There is something unnerving, even suffocating, about the complete lack of noise created in a soundproof space. The silence is so ‘loud’ that it fails to provide the relaxing environment normally associated with quietness.
The same applies to the silence inside a car. Although low noise levels are important in a luxury vehicle, allowing the occupants to enjoy music and conversation without difficulty, quietness should not be mistaken for a complete lack of sound. Creating a quiet atmosphere is actually about allowing sounds that are pleasing to the ear to flow freely, while doing everything possible to suppress unpleasant noises.
Lexus ES: quiet but not soundless
“Every generation of ES has had a reputation for offering an impressive level of quietness,” confirmed Hirotaka Tsuru, who designed the noise, vibration and sound controls of the new Lexus ES. “Naturally, we considered a quiet cabin to be the most important feature when developing the latest model. The LS served as our benchmark for this project.
Quietness is not a quality that can be improved by simply blocking out more noise
“Quietness is not a quality that can be improved by simply blocking out more noise. For example, we developed a test model that greatly suppressed bandwidths around 1.0kHz – the range most readily picked up by our ears. But doing so raised the air density inside the car and caused ringing in the ears, even nausea – not relaxing at all.”
To ensure the new Lexus ES inherited the right aural quality, Tsuru divided the development into three areas.
1. Noise source elimination
Tsuru incorporated wind tunnel testing – more commonly employed in reducing air resistance – early in the development of the ES to pinpoint every source of wind noise. He tested the car under a number of different circumstances, making tiny adjustments in the position of the mirrors, wiper arms and other car parts.
“The advantage of using the Lexus wind tunnel is that it is a laboratory designed for testing low-noise levels,” Tsuru continued. “This means we can quantitatively measure the wind noise level while controlling interior noise levels and interior noise sources.”
2. Sound insulation
Next, Tsuru focused on sound insulation as a way of reducing the level of noise entering the car. This phase involved cutting off passages through which noise could enter, filling or sealing openings in areas such as the floor and inner areas of the boot lid.
“From the time we began to develop the new platform, we were already studying ways to reduce the number of openings and considering covering the entire floor with silencers, which in previous models had only been placed on some parts of the floor. In other words, the new ES represents our effort to greatly improve the specifications of the base car.”
3. Noise absorption
In the third phase, Tsuru turned his attention to noise absorption, applying absorption material to the suspension towers, inner arches, undercarriage and other areas.
Every type of sound – both good and bad – is precisely adjusted
Factors such as road conditions are always difficult to account for when designing a car. Although you cannot fully prepare for changes in external factors, failing to account for certain bandwidths may result in those sounds being more perceptible than usual – in other words, an even noisier car.
“Changes in the environment are most often caused by natural winds and changes in the road condition. We needed to incorporate these factors into the design in order to produce a pleasing aural environment in which every type of sound – both good and bad – is precisely adjusted. It was a difficult process that required a lot of patience.”