Let us now reconsider Eq. (6.47) to see how to maximize the efficiency in terms of the actual coil dimensions. The resistance R
_{
E
} can be expressed in terms of the mass of the voice-coil winding M
_{
MC
} by writing

${R}_{E}=\frac{kl}{\pi {a}_{w}^{2}}$

(6.82)

where κ is resistivity of voice-coil conductor in units of Ω·m. The value of κ for different materials is given in Table 6.1. a
_{
w
} is radius of wire in m. l is length of voice-coil winding in m.

We also note that the volume occupied by the coil wire is

${V}_{w}=\pi {a}_{w}^{2}l$

(6.83)

where for simplicity we are ...

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