How to Soundproof a Room
Do you have a home recording studio, theatre or bedroom that needs soundproofing?
Let’s start with a quick lesson on sound…
How sound works
Sound is energy.
You can’t actually destroy this energy. But you can encourage it to turn into heat, or to disperse.
Sound passes through air, as well as solid objects and liquids.
When sound energy hits an object, like a wall, it causes the wall to vibrate. Those vibrations create new sound waves, so the sound continues beyond the wall.
And the solution?
Stop the wall from vibrating.
You do this by weighing the wall down and adding mass.
Create an air gap
After your wall (or floor or ceiling) has reached a certain mass, it becomes more effective to have two walls, with an air gap.
Just a few inches of air makes a big difference.
But a bigger gap is better.
To see this in action, take a look at double glazed windows. They’re made up of 2 sheets of glass, with a small air gap between them. This is a tiny air gap, so less effective on lower frequencies.
Stop the bass
Low frequency sound is the hardest sound to keep in or out of your room. Think about the rumble of traffic once you’ve closed the window. Or the bass from the other end of the street at 3am.
The lower the sound you need to isolate, the more soundproofing you’ll need. It’s easy to soundproof high frequencies, like a bird chirping, but difficult to soundproof the latest club anthem coming from your studio monitors.
Assess the room
The first thing to do is to find the best room.
Choose a room which has the least adjoining rooms, and is furthest from the street. Think about downstairs and upstairs neighbours too.
Once you have a room, your job is to make it as airtight as possible.
Listen to see where sounds are coming from. Look out for ducts, which can carry sound in and out. And listen out for noises from pipes or AC units.
You’ll probably notice that most of the sound is coming in from the doors and windows. These are the weakest links in the structure of any building.
How to soundproof a window
If you live in an old house, the windows might be rattly, and full of little air gaps. Get yourself some caulk (pronounced cork), and fill all the gaps you can see in the window frame.
Use a clear sealant to fill any gaps between panes of glass.
If it’s your house, look into upgrading to double glazing. Double panel windows are far more effective than single panel, and they tend to have better seals.
If you’re planning to add double glazing, try also adding an extra window layer.
Fit the double glazed unit flush with the outside wall, and fit a single panel window flush with the internal wall. That way there’ll be an air gap between them, the thickness of the wall.
You can line the air gap surfaces with some sound deadening material.
If you already have double glazing, check for air gaps in the window and in the frame. If the windows are old, the seals may be expired and need replacing.
If you want to keep them, you can attach removable glass panels called inserts. They’ll provide an extra layer for soundproofing.
How to block up a window
- Install a baton frame
Screw a wooden 1 x 1 inch frame into the window recess.
Set it back at least 1 1/4″ from the wall surface (or 30mm if you’re in the UK).
This is so you can attach drywall without protruding past the window recess.
- Fill the window recess
Use mineral wool slab to fill the space between the baton frame and window.
If there’s enough room, you could also fill it with bags of sand.
- Attach drywall to frame
Screw and glue 2 layers of 5/8″ acoustic drywall onto the frame.
In the UK, use 2 layers of 15 mm acoustic plasterboard.
Make sure any gaps are filled with acoustic sealant.
How to soundproof a door
The internal doors in most homes are incredibly lightweight. They’re either hollow or made from thin wood panels. They also tend to have gaps around their edges, where they meet the door frame.
There’s often a sizeable gap at the bottom of the door too. This is like having the door slightly ajar, even when it’s fully closed.
Make an airtight seal
The first thing to address is the gaps between the door and the door frame.
In a door frame, there’s a smaller wooden internal frame called a door-stop.
You can get a self-adhesive rubber gasket which sticks onto the doorstop. It forms an airtight seal when the door is closed.
This still leaves a gap at the bottom of the door. One solution is to continue the door stop, so it sits on the floor at the door threshold. This will form a solid air seal all around the door.
The only problem with this is that there’ll be a little piece of wood to step over, every time you go in or out.
There’s another more elegant solution to closing the gap underneath the door. Fit an ‘automatic door bottom’. It’s a small metal mechanism, which seals the door with a rubber stop every time it closes.
