What makes a High Efficiency Speaker

Thanks Duke your was the easiest to unnderstand after that it became more like Quantum physics to me.

The reason I asked was I am getting a pair of sixpacs and my speaker is the Gallo Ref 3's, which as I understand now is far from a High Efficiency speaker at 88db at 1w
But if I am not mistaken its 34hz-50khz is prety good in the sensitivity area
The Gentlman I am getting them from said he ran a High Efficiency speaker (klipsh cornwalls) with horns my concern is am I getting the wrong Mono Blocks for my speaker.
The room is small 18X13 and with kids and the wife I dont get to "crank" them up.
But I would hate to contine to make expensive mistakes in my journey to find that sweet sound I have yet to discover.

Very interesting. Great thread, one and all. Thank you for taking the time to provide all of this info. To this I would only add that having never heard the Zu speakers, if they sound good, then they are good, regardless of how they measure or how much hype or creative "accounting" their marketing department uses. And if they are only 97 dB thats still a pretty darn efficient loudspeaker and should be capable of being driven by small SET amps. To quote Duke "What Zu has done is build a speaker whose perceived bass extension is much better than I ever would have thought possible in that box size and efficiency combination." And that is quite an accomplishment, in my (technically ignorant, but interested) opinion.

Here are some SPL measurements.

Planar is a MG1.6. PS is a Dynaudio Gemini (small MTM).

Signal is pink noise generated by Prepro (intended for setting levels).

Distance is feet.

Distance..Planar...PS.....PS
........0........100.....100
........1.........98......90.....108
........2.........96......88.....102
........3.........96......85......99
........4.........95......83......97
........5.........94......81......96
........6.........93......80......94
........7.........92......79......93
........8.........91......77......93
........9.........91......77......92
.......10.........90......77......92
.......11.........90......77......92
.......12.........90......77......90
.......13.........88
.......14.........88
.......15.........87
.......16.........87
.......17.........86

The first PS column shows the SPL leveling out at 77 dB. I think this reflects room effect. For the second PS column I increased the volume so that the SPL at 12 feet was the same as the planar, 90dB. This required the near field SPL to be a lot higher, 108 dB at 1 foot.

I don't think anyone listens at a distance of 3 feet, although that is close to the 1 meter distance used for the spec. At a more reasonable listening distance, between 8 and 12 feet, the Planar SPL falls off by 1 dB over this distance range, while the PS falls off by 3 dB. To produce equal SPL at 12 feet the PS speaker would need to be about 3dB more efficient at 1 meter. I think that these results are generally in agreement with theory.