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Servo controlled subwoofers- why aren't they common in pro audio?

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  • Servo controlled subwoofers- why aren't they common in pro audio?

    A friend is putting together a hi fidelity system using a servo drive subwoofer.  After hearing the advantages, I became curious as to why they aren't common in pro audio.  Obviously, they're going to be more expensive, but for people willing to spend, they promise tighter, less distorted bass.  From what I've read, servo controlled subs have gotten better in recent years.

    From Wikipedia:
    Some active subwoofers use a servo feedback mechanism based on cone movement which modifies the signal sent to the voice coil. The servo feedback signal is derived from a comparison of the input signal to the amplifier versus the actual motion of the cone. The usual source of the feedback signal is a few turns of voice coil attached to the cone or a microchip-based accelerometer placed on the cone itself.[29][30] An advantage of a well-implemented servo subwoofer design is reduced distortion making smaller enclosure sizes possible.[31] The primary disadvantages are cost and complexity.[32]


  • #2

    Randyman wrote:
    From Wikipedia: The primary disadvantages are cost and complexity.[32]

    That says it all IMO.

     

    More expensive systems such as the Nexo PS-series, use DSP which monitors excursion and voice-coil temperature, and controls voltage for optimum performance. $$$$

    Veni, Vidi, Velcro;

    (I came, I saw, I stuck around)

    Comment


    • agedhorse
      agedhorse commented
      Editing a comment

      Servo systems are really only practical (in the pro world) on self powered speakers... the very speakers that are least likely to benefit. Today's amplifiers have very low output impedances at woofer frequencies, speaker wiring is insignificant, and distortion is not a practical issue in a well designed woofer product. The (potential) benefits do not justify the cost or complexity IMO.


    • agedhorse
      agedhorse commented
      Editing a comment

      Bobby1Note wrote:

      That says it all IMO.

       

      More expensive systems such as the Nexo PS-series, use DSP which monitors excursion and voice-coil temperature, and controls voltage for optimum performance. $$$$


      Note that the VC temp monitoring and excursion control are used for different purposes, and though "could" be called a servo system, it's very loosely coupled and slow by comparison to the servos being discussed.


  • #3

    A true servo sub setup has an acclerometer on the cone.  The input is on a comparator circuit and

    compared to the actual cone motion and then the cone motion corrected.    This is a closed loop system.  

    Arnie Nudell / John Ulrick started in their garage in like 68 and came up with a true servo sub. (Infinity)

    I have heard the Bag End Infra 18 pro subs in a house system in a club.   This was probably

    one of the best sub systems in a club I have ever heard.   Really awesome.

    A friend of mine has the Infinity IRS Beta loudspeakers in his home setup and they run with the

    accelerometer and servo feedback.

    One tower on each side along side the high panels with four 12" subs per cab in a house

    Truely amazing sub bass.

    Years ago a guy explained how they can do a sudo servo feedback with dual voicecoil but 

    I cant remember what he explained for the operation.

     

     

    Comment


    • dboomer
      dboomer commented
      Editing a comment

      Pro Sound Guy wrote:

       

      Years ago a guy explained how they can do a sudo servo feedback with dual voicecoil but 

      I cant remember what he explained for the operation.


      You can also do it with a resistor.  We did it that way with the Peavey powered PR Neos (first rev)


  • #4

    I remember the old folded horn Servo-linears I think they were. Very heavy!! But they did pound!

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    • #5
      Servo-drive is a trademarked technology. Not a technique. Like Kleenex.
      -------------------------------------------------------------------------------------------------------------------------------------------------------------------
      Former product development engineer: Genz Benz, a KMC Music/Fender Musical Instruments Company, continuing factory level product support and service for Genz Benz

      Currently product development engineer: Mesa Boogie

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