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In Reply to: A simple fix for a loudspeaker problem? posted by klausDK on March 30, 2007 at 03:29:21:
This is from a speaker manufacturer but IMHO is just one piece of the puzzle and by no means covers the story of linearity:
The voice coil should operate within the confines of the pole piece. Some distortion always occurs when the voice coil extends beyond the pole piece. When the voice coil is within the confines of the pole piece there is some dilemma. Most speaker manufacturers will call the region where the voice coil is within the confines of the pole piece the linear region, linear X-max, or something of the sort. But just how linear is it?? My crude theoretical compendium is that if the voice coil moves forward within the pole piece when responding to a bass note (50hz) it is off center for a moment and effects the field of the pole piece. Furthermore, the moving voice coil will induce current (eddy currents) within the pole piece. While the motor's field is disturbed by the voice coil, the disturbed motor must tell the voice coil to respond to an upper octave piano note (@2000hz) the motor will, in varying degrees, smear this note. This is because there are other currents in the magnet - eddy currents. The eddy currents interfere with the primary electrical field of the motor. The midwoofer magnet needs a clear (uninterrupted) path for this 2000hz waveform to be most effective.Asking a motor to perform 50hz and 2000hz is a tall order. Focus on the issue of magnetic linearity (eddy currents) within the normal operating range of the voice coil becomes important when the difficulty of the drivers task is considered. Just because the voice coil is within the confines of the magnet doesn’t mean that it is operating in totally "linear" fashion. In truth, all motors are effected by voice coil movement. Some are less effected than others. This fact isn't profoundly clear in factory advertised specifications. The closest number for assessing linearity is inductance. Better motors have lower inductance, and poorer motors have higher inductance.
Thus, the primary motor function is the voice coil inducing a varying electrical field upon the magnet/pole piece. But there is a reverse effect too. The pole piece induces an electrical effect from the eddy currents that messes up the magnetic field, and effects the voice coil. Shorting rings result in a drastic reduction of this reverse effect, and their result can be measured in lower inductance and increased clarity.
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- Re: A simple fix for a loudspeaker problem? - chocolate_lover9999@yahoo.com 11:21:06 03/31/07 (0)
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