Do you cringe every time a metal door slams in your home or office? The echoing booms and noisy creaks can shatter concentration and disrupt sleep.
But what if you could make metal doors as quiet as walls? With the right soundproofing methods, it is possible to transform noisy hollow doors into acoustic barriers.
Let’s dive in to simple DIY techniques and heavy-duty construction projects for blocking sound transmission through metal doorways.
Add Mass to the Door with Soundproofing Panels
One of the easiest ways to improve a metal door’s sound isolation is to add mass using self-adhesive soundproofing panels.
These panels are made of dense materials like rubber and stick directly onto the door surface. Adding mass is important for blocking sound because it makes the door more rigid and less prone to vibration.
The extra density prevents sound waves from passing through by forcing them to expend more energy vibrating through the material.
Soundproofing panels are most effective at blocking mid and high frequency sounds, like voices, music, pets, and television noise. Lower frequencies like footsteps may still pass through easily.
To properly install soundproofing panels on a metal door:
Clean the door surface so panels adhere correctly. Remove any dirt, dust, oil, or debris where panels will be applied.
Cut panels to size to fit door. Use sharp utility knife and measure precisely. Panels can cover entire door or just problem spots.
Peel off adhesive backing and carefully stick panels to door. Apply firm pressure across entire panel to secure adhesive.
Use butt joints between panels to avoid gaps. Seal edges with acoustic caulk for added sound blocking.
Verify panels are securely attached. They should not peel off when pulled. Reapply if corners start to lift.
The key with soundproofing panels is to cover as much surface area as possible. Prioritize placing panels wherever noise leaks through most.
Panels can go on one or both sides of door depending on needs. Combine panels with perimeter seals (discussed next) for greater noise reduction.
Properly installed panels can decrease sound transmission by 25-30%, providing a noticeable improvement in privacy.
Seal Air Gaps Around the Door’s Edges
In addition to adding mass, sealing all air gaps around the door’s edges is equally important.
Any cracks or openings along the edges allow sound to leak through, reducing the effectiveness of soundproofing panels.
Applying proper perimeter seals prevents this flanking noise transmission. There are several options for sealing air gaps around metal doors:
Door Sweeps
Door sweeps, also called door bottom seals, attach along the bottom of the door to cover the gap between the door and floor surface.
They are typically made of vinyl, brush, or rubber material that forms an acoustic barrier when the door is closed.
Door sweeps come in adjustable or self-adhesive styles to fit standard door thicknesses. Make sure to measure properly before purchasing.
To install a door sweep:
Clean bottom of door thoroughly to ensure good adhesion if using self-adhesive type.
For adjustable sweeps, position sweep against bottom of door and adjust endcaps to proper length. Tighten screws on endcaps to secure.
Peel off adhesive backing on self-adhesive sweeps and firmly press along entire length of door bottom.
Check that sweep makes full contact with floor surface when door is closed. Trim if needed.
Over time, adjust sweep if it starts to sag or loses contact with floor.
Door sweeps prevent flanking noise under the door and are essential for proper soundproofing.
Perimeter Seals
Applying perimeter seals around the sides and top of the door jambs seals any remaining air gaps. Materials like foam tape, silicone gaskets, or self-adhesive weatherstripping work well for this.
When the door is closed, the seals compress to close off gaps between the door and jambs.
For perimeter sealing:
Clean door jambs thoroughly to prepare the surface.
Measure jambs and cut seal materials to proper length. Leave 1/16″ compression gap.
Peel adhesive backing and carefully apply seals around entire perimeter. Do not stretch.
Make sure seals sit flush within jamb and compress when door is closed.
Use thicker seals for wider gap depths. Multilayer seal if necessary.
Replace seals over time if they wear out or become compressed.
Sealing the door perimeter blocks flanking paths for noise to leak through. Combining perimeter seals with a door sweep provides complete air gap sealing.
Consider Adding a Second Door
Where maximum soundproofing is needed, adding a second door can significantly improve acoustic isolation.
The main benefit of a double door arrangement, also called an airlock or sound lock, is preventing the direct transmission of noise from one room to another.
The airspace between the two closed doors forms an acoustic buffer that forces sound to take an indirect path.
This makes it exponentially more difficult for noise to transmit between rooms. Airlocks are commonly used in recording studios or other critical soundproofing applications.
There are two main approaches to creating an airlock:
Installing Two Separate Doors
This involves removing the existing door and framing to accommodate two identical doors spaced apart by 2-12 inches.
Each door should seal tightly within its own jamb using perimeter seals and door bottom sweep. The doors can both swing in the same direction or open away from each other.
