Lower frequencies certainly do carry farther. In addition to this, the Thunderbolt used a separate blower to provide a constant pressure to the chopper. The large horn also had a low cutoff frequency, which enabled the siren to maintain full output during wind down. Anyone familiar with a Thunderbolt can attest to the fact that it was most audible from indoors during its wind down from a distance.
As far as I'm aware, all current motor driven sirens use a common shaft for for both the blower and chopper. It doesn't take a rocket scientist to figure out that as the RPMs decrease, so does the pressure to the choper, along with the siren's output.
In other words the siren only achieves full output at maximum RPM. To be effective then as a warning signal, the maximum frequency should be no higher than 500 Hz, as the output will continue to fall off below this maximum frequency. Ironically, most sirens today have maximum frequencies well above 500 Hz.
Jpressman8 wrote:Bottom line a lower frequency carries farther. You should also know that the county has already spent 3 times what they are going to spend on these sirens for a reverse 911 system that does not work very well, and is going to cost a 250 to 500K a year to keep upgraded. You tell me which one is a waste of money.
The most overlooked opportunities are in the learning of and improvement in old technologies.
Richard Weisenberger