Thin sound-suppressing silk fabric works like noise-cancelling headphones

Researchers in the U.S. have developed an ultra-thin silk fabric embedded with a special, piezoelectric fibre that can vibrate to cancel out noise in a room. If made into drapery, the researchers say it could block noise from adjacent rooms from reaching through.

Experiments showed that the fabric with the piezoelectric fibre, which was developed and tested by researchers at MIT and elsewhere, could reduce sound by up to 75 per cent.

Noise-cancelling technology, like systems used in headphones popular among air travelers, use destructive interference to cancel out the noise of the plane's jet engines. The headsets actually generate noise to eliminate noise.

When two sound waves are out of phase, or directly opposing each other, they cancel each other out.

The same effect happens in water where waves have troughs and peaks. If two peaks meet, they amplify each other and create an extra large wave. But if a peak and trough merge, a flat spot appears.

Sound waves do the same thing. Noise-cancelling headphones record environmental sound then play it back with just the right delay. That causes sound waves to be out of phase with each other and creates destructive interference, offering an escape from jet noise for people on long flights.

The De Havilland Dash 8-400 twin-engine turboprop commuter plane, formerly known as the Q400 where Q stood for quiet, has actuators built into the fuselage that vibrate in tune with the propellers to reduce cabin noise. 

The new ultra-thin silk fabric, which is barely thicker than the width of a human hair, was designed to perform the same function using a piezoelectric fibre sewn into the fabric.

When piezoelectric materials bend, such as when sound waves hit them, they produce a small electric current. The opposite is also true: that if an electric current is sent through the materials, they will bend.

The idea with this study was to have the fabric vibrate in response to sound waves so the whole fabric acts like a speaker and cancels the waves out, becoming a soundproof barrier.

That works for smaller areas like inside your ears, but the researchers also found that using the piezoelectric effect to hold the fabric still causes it to act like a mirror, reflecting up to 75 per cent of the sound waves back so they don't pass through the fabric at all. This works in much larger areas, like in a room or a plane.

The researchers want to further study how changing elements of the fabric — such as the number of piezoelectric fibres and the voltage they apply to it, the direction they're sewn into the fabric, and the size of the pores in the fabric — can improve on their findings. They also want to tune the system to see if they can block out more complex sounds from multiple sources. 

Hanging silk drapery to eliminate sound is much simpler than installing thick insulation within the walls. They could also be incorporated into dividers to isolate workstations in open offices.

We live in an increasingly noisy world. If you have been bothered by noisy neighbours in the next apartment or thin walls in a hotel, a portable fabric that can be simply hung on the walls to create a quiet space would be a welcome relief.