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We recently replaced all the carpet in our home with hard floors, dramatically increasing the amount of noise transmission between bedrooms and the hallway. I've been researching the best ways to sound proof the doors, and I would like to seal the entire door, including the undercut at the bottom.

Regardless of what I end up using, I'm concerned this will impact the return air flow coming out of my bedrooms, as there is no other return. Is there a typical method for making up for this, while still also keeping sound transmission low? I've seen the return grills that attach to the door, but these aren't very aesthetically pleasing, plus I figured they would probably nullify the sound proofing I just performed. Is there another, not overly complicated way to have return air flow, maybe a vent above the top of the door?

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    A return air duct is about the only way that's going to stand a chance of killing sound transmision, IMHO, and at that only if it's implemented properly for that purpose - ducts can also act as speaking tubes carrying sound between rooms if not appropriately baffled... You might try doing something with a vent at the bottom of a stud bay on one side, and at the top on the other, and some non-flammable acoustic insulation (rockwool seems to be the common choice) helping to muffle sound in the cavity without blocking the whole thing.
    – Ecnerwal
    Commented Apr 4, 2020 at 18:54
  • Where are your supply vents? You would not want the return vent at the top of the door if you have a supply vent at or near the ceiling, otherwise the conditioned air will just go right out.But yes, any system of air flow is also going to end up as a system of sound transmission; sound transmits through air. The only possible low sound solution is to have separate return AND SUPPLY air ducts that only meet inside of the HVAC equipment, and that space itself is sound proofed.
    – JRaef
    Commented Apr 4, 2020 at 19:01
  • @JRaef The supply vents are in the floor.
    – ConcernedHobbit
    Commented Apr 5, 2020 at 18:18
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    I’m voting to close this question because it's been abandoned.
    – FreeMan
    Commented Jan 2, 2021 at 19:56

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Anytime you replace a soft flooring (carpet) with a hard flooring (hardwood) you get a noisy footstep. Isolating and soundproofing the bedrooms from the hallway is nearly impossible. If you have an older house, with supply and return ducting in that room, you can replace the doors with solid core doors and a reduced bottom undercut to help reduce the noise transmission. With a newer home that only has a central return duct, usually in a hallway, you can not reduce the doors undercut since this the return air from the room. The central return allows a HVAC company to save a few bucks at the home owners expense. To me, this is a crappy and cheap job. I got into the HVAC business in the late 1960's and this type of installation was unheard of. Today, almost every contractor is doing it. 20+ years ago, when I built this house all the contractors that wanted to install a central return were given their walking papers. I searched until found a contractor that would install an older type duct system. I do not know what you can do at the bedroom locations except recommend walking in your socks and leave slippers and shoes for the other areas. You could insulate the bedroom walls and install solid cor doors to reduce some of the noise but the solid surfaces are still going to be noisy. my 2 cents

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  • I'm not as concerned about footstep noise, as I'd like to reduce the amount of conversation and generally just make the bedrooms more private. As it is now, conversations can now be heard fairly well in the hallway and potentially to the other bedrooms.
    – ConcernedHobbit
    Commented Apr 5, 2020 at 18:21
  • You could insulate the walls of the bedrooms, I insulated mine.
    – d.george
    Commented Apr 6, 2020 at 18:36
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I’d seal up the doors, etc and use a sound baffling return air duct.

Install the duct between studs with an opening near the ceiling (on the hall side so you’re away from the footsteps) and the other opening near the floor (on the room side) with baffles about 2’ apart.

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