The Friendly Car Horn

Sounds are part of our lives; they evoke emotions, bring back memories and alert us to things around us.

One sound in particular is the car horn. The sound can spark feelings of road rage or urgency. It’s also the subject of new research on noise pollution, presented during Acoustics ’17 Boston, the third joint meeting of the Acoustical Society of America and the European Acoustics Association being held June 25 to 29, in Boston, Massachusetts.

The study, led by Myungjin Bae of Soongsil University in Seoul, Korea, and presented at the meeting by SangHwi Jee, introduced a new pedestrian-friendly car-horn sound identified through the Mean Option Score (MOS). The MOS is a simple ranking method commonly used to evaluate machine speech, sounds and noise. Test listeners used MOS to evaluate candidate horn sounds based on five different perceptual qualities such as stress and loudness. It ranks sounds on a scale from bad (1) to excellent (5).

"The sound of Klaxon heard outside the car of the driver is uncomfortable because it is too loud to the people around him," Bae said. "In our study we used the existing historic Klaxon sound source, but made some modification concerning its volume and rhythm with duration time by adding a power controller. Our new Klaxon sound can immediately alert the pedestrians of the danger while also reducing the unpleasantness and stress of the sound.”

That Klaxon sound they used is familiar, it’s the traditional “ah-oo-gah” heard in old-time cartoons and black-and-white movies.

To test the perceptual effects of their new horn sounds, researchers exposed 100 volunteers to a menu of sounds in hopes of finding those that were less irritating to the ear of pedestrians.

"For almost 100 years, the car Klaxon sound was almost invisible and its design was simple, and it had the advantage of being able to make a loud noise at low power. But the level of loudness could not be easily controlled. In this study, when a driver presses a Klaxon, a loud sound of 110 decibels or more is not transmitted directly to a pedestrian," Bae said.

Researchers intended to create a calmer driving environment, one that will make drivers have better focus and rational response. The selected sound can be applied to any motor vehicle. Its advantage is that it reduces stress on drivers as well as pedestrians or bikers, thus improving the city soundscape, rather than the aggressive horns of today.

"Everyone can live more comfortably without hearing any annoying noise from the streets," Bae said.