A door like a window can be a portal for noise or unwanted sound to enter our room. Acoustic doors have to perform a dual function. They must provide a barrier between the inside of the room and the outside noise levels. They also must keep sound energy generated from within the room from leaving the room and entering other adjacent rooms. They must do this on a temporary basis because they must open and close to allow for individual access into and out of the room. As they open and close continually, they must seal correctly, so that no gap exists between the door edges and especially the door bottom.
There Is s No Substitute For Mass
Our door through its use of barrier technology must have mass. Multiple layers of materials arranged in vibration reducing manners is the goal. Multiple density fiberboard (MDF) is a good material that provides us with the mass we need to begin our door construction. Remember from past discussions, that not only do we need mass in our material selection but we need to have different materials with different densities, so we can slow down vibrations coming through our door. Vibrations will lose energy if they have to struggle through different material types with different densities. If we use MDF, we can mate it with a plywood. Plywood has numerous layers that are fitted together into a single piece of material. Now we have two different materials that provide us with the appropriate densities.
Proper Assembly Required
We need to take our MDF and plywood and then assemble these two materials in a manner that reduces vibrations. Sound produces and is produced by vibrations. When electromechanical sound from our loudspeakers is produced and strikes our door surface, it is turned into vibrational energy. This mechanical vibrational energy sets the surface it strikes into motion. When it strikes our door, our door must be made in a manner that allows for this to occur, but reduces the vibrations through the way it is assembled. To reduce these vibrations, we use a process termed constrained layer mass damping to sandwich our chosen materials together.
Constrained Layer Mass Damping
Constrained layer mass damping is a process where we take different material types with different densities and arrange them in a manner that keeps vibration reduction in mind. We sandwich each material together with another material such as an acoustical glue. The more materials the vibration has to go through, the better for its reduction. With our MDF, plywood, and now glue, we have three materials that vibrations must go through. The more the better to a point.
MDF / Plywood
If we place MDF as the outside of our door surface, we then can add our plywood underneath the MDF. To secure the two materials together, we need to glue them together. We use an acoustic glue that will keep both materials together and provide another material type with a different density that our unwanted vibrations must go through. If we use MDF on the other side of the plywood we should use a MDF piece that is a thicker or not as thick piece as the front piece. Remember, we want to vary the density or mass of the piece and the thickness of the material to further “confuse” the vibration. We should have as our acoustic goal to have our finished door weigh at least 9/lbs./sq.ft. to provide the necessary noise stopping power.
How to Hinge
Once we have our door assembled with its associated weight, we will need to place it into the door frame. If it is an existing door frame, we must make sure it can support our new acoustic door’s weight and then seal correctly around all door edge surfaces. We may want to consider building a new door frame to support our new door. If we do not and choose to keep our existing frame, we must be sure it is sealed to the existing room structure with a healthy application of acoustic sealant.
To support our new heavy acoustic door, we will need hinges. A cam lift hinge will work well in this scenario. A cam lift hinge will assist us in proper sealing due to its construction method. A cam lift hinge can also support the weight of our new acoustic door. Numerous finishes are available on cam lift hinges to accommodate any decor.
Seal All Gaps
Finally, we must seal our new door to the door frame. All door edges must close squarely and seal properly. Special attention must be paid to the bottom of the door. This is an area where their is a lot of wear and tear and providing a continual seal every time is a must. We can use a brush type sealing strip that collapses when the door is opened or closed but then springs back into place to provide a good seal. There are numerous sealing strips available. Care must be taken to choose the correct stripping that matches the use of the door and the acoustical objective.
A door and window can be the weakest link in our room. We must use mass in our door to stop vibrations. We must assemble the materials in a manner that reduces vibrations and we must sure it seals correctly every time it opens and closes. It must be the correct mass and stiffness and be able to achieve a sound transmission class rating of at least 55.