Indoor plants for a quiet life

I recently came across an interesting video, via a post on LinkedIn, on YouTube that explained, with the aid of Nerf guns of all things, how room acoustics could be modified by using different shaped acoustic panels.

The explanation is simple and very elegantly delivered. It also reminded me of some research carried out in the mid 1990s by Dr Peter Costa at Southbank University in London. His research looked at how interior plants can be effective at modifying room acoustics and make loud places quieter.

Noise, especially in offices, can be very distracting and can even cause stress. Mental discomfort, as well as being distracted from the task at hand, can make work unnecessarily tiresome and unproductive.

As people start heading back to the office, they may rediscover the nuisance of noise that might have been missing when working at home. Most homes are actually quite quiet (apart from the noises of children, domestic appliances and pets), and this is because of the amount of soft furnishings, fabrics and carpets that are commonly found.

The office, however, is different. Large, open plan spaces with hard surfaces and lots of right angles can be very noisy places. Sound is reflected all over the place and often not well absorbed. Sometimes you can find yourself tuning into a conversation from several desks away just because you happen to be in the path of the sound that is being bounced around the place.

There are very many excellent manufactured acoustic products that can minimize the effects of distracting noise in such places, ranging from fantastically sophisticated computer-controlled sound masking systems, using arrays of microphones and speakers, to simpler (yet still highly effective) products such as acoustic panels that can be placed in just the right places to deaden the noise.

Noise reducing vegetation

Looking again at the video, the key point is that by introducing shapes that disrupt the path of soundwaves as well as absorbing them, is a very effective way of reducing noise. This is where plants can make a useful (and very cost-effective) impact.

Plants are very irregular in shape. Their leaves point in different directions, are often textured, and foliage comes in all sorts of shapes and sizes. Mix up a variety of plant types and you will have surfaces scattering soundwaves all over the place.

Plants reduce noise by either absorbing sound or by breaking up the sound and scattering it through diffraction and reflection.

Absorption

Plants alter room acoustics by reducing the reverberation time. Plants work better in acoustically live spaces, such as those that have hard surfaces like marble walls, exposed concrete and stone floors.

Diffraction and reflection

At lower frequencies plants may diffract and reflect sound. This is because the leaf size is small by comparison to the noise wavelength. Plants with lots of small leaves are useful as they scatter and diffuse sound. At higher frequencies the leaves may reflect sound towards other surfaces that may then absorb the noise.

By placing plants around a space where noise reflections are most likely to cause problems, you can achieve some meaningful improvements.

Green walls and moss walls have especially good acoustic properties. Green walls, as well as having a mass of dense foliage, are often mounted on panels made from products such as rockwool or dense foam plastics, both of which have excellent sound absorbing properties in their own right.

Green wall in the UK, designed by the author and installed by SH Goss and Co. Ltd

Moss walls are an excellent choice where a live plant green wall is not practical. The shape of moss deflects sound, whilst the texture of soft moss absorbs sound. Mounting materials also have some acoustic properties and, as they cover a large surface area, they absorb sound at different heights and from all directions.

Moss wall by Metiez Moss, Netherlands

As discussed earlier, noise levels in a large space are often not uniform. There are multiple noise sources, and the sound from any particular noise source can be magnified or focused some way from its origin due to the layout of the space. Sound might be reflected in one direction and blocked from going elsewhere. A distracting noise might be perceived some distance from its source. Sometimes the only way to be sure of where noise is coming from is to take some objective measurements with a noise meter and map where the noise ‘hotspots’ are found.

Measure the noise levels all around space, ideally when noise levels are typical for the location (e.g. during normal working hours for offices). You can create a map of the noise levels on a floor plan of the space by noting where noise levels are especially high or low. Then, try and identify the sources of the noise as well as where the noise is loudest (as discussed earlier – that isn’t necessarily the same place.

schematic of an open plan office floor plan
schematic of an open plan office with noise hotspots mapped

Noise meters are relatively inexpensive, and there are some quite useful apps for smartphones too that can be quite accurate (and are certainly capable enough to be able to measure relative differences in noise from place to place).

Once you have a map of noise levels and sound sources, then you can think about where vegetation will have its greatest impact.

Green multi-taskers

As well as being excellent noise management tools, don’t forget that plants in buildings have a multitude of other benefits, not least their ability to improve wellbeing (and workplace effectiveness) when used as part of biophilic design.

For more information about how plants can make buildings better places to be, please get in touch. I can help building managers with your properties, or interior designers and interior landscapers seeking to add evidence-based value to your designs.

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