ATI HPSS

The ATI HPSS is an electronic outdoor warning siren manufactured by Acoustic Technology, Inc (ATI) that is used to alert the surrounding populace of tornadoes, hurricanes, severe thunderstorms, fires and so on. It superseded an earlier rotating siren that ATI designed. 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. Like other electronic outdoor warning systems (such as the Federal Signal Modulator, for example), they can also be used as Public Announcement (PA) systems.

Problems and criticism

The sirens have drawn sharp criticism from civil defense aficionados for several reasons.

• Tone - ATI sirens, with the exception of the most recent models (and the ATI systems used in San Francisco, California), used a 1000 Hz Sine wave, that creates a high pitched tone. Some allege that this is much too high to be distinctly audible against a noisy background, or over acceptable distances. More recent ATI units use a improved, lower-pitched tone, which has given adequate results.

• Speakers - In San Francisco, many of their ATIs have the tone of an old Federal Signal STL-10, which has caused reliability problems as the programmed tones are far too low-pitched for the speakers to handle. As few speakers can tolerate such low-pitched sounds at high volume, this may not necessarily be the fault of the speakers used.