Noise can be one of the greatest challenges in designing buildings in the urban landscape. Unfortunately, it is often overlooked and later deeply regretted. Window attenuation considerations are essential for buildings situated near rail tracks, major highways, or commercial airport operations. Other noise-sensitive applications include hospitals and schools where external noise can be disruptive and distracting and downright unhealthy.
Attenuation performance is a result of the entire product.
The entire product not just the glass and should consider these four constants in noise attenuation:
- Mass – both window frame material and glass should create barriers of sufficient mass to attenuate noise
- Air space between multiple glass barriers – an increase in airspace will decrease sound transmission
- Acoustic decoupling of frame barriers – on multiple levels, mechanically separating the two sides of the frame prevents sound from passing through
- Window assembly air infiltration – sound follows air, block the air and the sound is also blocked
Sound transmission is measured in several ways.
Two primary measurements are used to compare sound transmission.
Sound Transmission Class (STC) provides a single-number rating for interior building partitions. It is calculated over the frequency range of 125 to 4,000 hertz and per ASTM E413. The STC rating can be assigned only to specimens tested in a laboratory. Specimens tested in the field will be indicated by an Apparent Sound Transmission Class (ASTC) rating. The higher the number, the better the noise attenuation.
Outdoor-Indoor Transmission Class (OITC) provides a single-number rating for blocking sound outside the building and is a single-number rating for exterior walls, windows, and doors that are subjected to transportation noises and other low-to-mid frequency noise sources. The OITC is calculated over the frequency range of 80 to 4,000 hertz and per ASTM E1332. An OITC rating can be assigned only to specimens tested in the laboratory. The higher the number, the better the noise attenuation.
Effective use of acoustic windows has become essential to keeping urban noise out and creating quiet interior spaces. Look for STC and OITC ratings to find the optimal levels of noise mitigation. Our acoustic window experts at St. Cloud Window can help you find the best window for your acoustic needs – request a quote today for more information.
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