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Thread: Cms vs Rms - what is the difference

  1. #1
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    Cms vs Rms - what is the difference

    These are the kind of explanations I see around the web:

    • Cms - Compliance of the driver's suspension, in metres per newton (the reciprocal of its 'stiffness').
    • Rms - The mechanical resistance of a driver's suspension (i.e., 'lossiness') in NĚs/m

    To me, those look very much alike. I would expect the compliance to be the reverse of the mechanical resistance. But I am obviously wrong. I would be very thankful, if someone would explain which parts of the driver construction/design affects Cms, and wich parts affects Rms - and in what ways.

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    Senior Member just4kinks's Avatar
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    Quote Originally Posted by Immanuel View Post
    These are the kind of explanations I see around the web:

    • Cms - Compliance of the driver's suspension, in metres per newton (the reciprocal of its 'stiffness').
    • Rms - The mechanical resistance of a driver's suspension (i.e., 'lossiness') in NĚs/m

    To me, those look very much alike. I would expect the compliance to be the reverse of the mechanical resistance. But I am obviously wrong. I would be very thankful, if someone would explain which parts of the driver construction/design affects Cms, and wich parts affects Rms - and in what ways.
    Compliance is springiness. Resistance is friction. The third one, Mms, is a mass with inertia. Together they form a damped oscillator -- Google it, it's an important concept for all kinds of engineering.

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    electro-mechanical analogies

    If You want to get the whole picture, google "electro-mechanical analogies".

    The mathematics for oscillations are the same in electrodynamics and in mechanics.

    There is one resistive element which dissipates energy, a resistor and mechanical friction (which is assumed to be proportional to speed, so far the model).

    There are two reactive elements, which can store energy. Inductor and capacitor in electrodynamics, and a mass in motion and a loaded spring in mechanics.

    The net result is, You can use the mathematical calculus which has been developed for electrical filters etc. for mechanical problems.

    ruediger

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