Well, Banjer, I didn't actually say "vacuum" because then the poor fragile harp-thing would implode from the air pressure outside (LOL). I hope you were impressed by my technical jargon.
The only reason I said it like that was: I had an Aoyama 36 string harp, which is a Japanese model shaped a lot like a pedal harp and which seems to be designed and marketed towards learners who aim to work towards getting a pedal harp.
The sound was very muffled and plunky, not at all comparable to any of the reasonably made Celtic harps I heard then or since (i.e. over 20 years). One of the reasons it had such a dull sound is probably because it had these huge bracings inside made of metal tubing or it may even have been solid metal. I haven't seen any other harp with such heavy plumbing inside, and I have only heard one other harp which had that plunky sound, and it was also marketed for future pedal harpists, either because they couldn't afford to plunge straight into the commitment of a >$10,000 harp, or, sensibly, they wanted to see how they went learning the harp before making that commitment. These harps seem to sacrifice sound quality, i.e. short term pleasure, for practicality and durability.