Silence is precious. According to the American Institute of Stress, as much as 77 percent of people in the United States show some physical signs of stress when living their everyday lives, and a period of silence each day can help them relax and reduce stress levels. 

Silence helps lower blood pressure, improve concentration and focus, improve insomnia, encourage mindfulness, and more. 

But is it easy to achieve silence in the urban life we lead today? Take Mumbai, India”s commercial capital, for example. It has witnessed its noise levels reach close to 124 decibels. Such high levels of sound could be placed somewhere between running a chainsaw (120 dB) and taking off military jets. 

In NYC, the New York City Department of Buildings received as many as 3,700 noise complaints in a year, including the sounds of construction noise, traffic congestion (75dB to 80dB), screeching subways (80dB to 100dB), and jackhammers (110dB).

The question is, how do we find a place of quiet when our inevitable daily living components are this noisy?

Researchers have been contemplating solutions for quite some time now. An interdisciplinary collaboration of researchers from MIT and elsewhere has developed a solution: a sound-suppressing silk fabric. 

Sound-Suppressing Silk Fabric to Create Quiet Spaces

The fabric used in the silk is hardly thicker than human hair. The application of a voltage makes the fiber that has been used to create this fabric vibrate. And it is these vibrations that help suppress the sound. 

At a primary and more predictable level, the sound waves generated by the vibrating fabric interfere with unwanted noise and cancel them out. This technique is effective only when applied within a small space. Noise-canceling headphones, since they work only on the limited space of our ears, thrive on this principle of noise cancellation. 

But this fabric goes a step above conventional noise cancellation by suppressing vibrations that are fundamental to sound transmission. It can suppress sound in a living room’s much larger space. 

The researchers tested the effectiveness of both noise suppression methods. In the direct suppression mode, the silk fabric could reduce the volume of sounds up to 65 Decibels. In the second mode, where vibration cancellation is the key, the fabric could reduce sound transmission by up to 75 percent.

Another crucial aspect of the invention was that it used easily found materials like silk, canvas, and muslin. It has high real-life applications, such as making dividers in open workplaces and offering thin fabric walls to prevent sound from getting through. 

While speaking about the success that this sound-suppressing silk could achieve, Yoel Fink, a professor in the departments of Materials Science and Engineering and Electrical Engineering and Computer Science, had the following to say:

“Noise is a lot easier to create than quiet. To keep noise out, we dedicate a lot of space to thick walls. [First author] Grace’s work provides a new mechanism for creating quiet spaces with a thin sheet of fabric.”

However, it is not the first time that the group of researchers involved in this attempt went for a novel approach to suppress sound. The group tried to create fabric microphones by sewing a single strand of piezoelectric fiber into the fabric. These piezoelectric materials produced an electric signal upon squeezing or bending. They converted sound vibrations into signals as well. Although the method could prove its worth, it could not work beyond a limited space. 

With the current research on sound-suppressing silk fiber, the researchers want to look into how their solution can block the sound of multiple frequencies in the future. 

According to Grace Yang:

“There are a lot of knobs we can turn to make this sound-suppressing fabric effective. We want to get people thinking about controlling structural vibrations to suppress sound. This is just the beginning.”

The urge to eliminate unwanted noise is a symptom of our times. Researchers have been inspired to develop solutions in this area. A couple of years back, researchers tried leveraging acoustic metamaterials to block out sound. 

Achieving Silence through Acoustic Metamaterials

In core scientific terms, a metamaterial is “artificially structured materials that control and mold the flow of electromagnetic waves or possibly any other type of physical waves.” 

Xin Zhang, a professor of mechanical engineering at Boston University, developed this silence-suppressing solution, built with acoustic metamaterials, to block noise while preserving airflow. 

Zhang formed a team with PhD student Reza Ghaffarivarda and used metamaterials, mathematical calculations, and an open, ring-like structural design to create an open silencer that could maintain efficient ventilation while reducing unwanted acoustic waves by up to 94 percent.

The silencing device the duo designed can be named or seen as an “ultra-open acoustic metamaterial silencer” that has a large central opening with 60% airflow. Its central port is wrapped around with six helical channels. Resultantly, the port can generate an out-of-phase wave on the transmitter side.  The acoustic waves that generate out of hitting the central and helical channels cancel each other out, nulling the transmission in effect and creating silence. 

For functional, on-ground implementation, the researchers sealed a loudspeaker into one end of a PVC pipe and fastened the acoustic metamaterial silencer at the other end. Sound was played through the loudspeaker at high volume at the closed end of the pipe and could not be heard at the open end till the silencer was there. 

While explaining his plans with the solution, which has already received interest from large companies across many industries, Zhang said:

“The ultra-open metamaterial silencer offers the potential to mitigate environmental noise from diverse sources. We are excited to explore many new opportunities where our design could benefit people, our environment, and working conditions by reducing noise.”

