Welcome rythmik, and thanks for the thorough explanation. From the outset (as I indicated in my original post), I needed no convincing that the series resistor would accomplish exactly what you and jagman have explained.
The concern I would have with this are the negative effects that result. I don't think they can be ignored.
Basically the series resistor modifies the output impedance of a solid state amplifier and changes its reasonable approximation of an ideal voltage source into a modified current source. This mod (if my memory serves), was actually incorporated into some Sunfire amps years ago by Bob Carver in his attempt to allow switching of his solid state amps into a tube sound. If anyone wants their system to enjoy the same distortion and high output impedance of a single-ended triode, install a one or two ohm power resistor on the output of your amplifier.
Anyway, it's quite simple to excel graph the change in Q of a frequency dependant resistance (speaker coil) using a current source dumping resistance as opposed to a voltage source. It's the side effects that are a concern.
I don't think it's arguable that a large portion of the amplifiers power is lost in the series resistor. This power loss alone would be unacceptable by most people.
The resistor would need to withstand considerable power when the driver was not in its resonance curve. For safety sake, probably a 200% over spec would be prudent. I would think a resistor of this rating would be wire wound and subject to inductance of its own. That wouldn't be good.
I would also have a concern over the drivers damping. A standard solid state amplifier with a typical output impedance of 0.01 ohms driving a 4 ohm load would create a damping factor of ~400 (ignoring wire impedance). The series resistor (of 4 ohms, for example) would create a modified output impedance of slightly greater than ~4 ohms, and would create a damping factor of slightly less than 1. What would stop the cone movement? It has no low impedance path to ground. I can imagine the bass would sound muddy as a result.
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So what is the solution? First, subsonic filtering is quite effective. But that is the obvious.
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hehe, yeah, exactly. As you say, it seem like an obvious answer. It's so simple and effective to add a high pass filter. I can't 100% agree with your excursion extrapolation (extension) without introducing the notion that most electronics adds its own inherent first order high pass filter response. This protection would often be enough, but that can be easily tested with a program such as REW. Either way, a subsonic filter adds much less problems than the dumping resistor, I would think. But I've been wrong before...
brucek