What does a sound whisperer do? Interview with Fazua developer Julius Thorwart
Christian Penning
· 04.11.2022
EMTB: Julius, designing motors that are as quiet as possible is one of your main tasks as a product development engineer at Fazua. Are you more of a loud or a quiet character yourself?
Julius Thorwart: I tend to be a quiet person. But when I make music, it can be as loud as possible. I used to have a metal band.
Are there parallels between e-bike motors and heavy metal sound?
Of course! Ultimately, both should sound good. And: With engines, as with music, everyone has their own individual taste. In the end, there should always be a positive feeling.
How do we perceive motor noise when e-biking?
This can vary greatly from person to person. When I sit on an e-bike for the first time, I register the noises differently than when I sit on a pedelec every day.
Is that what you want, that you can hear the engine while driving?
A certain engine sound makes perfect sense. It signals to me that the engine is running, ready for use and in good technical condition. A defective engine would be quickly identified acoustically. Irrespective of this, it is not only the volume that is decisive: the drive must also not sound disturbing when driving. The buzzing of a mosquito, for example, is quiet, but its tonality and high frequency make it stand out from the background and have a very unpleasant effect on us. We associate grinding or rattling noises with something: Something is broken. In contrast, we perceive broadband, low-frequency noises as less disturbing.
The finest acoustic technology for the rough and tumble of everyday e-bike use
You can find more information about Fazua e-bike motors in our articles:
How do you measure the drive noise with Fazua?
We deliberately measure both under laboratory conditions and outdoors. It also depends on what you are measuring. On the one hand, there is structure-borne sound: mechanical vibrations generated inside the drive by components such as motors, gearboxes and bearings. On the surface, they cause air molecules in the environment to vibrate. This creates airborne sound waves. These propagate in the surrounding air until they reach the ear or my microphone. We measure structure-borne sound with acceleration sensors and airborne sound with a microphone. The latter is often very complex, as the environment can influence the measurements. Forests and meadows muffle the sounds, in a narrow, rocky ravine the sound is reflected and sounds more intense. Ideally, we would go to an external sound laboratory. But that is very expensive. One day costs several thousand euros.
How can the sound of an electric drive be optimised in concrete terms?
You can imagine this as a chain reaction. If we as engineers succeed in minimising the structure-borne noise of the components, this also leads to less audible airborne noise. The biggest levers are the motor and gearbox. With electric motors, noise can be reduced by the shape and arrangement of components such as coils and magnets. A lot can be achieved with the gearbox by optimising the interaction of the gears and using noise-insulating materials such as special plastics.
Does the bike frame also influence the sound?
This also plays an important role - similar to the body of a Stradivarius. In a violin, the body is set in motion by the vibrations of the strings. The extent to which a bike frame absorbs the vibration of the drive unit, transmits it and converts it into audible airborne sound depends heavily on the frame design. Stiffness and cross-section play a role, as does the material. A frame made of carbon sounds different than one made of aluminium. We therefore pass on the acoustic analyses of our motors to the manufacturers so that they can adapt the frame accordingly.
Nowadays, drives are designed on the computer. Can the resulting noises also be simulated there?
There is still no software that faithfully reproduces the sound in the simulation programme. Simulations can be used to optimise individual noise sources in the system, such as the electric motor or the gearbox. We can calculate many different component combinations within a short space of time and evaluate and optimise
evaluate and optimise their acoustic qualities. Nevertheless, surprises can still occur afterwards with prototypes. This is why we usually test several variants in order to determine the best overall combination in the end.
What is the reason for the loud rattling of some e-bikes downhill?
This is difficult to say in general terms. It could be due to component play or the freewheel. But a vibrating battery cover can also be a reason - or cables that are not sufficiently fixed. A sound cam can be used to visualise the emitted sound and locate the source of the noise.
What does the ideal E-MTB motor sound like to you?
Quiet purring, warm and pleasant.
About Julius Thorwart, Product Developer at Fazua
Julius Thorwart sits in a spartanly furnished office. Alone. Hardly a sound penetrates the white room. His "assistant" - as Julius calls the bust he uses as a holder for his headset - silently observes the engineer. On the table is a Fazua motor connected to the laptop and measurement technology with thin cables. Julius uses a high-tech headset, which also serves as a measuring microphone, to capture the sound realistically.
