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Adding sound to a quiet electric vehicle


Anyone who has experienced a drive in an electric vehicle is surprised at how quiet it is compared to an internal combustion engine vehicle. But those who enjoy the sound of an internal combustion engine may find that the sheer quietness of an electric vehicle removes something vital from the driving experience. Is it possible to enjoy that active driving sound in an electric vehicle?

Electric vehicles are receiving attention for their many advantages over internal combustion engine vehicles. Such advantages include their eco-friendliness (zero carbon dioxide emission during operation) and excellent motor-driven performance actuated right from start-up. Also, thanks to an electric motor that spins with the utmost quietness and smoothness, noise and vibration (NVH: noise, vibration, harshness) permeating the interior are significantly reduced. These characteristics of electric vehicles can be compared to those of a model student: the kind who’s athletic and smart at the same time.

And yet there are drivers who are unfamiliar with the hush of an electric vehicle. This is because electric vehicles powered by silent electric motors make very little driving sound; some people even consider this ultra-quiet driving a little boring. In response, Hyundai Motor Group has developed “e-Active Sound Design (e-ASD),” a technology that makes it possible to virtually experience driving sounds in an electric vehicle. Let’s take a look at the technology that made it possible to create sound that captures the unique identity of electric vehicles.

The reason behind the difference in noise and vibration characteristics of electric vehicles and internal combustion engine vehicles

Why do electric vehicles need sound technology? First, no matter how quiet an electric vehicle is, it can’t block noise from outside. Generally, the sound that enters the interior of a car is divided into three main categories: the noise of the powertrain, including the engine and transmission; the wind noise caused by air resistance; and the road noise conveyed as the tire rolls on the road surface.

We analyzed the proportion of noise heard from internal combustion engine vehicles and electric vehicles and found that in internal combustion engines, engine noise accounted for 50% of the sound transmitted to the interior, road noise accounted for 30%, and wind noise and vehicle system noise accounted for 10% each. Noise from electric vehicles, in contrast, consists mostly of road noise (40%) and wind noise (30%). Electric motor noise took up only 15%.

This shows both sides of electric vehicle noise. It’s very quiet because it’s powered by a motor instead of an engine, but the absence of an engine means the driver is exposed to more environmental noise. This is why electric vehicles require more sophisticated noise reduction technology.

This is also about maximizing the immersive driving experience with auditory elements. Most drivers are highly tuned to their driving situations through the sounds of their engines. This is because drivers can recognize changes in sound caused by driving conditions such as acceleration, deceleration, and current speed.

In the case of an electric vehicle, it is difficult for the driver to feel a sense of acceleration because the accelerating engine sound is not heard. This may be an unfamiliar experience for someone who has only driven an internal combustion engine. Movement is suddenly inconsistent with the sounds the driver is used to hearing.

The sound of electric vehicles is also unfamiliar to pedestrians. When walking down the street, you may have already had the experience of being unaware of an electric vehicle moving slowly behind you. Since this is directly linked to safety issues, laws stipulate that the “Virtual Engine Sound System (VESS)” that generates sound on the outside and alerts nearby pedestrians to a moving vehicle is mandatory in electric vehicles. 

A quiet electric vehicle, reborn as a ride that stimulates all five senses

Hyundai Motor Group has been creating a driving sound that matches a vehicle’s power performance by harmonizing the vibration and sound generated during acceleration. The “Active Sound Design (ASD)” technology applied to internal combustion engine vehicles is a good example. ASD is a technology that combines engine sound with virtual sound designed in real time. The result is a three-dimensional sound that reflects the vehicle’s characteristics. For instance, a high-performance car produces a sound that hums with intensity when driving, while a luxury sedan produces a sound that resonates with elegance and luxury.

It is the e-ASD technology that expands the field by incorporating the characteristics of electric vehicles into existing driving sound technology. Above all, e-ASD is clearly distinguished from the ASD technology in that it implements virtual driving sounds in varied concepts, whereas ASD implements only one theme based on the conventional engine sound. Until now, the electric vehicle virtual sound implemented by some electric vehicle manufacturers has run up against technical limitations for different reasons.

