Are all dBs created equal?

@noske

A watt is the amount of energy used. Look at it this way. 24/7 your power company feeds you 240V at your main panel. That’s a matter of "pressure." You are not billed per volt though, since with no current (all breakers off) there’s no power used.

You get billed when power (watts) are consumed, by turning on a light switch, oven or amplifier. :)

The 1w/1m (1 watt at 1 meter) measurement tries to measure how much power is consumed, how much you would be billed for to generate a certain dB.

The 2.83V/1m (2.83 volts input, measured at 1 meter) is how the speaker responds to the voltage pressure. If the speaker is 4 Ohms, this is 2 watts. If the speaker is 8 Ohms, 1 watt, and half a watt at 16 Ohms.

Since most speakers impedance can vary a great deal, and many of us use beefy amps the 2.83V/1m rating makes more sense.  It tell us how loud it will be when you turn the volume a certain amount.

For tube users, knowing how loud per watt could be more important.

Sensitivity and pressure level explains the speaker having different SPL levels at a certain distance but it doesn't explain why the OP sitting in his chair using an SPL meter plays one speaker at 80dB which is comfortable and the other is at 70dB. Which is why the only explanation I can think of is his perception of the speakers which might be due to different frequency responses.

@djones51  You are correct.  Usually I see this with elevated treble or bass response.  Dali and Dynaudio sometimes exhibit this.  Some of their models are definitely better for low volume listening.

Does 90 db at 50 Hz sound just as loud as 90 db at 500 Hz?

I think that's what the OP means.

The spectral content of music can effect subjective loudness.  Research Fletcher Munson curves.  But I'm not sure this explains what the OP is experiencing.