EMI Shielding Vent

Deeper Honeycomb = Better Shielding? Not Always.

I hear this all the time. "Give me the deepest honeycomb you got. I want maximum shielding."

Sounds right, doesn't it? Deeper vent = more attenuation.

Not that simple.

Depth helps. Up to a point. Past that, you're choking your fans and throwing money away. Let me explain.

How Depth Actually Works

The honeycomb cells are little waveguides. RF goes in, bounces off the walls, dies. Deeper cell = more bounces. More bounces = more attenuation.

That's true. But only if the cell size matches the frequency.

If the cell is too big for the frequency, even a 2‑inch deep vent won't help. The wave just goes straight through. Cutoff frequency is set by cell size, not depth.

If the cell size is right, then depth adds attenuation. But it's not linear. After about a 4:1 depth‑to‑cell ratio, the improvement flattens out.

We tested a 1/8‑inch cell vent at 5 GHz. At 1/4‑inch depth, about 20 dB. At 1/2 inch, 35 dB. At 1 inch, 50 dB. At 2 inches, 55 dB.

See that? From 1 inch to 2 inches, you double the thickness for only 5 dB. Not worth it.

What's Wrong with Going Too Deep

Every extra millimeter of depth adds pressure drop. Air has to travel through a longer tube. More friction.

At 1/2 inch, pressure drop is small – maybe 0.1 inches of water. At 1 inch, it doubles. At 2 inches, it's four times. Your fans will scream.

Also, deeper vents are heavier. More metal. More cost. More shipping weight.

And they take more space. If your cabinet is tight, a 2‑inch vent might not even fit.

So you're paying more, getting less airflow, and only gaining a few dB you probably don't need.

When You Actually Need Depth

For really high shielding – military TEMPEST, MRI rooms, radar shelters – you might need 1 inch or more. Those call for 80‑100 dB.

But for most commercial and industrial applications, 1/2 inch is plenty. At 1/2 inch, a 1/8‑inch cell vent gives 40‑50 dB at 1 GHz and 35‑40 dB at 5 GHz. That's enough for FCC, CE, and most telecom specs.

Some suppliers push deeper vents because they cost more. More profit. But you don't need it.

Real Example – Cell Tower Cabinet

A customer had a base station cabinet near a tower. They asked for a 1‑inch deep vent for "maximum shielding." We recommended 1/2 inch. They insisted.

We installed the 1‑inch vent. Shielding was 55 dB at 2 GHz. The 1/2‑inch vent would have been 45 dB. They didn't need 55. Their fans were screaming because the pressure drop was too high. They had to upgrade the fans.

They ended up switching back to 1/2 inch. Shielding was still fine. Fans were quiet.

What Actually Matters

Cell size is the primary thing. Match cell size to your frequency. 2.4 GHz problem? 1/8‑inch cells work. 5 GHz problem? 1/8‑inch is marginal – go to 1/16‑inch. 10 GHz problem? You need 1/16‑inch or smaller.

Once cell size is right, adjust depth to get the attenuation you need. But don't overdo it. 1/2 inch is the sweet spot. 1 inch for critical. 2 inches only for extreme.

And don't forget the gasket and frame. A perfect deep honeycomb with a bad gasket leaks. A shallow vent with a good gasket out‑performs a deep one with a poor seal.

Cost vs. Benefit

A 1‑inch vent costs about 30% more than 1/2‑inch. A 2‑inch vent costs double.

You're paying for metal, machining, and weight.

Ask yourself: do I really need that extra 5 dB? Look at your EMC requirement. If it says 40 dB at 1 GHz, a 1/2‑inch vent delivers that. A 1‑inch vent delivers 50 dB. You don't need 50.

Save the money. Save the airflow. Your fans will thank you.

Deeper honeycomb doesn't always mean better shielding. Past a certain point, you're just wasting money and airflow.

Match cell size to frequency. Then pick the depth that meets your requirement – not the deepest you can find.

1/2 inch is enough for most. 1 inch for high shielding. 2 inches only for extreme. And always check the gasket and frame – they matter more than depth alone.

We make vents in all depths. We'll tell you what you actually need – not what costs more. That's what we do.