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The mechanic tuning of the loudspeaker usually shifts the main resonance
to the low end of the transmitted frequency range. Spherical waves are predominately
emitted in this frequency range, and, below a limiting frequency
ω'
, the real part of the radiation impedance, Zrad, increases proportionalto
ω^2.Tuning the mechanic resonance to lower frequencies extends the range. The
acceleration,
a, of the membrane should be constant to keep the radiatedpower independent of frequency since
|v^2| ~ 1/ω^2 means |a| = ω|v| = const.Electric equalization using the techniques discussed here can overcome
the mechanic deficiencies of the loudspeaker, but be aware that very large
mechanic forces may be needed, reducing the power efficiency. Monitoring the
movement of the membrane with sensors and controlling the driving force
accordingly is called
motional feedback and has been successful at reducingdistortions – particularly at the lower end of the frequency range.