low efficiency speaker vs. high efficiency speaker?

What are the advantages and disadvantages of high efficiency speaker vs. low efficiency speaker? Does it mean that 93db efficient speaker will sound better than 86db?
Speaker sensitivity is not directly related to sound quality. One advantage of higher sensitivity designs is that they can be match with lower output amplifiers. High quality, high wattage amplifiers are much more expensive than mid to low output amplifiers, whereas a high efficiency speaker is no more or less expensive than a similar quality low effieciency design. Remember, any speaker design involves making trade-offs.
There are two groups of audiophiles I believe on this subject. # 1. is the high efficient spkr. low watt amp guys.#2 are the low efficient spkr. high power guys. They both have good reasons why one is better than the other. I personally like somewhere in between,20-70 watt tube amp and 89-93 db spkr.The more efficient a speaker is,the louder it will play per watt, some believe the high efficient is thin and bright. Some believe the low efficient needs gobs of power to get them to sound good. You will have to come to your conclusion on this. Kind of like tubes vs solid state.
i think the major current emphasis on high effiency is due to the interest in low power set amps. you can experience some beautiful sounds with such. however one of the major potential practical down sides to the use of high effiency speakers is the demand of having a very quiet pre-amp and source - any residual humm or other noise, tube hiss for example, come to mind. i prefer lower effiency and higher power.
No. It means that the 93db speaker will play louder than the 86db at the same volume setting on yr pre (or yr integrated). Officially and usually, the db(a) rating documents the intensity of the sound reproduced @ 1 volt/1/2 kHz signal (unless otherwise specified).

Accordingly, if you have a low output (watt) amp that you love, it will probably drive the 93db (i.e. the sound quality will be according to speakers & amp specs) but not the 86db (i.e., the sound will be anaemic, NOT according to expectations).

So, matters of taste and sound quality remain. And, although "efficient" speakers are easier to drive (i.e. will play some music w/a low power amp) they can take the mikey out of the electronics in no-time. Speakers are often partial to (lots of) current...

Also, different speaker designs sport different efficiency ratings: horn-loaded ones have high db measurements. Boxes vary from OK to dismal and abysmal, and statics often have low-ish efficency. Fortunately the present trend favours efficiency... as equipment is revealing and our ears critical, and who can afford a 250W fully linear, hi-speed, pure class A or whatever, razor-edge precise on harmonics amp to drive 79db beauties.

Hence the practical advantage of the 93db. There's more, either way, I'll let the cognoscenti elaborate.

BUT I have found that, efficent or not, speakers require quality and horsepower anyway... i.e. current or voltage (i.e. amp power supply). Which kind of nullifies the efficency effect...

The advantage (all things being equal however...i.e, quality attempts at speaker designs here!!!) of higher sensitivity speakers overall, is that they usually have a much better dynamic efficiency and "snap" to em than lower counterparts!!! Super efficient horn designs (just go to any THX certified cinema where they use Horn speakers and listen!!!), like Avantegardes at 100db sensitivity and such, are way way dynamic and effortless sounding!...the dynamics just slap you in the chest with authority!..even with low powered amps driving em!...just more efficient and sensitive overall! The lower sensitivity speakers ask a whole lot more out of an amp for similar results!...but at that point, your already running out of the limits (and steam) for the drivers on the lower sensitivity speakers for the same volume or out put! For instance...the 87 db sensitive speakers, is running 3 time harder to try to match the volume of what a 93db sensitive speaker is trying to achieve!!! There's so much more head room and "acceleration" left in the 93 db speaker, that it's just effortlessly not hardly even working with much effort!...that's why it sound more powerfull and effortless dynamically overall than the lower 87db designs, and so forth...
Anyway, Unless your talking about "powered" or "active" speakers, which are more efficient as well, in that their amps are more efficient when they are dirrectly on top of the drives of a speaker, driving them dirrectly, your alway's going to get more dynamic finness and effortlessness out of a more sensitive design! Oveall however, you must look at the quality of the gear, and your system your running! If your running the speakers in a pre/pro set-up, using a subwoofer and thus bi-amping your system (say with lower sensitivity speakers), then it's effectively more sensitive than otherwise would be the case with only your mains running!...so it could depend. But, on their own, a more sesitive speaker simply has a dynamic advantage over a lesser sensitivity design!...
I'm sure that Gregm means well, but after reading his response, I have to confess that I would be really confused by now if I didn't understand the subject of speaker efficiency very well.

First of all, the speaker is usually fed the equivalent of a 1 Watt (not 1 volt) test signal at a standard test frequency (usually 1 kHz) and the speaker's output is then measured in decibels (dBs). Secondly, his references to voltage and current are essentially vague, meaningless generalizations -- and an entirely different issue unto itself. Lastly, can anyone tell me what Greg means by his statement that efficient speakers "can take the mikey out of the electronics in no time"? (This one really threw me!) Greg, who is this "mikey" you speak of, and how did he get into the electronics in the first place??

