Best Loudspeakers for Rich Timbre?

My Legacy Signature IIIs are 4 ohm and 94db efficiency but only dip a little lower.  They are very easy to drive.  I bought them when I brought along a Sherwood 7100 18 watt receiver.  Fantastic bass and dynamic as well.  I've driven them with Yamaha CR 620 35 watt receivers as well.  Tom Port of Better Records drives his Legacy Focus with the same Yamaha despite their 4 ohm impedance, 1 ohm lower bass impedance than the Signature IIIs but 96 db efficiency.  

I've noted whenever I see difficult to drive speakers like Magico, Wilson and B&W, that the bigger the better solid state amplification is needed.  I'll stick with high efficiency speakers despite lower impedances (which just means that they are often current hungry).  My favorite speakers generally have lower impedence, higher efficiency and easy to drive with smaller tube and solid state amps.   

The problems with measuring THD (Total Harmonic Distortion) in loudspeakers especially seem to be legion.

https://www.audioholics.com/loudspeaker-design/audibility-of-distortion-at-bass/total-harmonic-disto...

Not the easiest of reads, my head still hurts, but this following extract may be especially relevant to our perception of timbre.



"One more factor that can make it more difficult to detect distortion is personal familiarity and understanding of the intended reproduction. For example, most people know what a middle C note of a piano is supposed to sound like, but how many people know what a fist fight between two robots from another world is supposed to sound like? Furthermore, the timbre of musical instruments are heavily defined by the harmonic resonances of the instrument’s fundamental, and these resonances typically occur at even order harmonics, which is considered musical since an even order harmonic is always the same note in an upper octave.

These even-ordered harmonic resonances of musical instruments can make the detection of even ordered harmonic distortions very difficult, since they are ‘tuned’ to the instrument’s fundamental. On the other hand, this fact makes odd-order harmonic distortion a bit easier to hear since the frequency of that distortion doesn’t cleanly relate to the fundamental, at least in the scale of conventional musical notation. In other words, it’s easier to detect ‘off’ components in a sound we are familiar with.

If we have no reference by which to judge the sound, we have no way to know if what we are hearing is apart of the input signal or a distortion in the output. To tie this into the previous discussion, one test showed that even trained listeners were not able to identify as much as 30% distortion peaks from material which had a dense spectra with a high amount of transients and synthesized sounds."



Hopefully, in the not too distant future the type of data revealed by tests such as CEA-2010 will start to become more readily available to any potential customers of high quality loudspeakers.

One of my more surprising, and joyous pairings of amp and speaker actually turned out to be my MBL 121 monitors - spec'd at 4ohm/82db sensitivity, and my lil' old Eico HF-81 integrated tube amp.  A measly 14W/side.  It just sounded glorious:  rich, big, detailed, and the overall sound and bass just seemed to enlarge.  The speakers never sounded bigger and more authoritative than on that little Eico.  (Which, though out of my depth here, I presumed was likely due to some underdamping of the speaker, enrichening the bass). 

prof, I think you're right about the underdamping of the speaker. I recall getting a wonderfully unrestricted breathing bass from a pair of Rega bookshelves when driven by a cheap 7 watt amp.

The sheer unfettered free sound coming from those small boxes was highly compulsive listening. Rega don't give much away regarding construction but as the speakers don't feel particularly heavy I guess some form of thin wall cabinetry
(in best British style) must be involved.

I also remember that you had to turn up the volume to get them singing in this fashion. The timbre of the free flowing bass was as good as I've heard. If only the midrange had been as expressively free. 

Still, whilst not being ideal as main speakers, mainly in terms of scale, openness and bandwidth, they remain far too good for me to ever pass on.

@atmasphere 
I generally try to ignore your posts because many times you indirectly seem to be hawking your own amps. But I have interject here in protest of your negative statement about 4 ohm speakers. I owned on of your amps in the past and very aware of their limitations. Namely, your amps don’t do well with speakers that are 4 ohms or less.  But it doesn’t mean other great amps have this limitation.  In fact, some of the greatest speakers made are 4 ohm or less and are inefficient  (Apogee and Magnepan are few examples).  Paired to proper amp, these speakers can sound unbelievably real.  Sorry, Atmasphere amps paired with Classic horn speakers always sounded colored and unreal to me despite your claims.