Insulating case for speakers: for audio debugging without disturbing others.

I find myself having to work on a speaker, and to test it at maximum volume at home I am limited to pushing it to the maximum for a few seconds without disturbing the neighbors. This is limiting.

I would like to build an isolating case to attenuate the audio power as much as possible inside it and be able to listen for any distortions present at maximum volume, in a simple and DIY way.

I was thinking of lining a polystyrene box and mounting the speaker inside it, but would it be effective as an attenuator? Has anyone faced a similar problem or have a better idea? I know it's not ideal for evaluating audio quality and it could worsen it, but I could add a hole in this theoretical isolating box to bring the ear closer for a more realistic listening experience. In any case, it must be something temporary, not high engineering.