Joe Grado's little factory. Then I moved on to a Linn-Sondek LP12/Linn Ittok combo, which I replaced with the SOTA Sapphire (but held on to the Linn Ittok), always sticking with moving-magnet cartridges (I was impressed by the sound of moving-coil cartridges, but thought they were an awful lot of trouble to live with; I like being able to replace a stylus myself, and I like a pick-up that generates a decent amount of output).
     
  12. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    Alan, very helpful description. The bit about airborne vibration has me thinking that it has more to do with speaker placement relative to the cartridge. Did I miss that point? In my basement listening room the concrete floor doesn't have issues of footfalls, so the spring feet never really need to keep out mechanical noises--not sure how a different suspension system with help with the overall sound quality.

    If turntable suspensions have more to do with keeping out unwanted mechanical noises (including footfalls) are the arm and cartridge doing the lion's share of generating the table's sound (fidelity)? Seems like a lot of the design measures are around isolating the point of contact (stylus to vinyl) from the environment, like a booth in a recording studio.
     
  13. alan halvorson

    alan halvorson Cinematographer

    Joined:
    Oct 2, 1998
    Messages:
    2,009
    Likes Received:
    0
     
  14. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    I just tried a fun, cheap experiment!

    Based on the feedback here, I decided to make a new base for my turntable to further isolate it. I decided to use a stair runner made of 1.25" MDF. The length was fine, but the width was only 11". I glued a 4" piece of the same length to get the proper width and clamped it together with wood glue. The runner has rounded edges so it has a good look to it. The glue seems to hold fine and the platform is quite inert. I have it placed on top of some vibrapods I had, which sit on the .75" pine base the table originally sat on. The whole unit is on wall brackets.

    Results so far are a dramatic improvement in the midrange and a much quieter overall sound. The upper midrange was peaked with a "honking" sound, and that seems to have disappeared. The mid-bass is also more detailed. Cost was about $6, and it took about 5 minutes with a table saw. I'll test it out more and see if this impression holds.
     
  15. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    Okay I now have the new base attached directly to the wall brackets (not resting on the old platform) and the vibrapods directly under the turntable feet. There seems to be less vibration on the platform and none on the table while music is playing--this may have done the trick. Still no midrange peak and the sound seems very open.

    Without the vibrapods the sound is similar, but the table exhibits more of a problem with acoustical feedback (can't crank the volume). The pods are very helpful in that respect. Not sure if there's a better solution that will let me remove them from the system altogether (moving the table isn't really an option at this point).

    To confuse matters I'm playing with a new set of interconnects between the table and the phono stage. Getting closer I think, but need more time.
     
  16. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    Think I got it! Rubber washers between the brackets and MDF base eliminates the need for the vibrapods under the turntable feet ($0.39 each vs. $6 each). No problem with volume of peaked midrange. Sound it nicely detailed and lively. Midrange is rich and really pleasant to listen to. High end is delicate, but not rolled off. Low end is full but not muddy. With the metal brackets, total cost is about $15. I guess I should stop replying to my own thread and let this one rest in peace. [​IMG]

    Thanks.
     
  17. Philip Hamm

    Philip Hamm Lead Actor

    Joined:
    Jan 23, 1999
    Messages:
    6,873
    Likes Received:
    2
    Nope, I find it interesting. Perhaps I'll try rubber washers under the feet of my little Denon DP7F.
     
  18. Anthony F.

    Anthony F. Stunt Coordinator

    Joined:
    Jun 12, 1999
    Messages:
    93
    Likes Received:
    0
    Found one more tweak....I replaced the 1/16" flat rubber washers between the brackets and MDF platform with a 5/16" rubber slip joint washer. It looks kind of like a cone, but with the point cut off. Cost is also about $0.39 /ea.

    This seemed to further isolate the table--knocking on the MDF with the stylus down gave much less sound (almost none) through the speakers. The effect on sound quality was to smooth out the midrange and lower the low end. It also opened up the sound stage quite a bit (don't you just love audiophile euphemisms!). Anyway it's a big improvement over the flat washers. Happy listening.
     
  19. Chu Gai

    Chu Gai Lead Actor

    Joined:
    Jun 29, 2001
    Messages:
    7,270
    Likes Received:
    1
    Heck why stop there? Go get some of the vibration devices this person uses.
    [​IMG]
     
  20. Frank_S

    Frank_S Supporting Actor

    Joined:
    Oct 28, 1999
    Messages:
    565
    Likes Received:
    0
    Pocket rocket, no doubt![​IMG][​IMG][​IMG]
     

Share This Page