# Thirty-eight students heard spring water and traffic noise at 5 sound levels and the 50 dBA water recording produced the clearest heart and brain comfort pattern

> A 50 dBA water sound stood out Thirty-eight young college students sat through a carefully controlled sound test in which the same room, light, temperature and air movement were held steady while the acoustic setting changed. In a Scientific Reports study published...

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Byline: ARGO.net Editorial Team
Published: 2026-08-03T13:55:02+00:00
Categories: Humans, News

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## A 50 dBA water sound stood out

**Thirty-eight young college students** sat through a carefully controlled sound test in which the same room, light, temperature and air movement were held steady while the acoustic setting changed. In a [Scientific Reports study](https://www.nature.com/articles/s41598-025-96591-6) published in 2025, researchers compared **spring water sound** with **traffic noise** at five sound pressure levels: 40, 45, 50, 55 and 60 dBA. A no-sound condition served as the baseline.

The strongest comfort pattern came from the water recording at 50 dBA. At that level, participants gave the highest ratings for sound comfort and sound pleasure and their heart and brain readings also moved in the direction the researchers linked with a more comfortable state. The result is a measured laboratory finding, based on short exposure in a specific group, so it points to a promising soundscape design idea rather than a universal rule for every room or every listener.

The comparison was direct. The same people heard both sound types across the same five levels, which allowed the team to ask how sound source and loudness worked together. Spring water sounded helpful across much of the range, while traffic noise became more uncomfortable as the level rose, with the harshest pattern at 60 dBA traffic noise.

## Comfort was measured in the body

The study led with human response instead of treating sound as a number alone. Participants rated how comfortable and pleasant each sound felt, while the team recorded **electrocardiography** signals from the heart and **electroencephalogram** signals from the brain. Together, those measures gave the researchers a way to compare what people reported with what their bodies were doing during the five-minute listening periods.

For the heart data, the researchers looked at markers tied to the balance between stress arousal and recovery. One measure, LF/HF, tended to be lower under spring water sound than under traffic noise at the same levels. Lower values were interpreted as a sign of stronger parasympathetic activity, the branch of the nervous system often linked with calming and recovery. Another measure, SDNN, was higher under spring water sound, with the largest gap appearing at 50 dBA.

The psychological ratings followed the same broad direction. Spring water sound improved sound comfort votes compared with no sound by 0.16 to 0.95, while traffic noise reduced comfort as it grew louder. At 55 dBA, the difference between water and traffic was especially large, with water scoring 2.68 points higher for comfort and 2.47 points higher for pleasure. The single best comfort and pleasure response still appeared at 50 dBA spring water sound.

Those paired findings are useful because comfort can be easy to oversimplify. A person may say a sound feels pleasant, yet the body may show strain, or the reverse can happen. In this experiment, the ratings, heart signals and brain signals broadly pointed in the same direction, which made the 50 dBA water result stand out more clearly.

## The brain response had a pattern

Brain activity added another layer to the story. The team studied several brainwave bands and focused closely on **alpha power**, which is often associated with a relaxed and comfortable state during quiet wakefulness. Spring water sound produced higher alpha activity than traffic noise, especially in areas related to attention and visual regulation.

The highest alpha power appeared at 50 dBA spring water sound. Under traffic noise, alpha power fell as the sound level rose and traffic above 50 dBA was linked with weaker brain-comfort markers. The researchers also reported that the left frontal-parietal region and the right occipital region were especially sensitive to the sound changes.

Other brain bands helped fill out the picture. Under spring water sound, theta and beta activity rose most clearly around the middle of the tested range, while delta and gamma activity were lower than in the no-sound condition. Traffic noise moved in the opposite direction for several of those measures as the level increased, which the paper linked with higher stress demand and lower comfort.

The study also used a brain dynamics measure called the **avalanche critical index**. In this analysis, a lower value meant brain activity was closer to the state the researchers associated with comfort. Spring water sound lowered this index compared with no sound and traffic noise. At 50 dBA spring water sound, the index reached its lowest value and the paper reported that brain comfort was 1.74 times higher than under traffic noise at the same comparison point.

## Traffic became harder to tolerate

Traffic noise showed a more familiar pattern for anyone who has tried to work near a busy road. As the traffic recording grew louder, comfort and pleasure scores fell. The lowest sound comfort vote came at 60 dBA traffic noise and the heart and brain readings also moved toward the less comfortable side of the study's scale.

At 40 dBA, traffic noise and spring water sound were closer together in the ratings. The difference widened as sound levels rose, then shifted again at the top of the range. The research team interpreted this as evidence that both sound type and sound level must be considered together. A water sound can become less helpful when it grows too loud, while traffic becomes more intrusive as its level rises.

That finding fits a larger public health concern about environmental noise. The [World Health Organization's environmental noise guidelines for Europe](https://www.who.int/europe/publications/i/item/9789289053563) were written to protect health from road, rail, aircraft, wind turbine and leisure noise. The [WHO health and environment compendium](https://www.who.int/tools/compendium-on-health-and-environment/environmental-noise) also identifies road, rail, air traffic and building sites as important sources of environmental noise exposure.

The new study had a much narrower aim than those public health reports. It tested short sound exposures in a laboratory, while environmental noise guidelines are concerned with long-term exposure across communities. Even so, the paper helps explain why the character of sound may influence indoor comfort, especially in places where traffic noise is already part of daily life.

## Why the volume changed the response

A spring-water recording at 50 dBA was strong enough to produce a clear response, while still moderate enough to avoid the discomfort that can come with higher sound levels. The researchers described the effect as an inverted U shape: comfort rose from the quieter water conditions, peaked at 50 dBA, then declined at 55 and 60 dBA.

That shape is important for design. Adding a natural sound to a room could help some people feel more comfortable, but loudness still needs limits. The study suggests that simply increasing a pleasant sound may reduce its benefit once the sound becomes too strong. For offices, classrooms, hospitals and homes, a controlled level may be more useful than a louder water feature.

The paper also found individual differences. Compared with no sound, 64.65 percent of participants showed signs of higher brain power consumption under traffic noise, while 67.57 percent showed lower power consumption under spring water sound. For participants exposed to 50 to 60 dBA spring water sound, 52.63 to 63.16 percent fell into the lower power-consumption region used in the study's brain analysis.

## The study has clear limits

The experiment involved young college students, all sitting still with a low activity level. The exposures lasted five minutes. Only two sound types were tested and the sound range stopped at 60 dBA. Those limits mean the findings should be applied carefully to older adults, children, people with hearing differences, people doing demanding tasks and rooms where sound continues for hours.

The researchers also noted that laboratory studies cannot capture every part of daily life. A sound that feels helpful in a controlled room may feel different in an apartment, a hospital ward, a classroom, or an open office. Personal taste, culture, hearing sensitivity, task demands and control over the sound can all change the experience.

The next step is broader testing. Future work could compare more natural sounds, longer exposure times, different age groups and real indoor spaces. The study's strongest contribution is its method: combining comfort votes with heart and brain readings to judge an acoustic environment in a more complete way.

For now, the result is precise and practical. In this laboratory setting, **50 dBA spring water sound** produced the clearest comfort pattern across self-reported ratings, heart activity and brain dynamics, while louder traffic noise moved the same group toward lower comfort. Quiet rooms may still be best for many tasks, but carefully managed natural sound could become one tool for designing indoor spaces that feel easier on the mind and body.