[HIham] Re: [oahuraces] siren

[Jeffrey Herman]

My dad's company used to manufacture, among other products, "air-raid"
sirens during the cold war years -- our garage was part of his "lab"
where several designs were turned into actual products.

The one major variable factor contributing to the range of a siren's
coverage is the wind speed and direction. With the high wind velocities
we had on Friday, if you were upwind of a siren, its normal (still-air)
coverage was greatly diminished.

Of course, fixed factors include the height of the siren (think of the
Round Top and HMB sirens versus any siren on a utility pole) and
obstacles such as foliage or buildings (if you can't see the siren, then
whatever is obstructing your view will also absorb or reflect its sound).

Much to the dismay of many municipalities and counties, the new fully
electronic sirens, dB-for-dB, do not have the same range carrying
capability as the old mechanical sirens. The reason for this is due to
manner in which the sound is generated: The mechanical siren creates
its tones using a chopper or rotor -- high-volume air flow is interrupted
(the frequency of interruption equals the frequency of tone generated,
plus lots of harmonics -- its wave form is close to being a square wave);
if you're in close proximity to one of these puppies, you can feel the
sound pressure. On the other hand, an electronic siren produces its
tones via speakers; the actual air movement is much diminished.

By the way, since the removal of the Ala Moana Park siren, Ala Moana
Shopping Center is now in a siren-quiet-zone (as reported by WH6CVI
on Friday). Who's (bad) idea was it to eliminate that siren? That
decision MUST be reversed for the safety of the thousands of shoppers
at the AM Center. The AM Park location was perfect for alerting beach-
goers, drivers on AM Blvd., and shoppers at AM Center. It needs to be
reinstalled as soon as possible.

73, Jeff KH6O
Chief Petty Officer, U.S. Coast Guard
Mathematics Lecturer, University of Hawaii System


On Fri, 1 Apr 2005 terawaki at hawaii.rr.com wrote:
>
> Ray,
>
> Sorry I wasn't able to help today. I didn't have a radio with me in the
> car. But here's my feedback:
>
> I was at the intersection of Beretania and Punchbowl, at the Diamond
> Head makai corner, when the sirens went off. I had the windows up and
> the radio on -- audible, but not loud by any means -- and truthfully, I
> wouldn't even have known that there was a drill going had it not been
> for the radio interruption. The sirens just aren't very loud. I lowered
> my window a little (not all the way, b/c it was raining) to listen for
> them, but they were only just audible. If someone were driving along and
> listening to their CD player or something, they probably wouldn't have
> any idea that anything was going on. I realize these sirens are really
> loud at their source, though, so I'm really not sure what could be done
> to make the situation better.
>
> Oh yeah, btw, we're back, so . . . back to figuring out how to do the
> RACES badge exchange!
>
> Crissy