Wider spacing provides more soundproofing but takes up more space. Narrower spacing minimizes impact on room layout.
Soundproofing Double Doors
Instead of two separate doors, a specialized pre-hung double door unit can be installed. These feature two doors fitted into one jamb separated by a soundproof inner frame.
High performance acoustic seals fill gaps within the frame. This provides the airlock effect while only requiring one door frame.
Soundproof double doors are more expensive but easier to install than building a custom two-door airlock.
In both cases, the doors must remain fully closed to be effective. As one door opens, the other should be completely shut.
This prevents noise from sneaking through the opening. Proper installation is key – any air leaks negate the acoustic benefits.
Hinges, knobs, and locks also must be sealed or padded to prevent flanking noise. Overall, a well-constructed double door airlock can improve a door’s sound transmission class (STC) rating by 12-18 points, greatly enhancing sound isolation.
Improve Door’s Acoustic Rating
Replacing the existing metal door with one specially designed for soundproofing is the most effective option, but also the most involved.
Metal doors typically have poor acoustical properties due to being lightweight and hollow.
Heavy solid core wood or steel doors perform far better at blocking sound thanks to their higher density and mass.
The door’s STC rating indicates its sound blocking capabilities – higher numbers mean better soundproofing.
For reference, a standard hollow core door has an STC of 20-28, while acoustic doors range from STC 35-60+.
There are a few considerations when selecting an appropriate soundproof door:
Material – Solid core wood or steel provide the most mass. Fiberglass also works for interior doors.
Density – Doors with higher density block more sound transmission.
Construction – Sturdy stiles, rails, and core prevent resonance or vibration.
Gaskets/Seals – Pre-installed perimeter gaskets boost acoustic rating.
STC Rating – Select a door with suitable rating for noise blocking needs.
Fire Rating – Fire doors also require an STC minimum for code compliance.
Budget – Acoustic doors cost more than standard models. Balance needs and price.
In addition to the door itself, the installation method impacts effectiveness. A poor installation can result in air and noise leaks. Follow best practices for soundproof door installation:
Plumb and square frame – Eliminates gaps between frame and floor.
Caulk perimeter before installing door – Creates an air tight seal.
Use long screws into studs – Prevents movement and compression gaps.
Adjust door width for easy close – Doors that stick open create leaks.
Seal hinge gaps – Fill hinge recesses with acoustic caulk.
Weatherstrip/sweep – Perimeter seals are essential.
Add soundproofing panels – Boosts mass if needed.
Replacing a standard metal door with a high-performance acoustic door, combined with proper installation and seals, is the most failsafe way to soundproof the opening.
While more labor intensive, addressing the door itself provides lasting noise control.
Additional Soundproofing Tips and Tricks
Here are some additional ideas that can enhance the soundproofing efforts discussed above:
Add MLV Barrier – Installing mass loaded vinyl sheets creates a limp sound barrier. Works great for hollow core doors or to augment other materials. Stops noise that gets through door itself.
Acoustic Curtains – Hanging dense sound absorbing curtains on both sides improves sound blocking. Layer for max effectiveness.
Seal Electrical – Outlet gaps, conduit, wiring etc. compromise isolation. Caulk and seal openings.
Quiet Hinges – Replace regular hinges with sealed acoustic hinges to prevent vibration/flanking.
Sound Masking – White noise machines or systems prevent sound transfer by covering it up.
Rugs – Add heavy rugs on both sides of door to absorb noise and prevent echoes.
Door Frame Fillers – Injectable sealant fills frame cavities for improved soundproofing.
Damping Compound – Apply layers of viscoelastic material to door for vibration damping.
Solid Core Frame – Swap hollow jamb for solid wood frame to reduce resonance.
Layering several complementary soundproofing techniques provides maximum acoustic isolation.
A combination of sealing, mass loading, and damping the door and surrounding surfaces ensures no noise leaks or flanking paths remain.
With some time and effort, it is possible to effectively soundproof metal doors and prevent sound transmission.
Conclusion
Metal doors often contribute to unwanted noise transfer between rooms. Their lightweight hollow construction provides minimal sound blocking compared to solid wood or steel doors.
Thankfully, there are many options for retrofitting metal doors to improve acoustic isolation ranging from simple DIY solutions to full door replacements.
Adding sound dampening panels, properly sealing all air gaps, installing double doors, and upgrading to sound-rated doors can significantly reduce noise transmission through metal doorways.
While challenging, with the right set of soundproofing techniques, metal doors can be made nearly as quiet as walls.
This allows you to control noise and improve sound privacy wherever standard metal doors are installed.