How To Soundproof Walls Of A Home Theater Room

The task of soundproofing walls of a home theater room is not at all easy, that I can say with utmost certainty and sincerity.

For that matter, home theater rooms and recording rooms are most difficult to soundproof to the extent that is desired.

When I first decided to soundproof my theater room, I was looking at ways that would be cheap and effective.

Unfortunately, soundproofing does involve some investment. There is a lot of misinformation on the net with regard to soundproofing materials. The most popular ones among these, are about how egg cartons and foam do wonders for soundproofing.

Egg cartons and foam do absolutely nothing to soundproof a room. Read my articles on egg cartons and foam in which I describe how useless they are.

There are some really expensive soundproofing products as well. You don’t need them either for soundproofing your theater room.

With the materials and methods brought out in this article, you will be able to soundproof your walls to an extent that is desired for a theater room.

What is the extent of soundproofing desired in a theater room?

While soundproofing a theater, your aim should be to block the sound that enters through the walls in the theater as well as block the sound that leaves the theater.

It’s a common belief that there is no need to bother about the sound that is entering the theater through the walls. We will now discuss some stats to indicate why this assumption is incorrect.

In a theater, you’re going to hear sounds ranging from 10db to 110db. The actor’s breathing would be 10db, his whispering would be 20db and loud explosions during the movie would be 110db.

You will want to hear mostly everything for the best movie experience right from the breathing to the explosions.

If your room doesn’t block enough outside noise, you would have to crank up the volume of the home theater. But, this would make the explosions deafening.

So, there is a need to soundproof walls and other surfaces of a home theater to the maximum extent possible.

Sound Transmission

Sound waves are basically vibrations and you want to set up barriers that will prevent the sound vibrations from entering or leaving the room.

When sound hits these barriers in the form of walls, floors and ceilings, it sets up vibrations which tend to ‘move’ the surface.

When you’re soundproofing a wall, you are just trying to make sure that sound does not cause it to vibrate. Because, it is these vibrations that continue to the other side of the wall and transfer sound.

Sound Transmission Class (STC)

There is a common terminology related to soundproofing that you may have come across.

To measure how good a surface is at blocking sound, the metric known as STC is used. If a material has an STC of 40, it means that it will be able to reduce sound by about 40 decibels.

The table below will give you a fair idea on what to expect for a given STC.

STC RATING	WHAT CAN BE HEARD
25	Normal speech can be heard and understood clearly through the wall.
30	Loud speech can be heard and understood clearly while normal speech can be heard but not understood.
35	Loud speech can be heard but not understood.
40	Now we are getting somewhere, the speech sound is significantly reduced.
42	Loud speech is stifled, heard more like a murmur.
45	Loud speech is no longer heard. Instruments can be faintly heard.
50	Deafening sounds from machines and loud
60+	Soundproofing is at its best, here most sounds are inaudible.

A regular wall with 2×4 framing, one layer of drywall and without insulation has an STC of 32. A concrete wall of four inches thickness will have an STC of 48 and an eight-inch thick wall would have an STC of 52.

Though a concrete wall has a good STC, it performs very poorly at low frequencies and that is not what we want in a home theater. That is why most home theater owners frame an extra 2×4 wall covered with drywall over the existing concrete wall.

It is pertinent to note, however, that STC is an average value for frequencies from 125 Hz to 4000 Hz. It does not take into account frequencies below 125 Hz which are typical in a home theater environment.

Elements of Soundproofing

In many of my articles on this site, you will come across the four elements of soundproofing. I cannot overemphasize how critical these elements are for soundproofing a home theater.

The elements of soundproofing are as given below.

Mass –Sound vibrations can be minimized by having walls of high mass. The heavier the wall, more difficult it is for sound to vibrate it. Consequently, lesser the vibrations, lesser will be the transmission of sound.

Decoupling – Decoupling is the most vital element and we will be talking about this in depth.

Absorption – Absorption is achieved by having insulation in the air cavities of the wall structure.

