ATI HPSS

The ATI HPSS is an electronic outdoor warning siren manufactured by Acoustic Technology, Inc (ATI) that is used to alert people of Tornadoes, Hurricanes, Severe thunderstorms,fires and so on. It superseced an earlier rotating siren that ATI built. The introduction date is unknown, but thought to be around 1980. It consists of 4 speakers on the HPSS16 model, and 8 on the HPSS32 model. They can also be used as PA speakers. Despite functioning decently as a PA system, the siren function has been riddled with faults.

Problems and criticism

The sirens have met with sharp criticism from civil defense aficionados for a variety of reasons.

• Tone - ATI sirens, with the exception of the most recent models, used a 1000hz Sine wave, that creates a high pitched tone. In San Francisco, California , however, many of their ATIs have the tone of an old Federal Signal STL-10, which has caused reliability problems as the programmed tones are much too low-pitched for the speakers to handle. More recent ATI units use a improved, lower-pitched tone (albeit higher than the STL-10 tone used for San Francisco's sirens), which has given adequate results.

• Speakers - Many of San Francisco's ATIs have had blown speakers due to the low pitch STL-10 tone. In reality, no siren speakers can handle such low-pitched sounds, so this may not necessarily be the fault of the speakers used.