Sound transmission class
In the US, it is widely used to rate interior partitions, ceilings, floors, doors, windows and exterior wall configurations.
[1] There are many ways to improve the sound transmission class of a partition, though the two most basic principles are adding mass and increasing the overall thickness.
[3] The STC provides a standardized way to compare products such as doors and windows made by competing manufacturers.
The STC is a standardized rating provided by ASTM E413 based on laboratory measurements performed in accordance with ASRM E90.
The STC standard curve is based on European studies of multi-family residential construction, and closely resembles the sound isolation performance of a 9-inch-thick (230 mm) brick wall.
These Transmission Loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour provided by the ASTM.
There are nearly infinite field conditions that will affect sound isolation on site when designing building partitions and enclosures.
[19] Installing absorptive insulation, for example fiberglass batts and blow-in cellulose, into the wall or ceiling cavities does increase the sound transmission class significantly.
[14] The presence of insulation in single 2x4 wood stud framing spaced 16 inches (410 mm) on-center results in only a few STC points.
This is because a wall with 2x4 wood stud framing spaced 16 inches develops significant resonances which are not mitigated by the cavity insulation.
In contrast, adding standard fiberglass insulation to an otherwise empty cavity in light-gauge (25-gauge or lighter) steel stud partitions can result in a nearly 10 STC-point improvement.
Structurally decoupling the gypsum wallboard panels from the partition framing can result in a large increase in sound isolation when installed correctly.
[21] When heavy gauge steel or wood studs are spaced 16 inches (410 mm) on center, additional resonances form which further lower the sound isolation performance of a partition.
[13] Though the terms sound absorption and damping are often interchangeable when discussing room acoustics, acousticians define these as two distinct properties of sound-isolating walls.
Laminated glazing, which consists of a Polyvinyl butyral (or PVB) inter-layer, performs better acoustically than a non-laminated glass of equivalent thickness.
A 0.1% open area will reduce the transmission loss from 40 dB to 30 dB, which is typical of walls where caulking has not been applied effectively[26] Partitions that are inadequately sealed and contain back-to-back electrical boxes, untreated recessed lighting and unsealed pipes offer flanking paths for sound and significant leakage.
The sound isolation performance of a partition measured in the field according to ASTM E336, normalized to account for the reverberation time in the room.
The sound isolation performance of a partition measured in the field according to ASTM E336, not normalized to the room conditions of the test.
These walls vary in sound isolation performance from the mid STC-40s into the high STC-60s depending on the presence of insulation and the gypsum wallboard type and quantity.
[15] There are several commercially available software which predict the STC ratings of partitions using a combination of theoretical models and empirically derived lab data.
