The loud noise of leaf blowers has woken up many of us. And while these machines are practical, their noise and emission levels as well as dubious environmental credits have led to a bad reputation. Now, students at Johns Hopkins University have developed a silencer for leaf blowers that will go into series production, making our cities a bit quieter.

A team of four students at Johns Hopkins have developed a leaf blower that is up to 94 per cent quieter. Sponsored by the manufacturer Stanley Black & Decker, the project looked into silencing leaf blowers. Their loud noises are bad for the health of workers, while also creating harmful air flows and disrupting biodiversity. The new attachment that dampens the noise could be on the market as early as in two years.

Less noise, same performance

To develop a leaf blower that is quieter than the average, two male and two female students at Johns Hopkins first investigated how the annoying sound of these machines comes about. A battery-operated leaf blower from DeWalt, which is part of sponsor Black & Decker, was the research object. They found that the sound a leaf blower makes is complicated, containing many different frequencies. Alternatives with electric engines reduce the rattling noise of the combustion drive, but air noise still remains.

To reduce this noise, the student team experimented with 40 different 3D-printed plastic attachments for leaf blowers. These attachments are for the muzzle of the air nozzle, not unlike the silencers of firearms. In the end, the successful version managed to swirl some of the expelled air, superimposing it on the main flow and thus allowing the sound waves to partially cancel each other out. The combination of two air flows, one unchanged one and one displaced one, makes the leaf blower less loud without affecting its performance.

Analysing a leaf blower’s noise piece by piece

Overall, the team was able reduce the noise of leaf blowers by 2 decibels. This corresponds to a perceived noise reduction of 37 per cent, according to the Johns Hopkins University press release. Those frequencies that are particularly shrill and annoying could be reduced by 12 decibels, resulting in a 94 per cent reduction. A team member compared this to the difference between a high-pitched whistle and wind noise, which is much deeper.

Black & Decker asked the students to create a version for mass production that would use injection moulding rather than 3D printing. Currently, the patent application is in progress. The company is aiming to launch the product on the market within two years. It will work as both a retrofit accessory and as part of new leaf blowers by fitting over the end of the leaf blower. According to the students from the project team, the solution for noise reduction might also work with other appliances such as hoovers and hairdryers.

The student team consists of seniors majoring in mechanical engineering. In an interview, they said that they are very proud of their achievement. They started working on the challenges in September 2023, analysing the noises of every single piece of a leaf blower. After workshopping over 40 versions of the final solution, they found the attachment that reduces noise.

No noise limit for leaf blowers

Leaf blowers are attracting criticism for their noise and pollution levels. They also kill insects and chop up seeds, thereby threatening biodiversity. Some of the lawn care machines produce more than 100 decibels of low-frequency sounds that penetrate walls – that is about the equivalent of a plane taking off. Consequences for humans can include tinnitus and hearing loss after long exposure.

Gas-powered leaf blowers also emit pollutants into the air that are linked to cancers, heart disease, and asthma. They contribute to bad air quality in cities. And their blasting of air at temperatures of up to 450 km/h can erode topsoil, sending pollen, fertilisers and herbicides into the environment.

Most at risk from lawn blowers are workers who spend hours every day with this equipment. However, there is currently no noise limit for leaf blowers (or vacuum cleaners) in Germany. The European Commission is planning to introduce one soon. Neighbours are usually placated by quiet periods, but it might still be best to avoid using such devices at all.

Banning fossil fuel-powered leaf blowers

Lawn blowers are one example of how technology and costs can limit the pace of change. While there are many more environmentally and health-friendly options available, such as electric lawn mowers, their performance is not as good as that of gasoline-based tools.

In the end, it is worth asking not just how we can make leaf blowers quieter or less polluting, but also whether we actually need them. Getting rid of high-maintenance, perfectly “clean” yards and seeding native plants instead could be an option. The old-fashioned, but clean and quiet rakes are another alternative to leaf blowers, and they are much cheaper, while also offering a workout.

Some cities, such as Edinburgh in Scotland, are already considering banning the use of fossil fuel-powered leaf blowers due to concerns about the health impact on workers. The city council is recommending electric leaf blowers and rakes, concluding that “fossil fuel leaf blowers may well blow, but they also most definitely suck.”

Read more about air pollution and what it means for cities here.