In consumer psychology, there's a well-established principle: people judge product quality using all their senses—not just their eyes. And in many cases, the ear is the sense that makes a quicker and more unwavering judgment than any other sense.
A classic study by Rainer Guski at Bochum University showed that users form an impression of a product's quality in less than three seconds – and sound plays a decisive role in that timeframe. The sound of a car door closing, the click of a switch, the engine starting, the confirmation beep from a system – all are processed and assigned meaning by the brain before we have a chance to consciously think.
Applied acoustics is a science that stands at the intersection of acoustic physics, perceptual psychology, and product design—with a single goal: to ensure that every sound a product produces conveys the right message to the user.
Sound Quality: Beyond Decibels
For decades, the industry's benchmark for sound quality was a single number: sound pressure level, measured in decibels. The car that emitted fewer decibels was considered better in terms of NVH (noise, vibration, and noise) – and that was the end of the story.
But the reality of user experience is far more complex. Two sounds at the same decibel level can produce completely opposite sensations: a smooth, warm noise at 65 dB might be pleasant, while a sharp, high-pitched screech at the same 65 dB is extremely irritating. Humans don't hear decibels—humans hear the timbre, rhythm, character, and meaning of the sound.
From that understanding, the field of Sound Quality was born – a set of measurement indicators designed to reflect subjective human perception rather than simply measuring physical energy:
- - Loudness: This isn't simply measured in dB, but rather the level of loudness that the human ear actually perceives, in units of sones – because the human ear doesn't hear linearly according to frequency.
- - Sharpness: The degree of "harshness" or "sharpness" of sound, characterized by the high frequency content. An overly sharp sound can cause stress and fatigue even when not too loud.
- - Roughness: The "roughness" or "vibration" of sound due to rapid frequency modulation - older engine sounds often have a high degree of roughness.
- - Tonality: The degree of prominence of a pure frequency within a mixed sound spectrum - the howling of an electric motor at a fixed frequency is a prime example of high tonality.
- - Fluctuation Strength: Measures how much sound changes over time – slow fluctuation creates an unpleasant, "nauseating" sensation, while fast fluctuation causes excessive stimulation.
By combining these metrics, acoustic engineers can accurately predict whether a particular sound will be perceived as pleasant, neutral, or unpleasant by users—without having to invite hundreds of real users into a testing room.
Applications in the Automotive Industry
Engine Sound Design
This is the oldest and most heavily invested application of acoustic analysis in the automotive industry. Drivers don't just want a quiet engine – they want an engine that sounds "right." A sports car needs a powerful, responsive engine sound that accelerates with the sound – but without being irritating on long drives. A luxury sedan needs a subtle, refined engine sound that never drowns out conversation in the cabin.
Manufacturers like BMW, Porsche, and Mercedes-Benz have long had teams of engineers specializing in "sound design"—people who not only measure and reduce noise, but also shape engine sound like an artist shaping music. They use Sound Quality data to determine the allowable tonality range, the target roughness range at each RPM range, and how the sound should change from normal to sport driving mode.
Electric Vehicle Audio: The Biggest Challenges and Opportunities
With electric vehicles, the acoustic problem is on a completely different level. There's no internal combustion engine to design, no familiar exhaust sound to maintain – but at the same time, there's no natural "background sound" to mask unwanted noises.
At low speeds, electric vehicles are almost completely silent – to the point that regulators in Europe and the US have mandated that electric vehicles emit an acoustic warning sound below 20 km/h (AVAS - Acoustic Vehicle Alerting System) to protect pedestrians. This presents an interesting acoustic problem: the warning sound must be loud enough for pedestrians to hear, easily recognizable enough for them to be aware of an approaching vehicle, but not annoying or disruptive to noise pollution.
At higher speeds, electric motor whine and inverter noise become central challenges. Acoustic analysis helps engineers pinpoint exactly which frequency ranges and tonality levels of these sounds remain acceptable – and when they need intervention through redesign or soundproofing.
User Interface Sound (HMI Sound Design)
Every time you press a button on the touchscreen and hear a confirmation "beep"—that's no coincidence. Human Machine Interface (HMI) feedback is a rapidly growing area of acoustic application in modern vehicle design.
When vehicles switched to touchscreens replacing physical buttons, users lost tactile feedback – the "click" sensation of pressing a switch. Audible feedback became the only alternative channel, and if poorly designed, users would constantly doubt whether their input was being registered. Applied acoustic analysis helps design optimally sound-based feedback: loud enough to be heard in the cabin while the vehicle is in motion, short enough not to be irritating during continuous operation, and with a tonal quality that conveys the right sense of "solidity" and "reliability."
