The % times the input watts tells you the watts radiated as sound. At one meter these watts would cover an area of 4/3 PI R^3. The radiated watts are "proportional to" Pressure^2/unit area, with the area of the spher as noted. So multiply the radiated watts by the area of a sphear at 1 meter and you have pressure^2 (within some constants). From this you can get the dB with a log and some more constants. You can look up the constants.

I've seen various values used for half space pressure, from 112 -112.2 dB/m, though 112 seems to be the most common. FWIW, I calc'd it at 112.018, so rounding it off to 112 and 1 % eff.........

dBv = ~112+10*(log10(0.01)) = ~92 dB/~2.828V/m

Since 1 W = E^2/R = ~2.828^2/8 = 1, then dBa = ~92 dB/W/m for 8 ohm nominal loads.

To convert other nominal resistances (R) to dBa, add 10*log10(R/8) to the dBv, so if the above is a nominal 4 or 16 ohms, then dBa = ~89 or 95 dB/W/m.

GM

I think that 1/2 space is incorrect since sensitivity is ususally an anechoic measurement which is full space. The correction for speaker impedance is hardly ever used.

?? 120+(10*LOG10(1/'space')), where 'space' in this case is (2*pi), or half space.

GM

So where does the 120 come from? This seems too simple to me to be correct. Could you fill in the details?

Fairly simple, or I wouldn't understand it:

Lw = 10*log10(1 Wa/10^-12W) = 120

where:

Lw = sound power level in dB

1 Wa = one acoustic watt

10^-12W = sound power standard reference for the threshold of hearing

GM

Thanks

Best regards,

Walt