Do you remember when you were a kid that the closest thing you had to a cell phone at the time was two cups with a string tautly attached between them, and then speaking into one cup to see if your friend holding the other could hear you? That long-ago game worked because sound travels along rigid pathways. If you let the string between the cups go slack, the sound doesn’t travel. That’s all you really need to know to understand soundproofing – and you had already learned it in kindergarten.
The ABC’s of Sound – and Soundproofing
Sarah Marsh, President of MAAI Marsh Architects in New York City, says: “There’s no such thing as soundproofing; rather the proper term is sound attenuation.” Sound attenuation is the effective reduction of sound – not necessarily its elimination.
Michele Boddewyn and Alan Gaynor, President and Founding Principal respectively of the New York City firm Boddewyn Gaynor Architects, explain that noise in multifamily buildings can be broadly divided between two general categories: airborne noise and structural noise. Airborne noise filters in from adjacent units and outside. It includes things such as music from a stereo, raised voices, or the rumble of the garbage truck at 6:30 on a Saturday morning. Structural noise has to do with reverberations that come through the actual building structure – so the reviled ‘footfalls’ of your upstairs neighbor’s children and her high-heeled shoes clacking against the floor at the same time every day count as structural noise.
Solutions for these different types of noise vary in approach. In reality, the underlying science behind the solutions is pretty much always the same: relax the string.
An Unintentional History
Urban multifamily housing can be pretty much divided into three categories as far as sound is concerned. The first period stretches from World War I through the pre-World War II construction boom, and then on to the mid-1960s, when construction methods began to change for both economical and technological reasons. The second period covers the years from the late 1960s and early 1970s through the early 1990s. The third period begins in the 1990s and brings us to the present.
Older buildings (often referred as prewar) were heavier, built with more layers and solid materials. “Sound was less of an issue before World War II,” says Boddewyn. And adds Gaynor: “They had plaster walls and used gypsum block, and had high ceilings. They also used lots of concrete fill, which is like rubble, so it’s pretty quiet. There are many layers.”
Kevin White, Owner of Brooklyn Insulation and Soundproofing, which has offices in New York, New Jersey, and Florida, says: “The old buildings were soundproofed by density. Everything back in the day was built solid, and extremely dense. The denser the floor or wall, the harder it is for that sound to transmit through.”
From the late 1960s onward, “builders went for lighter-weight materials like sheetrock and studs, so you have much more sound transfer,” Boddewyn says. This has led to more issues with both airborne and structural noise. And according to Marsh, the level of noise in a building “has to do with math. And developers aren’t using math in their projects. They build as they do because they can – it’s all about the cost of the materials. A lot of developers on less high-end projects won’t put the expensive materials in.” Consequently, “there’s a poor quality of sound control.”
White agrees. “We see how fast developers are putting up new buildings, and with soundproofing it’s about quality, not quantity,” he says. “We see cheap materials that aren’t installed correctly in new units, and sometimes they don’t do anything to decouple the floors, which is bad for impact transmission.”
The proliferation of glass buildings over the past two decades has made the problem even more acute. Glass does not act as a sound reduction agent in any way. Many new buildings are constructed with shared walls between units, as well as between units and common areas, which adds to the likelihood of airborne sound infiltration, as well as structural transmission.
So back to the cup and the string. Dr. Bonnie Schnitta, President and Owner of SoundSense, an acoustical consulting and engineering company with offices in Long Island and New York City, says: “If we’re talking about a wall, a floor, or a ceiling, there are certain things that improve or are successful in inhibiting sound. The criteria are that it has to be dense, must have some level of flexibility or resiliency to it, and has to have a complete seal. You can have the best wall in the world, but if it’s got a hole in it, it’s not going to work.”
The culprits when it comes to sound transmission between apartments are often single studs and back-to-back electrical outlets, which do little to reduce or interrupt the flow of unwanted noise. Though strongly cautioned against by architects, developers will often ignore these pitfalls for the sake of saving a bit on construction costs.
Marsh adds that “some soundproofing materials are used within the initial construction, and some installed after. The easy ones are after construction – things like carpeting and curtains. Resilient underlayment is used in floor construction to reduce sound conduction. It might be foam or fiber. It could also be roof felting, cork or rubber.”
Bedrock for soundproofing between floors is a 9-inch-thick poured concrete floor. Anything else, according to Gaynor, will not prevent sound – particularly structural sound – from transferring from one floor to another. Schnitta agrees, but cautions that “a thick poured concrete floor itself is great for stopping sound, but if it’s not thick enough, it will be terrible for footfall,” or anything else with an impact on the floor, such as dropped articles. She explains that in New York there is a required ‘IIC,’ or Impact Insulation Class. “Many old buildings were not subject to this requirement. The requirement to cover 80 percent of your floor with carpet was enacted to account for this, but if it’s not the right carpet or padding, it won’t solve the problem. There is a special carpet pad called Vibramat that is very effective for this. It raises IIC by 20 percent.”
Schnitta explains there are many other sound-stopping options today. In new buildings, she recommends loaded vinyl as a means to reduce sound transference through studs. “It’s impregnated with non-toxic metals, and it’s dense to add flexibility,” she says. “This doesn’t contain lead—remember lead walls!—which they used to use. This vinyl has a better transmission loss factor than lead to eliminate sound, and it’s only an 1/8th of an inch thick.”
But what if your building is already up, and the sound just keeps on coming? Marsh suggests that you can either put up a false wall between your place and the next apartment, which could cost you a few square inches of space. But she says that may be well worth it for a good night’s sleep. Or you could build a closet along the offending wall and use it to store clothes and toys, sure to absorb the sound. She relates one client who’s neighbor had a very regular schedule for his “personal life.” Saturday morning comes once a week, as the adage says. The neighbor was like clockwork, and very noisy. Marsh suggested adding a false wall, which would have absorbed the sound. Ultimately, the client chose to do nothing. Perhaps the neighbor changed his schedule.
What’s New and Improving?
“More innovative sound control products have been patented in the last few years than ever before,” says Schnitta. “Before where there wasn’t a solution; now we have one. A good example is a type of pad that if you put this down before you pour concrete for a foundation, it will inhibit subway noise if there is one nearby. Knowing that resiliency is an important piece of the solution set for walls, there are new clips that have neoprene pads integral to the design to prevent connecting drywall to channel sound. Also, a lot of attention to acoustic leakage points like wrapping the backs of outlets helps. An acoustic muffler will inhibit sound from coming through recessed lights that are not fully insulated cans.” Clearly, every little bit helps.
A J Sidransky is a staff writer/reporter for The New Jersey Cooperator, and a published novelist.