Damping – Another important element that can do wonders for your soundproofing goals.

Now let’s examine methods to incorporate the elements of soundproofing and see what best suits us. Insulation will not be dealt with as a separate sub topic of this article but will be described in places as required.

Adding Mass for Soundproofing Walls

Let’s assess what happens if we simply add mass to the wall. As mentioned earlier, if you just have a single layer of drywall on both sides, the STC of the wall would be about 32.

If you add insulation and one more layer of drywall on both sides of the wall, the STC would only marginally increase to 38. For a home theater, this will definitely not be enough.

In this example, you can see the STC ratings for different wall constructions. Notice how removing the ‘inner’ drywall impacts the overall performance.

So, we need to explore additional ways to increase the STC of the walls.

Decoupling for Soundproofing Walls

To increase the STC further, we have no choice but to resort to some form of decoupling. Decoupling means ways to reduce the connection between surfaces like studs and drywall thereby creating an air cavity.

When sound passes through a cavity, it attenuates or loses energy to a large extent. Cavities, in other words, are highly beneficial to soundproofing.

Ways That You Can Decouple Walls

There are a few ways that you can decouple walls and each way has its own pluses and minuses.

• Room within a room.
• Double stud wall.
• Staggered stud wall.
• Sound isolation clips and resilient channels.

Room Within A Room

The most effective form of decoupling that can be achieved is by building a room within a room. Here, we are building two separate walls that are totally delinked with each other.

In other words, there is no physical connection between the two layers of studs. What this effectively does is that it creates a large cavity in between the space between the walls.

Also, since there is no physical connection, sound will not transfer from the inner wall to the outer wall. The ceiling too does not touch the existing ceiling giving maximum benefits of decoupling.

The air cavities are then filled with loose insulation. Insulation should not be dense so that sound ‘interacts’ freely with the fibers and loses energy on the way. The loose insulation will also make sure that the walls do not resonate.

The only common surface is the floor by which some amount of sound transfer will take place from the base of one set of studs to another. This can be minimized further by having a soundproof underlayment such as Acoustik Mat with a wooden flooring covering it.

The new flooring would be installed in such a way that it leaves a small gap from the walls. The gap can then be filled with acoustic sealant. This arrangement will decouple the floor from the walls and provide good sound isolation.

In a room within a room construction, you should install drywall on the inside of the new wall and on the outside of the old wall. You should not drywall in between the two sets of studs because that is the area where the benefit of the cavity needs to be exploited.

Each side (inner side of the new wall and outer side of the old wall) should have a double layer of 5/8 inch drywall with a damping compound sandwiched in between. The 5/8 inch drywall sheets will give the maximum mass benefit to soundproof the room.

The damping would prevent resonance and convert the sound energy into heat energy which will further reduce sound transfer.

With the room in a room construction method, insulation, double drywall and damping as described, an STC of above 60 can be achieved for walls. That is pretty good from a soundproofing point of view.

Double Stud Wall

A double stud wall is very similar to a room within a room construction except that the two studs are not completely separated from one another.

Unlike a room within a room construction, both sets of studs will be attached to a common base plate. Likewise, there will be a common top plate on which both sets of studs will be attached.

The double stud wall is easier to set up as compared to a room within a room set up. In the room within a room type construction, you will need to attach each set of studs separately to the floor.

The inner stud wall is unsupported as it is isolated from the outer studs. This causes complexities in structural stability.

The double stud wall is very effective at soundproofing as there is a large air cavity created with this type of construction. Like the room within a room set up, you will want to install the drywall on the outer sides and have loose fiber insulation in the cavity.

By installing double layers of 5/8 inch drywall sandwiched with damping material in between on each wall, an STC close to 60 can be achieved.

This is a bit lesser than the room within a room construction but the cost savings, the savings of space in your room and avoidance of tackling structural stability issues make the double stud wall construction a highly viable option.

