Driver efficiency vs. overall speaker efficiency

You can't measure the efficiency of a bare driver. It needs to be in some sort of test enclosure. The test enclosure is not the same as the final system enclosure, and may yield a lower efficiency measurement. This is not a problem if your objective is just to compare different drivers (all tested in the same box).

Twl is correct.

Though, one should question the heck out of companies who use drivers of 88 db/2.83 V sensitivity and then claim the speakers are 94 db/2.83 V sensitive. I know of one famous one that plays this game egregiously.

Sorry , I meant 87.5db. It was a typo. I was looking at various Vifa and Scan Speak mid-range drivers and almost all of them has an efficiency rating of 87db or less. So I was wondering how one can build a speaker using those driver but can achieve an efficiency rating of 90db or larger.

If you connect two drivers in an MTM configuration,the impedence will be halved,drawing twice the current, but about 6 dbs will be added. So,it is possible to wire two 88db,8 ohm speakers so that the final result is 94db sensitive into 4 ohms.

Pragmatist, if more current is drawn to achieve a higher sound level, the efficiency hasn't increased. Or am I making a mistake here? A higher efficiency means more output with teh same cuurent.