What makes a High Efficiency Speaker

Efficiency = how much work it takes to give a certain result.

Example a more "Standard" efficiency speaker at around 90 db rating with 100 watt amp, will give a certain output DB at certain Gain level(volume)

Now a 93 db speaker will Give you the same output(theoretically) as the 90 db speaker, but will not take 100 watts it will take 50 watts... Less Work for the same results.

Go up to 96 db and essentially it will take 25 watts to do the same as the 93 db with 50 watts...

every 3 db increase in efficency should basically take half the work for similar results.. of course with everything else being equal, so its not like a 50 watt Threshold is not going to sound as powerfull as a 100 watt SANYO, as a matter of fact it would probably get slaugtered, but thats getting into a whole other issue.

But more watts is not necessarily better, however bigger amps regardless of the efficiency of the speakers can have more Headroom, another subject.

so don't go off thinking that a 100 db speaker will sound its best with a 10 watt amp, and be equal to a 90 db with a 200 watt amp in the sense of final results. its all about combination of equipment and really HOW good an amp is regardless of specs.

In a general sense more efficiency designed speaker could be better at lower level volume sound wise, due to they are more sensitive as well. And sure some big time wilson's or something still need some big time power regardless of the efficiency due to the larger woofers and desired SPL's. And they can work fine with smaller more refined amps as well depending on the rest of the requirments of one's listening environment, preference, and pocket book.

Sorry if I confused matters at all and correct any of the above as seen fit.

Nowadays, many of the "high efficiency" speakers are made (or I should say Marketed) by sticking a dubious quality high power amplifier inside the woofer cabinet. Out of Sight, Out of Mind.

Of course, these speakers aren't really high efficiency at all - they're "high hyperbole". But since you can "run" these speakers with your flea-powered tube amp (which is actually just acting partially as a preamp now), the manufacturers seem to have people bamboozled. There's nothing at all wrong with this concept as an amplification solution - it's just that it can be done by anyone with ANY pair of speakers. It's called BIAMPING!

The only true high efficiency speakers are horn loaded - or headphones.

". . .The only true high efficiency speakers are horn loaded. . ."

Untrue. Fostex and Lowther make hi-efficiency drivers that do not have to be hornloaded. Zu makes speakers over 100 db efficient without hornloading. Dedaelus makes the DA-1 at around 96 db efficiency and it's a multi-way!

True - I should have said "full range speaker". I wasn't talking about individual drivers outside of a cabinet.

Sidebar - I don't want to start an argument about ZU's efficiency claims, because there have been plenty already, and it is a reasonably high efficiency driver - but I am very skeptical of their claims for 101db in a 1 cu ft. sealed box - and the only third party measurements I've seen indicate about an average sensitivity of 95db in the midrange (which ain't bad) by my eyeballing:

http://www.soundstagemagazine.com/measurements/zucable_druid/

(Also note a dramatic roll off in the lows well below the ZU advertised claims.)

In addition, the ZU super-tweeter IS (and needs to be) horn loaded.

As you've probably noticed, Punkuk, there's a wide diversity of opinion as to what exactly consitutes a "high efficiency" speaker.

One thing you should keep your eye on is exactly what's being specified by the manufacturer. Typically manufacturers of speakers with an impedance below 8 ohms specify the 2.83 volt sensitivity, as that gives more impressive looking numbers. And typically manufacturers of speakers with an impedance higher than 8 ohms specify the 1 watt efficiency, again because it looks better. Here's how it goes: 2.83 volts into 8 ohms is 1 watt, but 2.83 volts into 4 ohms is 2 watts, and 2.83 volts into 2 ohms is 4 watts. Going the other way, 2.83 volts into 16 ohms is 1/2 watt, and 2.83 volts into 32 ohms is 1/4 watt. When you turn the volume control knob on your preamp, you're changing the voltage output (and the wattage output changes along with it). When you leave the volume control setting the same and switch to lower impedance speakers, the voltage output stays the same but the wattage output increases (assuming the amp doesn't clip).

Let's do an example of converting sensitivity to efficiency. Suppose you have a "93 dB sensitive, 4 ohm" loudspeaker. Sensitivity refers to 2.83 volts input which into a 4 ohm load is 2 watts, so the speaker is really doing that 93 dB with TWO watts input, so the efficiency is only 90 dB with ONE watt.

Unfortunately, some manufacturers use the word "efficiency" when "sensitivity" would be more appropriate, and vice versa. And unfortunately some manufacturers use an "in-room" rather than "anechoic" or "simulated anechoic" measurement, which inflates the specification by 2-3 dB due to the added reverberant energy. Using an "in-room" measurement is not without justification, but does complicate things when you're trying to make an apples-to-apples comparison.

In my opinion efficiency is a more useful specification than sensitivity because wattage input (not voltage input) is what relates directly to voice coil heating and thermal compression. Then if you want to you can take into account how much power the amplifier you have in mind puts out into that particular speaker's impedance. Most solid state amps increase their power output into lower impedance loads, but often there's a sonic trade-off, as many amps distort less into a high impedance load.

I'm not qualified to say where anyone else should draw the line between "high efficiency" and "not high efficiency". Personally, I consider 91-94 dB as moderately high efficiency; 95-98 dB as high efficiency, and 99+ dB (all with a 1 watt input) as very high efficiency. But in my book those are only ballparks, and the lines are blurry.

I've focused on measurements, but your question could be approached from other angles as well (how is a high efficiency driver constructed, what are the techniques commonly used to build a high-efficiency loudspeaker system, what are the challenges involved in building a good one, why would you want one in the first place, etc.) But I'll save the muddying of those waters for another day.

Duke