Building Design for Sound and Acoustics, Part 4: Overview of Soundproofing Materials

By John J. Lupo

soundproofing-0516This is part 4 of a multi-part series of articles that will provide a solid understanding of the principles of sound and acoustics as it relates to design and construction of both public and private spaces. Part 1 covered the basics of Sound, Part 2 covered Decibels, Part 3 covered STC Ratings and Part 5 will cover Room Acoustics.

A basic understanding of the types of soundproofing methods and materials available is an integral ingredient in the proper planning and design of any room or public space.If you’re concerned about improving the experience of residents, occupants or guests utilizing you facility then learning about soundproofing is vital to the success of your project.

Quick Point #1

Completely soundproofing a room is a near impossible task. It can be done, but the costs involved are prohibitive in most applications. So the more realistic goal is to reduce the amount of sound transmission from room to room as much as possible within a given budget.

The objective of soundproofing is to impede the flow of sound energy through the walls of a given room and into the structure of the facility. Once the sound energy enters into the structure of the building it will be carried from room to room diminishing the experience of the residents, occupants and guests to your facility. The two most effective forms are isolation and density. There are many products and techniques offered by manufacturers and utilized by soundproofing companies. I will attempt to give you a basic understanding of the types of materials and systems available for your consideration. Before selecting any product or method it is important to analyze the purpose and uses of the space you are attempting to soundproof. What you want to avoid is selecting a product that may be too much or too little. Taking the “Goldie Locks” approach will provide you with the best solution. As with most products the better the performance will mean a larger investment on your part.

While the most effective methods of soundproofing are isolation and density, a hermetically sealed concrete bunker might not be a practicable solution for your application. The density of concrete does offer a solid level of soundproofing but, you are still faced with other soundproofing concerns such as the A/C, lighting, electrical, windows and entry doors, to name a few. A general rule to follow is that where air flows sound will follow.

OK, so the concrete bunker idea is not for you? Here are some soundproofing alternatives for you to consider. In the next section I’ll examine four types of soundproofing materials and do some comparisons of soundproofing performance. To understand the soundproofing performance of these products we need to understand the elements of the ratings. We’ll be using the Decibel(dB) & Sound Transmission Class(STC) ratings from Parts 2 & 3 so please take some time to review those articles.

Option # 1 is a product referred to as MassLoaded Vinyl (MLV) or Limp Mass Barrier.

Level 1 Soundproofing Material for soundproofing beyond standard drywall and fiberglass insulation.

MLV is a limp-mass material used to block unwanted noise and reduce sound transmission without reducing space. Many soundproofing companies offer this or similar product under different names but basically is the same product.

MLV products are typically installed over the framing studs prior to drywall. It can also be installed between two layers of drywall for enhanced performance regarding soundproofing. Generally these products achieve an STC rating in the 26-27 area. The performance will decrease significantly in the lower bass frequencies and will not perform well in a venue where low frequencies are prevalent such as music rooms or performance halls. Some basic characteristics are shown below.

1) Most common MLV product is a 1lb per square foot version.

2) Typically comes on a 54″ wide roll. It is flexible and available in varying lengths.

3) Can be cut with a carpet knife.

4) The weight and flexibility make it difficult to handle.

5) Requires additional labor to install generally requiring a crew of 2 or more installers.

6) Especially difficult on ceilings due to the weight and nature of the product

Option # 2 is a product referred to as Factory Damped Drywall. As the name infers this is a drywall based product that is specially manufactured as a sound proofing material. The formal name is referred to as a Ceramic Polymer Gypsum Composite Drywall Panel. In the manufacturing process a layer of sound damping product is sandwiched within the drywall panel. As with standard drywall the product is available in varying thicknesses ranging from ½” to 1 3/8″. The soundproofing performance will vary dependent on the product and the installation method.

The big advantage to this product is in the installation process. It is installed in basically the same manner as standard drywall. The product has a cost premium over standard drywall but the ease of installation may offset the increased cost with labor savings.

In regards to performance the product delivers as advertised. It offers good to great performance in the lower frequency ranges depending upon the product selected and the installation method. This would be one of my top choices for larger rooms simply based upon the ease of installation. It does not require any specialized installation crews so a standard drywall installer should not have any issues regarding installation. Some basic characteristics are shown below.

