Collisions between cyclists and headphone-wearing pedestrians are rising. Škoda's DuoBell uses a frequency gap to slip past noise-cancelling filters. As cycling grows in major cities — London expects cyclists to outnumber car drivers for the first time this year — so does a tricky safety problem. Pedestrians wearing noise-cancelling headphones can't hear conventional bicycle bells, and collisions between cyclists and distracted walkers are on the rise. Škoda Auto, working with acoustic researchers at the University of Salford, has developed a solution with its DuoBell : a fully mechanical bicycle bell engineered to bypass ANC algorithms. Through acoustic testing, the research team identified a narrow frequency band, between 750 and 780 Hz, that slips through ANC filters. The bell adds a second resonator tuned to a higher frequency and uses a specially designed hammer to produce rapid, irregular strikes — sound patterns that noise-cancellation software can't process fast enough to suppress.…