Acoustics
Frequently asked questions
Answers to commonly asked questions about acoustical assemblies and STC ratings
Can stud spacing, size and gauge influence the STC value of the wall?
Yes. A deeper stud section permits the use of thicker insulation, allowing for more absorption in the stud cavity. Thinner gauge studs provide less rigidity for the wall system, creating less sound transmission. A partition will perform better acoustically with a maximum spacing of 24 inches o.c. More framing stiffens the partition creating more pathways through the wall. National Gypsum’s technical resource, The SoundBook® 2.0 illustrates various acoustically tested assemblies and is organized by stud type, stud spacing, and assembly type (i.e. wall partitions, chase walls, shaftwall partitions, area separation walls, floor-ceiling assemblies, roof-ceiling assemblies). Acoustical terms and concepts are also included in the technical guide.
What is the difference between “lab tested” STC and “field tested” STC?
The Sound Transmission Class (STC) is a single-number rating of the effectiveness of a material or construction assembly to attenuate the transmission of airborne sound. The STC provides an indication of how loud transmitted sound is perceived to be by the listener. STC values are measurements that indicate a laboratory-tested assembly. Field Sound Transmission Class (FSTC) references the same measurement of assemblies, but they are tested on-site in the installed location. The field-tested values are normally lower due to building movement and different installation methods.
Can SoundBreak XP Wall® Board be used on both sides of a partition to increase the STC rating?
Yes, but installing the SoundBreak XP Wall® Board on both sides of the partition does not increase the STC value enough to warrant the additional cost. Our SoundBook® 2.0 shows many designs to help guide your decision.
Is there an STC value for 5/8” Type X board?
No, STC values are based on a complete wall or floor/ceiling system.
What’s the difference between an STC rating and IIC rating?
STC rating (Sound Transmission Class) is a single number rating showing the effectiveness of an assembly to prevent the transmission of airborne sound.
IIC rating (Impact Insulation Class) is a single number rating showing the effectiveness of a floor assembly to reduce impact sound, such as foot traffic.
What is the increase in STC points needed to hear a difference?
You must have an approximate 3-point increase or decrease in STC value to notice a difference in acoustic performance.
Can stud size and gauge influence the STC value of the wall?
Yes. A deeper stud section permits the use of thicker insulation, allowing for more absorption in the stud cavity. Thinner gauge studs provide less rigidity for the wall system, creating less sound transmission.
What is a flanking path?
A flanking path is a pathway around the sound barrier. To eliminate the flanking path, all gaps must be sealed around the perimeter of the system and any penetrations through the system.
Acoustically, does it matter if the studs are spaced 16 or 24 inches o.c.?
Yes, the partition will perform better with a maximum spacing of 24 inches o.c. More framing stiffens the partition creating more pathways through the wall.
Does it help to apply resilient furring channel over an existing wall?
No. To get maximum acoustical performance, a resilient furring channel must be applied directly to framing.
To reduce impact noise (IIC), what finished floor would be a good choice?
Impact noise is more readily transferred through hard surfaces. One of the best choices is carpet and pad which creates a soft surface.
Will adding additional layers of gypsum board decrease the STC performance?
No. Adding weight to the assembly will improve the overall STC value.
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