Flanking Sound Transmission Via Conjoined Fenestration in Buildings

Sound transmission between adjacent spaces in buildings is affected by several elements including airborne transmission loss of the primary partition including openings, penetrations, gaps, doors, ductwork, etc. The acoustical character of the primary partition is often expressed in terms of Sound Transmission Class (STC) rating, and field tests can be conducted to determine Apparent STC (ASTC) or Field STC (FSTC) to some degree of accuracy. Other paths of sound transmission can be hard to identify and distinguish using commonly available test equipment. Problematic paths of sound transmission that degrade the overall transmission loss are those called flanking sound transmission paths - sound transmitting around the perimeter of all elements of the primary partition, whether airborne or structureborne. This presentation examines four cases of conjoined fenestration in four multi-unit residential and commercial buildings that were tested in the field for ASTC and FSTC ratings. One involved modification of the intersection of a common window that spanned the primary partition. Another involved testing using the FSTC method, Annex A1 of the ASTM E336 test method by use of temporary shielding barriers. The third will express vertical flanking sound transmission with a comparison to a different pair of rooms in this same building. Comments will be made regarding the practicalities of building construction projects.