Sound damper

“Without acoustic measures, these sounds pile up on top of each other to create a high level of background noise. Important flight announcements can disappear into the sound morass and conversations are difficult”, explained Dr. Peter Brandstätt, Head of Acoustics at the Fraunhofer Institute for Building Physics IBP, Stuttgart/Germany. Hard materials intensify the effect. Glass walls and stone floors reflect the noise, leaving sounds playing virtual ping-pong. This prolongs the so-called ‘reverberation time’. In simple terms, this denotes the time that elapses before the reverberation of a sound subsides. “The higher the reverberation time, the more reverberant the room sounds and the more incomprehensible the individual noises become”, Brandstätt observed.

Especially in spacious entrance halls, this often leads to acoustic problems because the reverberation time increases with the size of the room. “I keep noticing how people prick up their ears because they find it hard to understand announcements in airport terminals.”

Floating wooden ceilings, 20 meters up

To improve room acoustics, many airports clad ceilings and walls with sound-absorbing slotted or perforated metal, wood or plasterboard panels. How such acoustic elements can be elegantly integrated into the architecture can be seen in the Calgary International Airport (YYC) terminal, which opened in October 2016. At Canada’s third-largest airport, more than 200 flights depart daily, checking in or out 15.7 million passengers every year.

Designed by the Canadian architectural practice Dialog, the five-story new build connects to the existing terminal on the eastside and comprises 24 gates and more than 50 shops, restaurants and services. The interior is characterized by natural materials such as Douglas fir and rundlestone, a rough sandstone from the nearby Rocky Mountains. In the two central spaces, the arrivals hall and the departure hall, visitors can look out over Calgary’s skyline and the mountain backdrop of the Rockies through room-high glass fronts.

As beautiful as the view is, the glass façade limited the acoustic planners’ room for maneuver. The more so as the floor is covered with a reverberant material: easy-care and robust stone tiles. “So that left just the ceiling for sound absorption”, said Matthew Faszer of FFA Consultants in Acoustics and Noise Control Ltd., Calgary/Canada. Among other things, the office advised the architects on the planning of space acoustics and acoustic surfaces. FFA created a 3D model of the two halls in an acoustical modelling software program. The model was used to calculate the expected reverberation time with different acoustic ceiling variants made of textiles, wood and metal.

The choice fell on a suspended acoustic wooden ceiling. The individual ceiling segments float as curved wooden bands up to 20 meters above the heads of the people who use the airport. Skylights between the ceiling sections filter light down. In total, the craftsmen working on the ceilings in each of the halls installed around 18,500 square meters of ‘Solo’ perforated acoustic wood panels from Decoustics, Woodbridge/Canada, a subsidiary of CertainTeed Ceilings. They absorb a large part of the noise and thus improve the ambient sound. With the installation of the acoustic ceiling, the reverberation time dropped from around six to approximately two seconds.

Lighter than copier paper

“The ceiling combines the warm, inviting atmosphere of wood with the latest in acoustics”, explained Simone Abele, Director of Sales & Marketing at Decoustics. The wood panels are made from fire-retardant MDF boards with a natural wood veneer. Instead of voluminous mineral fiber mats, a 0.27 millimeter thin Soundtex® acoustic nonwoven fabric manufactured by Freudenberg Performance Materials (FPM) is glued to its back. At just 63 grams per square meter, the nonwoven is lighter than standard copier paper and easy to install. Because the material is black, visitors see nothing of the sound insulation above the wooden ceiling.

Although the special nonwoven has a decisive influence on the sound of the room, many sound waves do not penetrate it at all, but are reflected by the ceiling. This preserves a certain reverberation and shapes the acoustics of the halls, giving the soundscape an air of size and spaciousness. However, some of the sound waves penetrate the perforations and pass through the underlying absorber nonwoven. There, air molecules vibrated by sound rub against the fibers of the nonwoven fabric. As a result, their kinetic energy turns into heat and the reverberation time decreases. “Soundtex® absorbs around 75 percent of the sound that penetrates through perforated wood or metal ceilings, thus reducing the reverberation time in airports, railway stations or other large public buildings”, explained Jochen Bechtum, Product Manager, Freudenberg Performance Materials.

This does not make the airport in Calgary completely silent, but the atmosphere is much more pleasant. “Conversations are less of an effort and announcements are easier to understand”, Bechtum observed. Anyone who has almost missed a flight because of bad acoustics knows how important that is.