What makes a speaker perform well at low volume?

IME, the amp, the speaker and the cable all make a difference. Tube amps can sound excellent at low volumes, but I've heard a couple of SS amps that can too. Some speakers are better than others at low volume, more efficient speaker generally being better. My Tannoys were outstanding at low volumes maintaining life and presence, my AN E's less so which seem to lose life at very low volumes (and are actually efficient speakers at 94 db). But this last point I think could be related to the cable. I'm running 17 feet of speaker cable and something tells me that the long length of cable is not good for low volumes. I have not been able to try the E's on shorter cable.

Another good low volume pair was my JMR Trentes with the Resolution Audio s30 integrated amp. This amp is based on a DNM design which is noted for maintaining life at low volumes. Conversely, I had a Blue Circle amp that went dead at low volumes.

Three words: Low level detail. Sometimes the problem lies in the passive parts of your louspeakers (binding posts, wiring, crossovers, etc). sometimes it's the drivers themselves. Sometimes the problem is farther up the signal chain. And yes, high-efficiency/high-sensitivity speakers, especially single driver speakers, and well executed multidriver speakers are usually good in this regard. It also helps to have speakers that sound coherent (as cut from the same sonic cloth) over as much of the volume range as possible.

I don't have all of the answers. I've only been at this for less than 4 years.

Lack of hysteresis provides good performance at low volume. A speaker has to settle exactly at the same resting point every time there is "0" signal. Most do not and they "oilcan" to some extent. This muddies low volume inputs.

I was not able to "hear" everything at low volume until I replaced my pre-amp with a Tom Evans Vibe and Pulse. This suggests to me that every component may have something to do with this. Any weakness can possibly hamper the ability to play properly at a low volume.

First, a speaker must have excellent low-level resolution. This is primarily a power-to-weight ratio issue, so high efficiency speakers do well here (very powerful magnets), as do electrostats (ultralight weight diaphragms). The suspension system comes into play as well; some suspensions exhibit hysteresis (slow return to rest position) that can reduce low-level dynamic contrasts.

Next, a speaker must have fairly smooth midrange to sound good at low volume levels. At normal volume levels prominent bass can mask midrange peaks and resonances, but very low volume levels can unmask these anomalies. The ear's sensitivity is weighted more towards the midrange at low volume levels, so glitches in that region aren't going to be masked by the bass.

Then we want the tonal balance to remain correct at low volume levels. We'd like to think that the woofer and tweeter both get loud at exactly the same rate (3 dB for each doubling of input power), but in reality that's seldom the case. The vast majority of drivers exhibit power compression of some kind, with the result being that a doubling of input power gives a less than 3 dB increase in loudness, and conversely a halving of input power gives a less than 3 dB decrease in loudness. Typically woofers compress more than do tweeters, so if a two-way speaker is voiced to sound right at say 80 dB, then up at 100 dB it will sound bright (tweeter louder than woofer) and down at 60 dB it will sound dull (tweeter softer than woofer). Single-driver speakers inherently do a fine job of retaining their tonal balance at low power levels; unfortunately many single-driver speakers have a somewhat thin tonal balance that leaves the bass completely out of the presentation at low levels.

Finally, at low volume levels good dynamic contrast is especially important, as we must rely on dynamic contrast to breathe liveliness into the sound because by definition we can't do it with impact. Dynamic contrast (lack of power compression) generally correlates very well with efficiency; in other words more efficient speakers are likely to have better dynamic contrast at low volume levels. The crossover seems to play a role here as well; this may be overgeneralizing, but crossoverless or simple-crossover speakers seem to me more likely to sound good at low volume levels.

Speakers that sound especially good at low volume levels include models from Quad (especially their original ESL, the "57"), Omega, Cain & Cain, Classic Audio Reproductions, Sound Lab, and Edgarhorn. These are all either high efficiency horn or single-driver speakers, or full-range electrostatics. Disclaimer - I peddle some of these. No doubt there are other speakers that sound quite good at low volume levels, but I'm just mentioning these as examples that I'm fairly familiar with.

In my opinion, if a speaker sounds good at very low volume levels, that's an excellent predictor of long-term fatigue-free enjoyment. I recommend that people listen at very low volume levels at some point in their auditioning process, because this will reveal a lot about a loudspeaker that can otherwise be overlooked in the excitement of how good they sound when cranked up. In particular, listening at low volume levels will reveal how good the low-level detail is, and that's often what separates the great speakers from the good ones. Also, midrange problems are often more easily highlighted at low volume levels. And if the speaker's tonal character changes markedly when you turn the volume way down, chances are it also changes markedly when a very loud peak comes along.

If I ever bring out a loudspeaker of my own, sounding good at very low volume levels will be a high priority.

Duke