True. I have factory tires (5K miles) but I can’t duplicate the road surface. Yes, the dB levels are online and are EU speced. They can’t be accurate for every car assembled, but seem reasonably competent as a guide.
There’s an increase in dB with the seats removed. (They are probably 80% of the rear dampening in this car.) At 70, the chart says 68.3 dB (gets louder with speed), but I’m pretty sure over 70dB seatless. Applying 1/2" insulating foam dropped it to speech level. I’m wanting reasonably accurate reads on future stages.
Anecdotally, after quieting the car, I had to fix a small rattle in the trunk mounted amp, and when I turn on the AC fan, a soft whoosh (tire noise) comes in from the rear air vent. Those were inaudible before. The automatic stereo volume can keep up with road noise; no more cranking it up 5 notches to hear commentary.