What makes a speaker perform well at low volume?

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

All speakers change "Q" ( tuning ) as they are driven at different levels. As such, they all have a specific point where they will operate most linearly. The problem with a multi-way design is that it is possible for each of the drivers used to experience their "optimum Q" after warm-up in different spl regions. The end result is a lack of cohesivity unless one can find an SPL that presents a happy medium to all of the drivers simultaneously. Most of the time, this won't be at a low listening level either.

Now factor in that all ported / bass reflex designs are subject to variations in the flow velocity of air within the vent as SPL is varied. Unless a vent uses a gentle radiused flare at both the inlet and outlet side, the bass tuning will be optimized over a very narrow SPL range. Once again, if one is trying to listen outside of that range and / or in a range where the other drivers aren't hitting their stride in sequence, the end result is less cohesive sound. In this regards, sealed designs are more linear over a MUCH wider spl range and retain a higher percentage of "bass weight" as spl's are reduced.

As such, it is easy to see why / how speakers using one dynamic driver ( Walsh's / Lowther's / Fostex, etc ) and / or full range planar / E'stat type speakers excell at low volumes. That is, there's only one driver or type of driver to excite and all of the operating characteristics will remain consistent over the entire band. In effect, the speaker is more uniform in its' presentation, regardless of spl range. There is no "confusion" as to when each of the drivers is working optimally as they are all working in unison sharing the same load and electrical characteristics. On a dynamic multi-way system, each driver has individual electrical characteristics and they are VERY different from one another. If they weren't, there wouldn't be a difference between a woofer, a tweeter and a mid.

On top of that, many of these designs, especially E'stat's and Planar's, have very considerable surface area to radiate signal from. Even though one is not moving a lot of air due to a lack of excursion, spreading the sound that is being radiated out over a larger surface tends to present a slightly different tonal and transient presentation to our ears and brain due to the way that it excites the room. The fact that ambience cues remain more consistent with omni & dipolar radiators regardless of spl range also factors in too.

Outside of that, you also have to consider the noise floor of the electronics, how linear they are at low power levels, etc... Most high powered amps don't do all that well at very low power levels, hence the move to lower powered levels and / or higher bias Class A or richer Class AB designs. SET amps are a "double blessing" in that regards as most are both lower powered and Class A biased. The reason that the higher powered amps don't do well is that they make use of a multitude of output devices, which typically aren't matched all that well. At low levels, they are all doing their own thing and it isn't quite in perfect unison. It is not until the drive levels are increased that they begin to work as a team and everything begins to fall into place. The end result is that there is greater "slack" or "tolerance" in the circuit at lower levels, resulting in poorer, less cohesive sound.

As such, there are many factors that add up to "good sound" at low listening levels. If one is going to do a LOT of listening like this, one might want to build their system specifically for this purpose. It is tough to achieve stellar performance levels at both high and low spl levels with good extension and it typically takes a LOT of money to do so. Factoring in realistic expectations as you build your system may make for both a more enjoyable and less costly experience than having to change everything as you find out your listening habits aren't quite as "wild" or "mild" as one originally thought.

As a side note, one of the things that i like most about my Ohm's was the fact that i could listen at low spl's and still achieve staggering bass extension out of this design. It is the only speaker that i know of that can shake the floor at very low spl's. Then again, in stock form, this speaker is not capable of high spl's with good linearity, so it is somewhat of a specialized speaker. As i mentioned above though, i took this factor into consideration when building the system that i use them in. That system is right in the same room as my computer, where i do a lot of late night, low volume listening. The fact that the amps driving them run in Class A up to 50 wpc with 800 wpc at actual impedance of the Ohm's ) assures both high levels of linearity with an iron fist in terms of control : ) Sean
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PS... These speakers are about 82 dB's and present a nominal 2-3 ohm load to the amp. NOT an easy speaker to drive and many amps aren't up to the task, even though their power ratings say they should be.

Currently listening to Cake: Pressure Chief on Redbook CD