Sound & Hearing

Picket Fence Beats

PICKET FENCE BEATS has two slightly differently spaced picket fences attached to each other. Because the picket spacing is slightly different, the pickets, which start out in step, are soon out of step. They then return back to being in step, but different now by one whole picket. From a few steps back, an observer sees a moire pattern or a visual beat pattern. If a slat of wood is run across the top of the picket fence the wood clacks where it falls between the pickets (where they line up) and slides with little noise where the pickets don't line up, making an audible beat pattern.