Today I had to go to Watertown to go to a FLL meet and I figured I should stop at some sirens to make the most of the long drive. I also stopped at a rare dampered P-15. Here are the photos.
Is that a factory installed damper, or was it custom? I remember a video of Tyler Shaw's with a 1003 and a Banshee with a damper, so I'm not sure if it was an ACA experiment or not...
There was a red dual-tone Penetrator part of the Eden Prairie, MN system that had the exact same baffle/damper in the intake. The video of it (not mine) was posted on YouTube back in 2008. There was some buzz about it awhile ago before I joined ARS when it was posted and I think on YouTube through the comments we determined it was to block some airflow to the chopper so it would not overload the motor. According to the YouTube user who posted this video, a new Federal Signal siren took it's place awhile back.
I always thought it was a spring-loaded damper that retracts back fully to muffle out the quieter bulk of the wind-down when the suction drops sufficiently.