Speaker drivers typically have 2 SPL ratings: dB/1W/1m and dB/2.83V/1m. The first is the dB level you get when you apply 1W of power to the speaker and measure it from 1m away. The second is the dB level you get when you apply a 2.83V signal to the speaker and measure it from 1m away. For 8 ohm speakers, these 2 ratings will be essentially the same because 2.83V applied to an 8 ohm speaker will result in 1W going into that speaker (P = V^2/R = 2.83^2/8 = 1.0011W). This is the reason that 2.83V was chosen by manufacturers to give one form of dB rating (because it corresponds to 1W with an 8 ohm speaker).
The dB/2.83V/1m will be higher than the dB/1W/1m rating if the speaker's nominal impedance is less than 8 ohms, as the above calculation would imply. For example, the speaker that this question is for is a 4 ohm speaker, so with a 2.83V signal, it will draw P = 2.83^2/4 = 2W from the amplifier. This is twice as much as 1W, and when doubling the input power, a speaker's dB output increases by 3dB, hence the 3dB difference in the ratings. Similarly, a 2 ohm speaker's dB/2.83V/1m rating will be 6dB higher than its dB/1W/1m rating because it will draw 4W at 2.83V.
The spec you want to use depends on your application. When comparing the relative efficiency of different drivers, you'll usually want to use the dB/1W/1m rating because this will tell you how many dB you will get from each speaker when applying a certain power level. So, if you have 3 drivers that are each rated for 100W, and you want to know which one will be loudest when applying 100W, it will be the one with the highest dB/1W/1m rating.
However, often when designing a speaker system, you'll want to use the dB/2.83V/1m rating. This is because most amplifiers are voltage amplifiers. That is, their output is a voltage signal; when you adjust the volume knob, you're simply adjusting the output voltage of the amplifier, independent of the actual power that the amp delivers to the speakers (well, not completely independent, but we'll just assume that for now). So, using the dB/2.83V/1m rating makes more sense a lot of the time because it is a rating that tells you the dB rating relative to the actual output voltage of the amp.
One application that requires the use of the dB/2.83V/1m rating is tweeter L-pad calculations. To figure out how much attenuation the L-pad must apply to the tweeter, you must use the dB/2.83V/1m ratings from both the woofer and the tweeter. This is because the amplifier will be applying the same signal (at the same voltage level) to both the woofer and the tweeter, and thus you must figure out the sensitivity difference between the two, in terms of the applied voltage. The dB/1W/1m won't always work here because it will depend on the impedances of the tweeter and woofer.
One way to summarize all of this is that the dB/2.83V/1m rating tells you the dB level you will get at a particular volume setting on your amp, whereas the dB/1W/1m tells you the dB level you will get when the speaker is drawing a particular amount of power, and these 2 ratings will be different if the speaker has an impedance other than 8 ohms.