Don’t be tempted to fit a plastic or brush sealing strip. These are too lightweight and flimsy to have any effect on sound control.
Fitting a heavy door
It’s much harder for sound to pass through a heavy door.
You can increase the mass of the existing door by adding vinyl barrier mat and MDF. Add another layer of plywood for a nice wood finish which you can varnish.
Remember to upgrade the hinges too, as the door will be substantially heavier.
If you want to buy a new door, look for a fire rated door, as they’re more dense than standard ones.
There’s also the option of buying an acoustic door, which will be the most effective. You can use this with a compression latch, which pulls the door closed into a tight seal.
It’s even better to fit two doors. One door opens into the room, the other opens out of the room. This will create the all important air gap.
Commercial studios use two doors, with both doors fully sealed. Sometimes the gap between doors in commercial studios is so big that the space doubles as a storage area for cables.
Heavy curtains can absorb a small amount of the sound in the room. This will have a minimal effect on soundproofing, by reducing the existing sound level. But it will have no effect on low frequencies.
Absorbent materials like curtains have more effect on the acoustic treatment of a room.
Room within a room
Once the doors and walls have been treated, you can turn your attention towards the walls, floors and ceilings.
The ideal solution to soundproofing a room is to effectively build a new room within the room. Firstly, a floor is constructed, which is acoustically separated (decoupled) from the existing floor.
There’s different methods of making the floor. A popular way is using timber batons laid in a grid. On the underside of each baton is a thick layer of neoprene rubber, where it meets the floor.
Next, the walls and a ceiling are added, leaving an air gap all around. None of this section makes contact with the existing room. There’s normally no windows in a room-within-a-room. And two separate doors – one for the existing room and one the internal room.
An airtight room within a room will also need an air supply. Air can be fed through a home made baffling system to reduce any fan noise at the source.
The room within a room technique is used by commercial recording studios to soundproof to a high degree. It’s probably overkill for most home studios. Try working on specific problem areas, such as the one wall with noisy neighbours on the other side.
There’s also a simpler way of building a room within a room – buying a sound booth.
If you don’t have the budget or space for a room with a room, you could consider a sound booth.
A sound booth is a small room you can build from a kit. They’re available in different materials, some using two layers, with an air gap between them.
Sound booths are normally used for recording vocals, voiceovers or solo instruments.
I once had a whole recording studio set up in a 4 x 4 metre metal booth. It included a grand piano and a sofa, and allowed me to practice and record at all hours.
Booths can get very hot, especially if there are a few people inside. Most of them have quiet fans to bring air in from outside. But these can be too noisy in practice. Some booth users open the door in between takes instead.
The advantages of sound booths are that they can easily be dismantled and taken to another premises if needed. I eventually sold mine to a sound engineer setting up a recording studio in another part of the UK.
How to soundproof walls
The external walls of a house are normally made of 2 layers of brick, with an air gap between them. These are solid and heavy – they have great sound proofing properties.
Internal walls are normally made from large sheets of drywall (plasterboard) attached to both sides of a wooden frame.
They’re much lighter than external walls, and provide poor sound proofing.
To soundproof a wall, you need to do two things:
- Add mass
- Decouple both sides of the wall
Adding mass helps to stop the wall from vibrating. The easiest way to do this is adding more layers of acoustic drywall. You can increase the soundproofing even more be adding a heavy sound deadening material, called barrier mat.
Decoupling both sides of the wall help to stop vibrations passing from one side to the other. This is best achieved with an air gap.
But where space is tight, you can use isolating materials, such as resilient channels.
Resilient channels (or resilient bars) are thin metal strips which absorb vibrations. They’re used as an isolating layer between the wooden studs of the wall frame, and the drywall.
Resilient channels are easy to fit, with one screw per upright stud.
They’re also very effective for ceilings, or wherever there’s a timber frame to attach them to.
Instructions for soundproofing a wall
- Take one side of the drywall off
Break off the drywall on the side of the wall you want to soundproof.
This will expose the wooden frame, the drywall on the other side, and any electrical wires for plug sockets or lights.
- Fill the voids with mineral wool
To find the right thickness of mineral wool slab, measure the depth of the cavity. It’s generally available in sizes between 1 inch (25mm) and around 5 inches (127mm)
Cut the mineral wool slabs to fit snugly between the wall studs with a wood saw.
