->I've seen them up to 115 but i'm sure there are higher.
-> TT> The Community RS-880 is rated at 131db @ 1w/1m ...
-> Surely you're not suggesting that any full range system, or even full -> 
coverage high frequency array, can acheive such an efficiency as an i -> 
comparable spec would reflect for it?
 TT> Actually, I'm quite sure that the 2" compression driver used in the
 TT> RS-880 can smack that 131db rating rather nicely.  As for the 15" LF
 TT> drivers and the 1" HF driver, I don't know, but I agree with you that
 TT> they're probably nowhere near as efficient.
They?  
You're carelessly mixing and matching several separate contextual meanings of 
"efficiency" with respect to audio transducers.  You've done it during this 
thread with implications that are essentially mixed apples and oranges.  
A compression driver dB/1w rating usually corrolates closely with an energy 
transfer efficiency.  A high efficiency, high accuracy mid/high compression 
driver from the better vendors is typically about 30-35% efficient, 
converting electrical energy to acoustic energy.  
Cheaper units are often less efficient, with poorer design or cheaper magnet, 
pole, gap, and diaphragm construction.  More efficient units exist, with 
inadequate damping to be of low distortion and good transient accuracy.  
Other designs exist, whether high efficiency piezo, low efficiency 
dome/concave direct radiator, or the esoterics.  
The next efficiency figure we encounter is that of a compression driver on a 
horn or other dispersion control (horn/lens array, or some industrial app's). 
 That is only indirectly reflective of transfer efficiency, and is more a 
combined performance guide, mixing driver transfer efficiency with horn or 
output directional pattern control gain or loss compared to whatever 
reference.  
Low end drivers by nature don't function apart from enclosures or baffles, 
and so have no comparable efficiency to that of the compression driver into a 
plain tube.  The typical small ported commercial PA bottom of about 100 
dB/1w/1m is about 5% efficient.  That would make somewhere around 113 
dB/1w/1m 100% efficient, a practical unattainable target.  Since there are 
some beaming and other directionality quirks even to low end boxes, AFAIK no 
figures that precise can exist.  The Klipsch type huge horns with high 100's 
dB/1w/1m ratings would appear to approach similar transfer efficiencies as 
good midrange drivers, however.  
Last comes integrated system efficiency.  This is generally very much 
weighted by the least efficient parts of the overall system, the low end 
generally.  It's also dependant on passive or active crossover headroom 
factors, and not reflective of overall transfer efficiency as directionality 
isn't uniformly part of such spec's.  Still, one would extrapolate that a 
home speaker of about 90 dB/1w/1m would be so low end/near omni weighted that 
it's likely about 0.5% efficient as to energy transfer from electrical to 
acoustic.  
Whether in a home speaker or near field monitor, or in a multi way high 
performance commercial system, the efficiency spec of a single component of 
the high end driver hardly reflects system efficiency.  A 1" plain wave tube 
has never to my knowledge been used to rate low end or full range.  
 TT> Community is known for making ridiculously efficient compression
 TT> drivers.  For example, their M-4 4" CD, when mounted on a narrow pattern
 TT> metal horn, is used by the Coast Guard's on-shore installations to warn
 TT> foreign vessels that they've left international waters and are
 TT> infringing on the United States' sovereign territory.  Typically these
 TT> announcements are given while the ship is still five miles from shore!
What's the directional beam height and width?  Does this driver compromise 
distortion and transient accuracy to exceed 50% efficiency?  That's possible 
and not unlikely for the application, but still only adds 2-3 dB.  If it also 
handles 300 W and has a very narrow aperture, well, maybe like an air raid 
siren other than of the direct motor/siren variety?  
Terry
--- Maximus 2.01wb
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