1) Soundproofing material offers different levels of soundproofing (STC Ratings) and can be used on walls, ceilings and even floors.

2) Installed similar to conventional drywall.

3) More expensive than conventional drywall but has certain advantages in regards to installation over other soundproofing methods.

4) Heavier than standard drywall, a bit more difficult to cut. Overall it is one of the least difficult to install in regards to technical labor.

5) Compared to some of the other methods it is a very effective method regarding soundproofing.

6) Test data is backed up by independent testing and the product performance is well documented.

7) Overall my experience with this product was good. It performed as advertised.

Option # 3 is a product known as a viscoelastic noise proofing compound (putty like substance) soundproofing material that is applied like caulk from a caulking gun between two layers of drywall. The product uses standard drywall but requires two layers of drywall. The first layer is installed in a normal installation manner. The viscoelastic compound is spread over the inside of the second layer of drywall prior to installation. The second layer of drywall is then mounted over the first layer with the seams in opposite direction overlapping each other. The objective is to have the seams of the first layer covered by the second drywall panel in a crisscross method. This technique eliminates the possibility of the seams lining up and providing possible gaps in the drywall that will allow sound to penetrate into the structure of the facility.

The big advantage to this product is that it can be utilized in existing situations to add additional soundproofing without having to reconstruct the existing facility. By adding an additional layer of drywall with the material over an existing layer of drywall the soundproofing performance of the wall and/or ceiling will be greatly improved. The material provides solid performance in the lower frequencies when applied correctly. Some basic characteristics are shown below.

1) Offers solid soundproofing performance but you will need to account for the installation cost of an additional layer of drywall. It will require supervision of application and installation.

2) The force of the compression of the two layers of drywall spreads the material between.

3) The material w ill take a few weeks to completely cure and reach maximum effectiveness.

4) Cost is approximately $15.00 per tube.

5) Suggested application rate is 2-3 tubes per 4×8 sheet of drywall.

6) Independent soundproofing test reports are available for review on the manufacturers website.

7) Overall a good soundproofing choice balancing budget vs performance but can be very messy to work with. The key is that it must be applied properly to achieve desired results.

Option # 4 is a process known as de-coupling. The basic idea is to eliminate the connection from the drywall to the framing studs. By accomplishing this goal the sound energy can be impeded from entering into the structure of the facility thus either eliminating or greatly reducing structure borne sound transmission. The process uses isolation mounting clips which are mounted directly to the framing studs. These clips are designed to impede the sound energy transfer. Then a strip of metal known as resilient or hat channel is installed perpendicular to the wall and ceiling framing studs. Resilient channels are strips of metal with an offset that spaces the drywall approximately ½” away from the framing. They’re typically installed 24 inches on center perpendicular to the studs. The use of resilient channels dramatically reduces the amount of sound that is conducted though the structure. When viewed from the side they can resemble an old top hat, hence the name hat channel.

When installed properly it is a very effective method of soundproofing. The key point is “installed properly”. The drywall is attached to the resilient channel and not the framing studs. It is extremely important that the installers do not place screws into the framing studs. If this occurs the decoupling can be compromised by allowing a path from the drywall into the framing infrastructure of the facility.Some basic characteristics are shown below.

1) Obtains separation without losing space compared to double wall construction.

2) Offers good performance across the frequency range.

3) Performs well at soundproofing low frequencies.

4) Isolates the room surfaces from the structure.

5) Utilizes, isolation clip, resilient channel (hat), Isolation Hangers and floating floor treatments to de-couple the room surfaces from the framing structure.

6) Clips attach directly to framing.

7) Drywall is attached to the resilient channel which impedes the transfer of the mechanical energy (vibrations) into the framing

8) Without the isolation clips resilient channel suffered from the issue of misplaced screws.

9) Screws entering the framing stud will short circuit the system reducing the effectiveness and soundproofing performance. The result is you will spend a lot of money and effort and it simply won’t work to its full potential. Not good.

The introduction of the Isolation Clip by soundproofing manufacturers to the system greatly improves on the installation issues eliminating the problem of misplaced screws which simplifies installation. My experience with this product was excellent. When installed properly its soundproofing performance is solid.

Hopefully this article gives you a better understanding of the different methods of soundproofing available. If you have any questions or comments please contact me.

John J. Lupo
Manager, Commercial Audio Video Systems
Electronics World
Gainesville, FL