Skoda's Duobell: This bicycle bell reaches you even with noise cancelling
Headphones with noise cancelling also block out bicycle bells. That's why Skoda has opted for a sound design in the Duobell that penetrates the sound insulation.
You're cycling through the city, but a pedestrian is blocking the cycle path in front of you. You ring the bell, but nothing happens. The reason is often in or on your ear: headphones with active noise cancelling. Modern Active Noise Cancelling (ANC) not only almost completely blocks out traffic noise, but often also the important warning signal of a conventional bicycle bell.
Skoda now wants to solve this problem with the Duobell. This special bell relies on acoustic tricks to outwit even the best noise cancellation algorithms.
When security is filtered out
ANC headphones work with microphones and algorithms. They detect ambient noise and generate a counter-sound in real time that cancels it out as completely as possible. This is particularly effective with constant, uniform noises such as motors, wind or road noise.
This becomes problematic in road traffic. This is because classic bicycle bells usually produce short but predictable sounds that are often effectively suppressed by the systems due to their uniform structure. For pedestrians with headphones, the warning signal then simply remains inaudible - with corresponding risks.
The physical weakness in the algorithm
To investigate how ANC systems react to different sound signals, Skoda teamed up with acoustics researchers from the University of Salford in the UK. The team identified a narrow frequency range between around 750 and 780 hertz in which many noise cancellation algorithms work much less effectively. This gap in filter behaviour forms the basis of the Duobell.
The bell specifically generates a sound in precisely this frequency window. In addition, it does not just produce a uniform sound. The Duobell employs fast, irregular beats that vary over time. This irregularity makes it difficult for the algorithms to calculate a suitable counter-sound wave. As a result, the signal is not treated as predictable background noise, but is perceived as a sudden event and reaches the ear of the headphone wearer.
Measurable advantages tested
Tests have shown a clear difference to conventional bicycle bells. Test subjects with active noise cancelling heard the Duobell signal on average around five seconds earlier and from up to 22 metres further away. At typical city speeds on a bicycle, this corresponds to several additional metres of reaction space.
The tests were not only carried out in the laboratory. Among others, couriers used the bell in everyday life in London's dense city traffic. The aim was to replicate the conditions that prevail every day on cycle paths and pedestrian zones.
Safety through pure sound design
The approach is remarkable: the Duobell completely dispenses with electronics. There is no battery, no app and no connection to the smartphone. Instead, the developers optimised the shape, material and mechanics of the sound bodies in such a way that the desired frequency and the irregular beat sequence are created purely mechanically.
Source: Skoda
This makes the bell not only robust and low-maintenance, but also universally applicable. Despite being specifically designed for headphone wearers, the signal remains a familiar warning sound for people without ANC. It is loud and present without being aggressive. The challenge was to find a balance between assertiveness and social acceptance in public spaces.
Not yet a series product
At the moment, the Duobell is a concept. According to Skoda, it is not planning to sell it directly. Instead, the manufacturer wants to disclose the research results and make them available to other manufacturers.
The fact that a car manufacturer is working on a bicycle bell seems unusual at first glance. Historically, however, it is consistent: Skoda once started out as a bicycle manufacturer, long before cars became its core business. In terms of content, the Duobell also fits into a larger topic: Road safety, which today affects all road users, not just motorists.
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