Open office designs have been hailed for their economic benefits and helping people work together. On the other hand, a survey by a research firm showed that workers in an open office can lose up to 86 minutes of productivity per day due to distractions, like the constant humming of machinery or computers. In this scenario, noise-cancelling headphones have emerged as an important tool for people working in open office environments. However, it is physically uncomfortable to wear such headphones for long hours. To enhance sound privacy while ensuring comfort, scientists at the Budapest University of Technology and Economics have designed an office chair that can control not only tonal noise like humming machines, but also broadband (random) disturbances coming from anywhere in a room.
The scientists customized a popular gaming chair that has a built-in sound system to design the noise-cancelling chair. They attached flexible “error” microphones to the headrest of a chair, in addition to other control circuitry. They also fixed reference microphones at various positions in a room furnished like an office. Their design to achieve noise cancellation is based on the feed-forward control system. In this system, reference microphones strategically placed around a room receive sound waves originating from any direction in a room, and send out reference signals. These are fed forward to a control system, which generates signals that make the loudspeakers generate the cancelling noise. Any remaining noise is measured by the “error” microphones, which send a signal to the control system, which in turn can help adjust the cancelling noise generated by the loudspeakers to ensure maximum noise cancellation.
The scientists first carried out a series of experiments in a classroom to determine where and how many microphones should be placed to achieve maximum noise cancellation. They also performed computer simulations to determine where the error microphones should be placed on the chair to create a “zone of quiet” that would be independent of the position of a person’s head. A dummy head with a sound level meter was placed in the chair to test the efficacy of this noise-cancelling chair.
The typical hearing range of a human is 20 Hz to 20 kHz. The chair was effective at cancelling tonal noise of frequencies ranging from 200 to 800 Hz. Tonal noise is typically annoying, often generated by electric motors, fans, or other machines, and has predictable frequencies. The chair could also cancel random noise above 1 kHz. According to the CDC, the most important sounds we hear, including speech, lie in the frequency range of 250 to 6000 Hz. Hence, the scientists consider the noise-cancellation ability of the chair to be promising. However, the chair could not suppress random noise below 300 Hz, which the scientists hope to address in future work. While noise-cancelling chairs will be welcomed by those who crave peace in open offices, they could also be useful in other types of work environments where noise is an occupational hazard.
The “Cone of Silence” was just a joke in the American satirical comedy Get Smart, but the noise-cancelling chair could very well make it a reality!