I've been looking at the kit in the link below and noticed that in their build there is no internal dampening foam. Does this seem right to anyone as the idea of just a sold box makes me think resonance. I've even purchased the PDF but my german isnt up to the translation but it doesnt show any use of foam either.
https://www.madisoundspeakerstore.com/2-way-speaker-kits/nada-2-way-klang-ton-kit-pair-using-illuminator/
https://www.madisoundspeakerstore.com/2-way-speaker-kits/nada-2-way-klang-ton-kit-pair-using-illuminator/