Plaster Walls

I have plaster walls and there's no need to put up sheet rock. Use carpeting or oriental rugs, hang drapes, and tapestries, and use soft furniture and bookcases to dampen the room. You'll need to use acoustic panels on the walls to treat the room for sound absorption and/or diffusion. Sometimes a panel is needed on the ceiling.

Look at the GIK Acoustic website for samples and advice. If the room is for listening only, you can use DIY foam panels; not as attractive but inexpensive.

Plaster/lath is much denser, more rigid and thus: less resonant, than the Sheetrock over stud construction, of later homes. The former retains less energy/returns less to the room, than the latter, which I've personally found; makes those rooms easier to treat. The shape and dimensions of any given room will have more bearing on the Sabine times, absorption or diffraction treatments necessary, for good audio reproduction. Plaster/lath also better reduces the sound & noise that is transmitted to/from adjacent rooms, or the great outdoors.

Yeah plaster should be fine. Plain sheetrock is the worst. I had to move back to the basement with stone walls because the modern sheetrock was thrumming. It you do ever decide to sheetrock, put it over the plaster.

Plaster is preferred for its acoustical properties. You did well. Rodman is right. Drywall is a step backward.

Rodman99999 nailed it (pun intended). "Plaster/lath is much denser, more rigid and thus: less resonant"

I agree with all of the above. I have had systems in both plaster and drywall, and I think plaster is preferable.

Sheetrock is unknown in Germany , Plaster is.
Every room I ever had in Germany was better than any American one I ever had.
Outer walls being 2-3 feet thick might have had something to do with it as well.

Thanks for all of the tips. Sounds like it won't be as much of a problem as first thought. Have started putting in drapes and will proceed from there with the panels and softer furniture.

There is a guy named Michael Green that runs a board called Tuneland. He seems to have a vastly different philosophy concerning room acoustics. He said Sheetrock is good while plaster is bad. He seems to believe equipment needs to be "tuned" and then put into an environment which does have highly resonant properties. At least that is what I can gather. Sounds like his goal is to create a sound that is perhaps bright vs. neutral.