Important background information: this post contains images of spectrograms, a quasi-three dimensional representation of sound over time. For the specific software that generated these, the graph scrolls from left to right, meaning older sound is on the right, newer is on the left. Brighter and yellower means more intensity, darker and bluer means less. The vertical axis of these charts is a logarithmic scale for sound frequency, starting at 10Hz, with the next major line at 100Hz, the next at 1,000, and the final at 10,000. These are probably done via a fast Fourier transform in software on a smartphone and are not likely super accurate, but make it possible to make interesting connections and comparisons in broad strokes.
Friday night, it became apparent that I wasn't going to be able to have a conversation with my friend while we were still on the metro. After we gave up, I took a quick spectrogram of the sound of a 7000-series Metro car* for recordkeeping purposes. That image is below:
The significant bulk of the background noise on a train starts at 40Hz and runs out around 3kHz. Earlier disclaimer about accuracy in mind...
The next night, I remembered to take a spectrogram of my own speech in the relative quiet of my living room. In a normal pitch, I said something to the effect of "so this is the sound of me talking." The second sentence is lost to the sands of my memory, but you can tell when I was making sibilant syllables by the stuff up around 5kHz. I ended the second sentence with a question, which you can tell as the harmonic series deflects upward as the lines approach the right (and you can tell my vocal cords had trouble staying together as I lost upper harmonics above 500Hz). My voice and most of its meaningful harmonics are between 80 and 800 Hz.
Because I didn't manually set the microphone gain manually, there's no way to directly compare the intensity of my voice to a train. I am willing to put as many as five dollars into a bet that the inside of a train is louder than my normal speaking voice, but I'd also bet I would compensate by trying to speak louder while on a train. Normally. Probably not so much if it's Friday evening and I'm trying to be considerate that I'm not yelling at a friend.
The entirety of my voice is within the spectrum of the train's background noise. I'd suspect I'm not special in that regard, but I do think it's interesting and wonder how many other people don't talk while on the Metro for this exact reason.
*7000 series cars make use of no carpeting and have more right angles present inside that older Metro cars, with taller, steeper seats. I have a feeling the cars have a different noise profile than the older models I would last have ridden on several years ago, but I don't know for sure. I just think it's worth noting for some reason.
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