The Siren Board

While visiting friends and family in Omaha, I decided to take the opportunity to swing over to Missouri Valley, IA (About 30 miles away) and record their STL-10 doing its daily noon blast:

http://www.youtube.com/watch?v=FIMLWv7Mre0

It's quite interesting that when she hits full cycle, The echo that gets thrown off sound almost a half-step note *higher*.

An unintended, yet intriguing combination of the Doppler Effect and vantage point, perhaps?

BTW: Great recording. It brings back memories of the Melville LI Fire Dept. Substation jewel. IIRC, what made it particularly loud was not only the low tone for the purpose of achieving distance in an area that has one of the busiest north-south suburban thoroughfares on Long Island running through it, but the fact that it was installed almost at *ground level*. And lest my understanding of siren sound dynamics betray me, the lower the siren installation, the easier it is--ideally, of course--for the soundwaves to reach their destination.

PhRed wrote:It's quite interesting that when she hits full cycle, The echo that gets thrown off sound almost a half-step note *higher*.

An unintended, yet intriguing combination of the Doppler Effect and vantage point, perhaps?

BTW: Great recording. It brings back memories of the Melville LI Fire Dept. Substation jewel. IIRC, what made it particularly loud was not only the low tone for the purpose of achieving distance in an area that has one of the busiest north-south suburban thoroughfares on Long Island running through it, but the fact that it was installed almost at *ground level*. And lest my understanding of siren sound dynamics betray me, the lower the siren installation, the easier it is--ideally, of course--for the soundwaves to reach their destination.

It sounds like either there's another STL-10 in there, or Windows Movie Maker messed with the pitch. If it was WMM, I may be able to help you with the problem. Did it really sound like that?

About siren sound dynamics, the higher the siren is mounted, the further it's sound carries, but it isn't as loud from the ground when you're close to it.

ver tum wrote:It sounds like either there's another STL-10 in there, or Windows Movie Maker messed with the pitch. If it was WMM, I may be able to help you with the problem. Did it really sound like that?

It's not a WMM artifact, the same effect is heard in the raw unedited recording from my camera. I'm thinking now that it probably just is echo and not a second siren, because I don't hear a second wind-up, and the "second siren" stops suddenly at the same time as the one shown.

It is possible Missouri Valley does have more than one siren, but exactly where any other sirens would be located I cannot say. There IS a 2001 about a mile west of I-29 just outside of Missouri Valley, but it is part of the Fort Calhoun nuclear plant siren system, not one of the town's sirens. Besides, a 2001 is, quite obviously, much higher pitch than an STL-10, so if that "second siren" actually is a second siren, it's certainly not the 2001 being heard.