The technical definition of reverberation time (RT) is “the time it takes for sound in a room to decay by 60 dB”. For the layman, that’s not hugely useful. So what is reverberation time? Well, it’s that characteristic of a room which makes it feel “echoey” or at the other end of the scale very “dead”.

Imagine spaces as different as a cathedral (St Pauls’ in London is reputed to have a reverberation of 11s at some frequencies), and a typical living room (which might have an RT of around 0.5-0.7s). Think what happens when you are decorating, and remove all the soft furnishings and carpet from a room – that change in how it sounds is due to the increase in reverberation.

Why does it matter? Well, different reverberation conditions are appropriate for different uses. For good speech intelligibility, a relatively low RT is desirable. For music, a longer RT is great – that’s why singing in the bathroom is always so satisfying. Get the wrong RT for the use of the space, and it can significantly impact the usefulness of the room as well as occupant comfort.

Controlling reverberation

Reverberation occurs when sound energy is repeatedly reflected from hard surfaces; the way that is is controlled is by introducing acoustically absorptive surfaces to stop these reflections and soak up the sound energy, much like a sponge soaks up moisture.

Selecting these surfaces is not simple, however. Different materials will help to control different parts of the frequency spectrum, so for example a thin surface like carpet will be of little benefit in absorbing bass notes. The thickness and porosity of the material used, as well as the use of air cavities behind the absorption, are specified by acoustic consultants in order to precisely “shape” the sound within a room.

For simple spaces (low volume and simple shapes), there are straightforward formulae which we can use to predict reverberation time. In larger spaces, diffusion (the scattering of sound from different surfaces) also comes into play. It’s in these situations that a consultant is likely to suggest a computer model of a space. Although some clients shy away from this perceived complexity, modelling can be a quick and cost effective way to determine the placement of acoustic treatment – it means that the absorption is placed exactly where it is needed, and where it will be most effective.

dBx Acoustics was thrilled to be part of the team behind the Beehive in York. A purpose-built centre, the Beehive is thought to be the first of kind in the country and it provides short breaks for children and young people with complex disabilities.

dBx Acoustics provided acoustic design advice as well as a planning noise impact assessment. The project was especially dear to Susan, dBx Acoustics director as both she and her daughter are autistic. Susan is also a member of the Institute of Acoustics Diversity and Inclusion committee.

The facilities at the Beehive include:

• a safe and accessible space for play and interaction with family members and with staff
• apartments for children and parents to stay in during longer term assessment of their support needs
• access to a range of professionals who can help to support families in meeting the children’s needs
• spacious bedrooms with state-of-the-art hoist and bathing facilities for children who have complex health needs and wheelchair users
• a larger, open-spaced area and bedrooms for children with learning disabilities or autism
• quieter self-contained areas that can be used for children who may struggle in a more open, busier environment and where their parents can accompany them so that their needs can be fully assessed
• an activity area, sensory room and quiet rooms
• a large outdoor play space with a variety of equipment suitable for children of all abilities.

Find out more about the Beehive here.