FWIW, a friend asked me how to determine % distortion from relative level. Use this site:
THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

For example, let's look at the following results at 102dB/1m equivalent:



Let's look at 1khz. At this frequency the fundamental is at approximately 114dB. The THD (blue) is at approximately 64dB. The difference between these two values is 50dB.
Punch (-50)dB in to the link and hit the "calculate" button and below it you'll get "0.3162278" %. That value is the distortion relative to the fundamental.

BTW, 0.32% THD is VERY low for a driver playing at 102dB/1m (102dB spl at 1 meter away).


Some common numbers worth memorizing are:
-30dB down from the fundamental = 3%
-40dB down from the fundamental = 1%