Acoustical Isolation 101: Sound Reduction in Buildings
Minimizing disruptive and undesired sound in buildings requires an understanding of acoustics, sound transmission, and sound control. This ensures
November 18, 2024
Maxxon Resources
For acousticians
Effective sound control in multifamily construction requires quality, scientifically tested products, collaboration with performance-focused professionals, and resources to support the architectural community.
Find Acoustic Data to Support Your Project
Explore our user-friendly resources that provide access to sound tests, help determine the IIC and STC ratings your assembly can achieve and ensure compliance with building codes and fire ratings.
Fire & Sound Manual
Access a comprehensive list of sound tests and Maxxon UL Fire Ratings organized by construction type.
Maxxon Supporting Acousticians
Access detailed data sheets and sound tests for every Maxxon Acousti-Mat®. Get the tools you need to guide architects, meet or exceed code requirements, and deliver acoustical comfort tenants can count on—all backed by responsive technical support.
Ready to Start your Next Project?
If you have any design or acoustical questions, or if there’s specific data you’d like to review, please reach out to your local representative.
Frequently Asked Questions
How is the minimum Gyp-Crete thickness chosen?
In our Fire & Sound Manual, we list both the type of Acousti-Mat and the thickness of Gyp-Crete. We typically test with the minimum allowable thickness of Gyp-Crete. The minimum thickness is driven by the substrate type or the Acousti-Mat thickness.
| Topping Minimum | Total System Height | |
|---|---|---|
| No Mat | ¾" | ¾" |
| Acousti-Mat® 1⁄8 | ¾” | 1 ¼” |
| Acousti-Mat® ¼ | 1" | 1 ¼” |
| Acousti-Mat® ¼ Premium | 1" | ~1 ¼” |
| Acousti-Mat® 3⁄8 | 1" | 1 3⁄8” |
| Acousti-Mat® 3⁄8 Premium | 1" | ~1 3⁄8” |
| Acousti-Mat® ¾ | 1 ½” | 2 ¼” |
| Acousti-Mat® ¾ Premium | 1 ½” | ~2 ¼” |
| Acousti-Mat® ¾ + SBR | 2” | 3 1⁄8” |
Does higher strength Gyp-Crete improve acoustic performance?
Not necessarily. While Maxxon provides formulations with strengths ranging from 2000-5000psi, the higher-strengths are achieved through chemical formulation, not increased density. Since there is not a significant mass difference across the strengths of Gyp-Crete, strength doesn’t necessarily correlate to improved STC ratings.
How much does Gyp-Crete weigh?
Gyp-Crete varies in density from 110pcf to 125pcf due to formulation, field conditions, and regional sand differences. This works out to 9.13psf per inch to 10.4psf per inch, a difference of +/- 5-8% in weight which would be less than 1dB of difference in acoustic transmission loss based on mass law alone. We typically use 10psf per inch as our “average” weight.
What is the acoustic benefit of increasing Acousti-Mat or Gyp-Crete thickness?
The benefit the Acousti-Mat and Gyp-Crete selections provide can change dramatically depending on the base assembly. A wood frame structure, where Gyp-Crete is likely more than half the mass, will see much more benefit from a thicker topping slab than a concrete base assembly would. If possible look for a laboratory test of your desired assembly. Acousticians can access extended test results by registering with Maxxon’s website.
What design criteria are appropriate by space type? (Good, Better, Best) Any resources?
Code Minimum performance: STC/IIC 50 or NNIC/NISR 45 per IBC. This is applicable in multifamily construction within the United States. The ICC G2-2010 provides enhanced performance guidelines of:
- Acceptable Performance: STC/IIC 55 or NNIC/NISR 52
- Preferred Performance: STC/IIC 60 or NNIC/NISR 57
Additional consideration should be given for assemblies adjacent to exceptionally loud noise sources or strict sound transmission requirements.
Where do current metrics like STC and IIC fall short?
STC and IIC are commonly used metrics when evaluating the acoustic performance of walls, floors, and ceilings. One of their biggest limitations lie in their frequency ranges. STC measures 125-4,000 Hz, and IIC 100-3,150 Hz. Both metrics were developed primarily around speech frequencies, but not all noise in a building is speech.
For example, fitness rooms, mechanical systems, or dropped objects often produce low frequency noise that falls outside these measured ranges. As a result, assemblies may perform well on paper but fail to block real-world noise that tenants or guests actually hear.
Additionally, IIC is measured using a standardized tapping machine, which doesn't reflect the variety of real-life impact sounds. The type of object, its hardness (e.g., padded foot vs. dropped pan), and force of impact (e.g., regular footstep vs. jumping) all affect the resultant sound on the opposite side of the assembly. This variability is not captured in an IIC test.
Another limitation is that the lab-measured IIC (ASTM E492) only measures sound transmission from a floor to the room directly below. In addition, the IBC Code language refers to adjacent residences and common partitions. Neither account for lateral transmission to adjacent rooms, or sound moving upward, which can be a major issue in buildings with mid-floor fitness centers. For example, unmitigated weight drops in a gym may be heard not just below, but also in rooms next to or above the space. These paths are not addressed by a simple lab test, although they can be measured in the field per ASTM E1007.
