introduction
Xiongqian is a manufacturer of perforated sheet and perforated metal mesh. We have been making these products since 2012. In this article, I will explain the acoustic principle behind micro-perforated sheets. I will keep the language simple. I will use short sentences. I will also share data sources and real applications
A Short History
Professor Dah-You Maa (马大猷) developed this idea. He worked in China. He worked at the Chinese Academy of Sciences. He introduced the idea in 1975. He showed that tiny holes can absorb sound. He showed that no porous material is needed behind them. This was a big step in acoustics.
Before this, people used foam to absorb sound. People also used fiberglass. Those materials are thick. Those materials can shed fibers. Professor Maa’s discovery changed sound absorber design.
What Is a Micro-Perforated Sheet?
A micro-perforated sheet is a thin metal panel. It has many small holes. The hole diameter is usually 0.5 mm to 1 mm. The holes are spaced very close together. The open area is often 0.5% to 3%.
This is different from a normal perforated sheet. A normal sheet has larger holes. Its open area is 20% to 50%. A micro-perforated sheet has much smaller holes. Its open area is much lower.
The Basic Principle: It Works Like a Bottle
Think of a glass bottle. You blow across the top. You hear a low sound. That sound comes from air. The air moves in and out of the bottle neck. The air in the neck acts like a weight. The air inside the bottle acts like a spring.
This is called a Helmholtz resonator. It is named after Hermann von Helmholtz. He was a German physicist. He described this effect in the 1850s.
A micro-perforated sheet works the same way. Each tiny hole acts like the bottle neck. The air cavity behind the panel acts like the bottle body. Sound hits the panel. The air in each hole moves back and forth. This movement creates friction. The friction turns sound energy into heat. That is how the sound is absorbed. This is the core of acoustic absorption in micro-perforated sheets.
Why Small Holes Work Better
You might think big holes absorb more sound. But the opposite is true. Small holes work better. Here are two reasons.
First, small holes create more friction. Air moves through a small hole. The air rubs against the hole walls. A smaller hole gives more friction. More friction means more sound energy turns into heat.
Second, small holes have higher acoustic resistance. This resistance matches the air better. So sound waves enter the holes. They do not bounce off. This is called impedance matching. Leo Beranek wrote about this. He was a British acoustician. He wrote the textbook “Acoustics” in 1954.
The hole diameter matters a lot. A big hole lets air move too easily. Then there is not enough friction. A tiny hole stops air from moving. The best range is 0.5 mm to 1 mm.
The Role of the Air Cavity
The air cavity behind the panel is important. The cavity depth controls the absorption frequency. This is called the resonance frequency.
The formula for resonance frequency is:
f₀ = (c / 2π) × √(p / (t × D))
Here:
f₀ = resonance frequency (Hz)
c = speed of sound (about 343 m/s in air)
p = perforation rate (open area ratio)
t = panel thickness (m)
D = cavity depth (m)
Let me give you an example. A panel has 1% open area. The thickness is 0.5 mm. The cavity depth is 30 mm.
First, change units to meters. t = 0.0005 m. D = 0.03 m.
f₀ = (343 / 6.2832) × √(0.01 / (0.0005 × 0.03))
f₀ = 54.6 × √(0.01 / 0.000015)
f₀ = 54.6 × √(666.67)
f₀ = 54.6 × 25.82
f₀ = 1410 Hz
The resonance frequency is about 1410 Hz. This is in the mid-frequency range. This is typical for micro-perforated panels.
Let me try another example. Thickness is 1 mm. Cavity depth is 100 mm. Open area is 0.5%.
t = 0.001 m. D = 0.1 m. p = 0.005.
f₀ = (343 / 6.2832) × √(0.005 / (0.001 × 0.1))
f₀ = 54.6 × √(0.005 / 0.0001)
f₀ = 54.6 × √(50)
f₀ = 54.6 × 7.07
f₀ = 386 Hz
A thicker panel and a deeper cavity give a lower resonance frequency. This is useful for low-frequency noise.
Typical Performance Data
A well-designed micro-perforated panel absorbs 60% to 90% of sound. This happens at its resonance frequency. This is comparable to traditional porous materials. Examples are foam and fiberglass. But micro-perforated panels have advantages. They are fireproof. They are clean. They are durable. They do not shed fibers.
The table below shows typical performance. The data comes from the Chinese Academy of Sciences. The data also comes from the Journal of the Acoustical Society of America.
| Panel Thickness (mm) | Hole Diameter (mm) | Open Area (%) | Cavity Depth (mm) | Peak Absorption | Peak Frequency (Hz) |
|---|---|---|---|---|---|
| 0.5 | 0.5 | 1.0 | 30 | 0.85 | 1400 |
| 1.0 | 0.5 | 0.5 | 50 | 0.90 | 800 |
| 1.0 | 1.0 | 2.0 | 100 | 0.75 | 400 |
| 2.0 | 1.0 | 1.0 | 150 | 0.80 | 250 |
Source: Chinese Academy of Sciences, Institute of Acoustics; Journal of the Acoustical Society of America, various issues.
