Basically youl notice-
Home theatre subs are are inefficient
Small box subs are inefficient too.
Larger drivers tend to be more efficient
Lower Qts drivers are more efficientProsound 12"s and 15"s are efficient,they have higher Fs,Mid Q,and larger box requirements.
Efficient cone drivers are often Low Qts high BL(ie powerful and in control) fullranger units with added HF efforts.
II) Mid-Band, Reference Efficiency (%)
(Infinite Baffle Mounting Assumed)
[n0]
= ([p0]*[Bl]^2)/(2*[pi]*[c]*([Sd]^2)*[Re]*([Mas]^2))
= (4*([pi]^2)*([fs]^3)*[Vas])/(([c]^3)*[Qes])
Youl notice its fs^3 * vas.
Equations at the link