Best speaker brands for transient response

I've owned/own four different pairs of ATC speakers.  Two active, two passive:  ATC 40A, 50A.  ATC 7, 20.  Even the small ATC 7 at 7 liters needs my Sugden A21SE class A at 33 wpc to properly push them around.  The ATC 20 needs the 125 wpc Luxman 509X to control massive magnets.  

Just saying that some may under power (translation, not enough stable current) sealed cabinet speakers producing anemic non-involving results.  Some will blame the transducer, that is not where the problem lay.

Active is where I live for reference, but the passives are also quite good.

@celtic66 thank you this really helps tell me that I'm likely not quite ready for ATCs. Like the ATCs, the Spendor D7.2s  are described as achieving the qualities I'm looking for most, and will be more flexible with amp matching. 

 

The best transient response I've ever heard, are ion plasma tweeters. 

It's hard to beat drivers with zero mass.

Lansche and AvantGarde Acoustics both have very impressive transient response behavior. 

Next in line would probably be ribbons and electrostatic.

Diaphragm mass does have a strong correlation to treble quality and perceived “transient response” IME, even among tweeters made of the same material from the same manufacturer.

Open baffle speakers give you what a panel speaker can or electrostatic speakers but with full dynamics and bottom-end impact. Transparent to the source and quality of the music. You have the best of both worlds. 

Years ago I tried to measure transient response to come up with an understanding of why I thought horns sounded better than direct radiators. In nearfield measurements I was shocked to see that cheap little bookshelf speakers that only sounded OK to me were actually faster and cleaner in the transients than my beloved horns, which were a bit messy because of ringing. I was looking for extremely high speed effects at the start and stop of notes at all frequencies, and what I learned is that my perception is far less effected by those than longer term effects of room reflections. My conclusion was that my perception of dynamics and speed from the horns involved time periods of 5 to 10 milliseconds or more - issues that arise from room reflections, not sub 1/10th millisecond issues that arise from the mass of the diaphragm, or slew times of amplifiers, or differences in arrival time between drivers. The improved direct to reflected ratio from the horns higher directivity, I concluded, was what was giving me the impression of horns being faster. I deduced this was also somewhat true for electrostatics and other dipole designs that tend to cancel along their sides, so the direct to reflected energy is higher at the listening position. I’m still not certain of this, because I have found ways to make horns sound really tame and seemingly lacking in dynamics, so a balance of frequency response is also important. Insufficient energy in the midrange, and other frequency response imbalances also seem to kill my impression of impact and speed. So a well balanced direct radiator may in some ways seem to hit harder.

Also the ability to turn up the volume without apparent strain on the system seems quite important.

This may not be true for everybody, so I’m not saying this is THE answer, but it’s an answer that at least partially explains what some of us our hearing that correlates to our perception of quick dynamics. I have heard plasma tweeters on various occasions, and they sounded good to me. But I’ve also heard little 3/4" doped silk dome tweeters sound every bit as fast. It always amazes me that a little soft piece of silk with rubbery goo on it can sound like a high pitched metal bell when asked to.