How Hummingbirds Hum

New measurement technique unravels what gives hummingbird wings their characteristic sound

Together with Stanford University and Eindhoven University of Technology, we researched the pleasant humming sound of the hummingbird when it hovers in front of flowers to feed. By using a total of 2176 microphones the team of engineers succeeded in measuring the precise origin of the sound generated by the flapping wings of a flying animal for the first time.

With this article we want to take you through the research, show you more about the technology and explain how we can use this study to improve products, like drones, and make them quieter.

The Research

The hummingbird is named after its pleasant humming sound when it hovers in front of flowers to feed. But only now has it become clear how the wing generates the hummingbird’s namesake sound when it is beating rapidly at 40 beats per second. Researchers from Eindhoven University of Technology, Sorama, a TU/e spin-off company, and Stanford University meticulously observed hummingbirds using 12 high-speed cameras, 6 pressure plates and 2176 microphones. They discovered that the soft and complex feathered wings of hummingbirds generate sound in a fashion similar to how the simpler wings of insect do. The new insights could help make devices like fans and drones quieter.

The team of engineers succeeded in measuring the precise origin of the sound generated by the flapping wings of a flying animal for the first time. The hummingbird’s hum originates from the pressure difference between the topside and underside of the wings, which changes both in magnitude and orientation as the wings flap back and forth. These pressure differences over the wing are essential, because they furnish the net aerodynamic force that enables the hummingbird bird to liftoff and hover. 

Unlike other species of birds, a hummingbird wing generates a strong upward aerodynamic force during both the downward and upward wing stroke, so twice per wingbeat. Whereas both pressure differences due to the lift and drag force acting on the wing contribute, it turns out that the upward lifting pressure difference is the primary source of the hum.

Bringing research into practice, making drones quieter

The knowledge gained in this research helps improving aircraft and drone rotors as well as laptop and vacuum cleaner fans. The new insights and tools can help make engineered devices that generate complex forces like animals do quieter.

Drones can be examined using the same microphones (sound cameras), to make them more quiet.

This is exactly what we at Sorama aim to do: We make sound visible in order to make appliances quieter. Noise pollution is becoming an ever-greater problem. And a decibel meter alone is not going to solve that. You need to know where the sound comes from and how it is produced, in order to be able to eliminate it. That’s what our sound cameras are for.

The hummingbird wing research gives us a completely new and very accurate model as a starting point, so we can do our work even better and support in making the world sound right.

High-tech sound cameras & Acoustic design cycle

To make sound visible in the “How Hummingbirds Hum” research and be able to examine it in detail we used in total 2176 microphones. This enabled us to see the 3D sound field around the hummingbird.

The specific research setup consisted of multiple CAM1K & CAM64 cameras.

At Sorama we are experts at low-noise and sound design. During our 10+ years of experience we’ve developed a solid acoustic design approach that we deploy in order to improve sound behavior in products.

It is an iterative cycle that relies on gaining insight into the problem and translating this to proper solutions, instead of the traditional trial-and-error method.