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About infrasound
What is infrasound?
Sound below ~20 Hz — the lower edge of human hearing. We don't usually hear it consciously, but instruments pick it up easily. Low frequencies attenuate slowly and bend around obstacles, so infrasound travels enormous distances. More in “What infrasound is”.
Can you hear infrasound?
Mostly no: below ~20 Hz normal hearing fades out. Very loud infrasound is felt as pressure or vibration rather than heard as a tone.
Is “19 Hz” really a fear frequency?
This is largely a myth. It grew from a single anecdotal account; careful reviews find no reliable evidence that any specific frequency consistently induces fear or “ghost” sensations. See the honest breakdown in “Infrasound and health”.
Is infrasound dangerous? Are wind turbines harmful?
At the levels people normally encounter, reviews find no established health harm. Annoyance can be real, but expectation (the nocebo effect) plays a large role. See “Infrasound and health”.
Was “Havana syndrome” an infrasound weapon?
No. Analyses did not support an infra- or ultrasound weapon; one study matched the recordings to a cricket's call. More in the health article.
About HERD
What is HERD building?
A citizen network of low-cost pressure (infrasound) sensors to notice dangerous events earlier — tsunamis, eruptions — plus a low-frequency acoustics lab.
Why a dense cheap network instead of a few precise stations?
Because density buys what sensitivity can't: localization and coverage of local events. That's our article “Density vs. sensitivity”.
Does HERD replace official tsunami warning?
No. We complement DART buoys and warning centres — we don't replace them. HERD is a research and data network, not a certified alarm. See “How HERD fits into early warning”.
Is this a product I can buy today?
Not yet — it's in development. There's a pre-order with a refundable deposit, and the project economics are open.
About the sensor
How much will the sensor cost?
The target is about $25 for a home station.
What's inside?
A high-precision MEMS barometer sampling ~25 readings per second across the 0.01–20 Hz band, with local storage and networking.
What are SPI and FRAM?
SPI is the fast serial bus the microcontroller uses to talk to the sensor. FRAM is fast, durable non-volatile memory used to buffer readings so data isn't lost if power drops.
How much data does it use?
On the order of tens of megabytes per month: infrasound is a stream of pressure values that compresses well. In economy mode it sends only summaries.