I get asked about windows constantly.

"Should I cover it?" "Is it causing reflections?" "Do I need special treatment?"

But the question itself reveals a misunderstanding about how rooms actually work.

See, most home studio owners treat their space like a checklist. Window? Potential problem. Corner? Definitely a problem. That bare wall? Add it to the list.

This surface-by-surface approach feels logical. It's how we solve most problems in life. Break things down, tackle them one at a time.

And it’s not wrong! But first you need to see your room as an entire system.

Every surface interacts with every other surface. And here's where it gets interesting: surfaces that look completely different often behave almost identically when sound hits them.

Take glass and drywall.

One's transparent. The other's opaque. One feels cold and fragile. The other feels solid and forgettable. You'd never confuse them visually.

But acoustically? They're practically twins.

Let’s look at some absorption data.

A single pane of 4mm glass has an absorption coefficient of about 0.3 at 125 Hz. It drops to around 0.1 at 500 Hz, then falls close to zero at 4 kHz.

A single layer of drywall on a standard 2x4 stud wall? Almost identical. Starts at 0.3 at 125 Hz, drops to just under 0.1 at 500 Hz, and stays around that level up to 4 kHz.

Double-glazed windows and double-layer drywall tell the same story. Different starting points, but the same pattern: both materials reflect roughly 90% of the energy hitting them, and both let slightly more low-end energy pass through than high-end.

So that window you've been stressing about? It's behaving almost exactly like the drywall next to it.

Now, you might say: "Okay, but reflections off glass sound different than reflections off drywall."

True. They do sound slightly different. But neither sounds good. And you gotta treat both.

Why Both Materials Act Like Filters

Here's where systems thinking matters.

Both glass and drywall are heavy membranes. Any membrane has a resonant frequency where it lets more sound pass through. For heavy materials like these, that frequency sits quite low.

At that resonant point, the surface acts like a filter. It affects not just how much energy reflects, but the timing of that reflection. The phase gets shifted. The energy that bounces back arrives slightly out of sync with the original signal.

This is why your room's acoustic dimensions rarely match its visual dimensions. The walls aren't behaving like perfect, rigid boundaries. They're flexing, filtering, and shifting timing in ways that calculators and guidelines can't predict.

That 38% rule for speaker placement? Room mode calculators? They assume your walls behave predictably. But a room full of drywall, windows, and doors introduces variables those tools can't account for.

This is why I always recommend testing your actual room rather than relying on calculations. You need to know what's really happening, not what should theoretically happen.

The Curtain Trap

Now here's where people accidentally make things worse.

The common advice for windows is to hang a heavy curtain. Block those reflections. Seems reasonable.

But look at the absorption data for a typical acoustic curtain draped with about 4 inches of space behind it.

At 125 Hz, it absorbs around 0.3, similar to the glass itself. But as you move up in frequency, the absorption climbs dramatically. By 4 kHz, that heavy curtain is soaking up most of the high-frequency energy hitting it.

Sound familiar? That's exactly how a thin absorber panel behaves.

If you've seen my video on over-absorption, you know I strongly discourage thin absorbers. They suck up highs and mids while leaving your low end untouched. The result? A dead, muffled room that still has all its bass problems.

A big heavy curtain is essentially a giant thin absorber. If your room feels lifeless and you've got thick curtains hanging somewhere, you've probably found your culprit.

What To Actually Do

Treat your window like you'd treat any piece of drywall.

If you identify a reflection point on the window's surface that needs treatment, handle it the same way you would a reflection point on a wall. The only real difference is practicality: how do you mount an absorber on glass? How do you keep it in place?

If you want curtains for aesthetic reasons, go thin. A lightweight curtain hung straight in front of the window has negligible absorption in the low frequencies. It still absorbs some highs, but nowhere near what a heavy curtain does. It's a far better compromise.

And if you've got a specific reflection point that bothers you, treat that spot locally with a proper deep absorber. Then use a thin curtain for the rest of the window. You can put the curtain in front of or behind the absorber. Doesn't really matter.

The Bottom Line

Your room is a system, not a collection of isolated surfaces. Windows behave like drywall. Heavy curtains behave like thin absorbers. And the only way to know what's actually happening in your specific space is to test it.

Stop treating surfaces in isolation. Start understanding how they work together.

If you want to stop treating your room surface by surface and start understanding what actually needs attention, consider checking out Absorber Placement Hacks. It takes you from chasing individual problems to treating your room as the system it really is.