Hmmm. Reminded me of some measurements I took a while back.
Inside:
Outside:
Sonarworks XREF20 mic via Rode A1 Audio interface into Audacity on MacBook Pro roughly calibrated so 0 dB = 100 dB SPL approx. Sampled early am in winter an hour or two before sunrise.
I was noticing a low frequency hum in the middle of the night when things are otherwise quiet, wanted to know if it was biological self-noise or an hallucination, but apparently neither. Sounds just like it looks, a bit more bias to higher frequencies outside, and likely resonating within the room inside (heavy timber-framed house but temperate climate thin walls attenuate higher frequencies but likely pretty transparent to lower).
There's a freeway up-river about 5 km which is audible—albeit low level—under the right atmospheric conditions. When that happens the hum is masked. The latter could simply be the lowest frequency component of the freeway bridge vibration coming through the earth, for example, even when the recognisable sounds are drifting the other way. Sometimes the house moves very gently when a big freight train crosses the railway bridge, so there's a definite path for mechanical transmission going on. Otherwise it's all national parklands surrounding a tiny pocket suburb on the very edge of the city. Just copper water pipe and electrics coming into the house, no sewer or HVAC. No wind farms, high tension power lines or not-so-secret military bases in the neighbourhood.
Inside:
Outside:
Sonarworks XREF20 mic via Rode A1 Audio interface into Audacity on MacBook Pro roughly calibrated so 0 dB = 100 dB SPL approx. Sampled early am in winter an hour or two before sunrise.
I was noticing a low frequency hum in the middle of the night when things are otherwise quiet, wanted to know if it was biological self-noise or an hallucination, but apparently neither. Sounds just like it looks, a bit more bias to higher frequencies outside, and likely resonating within the room inside (heavy timber-framed house but temperate climate thin walls attenuate higher frequencies but likely pretty transparent to lower).
There's a freeway up-river about 5 km which is audible—albeit low level—under the right atmospheric conditions. When that happens the hum is masked. The latter could simply be the lowest frequency component of the freeway bridge vibration coming through the earth, for example, even when the recognisable sounds are drifting the other way. Sometimes the house moves very gently when a big freight train crosses the railway bridge, so there's a definite path for mechanical transmission going on. Otherwise it's all national parklands surrounding a tiny pocket suburb on the very edge of the city. Just copper water pipe and electrics coming into the house, no sewer or HVAC. No wind farms, high tension power lines or not-so-secret military bases in the neighbourhood.
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