Anyway, as Onhwy61 notes, the speakers efficiency rating has no direct relationship to its sound quality. However, the efficiency of a speaker will dictate how much amplifier power you will need to achieve a given volume level in your listening room. The size of the room itself, its acoustic properties, and distance from the speaker to the listening position, as well as the listener's preferred level of volume all factor into how much amplifier power will be needed.

For every 3 dB you increase the volume you need double the amplifier power in watts. So, if you have a speaker that is providing 93 dB with 1 watt input (dB ratings are usually measured at 1 meter from the speaker), then to go to 96 dB the amp must deliver 2 watts, to get 99 dB the amp must deliver 4 Watts, and 8 Watts for 102 dB, etc. This is without considering room acoustics or the actual distance to the listener. If you are pumping up the bass then this compounds the required amplifier power likewise.

If you are using a speaker that delivers 86 dB output for 1 watt input then doubling the amp power every 3 dB will necessitate more than 40 watts to deliver the same 102 dB level that is attained with only 8 watts from the 93 dB efficient speaker.

So if you'd like to hit 110 dB peaks in a large room with 86 dB efficient speakers then you had better find an amp that can deliver a few hundred watts per speaker.

That's why folks who prefer to use low-power SET tube amps for their unique sonic qualities need speakers that border on 100 dB/watt efficiency. To hit 106 dB peaks with such high efficiency would only require 4 watts.

I hope this helps. :)
bear in mind that most listening happens w/ less than 10w--run the math on an 88db speaker, and you're well into the upper 90s w/ less than 10w. do the same w/ a 93db speaker, and you're more than covered.

however, its FAR more costly to build a quality 200w amp than it is to build a quality 20w amp. all amps are not equal! if the first watt isn't first class top notch, the other 199 only get worse.

as a result, you're often best served (financially and acoustically) if you go hi-sens, lo watt (class A only). it was one of the best decisions i ever made.
Plato, thanks for the corrections & for clarifying what I was trying (unsuccessfully) to convey! As to "mikey": my idea was that a good speaker, be it efficient, will reveal shortcomings in the electronics. So, "make fun" of those electronics... i.e. despite the fact that lower amp output + hi-efficiency will produce the same db level as mega horsepower+lower efficiency, the amp quality remains paramount. Higher efficiency does not make speakers forgiving.

Sorry for the confusion.

there are some very interesting answers. Maybe I can give an experience from the musical side. I used Planars, then dynamic speakers and now I use horns. Let's see it from speakers who does it right , no matter of construction.
With low efficient speakers you need some powerful amps to control them in every area. Powerful, when you want to hear every detail even with low volume. When you want full dynamic with low volume, then there is the first problem. Very difficult.
Next : Powerful amps are everywere, good sounding ones are available too, but the combination, powerful AND Good sounding is rare and normally not cheap.

With high efficient speakers there it is much easier to match this one with a good sounding amp. No matter solid State or Tube. Much more amps sound much better when they don't have to deliver all they can give.
There are people out there who believe that the first Watt is the most important, but this is another story.

So, you get much more satisfying listening results with such a combination when you want ( or have to ) listen with low volume.

You hear normally much more microdynamics and an absolutely effortless reproduction of music.
Sometimes when I listen to Radio ( MD 108 ) I am totally amazed when I hear the singer's breathing. Via Radio !
It's on the source.
My speakers have 99 dB and I use them with Pass mono amps ( 100 W per side, normally a total overkill, but it works excellent ).

The feeling of " being there " is with such a speaker really possible.
Some great responses above, and here's another point to consider. Many solid state desingers will not admit it, but quite a few designs sound better in their 1st 20% of power delivered, than in the next 80% left. In many ways this makes perfect electrical sense. One example: There are class A/B amplifiers that actually run in full class A up to a small point of the power amps rating, then "switch over" to full class A/B as they are required to deliver more power. If you had a speaker that was extremely efficient, you would then be having your amplifier run mostly in it's better sounding Class A state i.e., ending up with a better sounding system.
Thanks for thoghtful responses.
I want this thread open as long as possible to accumulate your information.
I have Totem Forest that is 87db sencitive.
I currently have Bryston 3b-st to drive them.
I've been offered to audition to Cary Cad 50M tube monoblocks which are 50W/ch. Along with that I've auditioned Quicksilver M60 monos in my current setup and they've literally outperformed my Bryston with clarity of midrange. Bass was a little-bit on the background with no significant difference in details. More clear on upper bandwidth and more musical. Dynamics havn't change at all!!!
I wonder if tube output power is more efficient than SS?
Or maybe this is just my imagination due to a transfer from SS to tubes? Another words is that true that tube amplifiers can drive with less power more efficient than SS?
I think Thomasheisig has the great set-up: efficient speakers AND fairly high-powered amps. This gives you a very effortless presentation and great microdynamics. What I would suggest is find the speakers whose characteristics you like then get amplification that will be more than enough.

As far as tubes vs. solid state, tubes tend to distort much more gradually and less harshly.