The voice coil of a loudspeaker starts from the rearward end point of motion at zero velocity and moves forward (out of the frame)at 0.01926 meters per second relative to the ground and a velocimeter. The center pole piece (which was also at zero velocity at the start) moves at
0.00061 m/s with respect to the ground and the velocimeter Now if the pole had been locked firmly in place so it could not have moved, would the coil velocity have been 0.01926 + 0.00061 = 0.01987 m/s?
Is it that simple, or would we need to know if the coil and pole move in phase, masses, coupling, and whatever? TIA
JC
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D
daestrom
Not sure I can help you too much. One question I have is about your measured velocities. If the two masses are at rest at one end of their travel, then clearly they are accelerating then decelerating as they travel to the opposite end of travel. Are your measurements some sort of average speed (average velocity, is of course zero), or peak velocities, or what?
This acceleration is, of course, due to the force developed by the voice coil in the prevailing magnetic field. Deceleration can be from elasticity of the support/cone and possibly also the voice coil. If the frequency is well below the fundemental, you can be sure that the two movements are in opposite directions. But if the frequency is near or above the fundemental, then the two movements may not be 180 out of phase. A lot of details about simple harmonic motion and applied 'excitation forces' change as one approaches resonance. But I don't honestly know what the typical resonance frequency would be for a speaker and cone, compared to audio frequencies. You may be far below resonance, near, or far above for that matter.
If the pole piece was more firmly locked into place, I suspect the force developed would be exactly the same *if* the voice coil current remained the same. But I also suspect that with only one piece moving, the emf induced in the coil will be different and thus the current will be changed.
Not much help, I know. But perhaps Don can chime in with some points to discuss.
daestrom
J
jclause
Thank you. Velocity is RMS. The frequency is *well* above mechanical resonance of the cone-coil mass and suspensions, however it is on the edge the magnet-plate-basket, i.e. the motor assembly resonance. I suppose one could use momentum conservation M'= Mv/v' with ' being the motor mass amd velocity to find the mass of the motor assembly and go from there, but not sure where.
JC
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