Make sure not to compress them, as that will change their sound absorbing capabilities. It’s best to wear gloves while you do this, as mineral wool can irritate your skin.
- Add resilient channels
Screw resilient channels to the studs (vertical timbers) of the frame.
Fix them horizontally, and space them around 24” apart.
Position the channels with the raised section (flange) at the top.
- Add acoustic drywall
Position sheets of acoustic drywall vertically against the resilient channels. Screw them directly into the channel flanges, spacing each screw around 12” apart.
Make sure to avoid screwing directly into the studs.
Leave a tiny gap at the top and bottom of the drywall, and seal it with acoustic sealant. This stops vibrations from the wall transferring to the floor and ceiling.
Look for gaps where the drywall meets other walls, and seal those too.
- Add more layers to increase mass
You can add more mass to the wall by adding extra layers of acoustic plasterboard. 2 or 3 layers are standard for soundproofing.
Make sure to stagger the joints.
For even more mass, you can sandwich a layer of barrier mat between drywall layers.
Sound waves really struggle with this variety of materials and thicknesses. For added isolation, glue all the layers together with green glue, an effective damping compound.
Mineral wool vs fiberglass for sound isolation
Mineral wool is made from volcanic rock fibers, and is denser and heavier than fiberglass. It is more efficient in absorbing sound and also has a higher thermal performance. The only time you would use fiberglass over mineral wool for sound insulation is if you needed to keep weight to a minimum.
Making a new soundproof wall
If you need to make a whole new soundproof wall, it’s best to use double thickness brick or blockwork. Only do this if your existing floor is strong enough to take that sort of weight.
You can also use the standard partition wall method with wooden frames and drywall. But instead of both sides of the wall sharing one frame, use two separate frames. Separate the frames from each other with a large air gap.
The bigger the gap, the better the isolation. Mount each wooden frame on a strip of neoprene rubber. This will isolate the wall from the floor.
You can fill the gap with mineral wool, or any sound absorbing material. Finish the wall with extra layers of acoustic plasterboard and barrier mat.
While soundproofing a wall, you may need to reposition some of the electrical boxes. Make sure to turn the power off at the mains before starting any work.
You can position them to be flush with the finished outside wall once the plasterboard layers have been affixed. Seal around the boxes with caulk, making sure there are no holes to let sound through.
A more thorough solution for soundproofing, is to mount the electrical boxes on the outside of the wall. This means you only have to make small holes in the drywall, for the wires to pass through.
How to soundproof a floor
A floor transmits sounds from both the air, and objects in direct contact with it. This could be anything from high heels to guitar amplifiers and monitors. These heavy objects send vibrations directly through the structure of the floor. From there, they can pass into the fabric of the building.
To soundproof your floor, you need to know the sort of floor construction you have.
Wooden constructed floors
Older homes often have floorboards nailed to a wooden structure. The floorboards are either left bare or covered in hardboard and carpet. This type of floor can be tricky to soundproof – wooden structures are lightweight, and there’s gaps between the floorboards.
The quick and easy solution
The easiest way to stop noise through a wooden floor is to install a thick acoustic underlay under the carpet. It’s the cheapest solution and can even be carried out in rented accommodation. This method helps with both impact and airborne sound.
If you have your own home, you can do a more thorough job…
Instructions for soundproofing a floor
- Take up the floorboards
Carefully prize up enough floorboards to access the voids underneath. Number each board you remove, so you can replace them in the right order.
You might have chipboard panels or another material instead of floorboards. Take them up and order them in the same way.
- Fill the cavities with mineral wool
You should now see the exposed timber joists laid in a criss cross pattern. Underneath that will be the drywall ceiling of the room below. Cut mineral wool slabs to fit the rectangular voids, and allow them to rest on the drywall.
Mineral wool is available in thicknesses between 1 inch (25mm) and around 5 inches (127mm). Alternatively, you could use fibreglass insulation, which is less structured.
- Replace the floorboards
Once the boards are back on, check for squeaks, and screw them down where necessary.
