Škoda redesigns bike bell to be heard through noise-cancelling headphones

Czech automaker Škoda has created the Duobell bicycle bell, which penetrates noise-cancelling headphones in a bid to tackle a growing cause of bike-pedestrian collisions.

Škoda Auto's bell is a simple, mechanical device that rings at a precise frequency of 750 hertz.

This corresponds with a narrow gap that the company found commonly exists in the audio filters of headphones with active noise cancelling (ANC) technology, allowing wearers to hear the DuoBell more readily than they would a regular bike bell.

The innovation has the potential to make city streets significantly safer, said Škoda, at a time when both cyclist numbers and ANC technology are on the up.

Using London as an example, the company said that bike-pedestrian collisions had risen 24 per cent in 2024, and that noise-cancelling headphones were a contributing factor, with 54 per cent of headphone models now including the technology.

Škoda design head Oliver Stefani called the DuoBell "a simple, analogue solution to a digital problem", stressing that it was "100 per cent mechanical".

ANC headphones work by detecting external sounds and generating an opposite sound wave to filter them out in real time before they reach the wearer.

However, the technology is known to not be equally effective at every frequency, excelling with steady low-frequency noise and struggling with high or rapidly changing sounds.

To investigate this in detail, Škoda partnered with the University of Salford to conduct a study examining how ANC affects the audibility of traditional bicycle bells.

They found what they are terming a narrow "safety gap", where sounds in the mid frequency range of 750 to 780 hertz consistently penetrate ANC filters. However, taking advantage of this gap presented an engineering challenge.

"The problem with creating a frequency that low is that the bell has to be huge – not ideal for a bike," said head of hardware development Hugh Boys. "We reduced the thickness of the metal and added precision cuts."

"We tuned it to our 750 hertz frequency," he added. "But to be reliably effective, we had to go further. To make the system more robust against ANC, we have added a second frequency."

The second frequency is higher, more like that of a conventional bike bell. In addition to this second resonator, DuoBell incorporates a specially designed striking mechanism that creates rapid, irregular impacts to fool the ANC algorithms.

Škoda and the University of Salford tested their innovation in a virtual reality environment and found it could be heard up to five seconds earlier and up to 22 metres further away than a standard bicycle bell through noise-cancelling headphones, providing what they consider a critical safety margin.

They also tested their invention in the real world with Deliveroo riders, who are recorded in a promotional video sharing their positive reactions.

Škoda says it wants to see broader uptake of this innovation among cities and manufacturers, and to that end has shared its research in a freely downloadable white paper.

The company worked with creative agency AMV BBDO, PHD Media's innovation team and production company Unit 9 on the project.

Škoda began life in 1896 as a bicycle manufacturer and continues to support cycling through its We Love Cycling platform.

Another recent development affecting city cyclists is a redesign of the vehicles from bike share company Lime, which are speculated to address the issue of "Lime bike leg" associated with the chunkier previous frame.

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