Different impedance/same system?

[mayhem13]

Consider a two way sealed system with a 4ohm tweeter and 8ohm midbass-midbass driver has 2db greater sensitivity. Any inherent problems that couldn't be reasonably accounted for in the x-over?
Another option would be to add a second midbass in parallel but i'm not sure my receiver will like the 4ohm load.

[Anthony]

You can pad the level of any driver down with a resistor (not an lpad, just a series resistor) and raise the impedance. However, that resistor has to pass through a significant amount of current to the drivers south of it. This is why you normally see this arrangement with a tweeter only: they are more efficienct (usually) and require much less power to drive than a woofer.

2dB is not that much, and many drivers (especially different brands) may end up being perfect matches, despite their SPL spec. It's not uncommon to see a 90dB woofer measure 88 or even 93.

so the simple answer is that you're starting in a hole with the mids being more efficient, especially since you need to raise the impedance of the tweeter a tad (which always comes with an efficiency hit). But it may be doable.

Another thing you can do if you absolutely want these two drivers, is you can use the DCR in any inductors for the woofer low pass filter to eat some of the efficiency. It is not ideal and makes you entire system much less efficient, but it can match the levels.

Last option is active crossover. In my mind, this is the only reason to resort to active crossover (flame on guys ) -- but it is the primary benefit of that route. You can match widely disparate efficiencies between drivers in the crossover to amp stage. Of course that comes at the expense of portability (i.e. plugging into anybody's system) and more gear. But it is an option if you are married to specific drivers that have this problem.

That's all I got now. Hope that helped some.

[BoomieMCT]

+1 what Anthony said about manufactuer's specs not always being spot on. Also the listed sensitivity is often an averaged value. You may find that once in the enclosure things aren't like what they are on paper. The best thing to do is make a test enclosure and go from there.