Can micro-perforations reduce noise inside a window frame?
If you’ve looked at the websites of online soundproofing suppliers, you’ve probably seen that some of them offer products like wall paneling with small perforations in them. These perforations are designed to diffuse noise or to absorb echo in a room. They might be used in a recording studio, a performance space, an office, or a home. But more recently, I’ve also seen perforated metal used around a window for noise reduction. And I wonder how to use perforated materials in tandem with other soundproofing materials to reduce noise. Does it work? How do you build a prototype? Where do you get the materials from? And how do you measure the results?
Acoustical studies on micro-perforations
In this paper, “Micro-perforated panels for noise reduction,” the authors state that “The simplest micro-perforated absorber (MPA) consists of one micro-perforated panel (MPP) and a hermetically sealed air cavity of length with a sound hard back plane.”
The researchers found that compared to an empty cavity, a fibrous, non-flammable filler material that’s used in ducts for trains performed better across the frequency range than a micro-perforated absorber. However, a micro-perforated panel was better at reducing the peak frequencies. They had mixed results when they tested these materials against a fan.
In this study, “Design of Honeycomb Microperforated Structure with Adjustable Sound Performance,” the researchers used a double-layered structure comprised of a micro-perforated flat panel over a honeycomb structure made of cylinders. Behind these materials was a cavity. By adjusting the height of the back cavity, they could increase or decrease the amount of sound absorption. The perforated holes had different apertures, which altered the path of the sound waves. And by turning a knob to adjust the height of the back cavity, the researchers could fine-tune the amount of noise absorption for different frequencies. This sounds great for a large space, but would it apply to a window frame?
D.I.Y. experiment
My interest in micro-perforated materials began when I saw them in a double-paned glass window. That window was very soundproof. Shortly thereafter, I saw a video that demonstrated how micro-perforated metal panels built into the window frame of an apartment reduced noise in a loud neighborhood. From those observations, I decided to make a simple, soft-fabric noise-absorbing stick covered with honeycomb-textured cloth to insert in a window frame. The absorber is flanked on one side by an external double-paned window that faces the street. And on the other side, a D.I.Y. indoor “window insert” panel fastened across the drywall. The insert is made with 1/4-inch plexiglass.
The decibel results are inconclusive thus far. The walls in this room aren’t soundproof, and they need improvement. The composition: 1/2-inch drywall nailed directly to the framing, and the framing is built from 2×4 wood. So there isn’t enough mass in the wall to effectively reduce incoming low-frequency noise in the building frame. And this could skew the decibel-reader results for any window treatment in that room. In addition, all four sides of the interior window frame need to get this acoustical treatment.
I encourage you to experiment with different materials, perforation types, and cavity depths in your own windows. For a low cost (I spent $23 on materials so far), you can see if you can boost the effectiveness of a plexiglass window insert by adding noise-absorption panels inside the perimeter of the window frame.
An exploratory video
Learn more:
- Acoustical surfaces – sells acoustical materials, including perforated metal panels
- ARCAT (architectural materials) – sells micro-perforated metal mesh fabrics for sound absorption
- Springer Link (paper) – “Micro-perforated panels for noise reduction” (Mikroperforierte Platten zur Schallreduktion), by Sebastian Floss, Felix Czwielong, Stefan Becker & Manfred Kaltenbacher
- Hindawi – “Design of Honeycomb Microperforated Structure with Adjustable Sound Absorption Performance,” by Shanlin Yan, Jinwu Wu, Jie Chen, Qibo Mao, and Xiang Zhang
- Science Direct – “Sound absorption performance of microperforated honeycomb metasurface panels with a combination of multiple orifice diameters,” by Suchao Xie, Da Wang, Zhejun Feng, Shichen Yang
- Purdue University – “The Effect of Honeycomb Cavity: Acoustic Performance of a Double-leaf Micro Perforated Panel,” by Yuxian Huang and Kai Ming Li (Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University)
- Joe Makes (YouTube): “These Bricks Can Absorb Traffic Noise – Thesis Presentation on Helmholtz Resonators”