Applications Outside the Automotive Industry
Applied acoustic analysis is not limited to cars. Any product that emits sound during use is subject to this field.
Home appliances: The sounds of washing machines, dishwashers, and air conditioners – all undergo Sound Quality analysis to find the balance between operational efficiency and user experience. Bosch and Miele are renowned brands that invest particularly seriously in the acoustics of their appliances – their washing machines are not only quieter but also designed to sound "robust" and "solid" rather than "cheap" or "fragile".
Medical equipment: In a hospital environment, sounds from medical equipment directly affect both patients and healthcare workers. Warning sounds from patient monitors need to be clear enough for nurses to hear in a noisy environment, but not frightening for patients. The noise from MRI machines – which are extremely loud and frightening – is being researched by manufacturers such as Philips and Siemens to improve sound quality and reduce patient anxiety.
Phones and electronics: Keyboard clicks, system sounds, camera shutter sounds – Apple has long been renowned for meticulously designing every sound in its product ecosystem, from the "swoosh" when sending emails to the MacBook startup sound. This is an application of acoustic analysis at the brand level – sound not only serves a function but also builds brand recognition and emotional connection.
Applied Acoustic Analysis Procedure
A project to optimize user experience through acoustic analysis typically goes through the following steps:
- Defining the perceptual goal: Before measuring anything, the design team must answer the question: how should this car (or product) sound? Luxurious? Sporty? Reliable? Friendly? The perceptual goal is expressed in emotional language first, and then translated into technical specifications.
- Current state measurement: Gather comprehensive acoustic data from the current product or prototype – frequency spectrum, Sound Quality metrics, and subjective assessments from a representative group of users.
- Distance analysis: Compare the actual sound to the defined perceptual target. Precisely identify which elements are deviating from the target – too sharp, too rough, too much tonality at undesirable frequencies.
- Technical intervention: Depending on the source of the problem, solutions may include mechanical redesign, adding sound-absorbing materials, changing surface materials, or active sound design.
- Verification and repetition: Re-measure after intervention, compare to the target, and continue until the desired result is achieved. Sound Quality measurements allow for quantitative tracking of improvement progress – rather than relying solely on the subjective perceptions of a few individuals.
Active Sound Design: When Technology Becomes Art
Applied acoustic analysis goes beyond simply reducing unwanted sounds. A branch that has grown rapidly in recent years is Active Sound Design (ASD) – proactively creating additional sounds to shape the user experience.
In electric vehicles, ASD is used to play simulated engine sounds through the cabin speakers, giving the driver a familiar auditory response during acceleration or deceleration – even if the electric motor doesn't physically produce that sound. Both the BMW iX and Porsche Taycan implement this technology with sound packages specially composed by professional musicians.
ASD is also applied in Active Noise Cancellation (ANC) in vehicles – similar to noise-canceling headphone technology but on a cabin-wide scale. A microphone system monitors cabin noise in real time, software calculates the phase difference of the sound signal, and speakers emit that signal to cancel out unwanted noise before it reaches the occupants' ears. The result is a significant reduction in interior noise without the need for additional heavy soundproofing materials.
Why This Is a Real Competitive Advantage
In an increasingly competitive automotive market—especially in the electric vehicle segment where specifications like power, range, and charging times are becoming more similar across brands—the driving experience becomes the ultimate differentiating factor.
Car buyers don't sit and read the specifications sheet when they decide if they like a car. They get in the car, close the door, start the engine, and listen. The feeling in those first thirty seconds—largely shaped by sound—determines much of the impression they'll carry throughout their ownership of the vehicle.
This is why investing in applied acoustic analysis isn't an optional expense for manufacturers. It's an investment in something customers experience every day—and something they'll tell friends when asked how their car sounds.
Sound is something we can't turn off. We can close our eyes, but we can't "close our ears." Throughout the journey in a car, thousands of auditory signals are processed, evaluated, and assigned meaning by the brain—mostly completely unconsciously.
Applied acoustic analysis is a tool that allows designers and engineers to control those signals – ensuring that every sound the car produces serves the user experience, not disrupts it. In the electric vehicle era, where the acoustic space is wider than ever, this is no longer the exclusive domain of luxury car manufacturers – but a capability that any serious manufacturer needs to develop.
GPower Vietnam provides equipment and solutions for sound quality measurement, applied acoustic analysis, and comprehensive NVH testing for the automotive and industrial sectors. Contact us for advice on building acoustic analysis capabilities tailored to your product development needs.
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