Dec 07, 2019 Last Updated 10:52 AM, Aug 14, 2019

The power of speech

Published in Talking Point
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Fifty years ago the ROCKWOOL Group launched acoustic ceiling division, Rockfon. Since then the specialist brand has grown from a single manufacturing site at its Hedehusene headquarters near Copenhagen to production in 27 countries. Tim Spencer is the Technical Manager for Rockfon in the UK and in this month's Talking Point explains the importance of good acoustics.


Speak with anyone involved in education, such as teachers, students, architects and contractors and the same major challenges will come up. Acoustics and noise is by far the largest problem.

Good acoustics in schools ensures that all children, particularly those with hearing difficulties, have access to a learning environment that will enable them to reach their full potential. It also ensures that teachers are less likely to suffer from acoustic environment induced stress and long term health and wellbeing issues.

What factors can affect the acoustics in schools? Modern classroom designs focus more on circulation and thoughtful layout, while group-work activities and individual learning programmes for the surrounding community require larger size classrooms and multi-purpose spaces. Architects now have to take into consideration the ever-changing role of the school as part of society, leading to more all-inclusive design.

Energy efficiency is also high on the agenda these days and in a quest to meet environmental ratings in public buildings, designers are increasingly using thermal mass solutions. In order to optimise thermal mass, it is necessary to use materials with a high inertia, like concrete, which need to remain uncovered to allow effective circulation of air and heat exchange. But materials such as concrete, steel and glass also reflect and amplify sound leading to noisy spaces.

Alternative solution

Traditional ‘wall to wall’ suspended ceilings made from a material, such as stone wool, provide excellent levels of sound absorption and can dramatically improve acoustic comfort. However, in thermal mass situations, the hard surfaces need to be left exposed and so other solutions are required. The alternative solution is to utilise ceiling islands or baffles which allow the air to circulate freely while absorbing sound from both sides, thereby optimising acoustic comfort.

Reverberation (the amount of echo in a room) affects how well speech is understood and typically occurs in rooms with hard reflective surfaces. If levels are high enough, students lose concentration, teachers have to speak louder and speech intelligibility diminishes. Young children are especially vulnerable to this, and the situation can be made worse in highly reverberant spaces. The main determinants of reverberation are the geometry of the room and the amount and distribution of absorbent materials. Utilising acoustic ceiling tiles, acoustic wall linings and/or islands will reduce reverberation and increase speech intelligibility in the classroom. For example, in a standard classroom of 180-250m3, the installation of a Rockfon stone wool ceiling with high sound absorption will reduce reverberation time to an acceptable level to create a healthy environment. The majority of Rockfon products have a sound absorption (αw) greater than 0.90, i.e. Class A, meaning at least 90% of the sound energy is absorbed or dissipated.

In the case of islands, for the greatest level of sound absorption to be achieved it is essential that they are suspended at least 200mm from the soffit and that the back surface is as absorbent as the front. Further improvements can be obtained by spacing the islands at least 300mm apart.

Rockfon has over 50 years of expertise within the education sector. Installing a Rockfon sound absorbing ceiling will contribute to a reduction in the ambient sound level of the space while specifying a Rockfon Sonar dB ceiling will also insulate against intrusive noise from installations in the ceiling void and adjacent spaces.

To enhance and complement its traditional suspended ceiling ranges, Rockfon has a mix of other acoustic solutions: Rockfon Contour acoustic baffles and Rockfon Eclipse ceiling islands. Baffles are particularly useful where frequent and unhindered access to service installations is required, but also for providing additional sound absorbency to existing acoustic ceilings. For areas where a traditional suspended ceiling cannot be used, such as glass roofs and thermal mass buildings, Rockfon Eclipse ceiling islands are the answer. Absorbent on both faces, the islands and baffles allow air to flow freely around the room for cooling and heating, while delivering best in class sound absorption.

Additional specialist products are Rockfon Boxer 1A impact resistant ceilings for areas such as sports halls, and Rockfon VertiQ acoustic wall linings for classrooms and other heavily trafficked areas. All Rockfon solutions provide good acoustics, excellent fire safety and humidity resistance combined with outstanding design. They are easily installed on site and can be suspended in a variety of ways from all types of soffit.

Part of the Rockwool Group, Rockfon is an environmentally focussed company. The rock used to produce the company’s stone wool is not a scarce resource. Every year the earth’s volcanoes and plate tectonics produce 38,000 times more rock material than is being used to make the stone wool used in Rockwool insulation products and Rockfon acoustic ceilings.

On larger scale projects, particularly those being developed with public funds, environmental concerns create new challenges. These often involve the need to minimise off-cuts and recycle where possible. We work closely with contractors to develop plans for sending off-cuts to the Rockwool manufacturing plant, where they are upcycled into energy saving and CO2 reducing stone wool insulation products.”

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