Infrasound is acoustic vibrations that occur at a lower frequency than the human

Question

Infrasound is acoustic vibrations that occur at a lower frequency than the human ear can detect. However, there is evidence that humans have some method of detecting this sound, since people often react to many frequencies of infrasound with feelings of horror or dread. This is often cited for a reason that some locations feel haunted, since their structure created resonance modes around these frequencies. If a particular stairway can be modeled as a closed-closed pipe with a fundamental frequency between 13Hz-18Hz, what are the possible lengths of this stairway?

Explanation / Answer

There can be a range of lengths for this fundamental frequency range.

For frequency of 18Hz, L = v/4f = 343/(4 x 18) = 4.76 m

For frequency of 13Hz, L = v/4f = 343/(4 x 13) = 6.6 m

Hence the possible lengths of this particular stairway lies between 4.76 - 6.6m

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