Photo: DTU Electrical Engineering

Room acoustics affected by light

Tuesday 30 Jan 18


Finnur Kári Pind Jörgensson
PhD student
DTU Electrical Engineering
+45 45 25 39 33
Acoustics researchers at DTU took part in a study that resulted in surprising new knowledge about the importance of light for sound in a room.

A cooperative venture involving Henning Larsen Architects, a light designer from The Royal Danish Academy of Fine Arts Schools of Architecture, Design and Conservation, and acoustic engineers from DTU recently showed that primary school classroom noise is significantly affected by the nature of the lighting.

The researchers carried out a series of tests in identical classrooms. These tests involved changing the lighting so that for some lessons, there was consistent ceiling light from conventional school lighting, and for other lessons, there was a concentrated light from pendants positioned above the desks—the sort of set-up we might have at home.

“We took measurements of noise levels with different lighting. It quickly emerged that concentrated light from the pendants caused the children to be significantly quieter than when the ceiling lights were on,” Finnur Pind explains.

Working with colleagues from DTU Electrical Engineering, he assisted with advanced measurements of the sound level, e.g. making it possible to distinguish between sounds from the pupils and the teacher.

“The measurements showed that using the pendants reduced the noise by between one and six decibels in three-quarters of teaching situations. A reduction of one decibel is barely perceptible to the human ear, but a reduction of three decibels in the noise level is clear—and a difference of six decibels is even more clear. We certainly weren’t expecting that result,” Finnur Pind comments.

Relevant to DTU auditoriums
The surprising findings may be relevant for creating good acoustics in rooms to be used for different purposes.

Finnur Pind cites DTU auditoriums as an example, where many have experienced the difference between attending a lecture and then taking part in subsequent group work.

“For the lecture, there is only one speaker—so the soundscape of the auditorium has been designed to enable everyone to hear what’s being said. But during group work, all of a sudden there are lots of people talking at the same time, and it’s difficult to tune into the person you’re trying to listen to. Ideally, therefore, there should be a means of changing the sound-absorbing material in the room to cope with these two different situations—but that’s a very expensive solution, usually only used in concert venues, for example. If, instead, you can switch between ceiling llighting for lectures and focused, pendant lighting for group work, that would presumably be a financially manageable way of producing the same effect,” Finnur Pind says.

About the study

The noise emission level was measured in conventional learning situations where pupils work on their assignments individually or in pairs at their desks, while the teacher walks around answering questions.

The study was conducted in preschool and intermediate stage classes in a Danish primary school.

In about one-quarter of learning situations, the noise level was reduced by less than one decibel, which is imperceptible to the human ear.

In about one-half the learning situations, the noise was reduced by between one and three decibels, which is significant to the human ear.

In about one-quarter of cases, the noise was reduced by between three and six decibels, which is very significant to the human ear.
22 FEBRUARY 2018