These numbers are called "small signal" values, and only have meaning at small power levels, i.e 1 watt.
One watt is more meaningful than 2.83 volts, because wattage is independent of the speaker load. For example, 2.83 volts into an 8 ohm speaker is 1 watt, but 2.83 volts driving a 4 ohm speaker is 2 watts.
Most sensitivity ratings are measured where they most benefit the manufacturer, typically 1,000 Hz. This is bullsh*t, because as a bassist, my primary focus is 40 to 200 Hz. The sensitvity here is a huge amount less. The only meaningful specs are plots of actual measurements taken across the useful frequency spectrum.
Bass drivers are severely limited in the amount of power they can accept, due to cone excursion limits. Typically, the voice coils will accept far higher power than the limits of excursion. Just because a driver is rated at 700 watts before meltdown, does not mean that driver will accept 700 watts without destroying the cone. Cone excursion is not a factor at 1,000 Hz, which is another convenient reason for taking SPL measurements here.
