Let's do the math and see where that leads us for the specification
offered:
SPL @ 1W/1m: 112.5dB

When driven by .0078 pw we find ourselves 140dB below the 1 Watt that
yields 112.5 dB SPL heard at 1 meter. That translates to -27.5dB re
the absolute lowest level of hearing.

Hi Richard.
Near the bottom of this page http://www.crystal-radio.eu/entrafounit1.htm
The author relates this about the use of his 1.62 Mohm input impedance
transformer driving the Adastra 16 ohm driver.

"when I connect a driver unit to the output of the transformer unit, a
1 kHz test tone on the transformer unit input with a amplitude of
1 mV peak-peak can be easily heard."

So, 1 mv peak to peak is .0003535V rms. V^2/R so .3535^2/ 1.62Mohm =7.7 x
10^-14
Or 0.077pw.
Hmm... that is a factor of 1 decimal unit from his earlier claim.
Or did I make the mistake???
Could this measurement have been made with a x10 scope probe and not noted
in recording of the measurement?
That would increase the power to 0.77pw, getting very close to the minimum
threshold
of hearing.
Inquiring minds want to know.
MikeK