November 2017 Newsletter: Discount Acoustics?

Black Friday and Cyber Monday are just around the corner, which means shoppers will soon be searching for the best deals. Building owners are no different when it comes to the design and construction of buildings. Decisions at all stages of a building project can have large budget implications, and understandably, there is a desire to find the most economical way to accomplish the project’s goals. When it comes to cost-effective acoustical design, there is a lot of misinformation out there. Would adding batt insulation help? What about another layer of drywall? What if we add acoustic panels? In this month’s newsletter, we sort out the facts to bring you the best bang for your buck.

Batter up

Without a doubt, the most common question we hear is “would adding batt insulation help”? The short answer is probably, but it depends upon the application. Fiberglass batt insulation or mineral wool is great for absorbing sound in cavities. Adding batts to wall and floor/ceiling cavities improves the sound isolation performance by reducing the resonance of the cavity. It doesn’t work, however, if there are structural connections between the two sides; in this instance, sound will travel through the structural studs or joists and bypass the insulation.

Batt insulation has very little mass, and as such, it is not well suited to block sound transmission. For example, draping batt insulation above a lay-in ceiling on either side of a demising wall between two rooms will not result in a significant improvement in isolation between the two rooms. Another common practice is installing batt insulation above a ceiling to reduce low-frequency noise from overhead HVAC equipment. Batt alone will not solve this problem; mass is needed.

If a little is good, more must be better?

Another common question relates to the addition of more drywall. Increasing the total number of layers of drywall on a partition from two to three, results in a 50% increase in mass and a noticeable improvement in sound isolation. However, adding a layer of drywall to a partition that already has multiple layers of drywall on each side of the studs only results in a small increase in the overall mass of the assembly, which does not result in a significant improvement. To achieve a noticeable boost in sound isolation, your money will be better spent changing the partition to a staggered or double stud wall rather than piling on the drywall.

What if we add acoustic panels?

Acoustical panels are great for absorbing sound that would otherwise reflect off a hard surface. In sufficient amounts, they can reduce the buildup of sound within a space; however, adding acoustic panels to a room will have a negligible effect on the transmission of sound through a partition into an adjacent room. Sound absorption and sound transmission are two different phenomena. If sound transmission is a concern, the demising partitions need to be designed to provide the right combination of mass, cavity absorption, and resiliency.

Impossibly Low Prices!

You can always do the bare minimum to address sound transmission; you can do nothing at all, you can cut corners, or you can go bargain shopping. But if you are building a school, a hotel, a condo, or an office building where there is some expectation of sound isolation, your occupants may not be happy. Proper planning, design, and construction are significantly cheaper than tearing it all apart and redoing it later. When it comes to sound control, it’s probably best to make the investment or you may find yourself “penny wise and pound foolish”.

1628 JFK Blvd. | 8 Penn Center, Suite 1902 | Philadelphia, PA 19103 | (215) 248-4352
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