It doesn't matter whether you connect in series or parallel; that only affects drive impedance.
You won't get 3dB per driver, but at most 3dB per doubling. Four drivers would give 6dB (two lots of doubling). This assumes, of course, that adding a driver affects efficiency at all - I don't know as I am not a speaker expert.
Note that you have to compare like with like: sound power out for electrical power in.
If that is what happens then that is a rise of 6dB in efficiency, which is what I said.Ron E said:Think of it this way: If you take a single driver and measure, then add three more in parallel without changing amplifier settings, the SPL will go up 12dB and the power will go up by 6dB.
I'm dealing with an amp that operates @5vdc. The voltage can't increase much BUT there is a difference in SPL between 4 ohm and 8 ohm drivers.. (Shorter battery life/Same basic driver with different impedance)
I understand the resistance is more (lower) with a 4 ohm driver but wouldn't the increase in SPL be power? (Current)
If that is what happens then that is a rise of 6dB in efficiency, which is what I said.
If you define 'efficiency' simply in voltage terms then you can get increased 'efficiency' just by using very low impedance voice coils.