DEAR ABBY: Have you noticed how often people fail to get out of the way of electric carts used to transport people who can't walk long distances at airports? It isn't pure cussedness. It's because the "warning beep" used by these carts is near a sound frequency that cannot be easily processed by the human ear. (See: "How We Localize Sound" by W.M. Hartmann in the November 1999 issue of Physics Today.) Thus, airline commuters cannot tell where the sound is coming from, which is hazardous to both walkers and riders.
This is actually a common engineering blunder. The "beep" to announce an incoming fax on a computer modem and the beep of a modern range timer are both typically at a pitch just above the hearing range of a host of older people. The back-up beeper on trucks and heavy equipment is also in the same frequency range. (The higher sound frequencies are usually the first to go.)
We all know that engineers are set in their ways, but perhaps a wake-up call from you will jolt them out of their ruts. -- JACK SALISBURY, PALM COAST, FLA.
DEAR JACK: Yes, I have observed pedestrians failing to get out of the way of carts at airports -- but I had assumed it was because they were electric vehicles and didn't make much noise. Of course, the drivers of those vehicles usually wind up warning pedestrians to "step aside!"
However, assuming that engineers responsible for designing modern equipment are younger people in full possession of all their faculties, your letter should serve as a reminder that our population is aging, a condition frequently accompanied by some degree of hearing loss.