Need help with a webpage showing up only at certain speeds for an overlay

I know how weird the title sounds, but let me explain. I'm trying to create a speed chime for a car, and found a way to have SimHub host and play the sound, via the webpage overlay. If you set it to display a website playing the sound constantly, it will play the sound just fine, however, the issue begins at having it only start at, say 150km/h, but once it goes below, the webpage overlay disappears. With my current knowledge of simhub, I don't know what the code line should read for that, if anyone knows, please help me out.

Thanks in Advance!