I received a call from the head of development at a medical device manufacturer.
Can our oxygen concentrator reduce noise to 38 dB(A)? The current limit is below 50 dB(A), and internally, it’s said ‘no more is possible.’
The voice on the other end of the phone was someone who had been fighting this issue for over ten years.
The difference between 50 dB(A) and 38 dB(A) is 12 dB. At magnification, the sound pressure differs by about 4 times in the auditory perception. The goal was for a device placed in a late-night hospital room one meter from the patient’s bedside to become so quiet it was indistinguishable from the dark noise of midnight.
“I will come to hear your story,” I replied. At that time, I had no concrete plan at all about where to start.
The idea of eliminating the vibration source
The first month I spent in the medical device manufacturer’s testing room was solely about measuring vibration and noise. Every time a piston-type compressor compresses, what happens inside the device — the kinetic force generated by the piston’s acceleration and deceleration, the crank mechanism that transmits that force, the base supporting the mechanism, the cabinet on which the base rides, and the radiated sound emitted when the cabinet surface vibrates the surrounding air. Data showed that sound pressure was amplified at every link.
What this manufacturer has been doing so far has been an approach of “cutting off the transmission path of vibration.” Vibration-damping rubber, sound-absorbing materials, double cabinets, active noise control. But at that point, I was convinced.
“Unless the vibration source is physically eliminated, it’s impossible to lower it by 12 dB,” he said. As long as the reciprocating motion of the piston continues to generate structural vibrations, no matter how much the transmission path is narrowed, it will reach a ceiling at some point. This was the true nature of the 50 dB wall.
“We came to create equipment that other companies can’t make.”
At the first meeting, I said the following to the head of development.
“With our fully rotating balanced cylinder device, we physically convert the piston’s reciprocating motion into uniform rotation. This method reduces the inertial force itself to almost zero. “This is a proprietary mechanism developed over 20 years, and we have obtained patents both domestically and internationally.”
“However, you need to customize it to your product requirements: the gas (oxygen) handled by the compressor, flow rate (5L per minute), lifespan (24 hours, 365 days a year, 10 years), and size constraints (fits into existing cabinets). While meeting all requirements, we aim for a noise level of 38 dB(A).”
“So you mean you’re going to do it, right?” Yes, I’ll do it.
I was a little surprised that night when I immediately replied, “I will!” Even so, I didn’t get off. The reason I didn’t get off was not because I had a technical advantage, but because I couldn’t get out of my mind for a while that if this device could be made quieter, the quality of sleep for patients in hospital rooms around the world would change.
What happened in 14 months
4 months for custom design and 8 months for evaluation testing. Along the way, I rewound the design twice. The first time, at a specific rotational speed of the prototype, natural vibrations and resonance points in the base area appeared, taking three weeks to identify the cause and two weeks to address it. The second time is when part wear data from long-term continuous operation is found to not meet the lifespan requirements. The material of the second crankshaft was changed to stainless steel, and it lasted 4 weeks.
The process was delayed. Costs have ballooned. This phase could have led to a decision to withdraw.
However, the manufacturer’s development manager was truly persistent. “Please show us the data,” “Please reproduce the measurement conditions by changing them,” “We will take this back inside the company”—they continued reading the data together. We were both technical professionals.
Values measured in the laboratory
In the end, the goal was exceeded.
- Noise (1m distance): 52 dB(A) → 38 dB(A) (-14 dB)
- Vibration acceleration (installed surface): 0.18 m/s² → 0.04 m/s² (-78%)
- Energy consumption: -38%
- Continuous operating temperature rise: +35°C → +8°C
Conclusion — Who made the decision of ‘impossible’?
There is a phrase that came to mind many times during this project.
Within our company, this target value was considered impossible
Ten years ago, when the manufacturer internally decided it was impossible, that decision might not have been wrong. However, judgment lives on even after that. The memory of “it’s impossible” is passed down to the next generation of engineers, becoming a theme no one else attempts.
In the tech world, there are many cases where “past judgments narrow down current options.” At Air Surf, we want to be a company that reconsiders the “impossible of the past” from the perspective of physics.
If anyone is struggling with a problem that has been told “impossible,” please feel free to share your thoughts with us. The physics hasn’t changed since 10 years ago, but the options have changed.
Author Profile
Chief Research and Development Officer at Air Surf Co., Ltd. Engaged for many years in research and development of power technology.