- Install barrier mat
Soundproofing barrier mat is a very heavy rubber or vinyl membrane. It’s just a few millimetres thick and can weigh up to 10kg per square metre.
It can be laid loose across the floor, with each piece butted up against each other. The mat blocks all the gaps, and adds some weight to the floor. It can also be nailed in place, or glued for even more sound efficiency.
- Install floating floor
Now all the gaps have been addressed, you can install a floating floor. The first layer of this is a rubber acoustic underlay. This is placed without fixing down, all joins abutting each other.
- Install hard floor
The final layer can be a tongue and groove flooring of your choice. It could be solid timber, engineered wood or an acoustic chipboard. Make sure to leave a gap around the edges, so the floor doesn’t make contact with the walls.
You can also work on the ceiling underneath the floor for extra sound protection.
Concrete floors tend to be good for stopping airborne sound, but they can suffer from impact noise. The answer to this is a floating floor.
The quick solution
The easiest method is to install a simple floating floor. Lay down an acoustic underlay, and cover with a hard floor, as above.
An alternative solution
Another method is to use 2 x 1 inch wooden batons, and 2 inch wide, self adhesive neoprene rubber. Stick the neoprene onto one side of the batons, and lay them in rows, rubber side down.
Screw a layer of acoustic chipboard directly onto the batons, gluing the seams, and screwing directly onto the batons. Make sure not to screw directly into the floor beneath. You can add a finishing layer of solid wood or laminate.
This is how my current apartment is soundproofed. It’s a converted factory with concrete floors, and has incredible soundproofing.
If you have drums, subwoofers or amplifiers on the floor, they’ll transfer vibrations directly into the floor and cause impact noise.
You don’t necessarily have to soundproof the whole floor. There’s an easier solution – a smaller isolation platform. You can buy these, or make one yourself quite easily.
How to make an isolation platform
Decide how big you need the platform to be. 6 x 8 foot is the minimum for a drum kit, though its best to make it slightly bigger if you have the room.
I made a large one of these for an apartment I was living in, for an upright piano. Instead of mineral wool, I used special acoustic feet, as the piano and player weighed around 350 kg.
- Lay isolation layer
The first layer can either be 1 inch (25mm) acoustic foam, or mineral wool slab.
- Lay chipboard and plywood
Lay a layer of tongue and groove chipboard on top of the mineral wool, glueing the seams together. Then add a layer of plywood, at least 5/8 inch (or 15mm). Cover the joins of the chipboard with the plywood wherever possible. Glue and screw them together
- Add carpet or rug
This is entirely optional, depending on the type of acoustic you need
For studio monitors on stands or on a desk, you can use neoprene isolation pads. They’re the size of a speaker footprint, and will decouple the speakers from the surface they’re sitting on. They’ll also help contain the bass response, giving you a more accurate listening experience.
How to soundproof a ceiling
Ceilings are best treated by adding a second ceiling, suspended below the original. The bigger the air gap between these two ceilings, the more effective the soundproofing.
Working overhead can be difficult, so think about hiring a contractor to do this work for you. I’ll describe 5 methods, starting with the most space saving, and ending with the most efficient.
#1 Add mass to the ceiling (3/4″ or 20mm thick)
This is a method of beefing up the existing ceiling. The heavier it is, the less it will vibrate, and pass sound on.
- Glue a layer of barrier mat directly onto 5/8″ (or 15mm) sheets of acoustic drywall (plasterboard).
- Find where the hidden joists are in the ceiling and mark them out.
- Screw the drywall onto the joists, barrier mat side up.
This is also good for old-style lathe and plaster ceilings, which have good acoustic properties, but are prone to crumbling.
#2 Replace the existing ceiling (11/8″ or 35mm thick)
Remove the existing plaster, so you’re left with the exposed timber joists.
Screw on resilient bars perpendicular to the joists every 16 inches (or 40cm).
Fill the gaps between the joists with 4 inch (or 100mm) mineral wool slabs. The resilient channels should stop them from falling.
Screw 5/8 inch (or 15mm) acoustic drywall (plasterboard) onto the resilient channels, watching that you don’t screw into the joists as well.
