Few bring up high efficiency subs from a point of home experience, probably because they take up too much space (i.e.: Hoffmann’s Iron Law), and yet others seem not to believe high eff. down into the lower octaves is even possible. Well, it is, and there’s no way around indeed very large size here.
What may surprise some is that despite being highly efficient, many if not most such subs still require sturdy, very high power amplifiers to properly run the typically large diameter woofers with big voice coils and relatively heavy cones. Depending on how these drivers are loaded in their specific designs could mean yet another factor that stresses the amplifier, so that even at lower SPL’s it becomes obvious whether a given amp controls the woofer/design properly. I recently went from a 500W/8 ohm class I (iteration of class D) power amp driving my tapped horn subs to a 1.3kW/8 ohm class TD ditto, and with 97dB sensitivity one would gather no more than around ~20W would be necessitated for general use, making such a swap/power upgrade seem meaningless.
However, the fact of the matter is that the more powerful/different amp is able to have the woofers of the TH subs resonate the horn much more effectively, which is clearly audible/sensed at quite low SPL’s. Turn up the volume and that sensation is viscerally magnified, so much so that one quickly realizes the intimidating (and thrilling) power such a design is capable of.
Is it all all bonkers then - why such a powerful combo of high eff., extension down to 20-25Hz (at full tilt) and a bucket load of power to boot? Because it sounds so utterly effortless, smooth, inherently powerful and immersive at any desired SPL, but not least also at more "sane" and even low playback levels. Many an audiophile isn’t aware of that. Moreover, when the bass is so clean it means that it can (and should) be dialed higher in gain, because less clean and too conspicuous sounding bass is usually dialed lower and in fact too low for it to have proper fullness and presence in the sonic presentation.
