There are good and bad examples of all kinds of speakers with different attributes. Assuming the speaker has a reasonably smooth and balanced frequency response, the efficient speaker has several particularly important advantages. The primary advantage is that, at least for my taste, the very best amps are low in power output. I like tube amps, but, mostly those that do not use higher powered pentode output tubes that are used in large quantities to achieve high power, and even solid state amps seem to be better sounding if they are not extremely powerful (e.g., First Watt amplifiers).
The other advantage is that high efficiency speakers tend to have better dynamics because they will deliver decent volume without as much power being dissipated as heat. That heat being dissipated in low-efficiency speakers increases the resistance of the electrical component, which means less current/power can be delivered; this is thermal compression that means the volume level does not increase in proper proportion to the signal level.
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I can see how it would be harder to control resonance of larger boxes. But, many of the designs that employ heroic measures to control resonance tend to sound a bit sterile, lifeless and lacking in "weight" (thin and anemic sounding). I have no idea if this is because of the resonance control or some other design choices, but, I will say that I don't look at ANY design choice as being dispositive of whether the sound will be good or bad and I don't rule out any speaker just because it is designed or built in a particular way. I've heard some really nice speakers with big cabinets with thin, almost flimsy looking walls that have to be resonating--whether they sound good because of the resonance or despite it, I cannot say for certain.
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There are many low efficiency speakers that are quite good sounding, but, that is despite being low efficiency--there is nothing favorable about that attribute. For example, Soundlab electrostatics, Magneplanar planar magnetic/ribbon, Falcon LS3/5A small box speakers sound pretty good, but, because they are low in efficiency, they are more limited in the ability to use amps such as single ended triode tube amps or lower-powered pentode/tetrode tube amps like those employing the 6L6 tube. Everything else being equal, I will take a high efficiency speaker any day over a low-efficiency one.
Most high efficiency speakers take advantage of very big boxes to deliver higher bass volume. When stereo came along, it became harder to fit two big boxes in a room, which is why smaller, less efficient speakers were favored. The use of transistors made it easier and cheaper to provide the necessary power for these less efficient boxes. These practical considerations played a big role in low-efficiency speakers taking over.
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phusis,
Thank you for an excellent description of what is most prized about the sound of high efficiency systems, particularly, horn-based systems.
While good design of such systems will ameliorate midrange "peaky" or "nasal" colorations, such systems do tend to be a bit less smooth in frequency response than better low-efficiency direct radiating speakers. I hesitate to say this because so many people have heard grossly uneven horn and wide range high efficiency driver systems, and do associate such systems with such coloration, but I will say that such problems can be effectively ameliorated in better designs. Still, I can see why such systems will not be to everyone's taste.
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I sort of think that 95-96 is at the low end of the range. My speakers are 99 db/w efficient, and friend calls that medium efficiency (his speakers are above 112 db/w efficient. It also matters how smooth and high is the impedance curve of the speaker. I recall how one of the Wilson Watt/Puppy speakers was supposedly 95 db efficient (at a nominal 4 ohms, meaning some more realistically at 93 db/w efficient) which should have made it fairly easy to drive, but it turned out to be a very demanding and difficult speaker to couple with some tube amps. On the other hand, the original BBC monitor LS3/5A (15 ohm version) which is rated in the low 80's as far as efficiency goes, couples well with even somewhat low-powered amps because it is a very easy load.
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As someone above mentioned, most of these high-efficiency systems do not do really deep bass. That is one of the tradeoffs that attend going this route. For my taste, the very best woofers for a high efficiency system must be very agile to match the other drivers. This typically means very light paper cones, and somewhat limited excursion (I particularly like drivers with pleated fabric or paper surrounds). I've heard systems with twin 18" woofers per side that were still a touch limited in very deep extension, but, I really did not care much--the bass was clean, fast, and had "tone," which is more important to me. I have no interest in a subwoofer, and several of my friends who are horn-based system experts say that subwoofers are NOT the way to go. My system has very modest twin 12" woofers per channel (pleated fabric surround, alnico magnet) in a Jensen-Onken bass reflex cabinet; it does not do deep bass. With every system, you have to live with some limitations.
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While it may not be optimal, I’ve heard large horn systems in some really small rooms that sounded very good. Check out Japanese audio magazines and you will see large horns in tiny Japanese apartments. Japanese people are very considerate and would not be inclined to bother their neighbors so they would play their systems at low volume. It is at LOW volume that horn systems shine.
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SET amps are silly if you use them in the wrong system, or, if you get cheaply built crap that stint on the quality of the output transformer and other critical components (because they are simple in design, some mistakenly think they can spend less on SET amps and still get reasonable quality). That said, I am not particularly wedded to any type of tube amp design. My all-time favorite amp is an OTL design, my next favorite is a push pull triode amp, and the favorite among the amps I own is a push pull pentode amp; my next favorite is a parallel SET.
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I have heard quite a number of big, high efficiency systems running multiple 18" drivers (e.g., Western Electric M10, G.I.P. reproductions of M10, Goodman 18" permanent magnet and fieldcoil woofers) and they deliver the speed, impact, and tonality that I think are most important in such drivers. But, I have never heard these systems deliver really low bass at a high level. I just don't care that much that they don't do subwoofer stuff and I don't really like subwoofers in these sort of high efficiency systems. There are compromises in any kind of system one assembles, and these kinds of woofers deliver what matters to me. Do they measure impressively? I don't know or care. I like Rolls Royce's specification of horsepower in the old days: "Sufficient."
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Johnk is not wrong. High efficiency speakers are much more dynamic sounding, at least in part, because they suffer less from thermal compression. When playing at any given level, the higher efficiency speaker will be passing much less current and the voice coil will not be heating up as much as is the case with a low efficiency speaker. That heating of the wire causes an increase in the resistance of the wire, which means, when there is an even stronger current that is suppose to flow, the amount that can flow is reduced and not proportionate to what is supposed to flow. This results in compression (less than proportionate increase in the current flowing and the resulting movement of the diaphragm).
The increase in dynamics of high efficiency horn systems is evident even at quite low volume levels. In fact, I tend to find that it is MOST evident when playing music at modest levels--high efficiency systems sound more lively.
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