Excited to introduce my UPS (or APU) noise-reduction box. Here’s the magic: a maze design for effective noise trapping coupled with a natural convection cooling strategy. The bottom cool air inlet and top hot air outlet capitalize on the principles of convection, promoting passive airflow and efficient cooling.
Attached is a screenshot and the Rhino 3D file. Everyone’s invited to tweak and enhance! Replace it with a new screenshot and Rhino or link. Your feedback and insights will be invaluable.
I’m curious, is there any science behind this design? From what I can remember of noise attenuation from half a century ago (and I recognise that is plenty of time for things to move on!) I wonder about these considerations:
Hard surfaces are bad because sound bounces off them. Noise reduction usually employs foam or blankets.
Mechanical/Electric noise sources should not be in contact with surfaces that can resonate. Spiked and/or rubber feet or elastic suspension should be used.
Thank you for taking the time to engage with my design. Your questions and insights are invaluable, and I’m excited to discuss the science behind my UPS noise-reduction box.
Mass Blocking and Mass-Loaded Barriers: One of the primary principles of soundproofing is the idea that mass blocks sound. Dense materials like brick or concrete are particularly effective at preventing the transmission of sound waves, especially for low-frequency noises. Mass-loaded barriers inherently have the ability to interrupt and reduce the transmission of these sound waves from one side to the other. In essence, the more mass you introduce between a noise source and the receiver, the less noise will penetrate through.
Dampening Noise with Absorptive Materials, Maze Design, and Muffler Principle: Within the main body of the box where the UPS will be contained, there are holes on the wall coupled with fiberglass inside, drawing inspiration from the principles of a Straight Through Muffler. This design not only aids in absorbing sound but also dissipates the energy of the sound waves. Additionally, materials like foam or blankets further dampen sound by preventing it from reflecting and echoing within the space. The maze structure complements this by capitalizing on the principle that sound waves, especially higher frequencies, struggle to navigate sharp 90-degree turns. This causes multiple reflections and scatterings, attenuating their energy further. Combined, these design elements offer a multifaceted approach to noise reduction, tackling both transmission and reflection.
Mechanical/Electric Noise and Resonance: As you rightly pointed out, mechanical or electrical devices can amplify noise when in contact with surfaces that resonate. The design I’m proposing leans on the natural convection cooling strategy, which avoids any direct contact (with the fan cooling system) and potential active cooling noise. Incorporating isolation methods like rubber feet on the base of the box or elastic suspensions for the UPS would be valuable, minimizing any vibration-induced noise and extending the lifespan of the UPS (or APU) due to reduced vibrations.
In conclusion, the design integrates the benefits of both mass blocking and sound absorption, leveraging the labyrinthine nature of the maze and the principles of a muffler to effectively attenuate noise. Your feedback has been essential, and I look forward to any additional insights or suggestions you might share.
Thank you for your kind comments. They embolden me to further speculation. It seems to me that a muffler is fundamentally different, in that gases are forced through it under pressure. (And the more you muffle, more you limit peak power, but that’s another story.) If you are relying on natural convection for cooling, will the air travel through the duct sufficiently or will turbulence slow it too much, allowing the UPS to overheat? Or will it be moving so slowly anyway that turbulence isn’t an issue?
Thank you for such an interesting thread. I may have forgotten the fluid dynamics they tried to teach me [cough] years ago but its good to try and exercise the remaining grey cells!
I speculate that we’ll be operating within a low Reynolds number regime with no laminar flow. Airflow out from the UPS itself is inherently very turbulent, low Ncrit value.
Indeed, the dynamics of a muffler dealing with pressured gases is fundamentally different from a naturally convective system
I know three options. Each has its merits and challenges (with the third adding more skin friction).
This box is designed to encase auxiliary power units, loud industrial equipment with small fans, servers, UPS units, or PCs located in a quiet room.
Different materials vary in their effectiveness at reducing specific frequencies. Low-frequency noises, such as hums, are more challenging to block than high-frequency noises, like beeps or clicks.
I’m optimistically aiming for a 10-decibel (dB) reduction for my UPS with 3000Hz fans. However, that’s a significant reduction, and temperature is a major concern. I need to cut the wood and conduct a temperature test first.
