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Horn driver displacement below FL

Does anyone know why, or for what relevant specs of a driver, the driver displacement drops below electrical resonance at FL, yet remains high (i.e., at the same displacement as at FL) at freqencies below FL. As an illustration, compare the McCauley 6342 8ohm version vs. its 4ohm version. In the 8 ohm version, displacement drops below electrical resonance at FL, but in the 4ohm version, it doesn't drop. (This is in a McBean model, 80-500Hz, t=.6.) Thedriver specs are at www.mccauley.com. The BL factor is only listed for 8 ohms. I took it to be the same for 4 ohms:

  
Bl Factor 25.3 T*m(8)
Moving Mass 0.099 kg

Fs Free Air Resonance 40 Hz
Re D.C. Coil Resistance 3.4(4) 6.0(8) 11.5(16) ohms
Qts Total Quality Factor 0.20
Qms Mechanical Losses 7.40
Qes Electrical Losses 0.21
Vas Equivalent Volume of Air 200 L / 7.07 ft3
Sd Effective Piston Area .089 m2 / 138 in2
Xmax Excursion - Max Bl 4.6 mm / 0.18
Vd Sd x Xmax 411 cm3 / 25.1 in3
Le Inductance of V.C. 0.6 mH (4) 1.1 mH(8) 2.2mH(16)





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Topic - Horn driver displacement below FL - pooge 07:06:17 06/16/03 (4)


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