First, there is the case where the waveform generation method linked to engine speed is applied to an electric vehicle. It’s based on the same principle as the ASD technology of the existing internal combustion engine vehicles described above. This method has a disadvantage in that it is difficult to create a sound that is unique to electric vehicles, other than the engine sound that is familiar to our ears. Some manufacturers also use the engine sound recorded for each RPM section and play it according to the acceleration situation of the electric vehicle. It’s a method that divides engine RPM by section and plays each separately recorded sound in turn. However, in this case, the sound may not connect naturally and may be cut off by section. The virtual sound produced this way fails to reflect the change in sound heard when the accelerator pedal is operated and makes it difficult to create a unique sound.

To overcome the limitations of existing technologies, Hyundai Motor Group’s Sound Design Research Lab introduced the “Granular Synthesis” method, which creates virtual sounds in real time. Granular Synthesis is an acoustic synthesis technology that decomposes sounds into very small units and then collects these short sound bites to create new sounds. This principle of arranging, processing, and recombining fine sounds to create one high-density sound is the same technology used in electronic music. Just as a DJ creates new music by mixing different types of recorded music, the technology uses signals from the car to create the unique sound of an electric vehicle. Hyundai Motor Group’s electric vehicle sound, which applies the Granular Synthesis method, has the advantage of harmonically implementing multiple tones. It’s also possible to incorporate driving sounds with various themes, such as a sound similar to conventional engine sound and a futuristic sound of a moving spaceship.

High-preference sound design and user-customizable features

One of the characteristics of e-ASD is that the driver can feel the power of the tone adjusted to their driving speed. The e-ASD creates virtual sound that harmonizes with the driving situation, monitors the motor RPM and driving load in real time to determine optimized sound and volume, and then delivers it to the passengers.

People enjoy listening to their preferred musical genres and tune them to their tastes with an equalizer. Sound, after all, is in the realm of emotion, and personal taste will always play a significant role. The first question that the Sound Design Research Lab, which developed e-ASD, considered was “what kind of sound does a car make?”

In order to fully convey the feel of a moving car and ease passengers into a state of psychological comfort, a popular yet familiar sound had to be produced. The Sound Design Research Lab therefore devised a development process that considered customer preferences to produce the optimal sound. 

First, a sound designer developed hundreds of sounds in advance, and these sounds went through user surveys and comprehensive evaluation. After that, the sound design was further refined by identifying the sounds preferred by users in different countries. Lastly, by applying this to an actual vehicle, the final candidates optimized for the driving situation were selected, and a sound tuning process was performed to enhance quality.

It was found that drivers in Europe preferred an engine sound close to an internal combustion engine, while drivers in Korea preferred a more future-oriented sound. The results of this global survey are reflected in the Kia EV6, to which Hyundai Motor Group applied the e-ASD technology for the first time. Three sound themes — stylish, dynamic, and cyber — were applied to the base model of the vehicle so that the driver could make a selection according to preference. Electric vehicles of other companies usually feature only one sound theme in their vehicles. This personalization option is what sets Hyundai Motor Group apart.

Three Kia EV6 sound themes to choose from

Listen to the three e-ASD sound themes implemented in the EV6 

The stylish theme creates a natural and sophisticated atmosphere with a familiar sound of an electric vehicle. The unique electric vehicle sound that can’t be experienced in existing internal combustion engine vehicles is a key aspect of the stylish theme. The dynamic theme, in contrast, delivers Kia’s dynamic brand DNA by reinterpreting the intense sound of an internal combustion engine for electric vehicles. It’s a sound with a distinct presence, one that emotionally reproduces the high performance of the EV6. Finally, the cyber theme is a new and creative design that produces a sound similar to what a futuristic flying object might make. Users can enjoy a unique sound in electric vehicles that they have never experienced before. 

The e-ASD also features more personalized and customizable settings. The user can adjust the sound volume to Low, Normal, or High, or completely turn off the sound. It also supports the “Accelerator Pedal Sound Response” function, which directly sets the degree at which volume and tone change according to the operation of the accelerator pedal. For example, if you select “Quick sound response” from the e-ASD setup menu, the tone changes dramatically, even if you step more lightly on the accelerator pedal. The result is more dynamic sound feedback. Conversely, if you select the “Slow sound response” option, the tone changes relatively slowly for smoother sound changes. With this sound response, the driver can receive audible driving information more effectively and further enhance the immersive driving experience.

For internal combustion engine vehicles, reducing all noise entering the interior was paramount. However, e-ASD is not just limited to reducing noise. It expands the user experience and facilitates a quiet indoor environment by creating a new sound suitable for electric vehicles. Going forward, Hyundai Motor Group plans to provide more valuable experiences through new technologies that reflect customer sensibilities and pave the way for the driving environment of the future.