Where I live I'm not near any of the sirens in my county however, I live about a mile from a Whelen WPS-4004 from the next county. They are working, however, to get a countywide siren system where I live.
I've been doing alot of work in a neighborhood a few miles away from me in Dublin, OH. I've heard their system of Whelen 2750s and 2805s several times but never heard them up close until yesterday. I was able to catch a recording of one of the 2750s but I can't find the cord to transfer it to the computer. I'll post it once I get it uploaded which will most likely be later tonight.
Here's a map of the Dublin system. The red circle os the one I recorded and the blue circle is the one I took pictures of.
Here's a map of how far I was from the siren. The yellow box is where the house I recorded from was
This is the siren I recorded which is located on Bright Rd. between Campden Lakes Blvd. and Connie Dr.
Here's another one of Dublin's 2750s located in Scioto Park along Riverside Dr.
The siren head.
Underneath the head.
And here's the control/battery box. See that green cylinder with the cone on top? My best guess would be that it's some kind of insect trap because underneath the cone is a light bulb and beneath that is some kind of conve shaped screening. All of their sirens that I've seen has these and if I guessed correctly on what it is I assume it's to help prevent insect nests being built in the controls and speaker arrays.
The visual difference between a 2750 and a 2805 is that the supports between each "plate" on a 2750 are silver and on a 2805 are black. Also, 2750s have no visible screening between speaker driver housings and the 2805s do. Sound wise a 2750 sounds pretty much the same as a 2016 or a 3016, high pitched, aprupt windup and slow windown. 2805s have a much deeper tone.