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noise reduction

Most car enthusiasts love modifying their brand-new cars, knowing that doing so may affect the warranty. One common modification is a rim change to give their rides a more “sporty” look. However, with the new Honda CR-V e:HEV RS, doing so may take away one important feature that the SUV has: the wheel resonators, also known as noise-reducing wheels.

Continuous noise emitted by tyres while driving on highways can become a source of irritation for drivers. This noise results from resonance occurring within the hollow spaces of the tyres when encountering uneven surfaces on the road. For automobile manufacturers aiming to offer a smooth and quiet driving experience, this has posed a significant challenge. To address this issue, noise-reducing wheels have been developed, employing hollow resonators to dampen unwanted resonance and ensure a serene and comfortable ride.

The noise produced within the tyre resembles the resonant sound of bouncing a basketball or volleyball on a hard surface. In cars, this pipe resonance, along with accompanying vibrations, travels from the wheels through the suspension and into the cabin, creating undesirable and bothersome noise.

Honda embarked on a mission to mitigate this noise problem. Recognising that the frequency of pipe resonance varies based on the shape and volume of the air enclosure—similar to the differing sounds produced when bouncing different types of balls—led to the realisation that tyre size determines pipe resonance frequency. Armed with this understanding, Honda devised a method to counteract pipe resonance by generating sound waves that neutralise this specific frequency.

To achieve this, Honda explored the concept of Helmholtz resonance, where sound is produced when air is blown across the opening of a container, such as an empty bottle, with the container’s shape and air volume dictating the resulting frequency. Leveraging this principle, Honda devised a resonator encircling the wheel, capable of emitting sound waves matching the frequency of pipe resonance generated by the tire. This innovative design effectively suppresses unwanted noise, enhancing the overall driving experience.

Now, you may have the idea that you can purchase the wheel resonators separately and apply them to your new rims, but during a recent press conference, Honda stated that it is not possible to do so. Mr. Sarly Adle Sarkum, President and Chief Operating Officer of Honda, stated, “Someone had tried to purchase the resonators and apply them on the lower variant CR-Vs, and that’s just not possible because it would not fit.”

When Piston Malaysia asked Mr. Yujiro Sugino, Executive Coordinator, and Mr. Eisuke Sato, Large Project Leader (CR-V), about the wheel resonators, as well as the Bose sound system being introduced into the lower variants, they stated, “There is a possibility of doing so, but we would need to consider the model positioning and what is required for those models.” Sugino also stated that “The resonators were designed specifically for the hybrid variant for higher noise, vibration, and harshness (NVH) performance, which is why the other variants do not have it.”

On another note, since the Honda City now comes in five variants rather than the previous four since the petrol versions now also have their own RS model, we asked if the same concept would be applied to the new CR-V, and Sugino replied with a simple “As of now, no.” It would be a nice touch if Honda did so.

When asked about the introduction of the AWD hybrid variant, similar to the one offered in Thailand, Sugino said that “If we were to do so, we would be adding another option of variant, which would give customers more choices but at the same time it would not be optimal for efficiency in production, which is why we decided it was best to go with the 2WD option.”

Installed at the centre of the wheels, these resonators are crafted from a lightweight resin and utilise the forces of physics, specifically centrifugal force, to make a significant impact on reducing tire noise.

One of the remarkable features of wheel resonators is their ingenious design, eliminating the need for additional connecting parts such as bolts. Instead, they leverage centrifugal force to establish a secure connection with the wheel, showcasing a streamlined and efficient approach to noise reduction.

The core functionality of wheel resonators lies in their ability to counteract tire noise through the power of resonance. By strategically creating vibrations at a specific frequency, these resonators essentially cancel out the unwanted noise generated by the tires, providing a more serene and enjoyable driving experience.

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Noise is something we adapt to over time (if it is not very loud) and where noise inside cars is concerned, different models will have different levels. The more expensive ones with better insulation and more damping materials will have a quieter interior while occupants in the lower-priced models may hear more noises.

Over time, the ears get used to the noise levels and what may have seemed ‘noisy’ might seem to fade away. Or the opposite can also occur as time will see some parts loosening, gaps widening so noise from outside can seep in.

Ford

Where drivers used to have to shout to make themselves heard above certain speeds, modern-day cars are comparatively quiet. Conversations and music are clearly audible, even at low volumes. But the quest for quietness in the cabin has not ended and Ford’s ‘Whisper Strategy’ delivers lots of small noise improvements around the vehicle that add up to a big difference. Lower noise levels will not just enhance comfort but can also reduce fatigue.

Ford

The ‘Whisper Strategy’
Take the new Kuga sold in Europe, for example: Ford engineers examined noise‑generating elements from the suspension to the door seals to help find ways to optimize interior refinement. Adding perforations to the leather seat bolsters reduced the total area of flat surfaces inside the cabin, helping absorb rather than reflect noise.

Aerodynamically-tuned sound shields are also added underneath the body of the vehicle that help limit road and wind noise entering from outside.

Ford engineers spent two years testing more than 70 different tyres over surfaces from smooth tarmac to rough concrete and cobbles, in wet and dry conditions and at a range of speeds to find the exact specification that kept road noise to a minimum.

They added smaller and narrower channels behind the exterior panels that allow hidden wiring and components to pass from one area to limit airflow inside the body.

“Our ‘whisper strategy’ is designed to make journeys as quiet as they can possibly be – from absorbing sound through perforated seats to testing that involves listening carefully to the different sound patterns created by dozens of different tyres,” explained Glen Goold, Chief Programme Engineer for the model.

A generational divide
To ascertain just how much quieter today’s cars are, the engineers got hold of a 1966 Ford Anglia and measured sound levels. They found that the interior noise levels in the latest Kuga Plug-In Hybrid are just one quarter of those experienced by motorist in the 1960s.

Noise levels

All-new Ford Kuga
Today’s Kuga PHEV (above) has a quarter the amount of noise in the cabin compared to the 1966 Anglia (below)

1966 Ford Anglia

With the quality of musical sound reproduction in cars getting higher and higher, ensuring that undesirable noises are kept out or suppressed is important. Quietness also gives a more premium ambience in the cabin, increasing the appeal of the model.

To view, test-drive or buy Ford vehicles in Malaysia, visit www.sdacford.com.my.

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