Sound Study in Shotgun Duplex Home
Commercial Acoustics performed a Sound Transmission Leak Check test on an interior, demising wall partition on site. Per the client’s request, there was excessive noise transfer between the adjacent units of a duplex, “shotgun” style home. Once one of the tenants moved out, the wall was cut open and revealed a 2×6 wood stud wall, with spray insulation and 2 layers of drywall on one side, one layer on the other. This type of wall typically achieves an STC of 35-37 per standard lab test values.
The wall tested was between the two front rooms facing the street. A white noise source was used on one side of the wall, and type 1 SPL meter used with instantaneous readings and 10-second readings on the receive side. NOTE: Unlike a certified ASTC test (per ASTM E336), the leak check and baseline dBA readings only take a few moments, and do not require reverberation adjustments and 10-second averages. However, when a certified STC reading is needed, the SPL meter must be calibrated and a number of additional constraints are imposed.
The technician checked for sound transmission flanking path locations and decibel (dBA) levels along the wall, looking especially for flanking along baseboards, perimeters, outlets, and any other wall penetrations.
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Sound Test Findings:
The dBA level at the source was set at 101.3 dBA.
The recorded dBA level in the receive room was 67.0 dBA.
The calculated ASTC of the partition was 35.6.
This field STC (also known as ASTC, or Apparent Sound Transmission Classification) is well below the building code, so a number of modifications were offered to the client. Unfortunately, since there were no prevalent leaks, the drywall needed to be removed and replaced with a layer of soundproofing membrane and then re-installed to achieve a field STC of 45+.