Staggered Stud Wall

The staggered wall is also an effective solution for decoupling walls. This is a more economical and space saving option. In a staggered wall, the 2×4 studs are placed on either side of a six inch or more base plate.

With this type of ‘staggered’ arrangement, there is an air cavity created which provides the decoupling that we are looking for.

As you can see that having a wall which is just six inches wide (excluding the drywall), you have a decoupled wall with a large cavity which is highly beneficial for soundproofing.

A staggered stud wall with two layers of drywall and damping compound would give an STC of about 55.

Read my article on the differences between staggered stud wall and double stud wall.

As seen from the three types of decoupled walls, the larger the cavity, more is the STC achieved. Maximum STC is achieved in the room within a room construction followed by the double stud wall and staggered stud wall constructions.

Sound Isolation Clips and Resilient Channels

Without building a room within a room, double wall or a staggered stud wall, decoupling can be achieved on a single wall with the help of resilient channels and sound isolation clips.

Resilient Channels

Resilient channel is basically a metal channel which is flexible. The resilient channel is screwed on to the studs after which the drywall is attached with screws into the resilient channel not touching the studs.

In this setup, the drywall is connected only to the resilient channel. The resilient channel is connected to the studs at only some points. In effect, there is a ’floating’ wall that is created which is decoupled to a large extent.

Care must be taken not to allow the screws of the drywall to touch the studs instead of the resilient channel or else the decoupling effects would reduce.

So, if you decide on using resilient channels, you will need to spend extra amount of time to be doubly sure that screws of the drywall do not touch the studs.

Resilient channels are the cheapest option for decoupling and cost lesser than even sound isolation clips. However, any mistake in the installation may lead to an unsuccessful decoupling project.

Sound Isolation Clips

Besides the resilient channel, sound isolation clips can be used for decoupling in case of a single stud wall.

Instead of a channel that covers the width of the wall, sound isolation clips are placed on the studs.

Hat channels are then placed inside the sound isolation clips.

The drywall is then screwed onto the hat channel while avoiding any contact between the screws and the studs.

Sound isolation clips are of many types but the popular ones for walls are as follows:-

• IB-1 Sound Isolation Clip
• RSIC-1
• Whisper Clips

IB-1 Sound Isolation Clip

The IB-1 clips are the simplest in construction and cheapest too. They do not have a vibration damper.

RSIC-1

RSIC (Resilient Sound Isolation Clips) -1 are clips which have a vibration damper. The vibration damper dampens the sound vibrations of the hat channel. Because of this, the RSIC performs better than the IB-1.

Whisper Clips

Whisper clips perform the same way as RSIC-1 except that they have spring mechanisms in them instead of vibration dampers. The spring systems flex when sound vibrates the hat channel thus dampening the sound.

Resilient Channel vs Sound Isolation Clips (Performance Overview)

A very important factor when we are comparing performance differences between resilient channels and sound isolation clips is resonance.

In layman’s terms, the rattling of windows and doors that you hear is basically resonance. And this rattling happens at a particular frequency which is generally in the lower range. You would have noticed that the rattling occurs because of bass.

Likewise in a home theater, the walls are going to rattle at low frequencies and that is what we want to avoid. If we can lower the resonance frequency sufficiently, then we will not have too many problems.

For example, if your subwoofer is capable of going down up to 25 Hz, if the resonance frequency is brought below 25 Hz, then resonance will never be experienced in the theater room.

Lowering the resonance frequency below the maximum capability of the subwoofer may not be practical but it would always be beneficial to have the resonance frequency as low as possible.

A resilient channel has a very good performance at high frequencies. The resonance frequency also reduces but low frequency performance is poor.

Sound clips perform better and will lower the resonance frequency even further than the resilient channel.

Recommended Read: Sound isolation clips vs resilient channel

Damping

Viscoelastic damping is revolutionary in the soundproofing industry. A damping compound such as Green Glue is considered by some as a miracle product.

Read all about Green Glue in my article here.

