Base on the premise that
all the conditions are the same, if the drive circuit provides enough
voltage, the speaker can generate higher sound pressure level. However,
with the same voltage, but we use another speaker which applies
higher rated power, it will be difficult to drive and output lower
sound pressure level.
For example, a circuit can only provide the power of 8 ohm 1 W,
in order to generate higher sound pressure level we collocate a
2W speaker, the SPL will be lower instead of higher. It is because
with the increasing of the power, the diaphragm should be thickened.
The coil also needs to be replaced by thicker wires. However, the
thicker wires results in lower impedance so we have to wind a bit
longer more, and that makes the coil heavier than before. Oppositely,
if we use another speaker which loads lower power or with lower
impedance, it is likely to make a little bit higher SPL, however
the noise or burning down will possibly happen in this condition.