ᐅ Sound Insulation at Door Openings: Why Does Using a Shelf Instead of a Door Provide Little Noise Reduction?

Hello,

I have a question about soundproofing and hope someone can give me some advice.
I combined two rooms into one and removed the door. On the outside, there is now a shelf placed in the doorway. Inside, I screwed a 19 mm (3/4 inch) chipboard panel (smooth, melamine-coated) to the wall and glued cork on top. On the left and right sides, there are studs covered with drywall panels. In front of this setup is a wardrobe.
The chipboard panel is about 5 cm (2 inches) larger than the doorway on all sides, so basically no gaps are visible—except maybe about 1 mm (approximately 1/32 inch) at the bottom.

The shelf looks great but hardly provides any sound insulation—it feels almost like the doorway is open. With the door in place, it was quieter.
Can I improve the soundproofing without removing the shelf? Or should I take the shelf away and brick up the doorway? I do not want to use glass wool or wood fiber insulation.

Hi,

The effect is surprising at first, but unfortunately logical, even if it’s unpleasant to hear. Essentially, you have created a very stylish visual solution, but acoustically it’s almost a facade because mass and airtightness are missing. The shelf is more decorative than a structural element, even if that sounds a bit harsh. The 19mm (3/4 inch) particle board might weigh around 12–13 kg/m2 (2.5–2.7 psf), whereas a simple door often reaches 20–25 kg/m2 (4.1–5.1 psf) without any tricks. Cork is nice for peace of mind and to reduce reverberation, but for airborne sound it’s practically irrelevant. The key point is whether the assembly is truly airtight all around, including top, bottom, and behind the cabinet. Just a few millimeters of gap are enough for sound to sneak through easily. Have you checked by hand or with a candle if there’s any air leakage? If you want to keep the shelf, I’d recommend reinforcing the back panel with a solid material and sealing everything thoroughly, rather than tinkering further with soft layers—otherwise you’ll end up with a lot of work and little effect, maybe you know that feeling. Filling the cavity completely is, of course, the brute force method, but it only works if it really adds mass and isn’t just made of light drywall again—you can save yourself the dust otherwise.

Hey, thanks. Do you maybe have a suggestion for what I could screw onto the board? I would then remove the drywall panels.
And would it help at all if I put a sealing tape between the wall and the board?

As I said, there is maybe a maximum gap of 1–2 mm (0.04–0.08 inches) at the bottom.

A standard hollow core door has a surface weight of 12-16 kg/m² (2.5-3.3 lb/ft²)... Solid wood or glass doors weigh about 20-25 kg/m² (4.1-5.1 lb/ft²), and those are hardly manageable for one person alone unless they have professional experience like a bricklayer or scaffolder. I have two glass doors... I couldn’t carry or install them by myself.

A 1-2mm (0.04-0.08 inch) gap at the bottom is already enough for sound to pass through. Proper soundproof doors have a mechanism to seal this gap completely when the door is closed, exactly for this reason.
Also, don’t forget that sound can travel through the screed (concrete floor) and a suspended ceiling, so even a masonry wall made of sand-lime bricks won’t help if the screed supports it directly... That’s why the screed is usually decoupled from the walls with edge insulation strips during installation.

Why not just try stuffing mineral wool in there as an experiment? What’s the problem?

Hey,

I got one of those sealing tapes for doors and also sealed the sides and bottom. It doesn’t help much.
Should I just screw something heavy onto the chipboard? Would that be more effective? Like an old solid door?