It is now clear that these solutions, irrespective of how simple they appear through their efficient designs, are effective in serving their purpose. It is quite obvious that companies in the field of sound and acoustics will deliberate on such solutions. Below, we will discuss a couple of companies that have invested research and resources into finding new ways to suppress noise. 

#1. Silentium

Silentium is known for its unique Active Noise Control (ANC) technology. It offers a full-spectrum disruptive sound management solution involving proprietary algorithms. These algorithms can adapt to changes in the noise spectrum and achieve results of almost 10 dB (A) noise reduction. 

Like the sound-suppressing silk, Silentium’s solutions also work in comparatively larger spaces, like the inside of a car. Its ‘Quite Bubble’ technology reduces noise by synthesizing the physical characteristics of the unwanted noise field in a desired zone of quiet. The method is built upon a multichannel algorithm capable of controlling the sound field produced by an array of loudspeakers. 

The Silentium Quiet Bubble solution can be used on noisy home appliances, in automotive products to reduce the sound coming from wind, tires, engine, and HVAC, in industrial setups to create a quiet work environment, and even within modes of transportation like trains, airports, and stations. 

The Quiet Bubble end-to-end solution by Silentium comes as a complete turnkey offering with both software and hardware elements.  

According to the latest news, Silentium had an extended Series D. The company closed the round with a total of US$63 million. Menora Mivtachim and Meitav Dash, both Israeli institutional investors, led the round. 

The company also has the global electronics leader Molex as one of its investors. While giving an idea of what the future might look like for Silentium, Yoel Naor, the CEO of the company, had the following to say:

“We welcome new partners that share the same passion for acoustics and see the value in enhancing privacy and wellbeing through personal sound spaces. With this new investment, we will scale up the development and roll-out of our Active Acoustics software solutions for vehicle manufacturers and automotive suppliers – especially as NVH requirements evolve in the new era of electric and autonomous mobility.”

#2. Zero Sound

The company promises high-quality active noise cancellation for a range of use cases, from the inside of a noisy cab to large outdoor stadiums. Scaling up is possible because the core solution is comprised of a panel. The number of panels can be increased to cancel noise as per the field of application. Zero Sound claims that its solutions can actively cancel noise, reducing it by up to 92%.

Deploying more than ten ZS active digital noise suppression panels together, one can cater to the noise cancellation needs of industrial complexes, construction sites, stadiums, rail & road crossings. 

Anywhere between one and nine panels is enough to create a suppression network for power generators, industrial equipment, drilling, and construction sites. 

More than five panels are enough for an enclosed space, such as those found in office interiors, hospitals, server rooms, and hotels. And anywhere between one and four panels is sufficient for the cabs of emergency vehicles, heavy equipment, and agricultural equipment. 

According to available data, Zero Sound had a funding round closed at CA$880,000 in May 2018. 

Tackling Noise: the Ubiquitous Hazard of Crossed Limits

The European Union, in no uncertain terms, recognizes noise pollution as a major problem, both for human health and the environment. While long-term exposure to knowledge can result in annoyance, sleep disturbance, and negative effects on the human heart and the metabolic system, environmental noise may result in cognitively impaired children. 

According to the EEA estimates, environmental noise is the driving cause of 48,000 new cases of ischaemic heart disease a year and 12,000 premature deaths. Environmental noise also contributes to chronic high annoyance among 22 million people and chronic high sleep disturbance among 6.5 million people. More than 12,000 schoolchildren suffer reading impairment as a result of aircraft noise alone. 

Tackling the hazards of noise, therefore, is a task that needs all-around combatting. One of the most vulnerable areas among all these, where a large number of people get affected within a very small space, is the industrial space. 

Numbers suggest the possibility of as many as 22 million US workers facing hazardous noise levels at work. Many new strategies have been deployed to keep this menace of industrial noise under control. 

Constrained layer damping—achieved by placing the dampening material between two metal sheets—has been a useful method for reducing vibrations generated by machines. 

For domestic purposes, a band of researchers in Singapore has come up with the innovative idea of noise-canceling windows. Mounting these system solutions to window grills can reduce incoming sounds by 50%. 

Sensors play a key role in making this method a success. These sensors detect incoming noise and play a sound with a similar but inverted waveform so that these out-of-phase sound waves may counteract the incoming waves, dissipating them before they go any further.

One of the most sophisticated and exciting solutions to appear in recent years has been nanotechnology soundproofing foam. It uses nanotechnology to turn sound waves into heat. The solution is accessible and scale-up-ready, as it uses available off-the-shelf soundproofing foam as its base. Such foam is then injected with a nanopowder to create microscopic channels within it. These channels or tubes turn acoustic vibrations into heat, dissipating the sound. 

Combating the menace of sound requires more innovative solutions and the willingness of large manufacturers and industry players to invest judiciously in sound suppression solutions. Since sound is not visible, its threat often misses the radar. Its harmfulness only comes to the fore when we realize the damage it has done to our bodies and our inner selves. It requires more awareness, for sure!

Click here to learn all about saving lives with AI-enhanced noise suppression.