Comparison with Traditional Sound Absorbers
Micro-perforated panels are not the only way to absorb sound. Here is how they compare with common materials.
| Feature | Micro-Perforated Panel | Glass Wool | Acoustic Foam |
|---|---|---|---|
| Fire resistance | Excellent | Good | Poor |
| Cleanliness | Excellent (no fibers) | Poor (sheds fibers) | Good |
| Durability | Excellent | Fair | Fair |
| Moisture resistance | Excellent | Poor | Fair |
| Thickness needed | Thin (0.5–2 mm) | Thick (25–100 mm) | Thick (25–50 mm) |
| Low frequency absorption | Good with deep cavity | Good | Fair |
| Cost | Medium to high | Low | Low |
Source: Industry data and manufacturer specifications.
Real Applications
Micro-perforated panels are used in many places. Let me give you some examples.
Noise barriers. Highways use them. Railways use them. The panel absorbs traffic noise. It does not need porous material behind it. So it lasts longer. The Hong Kong–Zhuhai–Macau Bridge uses micro-perforated panels. They are in some noise barriers.
HVAC systems. Air ducts use them. They reduce fan noise. They are easy to clean. This is important for hospitals. It is also important for clean rooms. Many modern office buildings use micro-perforated ceilings.
Theaters and concert halls. They control echo. They control reverberation. They look good. They can be painted any color. The Shanghai Symphony Hall uses micro-perforated panels. They are in its acoustic design.
Offices. They reduce background noise. They are often used in ceilings. They are also used in partitions. They help meet acoustic standards. These standards are for open-plan offices.
Transportation. Cars use them. Trains use them. Airplanes use them. They reduce engine noise. They reduce wind noise. Some high-speed train ceilings use micro-perforated panels.
Installation Tips
You need to install the panel correctly. This gives the best performance. Here are some tips.
The cavity depth must match the design frequency. Do not guess.
The cavity must be sealed. Air leaks will reduce performance.
The panel should not touch the back wall. Leave an air gap.
You need a wider frequency range. Use multiple panels. Use different cavity depths.
You can add a thin layer of porous material. Put it in the cavity. This broadens the absorption peak. But this is optional.
FAQ
Q: Why do small holes absorb sound better than large holes?
A: Small holes create more friction. Air moves through a small hole. The air rubs against the walls. This friction turns sound energy into heat. Small holes also have higher acoustic resistance. This matches the air better. So sound enters the holes. It does not bounce off.
Q: Do micro-perforated panels need porous material behind them?
A: No. This is a key advantage. Traditional acoustic panels need foam behind them. They also need fiberglass. Micro-perforated panels work without any porous material. The air cavity alone is enough. You can add a thin layer to widen the absorption range. But it is not required.
Q: What is the best hole size for sound absorption?
A: The best range is 0.5 mm to 1 mm. A big hole gives too little friction. A tiny hole stops air from moving. The optimal size depends on the frequency. You want to absorb that frequency.
Q: Can I make a micro-perforated panel myself?
A: It is possible. But it is not easy. You need a laser. You also need a precision punch. The holes must be very small. The holes must be very uniform. The cavity depth must be precise. It is better to buy from a professional manufacturer.
Q: What materials are used for micro-perforated panels?
A: Aluminum is common. Stainless steel is also common. Aluminum is light. Stainless steel is strong. Stainless steel is corrosion-resistant. Some panels use coated steel. These are for outdoor use.
Q: Where can I buy micro-perforated panels?
A: You can buy from perforated metal sheet suppliers. Xiongqian is one option. We make micro-perforated sheets. We make them for acoustic applications. We can help you choose the right hole size. We can help you choose the right open area.
Q: How do micro-perforated panels perform at low frequencies?
A: Low-frequency absorption needs a deeper air cavity. A 150 mm cavity absorbs sound around 250 Hz. You need lower frequencies. Then you need an even deeper cavity. You can also use a different design. Multiple panels with different depths cover a wider range.
Q: Are micro-perforated panels suitable for outdoor use?
A: Yes. You need the right material. Stainless steel works well outdoors. Coated aluminum also works well. The holes can get clogged with dust. So you may need to clean them periodically.
Conclusion
Micro-perforated metal sheets absorb sound through a simple principle. Each tiny hole acts like a Helmholtz resonator. The air in the hole moves back and forth. Friction turns sound energy into heat. Small holes work better. They create more friction. They also have higher acoustic resistance.
The cavity depth controls the resonance frequency. You can design panels for different frequencies. A well-designed panel absorbs 60% to 90% of sound. This happens at its peak.
Micro-perforated panels are used in noise barriers. They are used in HVAC. They are used in theaters. They are used in offices. They are used in transportation. They are fireproof. They are clean. They are durable. They do not need porous material behind them.
You need micro-perforated sheets for acoustic applications. Ask a reliable supplier. They can provide samples. They can provide test data. Xiongqian has been making perforated sheet and perforated metal mesh since 2012. We are happy to help you find the best solution.
