[jaggederest]

Argon transmits sound much worse than air. I believe it's due to the fact that denser gases require more energy to compress and decompress, thus dampening sound vibrations.

Even more fancy windows use Krypton, since it has superior thermal and acoustic properties over Argon, but is about 60 times more expensive.

Xenon would also be a candidate, but it's about 10 times more expensive even than krypton, and also has the extreme downside of being an anesthetic when inhaled.

Edit: Sorry, I guess it has better thermal properties but worse acoustic ones. Helium or Hydrogen would be the ideal gasses for sound reduction.

[Terr_]

> Xenon [...] an anesthetic when inhaled.

That reminds me of a bit of dialogue from the classic game Deus Ex (2000), where a biotech office-worker is complaining about their job:

> This chemoreceptor patent-proposal is kicking my ass. Hundley won't let me down until it's done. Hardly worth filing for, in my opinion. Who wants to smell the difference between xenon and radon?

[pclmulqdq]

In general, denser materials are better (and faster) at transmitting physical waves sound and worse (and slower) at transmitting electric waves like heat.