The ATI Soundblaster HPSS (or High-Power Speaker Station) is an electronic outdoor warning system manufactured by Acoustic Technology, Inc (ATI) that is used to alert the surrounding populace of tornadoes, hurricanes, severe thunderstorms, fires and so on. The recent HPSS systems use high-powered electronic speakers, which can be independently arranged to provide directional or omni-directional coverage, depending on installation. The HPSS16 provides up to 1600 watts of continuous power to drive up to four 400 watt speaker units, whereas the larger 3200 watt HPSS32 can drive up to eight 400 watt speakers. Like other electronic outdoor warning systems (such as Federal Signal's Modulator, for example), they can also be used as Public Announcement (PA) systems, and can play a number of programmed tones. Options include solar-powered operation and pre-recorded voice messages.
The HPSS sirens have drawn some criticism from civil defense aficionados for several reasons. Most 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 tone, which some allege is not sufficiently distinct against very noisy backgrounds, or over acceptable distances. More recent ATI units use a lower-pitched tone which has given adequate results.
In San Francisco, many of their HPSS units have the tones of a Federal Signal STL-10 siren, which was one of the sirens used by San Francisco until the whole siren system was replaced with HPSS systems. While this added voice capability to San Francisco's warning network, it has also caused some reliability problems as the comparatively deep-pitched growl of these tones can damage the speakers when playing at high volume. However, seeing as few speakers can tolerate such low-pitched sounds at high volume levels anyway, this may not necessarily be the fault of the speakers used.