Baby and kids

Overview Room-to-room noise reduction is rated in terms of sound transmission class (STC). The acoustical performance of common 16″ OC wood stud walls is typically STC 30 to 34, and 24″ OC wood stud walls is STC 36 to 39. This is considered poor, as conversation can be easily heard. An old method to improve wall isolation since the 70’s is a product called mass loaded vinyl. It is sold under a number a brand names, such as AcoustiBlok, SoundBarrier and others.

Acoustics and Vinyl Noise can be attenuated with additional mass and many companies make vinyl sheets weighing about one pound per square foot. For this type of acoustical treatment, the mass of the materials is the dominant factor. However a wall already weighs 4 to 5 pounds per square foot before mass loaded vinyl is added, so the extra pound added by a single layer of vinyl is only a small amount of added mass.

Vinyl sellers display transmission loss data of bare sheets showing an STC of 26 or more. However presenting bare product performance is not related to the performance in an actual wall. The acoustic ratings of individual materials cannot be added to existing walls. For example, a single sheet of 5/8 inch thick gypsum board by itself has an STC of 28 — 2 points higher than that of one pound vinyl. But you cannot add that 28 to a wall of 30 and get 58. In fact, an extra layer of gypsum adds only 2-3 STC points to any wall.

Adding mass to a wall follows mass-law which states that a doubling of wall mass adds about 5 to 6dB of isolation. That is, a doubling of mass of the entire structure!

When considering any product for soundproofing it is imperative to look for independent lab tests on full scale 8′ x 12′ walls performed to a current ASTM test method (ASTM E90 and E413). Remember individual STC values do not add up.

Sound Transmission in Walls In a single stud assembly, the major path of sound transmission is directly through the studs rather than the air in the cavity. The addition of a vinyl layer does little to change this since the outer gypsum will be nailed or screwed directly through the vinyl into the stud. For significant improvements, one must change this path fundamentally, or introduce specific damping into the structure.

Actual Performance There is one test from an independent lab showing a branded mass loaded vinyl at over STC50 on a 24OC wood stud wall. Unfortunately that test was conducted on a single wall section (4′ x 8′) rather than the required 8′ x 12′ wall, thus rendering the test invalid as it does not meet the requirements of ASTM E90. Three other full scale tests have now been published which show MLV on one side of a 24OC wood stud wall at STC 43 to STC 45. This is an improvement of about 15% less noise as heard by humans.

Cost Considerations One pound per square foot vinyl sells for $1.50 to $2.00 per square foot at many online stores plus shipping (add about $1 per pound for UPS). So the delivered material cost averages $2.50 to $3.00 per square foot.

Vinyl installation is labor intensive. The vinyl needs to be unrolled, cut by hand around obstacles, attached with fasteners and carefully taped along every seam prior to the installation of the drywall layer. If one is not doing the work themselves, subcontractors charge $1.00 to $2.10 per square foot for installation.

Thus, in reasonable sized projects, one can expect an increase in wall costs of $3.50 to $5.10 per square foot. Consider a base of about $4.00/sqft if it is new construction for the studs, gypsum, and standard labor, and this results in a wall that averages $8/sqft. This will result in an STC 43 wall assembly with 24″ OC studs.

Comparison Soundproof drywall, such as QuietRock, creates a damped structure and thus behaves differently than MLV. Lab tests on soundproof drywall show STC’s of 50 or better when used on one side of a 24OC wood stud wall. And this material replaces one side of drywall, saving money and time.

Low cost soundproof drywall today runs about $1.20/sqft (and is available at local dealers). Labor is about $0.60/sqft. Thus total wall costs can be under $5.30 per square foot depending on performance required. No special training or labor is required, since it installs just like drywall. The resulting performance is a 50% noise reduction (versus 15% for vinyl), the overall cost is 30% lower.

Resilient Channel is another technique which has been used since the 1960’s. This requires hanging metal channels on the studs and then hanging drywall on the channels. The drywall must be isolated on all sides since touching the floor, walls or ceiling could acoustically “short out” the floating wall and reduce the performance.

If done right, with a double drywall on the RC side, and no shorts, it is reasonable to achieve an STC 48. The cost of this wall is under $6.00/sqft including labor. While the performance is less than soundproof drywall and the difficulty is higher, it is a mature method which was popular before the advent of soundproof drywall. So it may be worth still considering as an option.

Conclusion Mass Loaded Vinyl has been sold for many years to help with sound isolation between rooms. They can provide limited increased STC values by adding additional mass and impedance changes to the wall. However, the effort, cost and detail required to use these materials needs to be compared to other more established and tested methods including soundproof drywall and resilient channels.