What component is responsible for dynamics ?

They all contribute to different extents case by case. It depends on the specific system.

The component used with the worst dynamic range is teh bottleneck and is responsible for whatever dynamics you hear or not. Improve that piece with one that does dynamics better and your dynamics should improve the most.

In most cases, it might be either speaker, amp, pre-amp or source that is the bottleneck. With digital sources, nowadays I think most decent digital sources are less likely than the others to be the bottleneck. I think the same is true in general regarding ICs and speaker wires. With most decent ones, these are less likely to be the bottleneck in most cases.

Also, its not just the individual pieces but how they interface together in terms of impedance that also matters for best dynamics. Higher ratios of device input impedance to output impedance of the device feeding it will help assure that dynamics are retained at each step in the component chain.

A common mistake that often results in bad dynamics is using a high output impedance tube pre-amp with a lwoer input impedance SS amp not designed to work well with a tube pre-amp. or similarly, a tube output source device like a DAC used with a pre-amp with lower input impedance. Both together would be a double whammy in terms of dynamics. However, a combo like this might sound very good in other ways, ie not fatiguing, smooth, involving, etc.

Another is having small or underbuilt speakers that cannot handle dynamics sufficiently,

A third is having an amp that is underpowered or not capable of driving a good pair of speakers properly to to their maximum potential.

Hiefficiency speakers and flea power tube amp is one way to skin the
cat, but far from the only one.

Listening volume should be a concern. I've read regular listening above
80 db or so causes hearing loss. Hi effspeakers can be like a weapon,
and so be careful. And yes setup is everything especially with hi eff horns
which can be like listening under a microscope.

Noise floor might be more of a real issue with older analog sources than
modern digital.

Hey guys, its that time of year?

Ho ho ho, Merry Xmas, Peace on Earth, and all that?

Dynamics rule!

"However I don't normally listen very loud- this results in the system being so effortless that it has no sense of loudness at all- you can't tell how loud the system is playing unless you try to talk to someone standing next to you. This to me is the sign of a good system- one that does not sound loud even when it is. Such systems tend to have more 'impact' as well. The two qualities go hand in hand, even though it might seem counterintuitive. "

Agreed.

OF course, being hard of hearing could be another explanation for the system not sounding as loud as it is. :^)

I've heard the effect Ralph describes on some amps but not others in recent years. Mostly with tube and Class D type amps.