Fun fact: the International Bureau of Weights and Measures in Paris is the owner of a perfect 0 dB noise floor enclosed in a perfect titanium sphere (with some

Fun fact: the International Bureau of Weights and Measures in Paris is the owner of a perfect 0 dB noise floor enclosed in a perfect titanium sphere (with some sheep's wool filling to avoid reflections). There is a small door on the side over which microphone capsules can be inserted for calibration. (/joke)