Obviously, it's a camera looking at the strings of a guitar from inside of the sound hole. The illusion is caused by the way the iPhone captures video; it's called the rolling shutter effect ...

A little over 10 years ago, a Phoenix-based startup treated acoustic pickers to a bunch of effects directly through the sound hole courtesy ... of a host acoustic guitar via magnetic rails stuck ...

or “SHamp” is a compact amplifier that fits into the sound hole of an acoustic guitar to give it that bit of extra oomph when you need it. The SHamp features a specially designed speaker and a ...