Damping is very good for low frequencies as it damps out the sound vibrations of the walls. Damping of sound vibrations means that you hear less of that rattling at low frequencies.

Even if you choose not to decouple the walls, just by using viscoelastic damping can give very good results. In fact, the improvement in performance is experienced for all frequencies and not only the lower range.

The most effective way of soundproofing is to have a combination of decoupling and damping.

Whether you have a room within a room construction, double stud wall or staggered wall, by having double layer drywall which is damped will yield the best results for soundproofing.

With this arrangement, you have the advantages of decoupling, an improved low resonance performance and increased sound isolation for all frequencies.

Concrete

Many people have basement home theaters. If you are planning to set up one, you will have concrete walls to deal with.

Concrete may have a good STC value but it is a good transmitter of sound at low frequencies. To counter this in a home theater, you will need to install another wall made of drywall.

To decouple the studs for the new wall, you will have to use suspension brackets or spacers. These spacers create a gap between the concrete wall and the studs and ensure that there is minimal sound transfer between the studs and the concrete wall.

Do note that the wood that is coming in contact with the concrete floor should be pressure treated. This is because the concrete floor is prone to moisture which will ruin the lumber if it is pressure treated.

An alternative to pressure treated wood is a vapor barrier. The vapor barrier can be placed between the wood and the floor.

Mass Loaded Vinyls

If you have a small room and just cannot afford to sacrifice that extra space required for decoupling or..

You live in a rented house where you cannot obviously modify the existing structures, mass loaded vinyls are a good option and are available on Amazon.

The mass loaded vinyls should be ideally sandwiched between two layers of drywall. It is not advisable to attach them to the studs as this causes a triple leaf effect which is detrimental to soundproofing.

What is the triple leaf effect?

Each ‘leaf’ is referred to as a layer of mass. So, a typical wall construction that has drywall on both sides will consist of two leaves with one cavity in between.

Now, let assume that you have a double stud framing done. If you install drywall in between the two frames, you will have three leaves which comprise of three drywall layers.

Here, you end up with two cavities, one large and one small. Tests have shown that having two cavities of different depths causes the resonance point to increase and that is something that is not desired.

This is known as triple leaf effect.

Coming to Mass Loaded Vinyls. If you install them directly over the framing and then cover them with a drywall layer, the Mass Loaded Vinyl will tend to bend thereby creating a small cavity between it and the drywall.

The triple leaf effect will then come into play. That is why it is advisable to sandwich the Mass Loaded Vinyl between two layers of drywall so that it stays firm and does not create an air cavity.

Performance of this wall set up can be further enhanced by applying viscoelastic damping.

Tips for Soundproofing A Wall

While employing some of the methods as mentioned in this article, there are some helpful tips which you need to keep in mind.

• The drywall that you use should be the heaviest (5/8” thick). Whenever you are soundproofing, the extra mass helps.
• Try to have the maximum cavity depth as you can afford. The cavity of slow-moving air is highly beneficial and the more you have it, the better.
• For drywall installs in a home theater, do not do any mudding. Instead, caulk the seams with acoustic sealant to reduce sound transmission further.
• Make sure to fill the cavity of the wall with standard fluffy fiberglass or loose cellulose insulation. The insulation will help in dissipating the sound energy as it travels through the fibers.
• Do not to use blown-in insulation as the density of insulation would become very high. This would, in turn, be counterproductive for your decoupling efforts.

Final Thoughts

Soundproofing is a complex task and requires effort and investment. If you can’t afford professional help for the entire project, explore the option of consultations.

Consultations with a soundproofing professional on site could help avoid costly mistakes and actually be a money saver in the long run.

Secondly, avoid getting influenced by articles on the internet claiming the effectiveness of cheap methods like ‘soundproofing’ foam and egg cartons.

I highly recommend the soundproofing master thread on Avs Forum in which every aspect related to soundproofing is discussed and where tips from the best experts can be found.