Two weeks ago I experimented with diffusors on the ceiling. I took them down after a few days, to see how things sounded without them: not as pleasant, for sure.
Instead of putting them back up, I decided to try some absorption instead (something I had already played with a year ago, with my open baffle speakers). I ordered 4 panels of 10cm (about 4") thick basotect foam, which I cut up in squares and managed to fix - temporarily - to the ceiling:
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Foam made of Basotect is an exellent insulation guzzler. It reduces noise and resonance enormly within a room (or a hall) and ensures a quiet surrounding. Also the maximum fire protection in this building ...
www.panasorb.eu
I screwed 4 nylon wall plug into the small square panel, then put strong double sided tape on the plugs' heads and pressed them onto masking tape stuck to the wall. I used 3M masking tape for "delicate surfaces", which you can theoretically leave on for 60 days.
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The total surface of the panels were 4 meters by 2 meter. I may add some more.
At this point, and in my room, absorption is probably the way to go (though I could try mixing the two). Will report back in a few weeks.
Everyone knows that each combination of speaker, room, and listening preferences, is unique and may result in different acoustic treatment solutions. So I'm not sure there is much to learn from my experiments, but perhaps it will motivate some to experiment as well.