I've never heard an STL-10, but have seen a couple.
Several years ago I noticed one atop a building in downtown Jackson, MS.
It was painted yellow. I'd been in Jackson for a convention; spotted the siren while riding shuttle back to the airport.
I also saw a red one somewhere in PA the next year. It was mounted on a platform between two poles; rather low; right near the side of the road.
I'm not sure just what city/township it was in. I was with group on a bus going to an event somewhere outside Philadelphia.
As others have mentioned, the STH-10 has 12 ports. It has the 12 "megaphones" around its circumference; the motor sits atop the siren.
I've made the observation on this board that the STH-10 is my 2nd favorite siren after the Thunderbolt.
The city of Smyrna, GA(where I used to live) began installing a tornado warning system about 30 years ago. Initial installation was 4 or 5 STH-10s; over the next several years it was expanded to 11 of these sirens(system also has 3 Whelens and 2 of the old DeKalb County, GA thunderbolts).
Smyrna used to test the sirens every Saturday at noon. I thought the STH-10s had a great startup sound; they took a long time to wind down.
The sirens are still in place(I visit the area twice a year) and to my knowledge are still sounded for tornado warnings.