What are HIIC and LIIC, and why were they developed?
HIIC (High-frequency Impact Insulation Class, ASTM E3222) and LIIC (Low-frequency Impact Insulation Class, ASTM E3207) are newer acoustic metrics that complement the IIC metric by providing more detailed insight into impact sound performance across the frequency spectrum. While IIC gives a single number to represent overall impact isolation, focusing on mid-frequencies, it doesn’t show important differences in how an assembly performs at the high vs. low ends of that spectrum.
Changes in impact insulation performance aren’t always uniform. For example, adding a topical mat to an assembly can often provide significant improvements in the high frequencies but less significant improvements in the low frequencies.
The JASA paper these metrics are based on, ”A dual-method for evaluating impact noise isolation of floor-ceiling assemblies” was published by John LoVerde and Wayland Dong in 2017 (JASA 141(1): 4280440)
What should I look for while overseeing an Acousti-Mat & Gyp-Crete installation? What can go wrong?
- Gaps in Perimeter Isolation: Watch for gaps between the perimeter isolation strip and the wall. These often occur when installers stretch or tug on the isolation strip, causing it to pull away and leave gaps - especially around corners or irregular walls.
- Exposed Subfloor: Acousti-Mat must completely cover the subfloor without any gaps or overlaps. Exposed subfloor, particularly at penetrations (e.g., plumbing or conduit) or at seams between sheets, can significantly compromise acoustic performance.
- Damaged Mat: The mat is designed to function beneath a topping slab. If heavy equipment is moved across it before the topping is installed, the mat can be crushed or torn, reducing its effectiveness.
- Ideal Installation: Here’s what you should see at an Acousti-Mat Installation:
What can go wrong in a sound control system?
The Acousti-Mat and Gyp-Crete are just part of a high-quality sound control system. Attention is needed from the beginning of design through the end of construction to ensure the acoustic goals of the project are met.
- Ensure the design matches the tested assembly: for example, structural and resilient channel spacing is guided by both fire and sound considerations and resilient channel quality varies depending on design and manufacturer.
- During construction, ensure that VE decisions don’t reduce the acoustic isolation by eliminating the mass of the Gyp-Crete or substituting a lower performing resilient channel.
- Use certified Maxxon applicators who are trained to properly install both Acousti-Mat and Gyp-Crete and are supported by the Maxxon R&D department.
- Visit the site to ensure proper installation of all the acoustic isolation products, including both the Acousti-Mat and the resilient channels. Any deviation from proper installation can cause a flanking path in the and hinder the isolation provided by the Acousti-Mat and resilient channels, degrading the performance of the entire assembly. Flanking paths in an acoustic assembly are unintentional routes sound can travel. These flanking paths are extremely difficult and costly to correct once the rest of the build-out is complete.
How durable is Acousti-Mat?
Acousti-Mat has been tested to compression of 500-1,000 psi before compromising the integrity. The mat is designed to be evenly loaded under a topping slab. If point loaded with heavy equipment, like drywall carts, before a topping slab is in place, the mat can be damaged. Light activity on the mat, such as walking, is permissible.
Field tests after installation are consistent with field tests decades later, indicating there is little degradation of the acoustical products over time.
Built for Acousticians: The Industry’s Leading Sound Testing Lab
Maxxon’s state-of-the-art acoustics lab features the world’s largest floor-ceiling sound chamber—purpose-built to support acousticians in performing precise, accredited testing across a wide range of assemblies in a controlled environment.
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Maxxon's "Science of Sound" video series. Explore acoustics with us, starting with the basics of sound and its measurement. Learn about sound transmission, including Airborne and Structureborne types, and understand STC and IIC ratings. Finally, discover how Maxxon's solutions control sound in buildings, ensuring quiet and comfortable spaces by addressing floor, ceiling, and flanking path challenges.
Meet the Maxxon Acoustics Team
Evelyn Way
Lead Scientist, AcousticsEvelyn oversees technical support for acoustic isolation products, leads product development, and manages Maxxon’s NVLAP-accredited (lab code 600320-0) floor/ceiling acoustic test chambers.
Aimee Ramfjord
Scientist, AcousticsAimee specializes in experimental sound and vibration testing. She has extensive experience in identifying noise sources through acoustic testing and providing data-driven recommendations for noise reduction.
Drake Hintz
Scientist, Acoustics | Consultant Liaison
With a background as an acoustical consultant and an education in physics and architectural engineering, Drake brings industry experience to his role as a consultant liaison and technical expertise to acoustics R&D team.
Ben Schave
Lab Technician & Construction SpecialistBen manages detailed record-keeping and quality control to support consistent, reliable acoustic testing.
Matt Stanton
Lab Technician & Construction SpecialistMatt supports acoustic testing with a focus on accuracy, consistency, and data integrity—playing a critical role in maintaining the high standards our partners expect.
Annual Acoustical Symposium
Each year Maxxon hosts an Acoustical Symposium at our headquarters in Minnesota. With in-depth presentations and robust discussions on the latest advancements in sound control for the building industry, the event is a valuable learning opportunity for acousticians from around the world.