So you need 5.215 ohms (Min.) to have a 6 ohm nominal correct?
Wouldn't the dip up top not really matter much? The dip at 500hz surely hurts worse, but how bad?
Red line at 5.215 ohms (roughly)
If one allows for rounding, having an impedance of 5.5 ohms nominally could be called 6 ohms nominally. Thus, a minimum impedance of 4.7827 ohms could be called "6 ohms nominal."
But your other point is well taken. How much it matters does very much depend on the frequency. If it is at a frequency that requires minimal power, then it will matter less than if it is at a frequency that requires a lot of power. In general, this means that the higher the frequency, the less it matters.
There is also another consideration from the fact that such impedances will matter more for some amplifiers than others. With my Crown K2 power amp, none of this would make any significant difference with the impedances we are discussing.
Also, even with an amplifier not designed for low impedances, how much such things matter also depends upon how hard one wishes to drive the speaker. If one is listening to soft background music, instead of trying to recreate the loudness of a live concert, this, too, will make a significant difference for the question of how much such impedance dips matter.
So for your second question, how bad does it hurt?, there is not a single, simple answer. However, my point was not about whether it would matter or how much it would matter, but is about the honesty and accuracy of the claims made by the manufacturers. If they cannot get something this simple right, for which there is a standard mathematical determination from a simple formula, how much do you think you should trust their other claims?
But in this sort of case, it
can matter very much if one is pairing the speaker with an amplifier that is not designed for low impedances, and one wishes to play things very loud. With such an amplifier, one might destroy it due to trusting their lies about their speakers. And, of course, you will never get them to pay to have your amplifier repaired, even though it is their fault by selling you speakers that are unsuitable for such amplifiers while claiming that they are suitable for them.
Quite simply, speaker companies ought to follow the standard for rating their speakers, and not simply slap higher numbers on them in order to sell them to people who might otherwise reject them, as they are unsuited to their present amplifiers. So what we have are companies lying about their products in order to make more sales. That is what is known as fraud. In this case, however, it appears that there is no LEGAL definition of "nominal impedance," and so they say whatever the hell they want. This, by the way, means that one cannot trust those numbers, and should look either for professional reviews in which speakers are properly measured, or judge based upon the minimum impedance instead of the nominal impedance, which, with some manufacturers, is a completely misleading and totally useless number. Evidently, this comment applies to both B&W and EMP, who obviously are not to be trusted when they tell you about their products, because we know they lie about them. Their claims about nominal impedance are pure BS designed to sucker people into buying their speakers, even though they are not a good match for amplifiers designed for their claimed impedances, that are not also designed for lower impedances.
