Here’s the bottom line: all of Trim-Tex’s code compliance solutions, from Sound Gasket to Fire Bead, have the same or better soundproofing capabilities as acoustical caulk, with none of its drawbacks. But how do we know that? If we say something like, “This vinyl bead achieves a Sound Transmission Class (STC) rating of 50,” how did we land on that number? Well, rest assured, we didn’t just make it up — they have been rigorously tested by a third-party lab long before you install them into your walls. Curious? Here’s how Trim-Tex’s code compliance solutions are tested for soundproofing power.
In December 2021, we visited North Orbit Acoustic Laboratories in St. Paul, Minn., where the team there was putting three of our fire rated drywall accessories — Hotrod XL, Fire Bead and Fire Gasket — to the ultimate soundproofing test against acoustical sealant. Check out the video below to see for yourself what happened when Hotrod XL and Fire Bead went head-to-head against sound-rated caulk, and read on to learn more.
WHAT IS AN STC RATING?
We don’t have to explain STC ratings to many of you in the construction industry, especially those working in the residential and multifamily sectors, because STC values are constantly being discussed in this industry right now.
But for the uninitiated, when we talk about “STC,” we’re talking about a partition’s ability to prevent sound from passing through it. In particular, we’re talking about sounds with a frequency of 125-4000 Hz, which usually means noises like human speech. Soundproofing is typically going to be in your building codes. For wall assemblies, Uniform Building Code (UBC) requires an STC rating of 50 of Group-R occupancies (hotels, apartment complexes, condos, et cetera).
Fire-resistant drywall is naturally sound dampening, but the gaps around that drywall still leave a lot of room for sound to pass through it. For many years, the common way to seal these joints was with acoustical caulk, but as anyone who’s worked with this kind of sealant knows, it’s tough to apply evenly, and only lasts so long. Over time, it hardens and shrinks back, and a good soundproofing solution needs to remain flexible to remain effective.
HOW DO YOU TEST FOR STC RATINGS?
At large facilities like the one at North Orbit Acoustic Laboratories, you essentially have two nearly identical rooms outfitted with cutting-edge audio technology, with an opening between the two areas. In that opening, we built our wall.
While a lab setting like this is not much like a typical jobsite, the wall assembly is built to be as close to what you’d find in the field as possible. Like many wall assemblies you’d find in the field, we used 3 ⅝” metal studs at 24” on center, hard attached to the slotted track at the head-of-wall for a more real-world construction. (Most third-party sound tests decouple the studs from the test opening in order to artificially boost STC ratings. For us, realism was our goal.) The wall assembly used ⅝” fire-resistant Type X drywall and R-13 batt insulation.
With this wall assembly constructed and the joints sealed, one side of the testing facility is repeatedly blasted with a loud sound. On the other side of the wall, high-tech recording devices capture how much sound passes through it. From this process, they are able to calculate an accurate STC value.
HOW DID TRIM-TEX STACK UP TO sealant for soundproofing power?
On day one of our testing process, we tested our Fire Gasket solution. Here we used a single layer of ⅝” drywall on each side of the wall assembly/test opening. The half-inch head-of-wall joint was filled with acoustical caulk on both sides. (Sealant would take weeks to fully cure, so in this test, it was left in a wet state, which would give it the best possible STC value — after the sealant hardens, its sound-dampening ability would decline.) Sealant along the sides and bottom perimeters of the walls were further sealed with putty rope and additional silicon and foil tape; the point of this test was to isolate the passage of sound only through the head-of-wall joint.
With this setup, the test gathered a result of STC 45.
All the sealant was removed from the wall, and the drywall was temporarily taken down for our team of experts to install Fire Gasket onto the slotted tracks on both sides. Once it was properly applied, the drywall was reattached to the studs, and sealant was reapplied to the vertical and bottom-wall gaps, along with the same putty rope and foil tape system to, again, isolate sound passage on the head-of-wall joint.
The result? The same as before: STC 45.
So what this test proved is that Fire Gasket, with this wall assembly, provides the same soundproofing capabilities as acoustical sealant, with none of its drawbacks. Caulk application is often tricky and time-consuming, and over time will lose its sound-dampening power as it shrinks and hardens. Meanwhile, Fire Gasket is easily installed, up to five times faster than sealant, and is designed to remain effective and flexible for the lifetime of the structure. Plus, of course, Fire Gasket also provides firestopping protection against the spread of smoke and fire that acoustical caulk cannot.
This was the test we were most excited to conduct with NOAL, combining two of our fire rated solutions into one powerful soundproofing wall assembly.
As before, the team at NOAL constructed a true-to-life wall assembly. It featured 3 ⅝” metal studs at 24” on center, R-13 batt insulation and, this time, a single layer of ⅝” Type X drywall on one side and a double layer of ⅝” Type X on the other.
For the first test, sound sealant was applied on all four sides, filling the half-inch gaps between the drywall and the test opening. This time, though, the sealant on the sides was not sealed off with putty rope — today, we were testing the whole wall for sound transmissions. The sound test commenced, and soon enough, we had our result: 50 STC, the accepted standard for most building codes.
This time, we did not take off and replace any of the drywall; for a completely fair head-to-head matchup against our firestopping solutions, everything was left in place. The sealant within the sides and top of the wall assembly was painstakingly removed. Our team came in and installed Hotrod XL along the head-of-wall joint. Hotrod XL’s compressible foam center is designed to form a perfect seal upon installation, providing ¾” of structural movement and staying permanently flexible. Meanwhile, Fire Bead, with its flexible apex gasket, is perfect for finishing vertical gaps and protecting them from the passage of fire, smoke and, yes, sound — we used it along the sides of the test opening.
The two different fire rated vinyl beads were stapled into place every two to four inches, and finished with five-minute hot mud to get it ready in time for our test. With the doors sealed and the high-tech audio equipment primed to start booming, we were ready to start the most anticipated test of our stay in St. Paul.
And once all was said and done, we had our result: a 51 STC, a full point higher than acoustical sealant. A single point may not mean everything in every field, but for acoustical testing, it’s a major statement.
Conclusion: With third-party sound testing completed, we were able to prove that Trim-Tex’s code compliance solutions provide the same or better STC values as acoustical caulk. And, oh, by the way, with these fire rated drywall accessories, you also get the most advanced firestopping proficiency you can get, due to intumescent tape that expands to 30 times its size when exposed to intense heat. And you get far longer-lasting flexibility for building movement — anywhere from ½” (Fire Bead) to a full 1½” (Fire Gasket 1.5”) — preventing cracks in your finish and other, more serious damage. And you’re getting a cleaner, faster, more foolproof installation. And you’re getting a more aesthetically crisp finish on your drywall. And you won’t have to rip it all out and do it again in five years; you've got an effective fire-resistant, soundproof setup that will last the life of your wall.
While the STC values are often comparable between acoustical caulk and Trim-Tex’s groundbreaking firestopping solutions, when you add up the true value you’re receiving, there’s really no comparison at all.
You can view a quick recap of the specifications on each test NOAL conducted for us below. Learn more about our full line of code compliance family by hitting the button below — and be sure to request a copy of our full technical code compliance catalog while you’re there.