The problem of increasingly effective active noise cancellation (ANC) built into headphones has become a serious safety challenge in urban traffic, as pedestrians often fail to hear cyclists’ warnings. According to available data, collisions between cyclists and pedestrians have increased by 24%, which has prompted the development of a solution that breaks through such “personal sound insulation”.
A possible solution was presented by the Czech car manufacturer Škoda, which has its historical roots precisely in the production of bicycles. Their product is called the DuoBell, and it’s the first mechanical bicycle bell designed to intentionally “cheat” the algorithms of modern headphones. Although it is a hi-tech product, DuoBell is a completely mechanical device, independent of batteries or digital components.
Not louder, but smarter
In collaboration with scientists from the University of Salford, the research identified a “safety zone” within the frequency spectrum. ANC algorithms were found to be weakest in the narrow band between 750 Hz and 780 Hz. It is at this frequency that the DuoBell emits its primary sound, which allows the sound wave to reach the pedestrian’s ear despite the included noise-cancelling technology in headphones, such as those produced by Apple, Sony or Bose.
The very name of the device, DuoBell, comes from the built-in double resonator system. In addition to the basic tone, the bell also uses an additional resonator tuned to a higher frequency. The key element is a specially designed hammer mechanism that produces fast and irregular blows. Such irregular sound waves are too fast for the digital processors in the headphones to process and cancel them in real time, thus ensuring that the warning actually reaches the ears of “isolated” road users.
The test results showed a significant increase in safety. Pedestrians with ANC on heard the DuoBell up to five seconds earlier than standard bells, that is, at a distance of as much as 22 meters. Those five seconds represent the critical time that allows the pedestrian to move out of the cyclist’s path in time, thus directly reducing the risk of serious traffic collisions. In addition to the laboratory, the doorbell was successfully tested on the noisy streets of London.