#3 Shallow suspended ceiling (4″ or 100mm thick)
Locate the positions of the joists behind the existing drywall (plasterboard). Mark them directly onto the ceiling, and also at the tops of the walls.
- Fix 2 x 2 inch batons onto the ceiling, screwing into the joists.
- Glue 2 inch (or 50mm) thick mineral wool slabs onto the ceiling, between the batons.
- Screw on resilient channels perpendicular to the batons, every 16 inches (or 400mm)
- Screw 5/8 inch (or 15mm) acoustic drywall (plasterboard) onto the channels.
- Glue and screw a second layer of 5/8 inch acoustic drywall onto the first. Stagger the joints.
Independent suspended ceilings
If you have enough headroom, you can create a large gap between both ceilings. The larger the gap, the better the soundproofing.
There’s two variations – with metal frame, and with wooden joists. Both of these should be made by builders or very experienced DIYers.
#4 Metal frame
In this system, a lightweight metal frame is suspended from the ceiling. It’s attached with height adjustable, metal strips.
Once the frame is in place, mineral wool is fed through to loosely fill the cavity.
2 layers of 5/8″ (or 15mm) acoustic drywall (plasterboard) are screwed directly onto the metal frames.
#5 Independent joists (13″ or 330mm thick +)
In this method, an extra set of joists are fixed to the walls with wall hangers.
Make sure the joists are thick enough to support 2 layers of acoustic drywall. Position them so that there’s around 12 inches (or 300mm) gap between the underside of the joist and the existing ceiling.
Each joist sits on a neoprene pad within the hanger, to stop acoustic transmission.
Resilient channels are attached, perpendicular to the joists, every 16 inches (or 400mm).
Mineral wool slab is fed through into the cavity.
2 layers of 5/8″ (or 15mm) acoustic drywall (plasterboard) are screwed into the channels.
Most soundproofing myths arise from a confusion between
Soundproofing – stopping sound entering and leaving the room, and
Acoustic treatment – improving the quality of sound within a room.
#1 Moving a bookcase or dresser against a wall
This will have zero effect on soundproofing. The closest thing to this that might have a slight effect, is installing a heavy fitted bookcase directly onto the wall, as it will add mass and weight.
#2 Hanging sound absorbers or acoustic foam
Sound absorbers are for acoustic treatment – the quality of sound in the room.
They only have a minimal effect on soundproofing, which is stopping sound entering and leaving the room.
#3 Soundproofing curtains
While these can have a small soundproofing effect for doors and windows, they are nowhere as effective as the methods described above.
They should be used for acoustic treatment instead.
#4 Soundproofing wallpaper and soundproof paint
Because so called soundproof paint and wallpaper lack mass, they will not help with soundproofing.
#5 Egg box cartons
Egg boxes may have a slight effect on room acoustics, but will have no affect on soundproofing.
#6 Carpet, rugs or blankets on the wall
These soft furnishings will help reduce reverberation in a room. But they won’t have a noticeable effect on stopping sound entering or leaving.
Although there’s many low cost DIY solutions, it can take considerable expense and effort to do a thorough job.
So have a think about what you can do about stopping those sounds at the source.
Can you listen to your mixes at lower levels? Record instruments during the day when the neighbours are at work? Or use electronic piano and drums instead of acoustic?
Make your loudest sounds during the day, when the ambient noise level is high. And record those delicate vocals in the evening, when most people are asleep.
If its your neighbours making the noise, see if you can come to an arrangement, where they keep quiet at certain times.
There’ll always be some compromise, so don’t worry if you can’t achieve your full soundproofing goals. Work within your limits, by choosing the right types of microphones, such as a dynamic microphones to pick up less background noise.
A s well as soundproofing, make sure to optimise the acoustics of your studio for quality recordings.
Author: Daren Banarsë
Daren Banarsë studied classical piano and composition at Trinity College of Music, at undergraduate and postgraduate level.
His music has been performed at the Southbank Centre, Tate Modern, and the Courtauld Institute, and broadcast on BBC Radio 3, Radio 4 and countless TV shows, including The Apprentice, Top Gear and Horizon.
Daren is a former lecturer on the BA Music Course at Goldsmiths College, University of London. He currently works in London as a composer and psychotherapist.