Wife compliant acoustic treatment

Hi Harald, thanks for posting.

First off, I'm glad you're interested in treating your space. It's an investment you won't regret.

Secondly, I'm on Windows 10 and can't find an app which opens .heic. If you can convert to .jpg and upload the smallest useful file, that'd be best.

Third, we need to quantify 'unobtrusive' and 'effective'. Like Ethan has said, even a washcloth will absorb something. If you want to get down to the second octave, which begins at C2/~65.5Hz then you will need something perhaps more substantial than what those qualifiers typically imply.

If you put a puzzle, which is likely made of rigid pieces, in front of an absorber then it will make the absorber reflective above 1kHz yet it's bass-mitigating properties should remain intact.

If you place 1.5' of rockwool behind a bookcase then it will do something but I hypothesize that you will be disappointed with the result. The reason is that broadband treatment, such as rockwool, is incident-dependent. In other words, you want to have the face of the material directly available to the energy you intend to absorb.

Here's my advice: create squares about 2" thick of rockwool and cover them with an artistic print. Maybe a mosaic/composite pattern where several pieces make up one image. That will be for general 'reflectiveness'. For the piano, you'll need thicker and larger panels - like a standard 2x4'x4" panel or up to 8" thick. That can surround the instrument to great effect forming what's called a recording zone. Basically, you want full absorption 4' in every direction from the source of the sound. For a piano, you'll want to extend the treatment 4' out from where you'd place the microphone. This should help a lot.

Hope that helps, let me know if you have further questions.