gobble,
this is going to be a tough one! i'll try to be as objective as i can.
a single driver is usually made of a cone that is very very responsive. mine are made of paper. imagine two things on a table, a feather and square piece of denim cloth. if you put your face close to them and exhale the feather will fly some distance, the square piece of denim might not even move. now if you blow a little, the feather will fly further and the denim piece might move a little or flap about. single drivers are like feathers, even the smallest signal is converted into sound cos the drivers are so responsive. speakers with cones made of heavy material take more power to produce sound. i found that while listening to cadence aritas, the amp had to driven at higher volume for the speaker to sound decent. at lower volumes it lost out on a lot. if i remember right the aritas have some sort of sandwich cone with nomex? and a lower sensitivity of 88 db or so. this is one part of the single driver charm, most of the signal flowing from the amp is translated into sound whereas in a conventional speaker if the driver is of a heavy material, you lose out on quite a bit of information.
second benefit is there's no crossover so no musical signal getting lost as heat in the crossover. also since no crossover no splitting of signal so a really nice 'whole' sound!
of course there are negatives too like cone resonances which are not damped cos of the light cone and other stuff but overall, a single driver tends to reproduce a lot of micro dynamics that make the music rich. its like a song in lossless format, 320kbps and 128kbps, sure the song is still there but you keep losing out on detail.
so to answer your question of whether single drivers are always better, well they're better making music come alive with the low level cues that are generally lost in two/three way designs. they sound more 'natural' than multiway designs where the sound seems to be split up. and that's why they're a perfect fit with a SET amp. a lot of people say there's magic in the first watt cos all the micro dynamics is encoded in that first watt. i dont really understand this too well but in my listening experience between solid state amps, tube push pull amps, a SET amp is far more natural and alive in its presentation with subtle ambient cues and micro details adding up to make the sound rich and full.
a single driver is a good match for a SET amp cos it can reproduce all the magic that a SET amp puts out. also since the single driver is of a higher efficiency, it can make do with the low wattage of the SET amp.
a SET amp is a good match for a single driver cos most of the low level important information it is putting out is not lost in a crossover but is reproduced as sound.
so regarding your other question of cd playback versus vinyl playback on a SET amp single driver combo, you get the type of sound i've detailed above with both. vinyl being natural and warm matches the combo perfectly. cd playback by itself i prefer on the combo compared to multiple driver systems cos although there's more extended treble and tighter bass, these systems for me simply dont have any 'soul'.
the last speaker i heard was the monitor audio bronzes before choosing the single driver. the bronzes had far more treble information but just didnt connect with me emotionally.
if you're the kind who listens to treble, mid bass, bass, midrange you're likely to not want the SET amp single driver combo. if on the other hand you're the kind of listener who wants the hear the soul of the artist, and not bother about traditional hi-fi attributes, a SET amp and single driver will generally make you far happier.
also the type of tubes in a SET amp make a difference. so you might prefer one type of SET amp over another.
regards
hyeah: !!
