page_title: Sound transmission class
section_title: Sound leakage
hierarchical_section_title: Sound transmission class / Factors affecting sound transmission class / Sound leakage
caption_attribution_description: English: Small gaps, such as this opening at the base of a stud wall, can greatly decrease the STC rating of a partition
context_page_description: Sound Transmission Class is an integer rating of how well a building partition attenuates airborne sound. In the US, it is widely used to rate interior partitions, ceilings, floors, doors, windows and exterior wall configurations. Outside the US, the Sound Reduction Index ISO index is used. The STC rating very roughly reflects the decibel reduction of noise that a partition can provide. The STC is useful for evaluating annoyance due to speech sounds, but not music or machinery noise as these sources contain more low frequency energy than speech.
  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. In general, the sound transmission class of a double leaf wall is greater than a single wall of equivalent mass.
context_section_description: All holes and gaps should be filled and the enclosure hermetically sealed for sound isolation to be effective. The table below illustrates sound proofing test results from a wall partition that has a theoretical maximum loss of 40 dB from one room to the next and a partition area of 10 meters squared. Even small open gaps and holes in the partition have a disproportionate reduction in sound proofing. A 5% opening in the partition, which offers unrestricted sound transmission from one room to the next, caused the transmission loss to reduces from 40 dB to 13 dB. 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 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.
  Acoustic joint tapes and caulking have been used to improve sound isolation since the early 1930s. Although the applications of tapes was largely limited to defense and industrial applications such as naval vessels and aircraft in the past, recent research has proven the effectiveness of sealing gaps and thereby improving the sound isolation performance of a partition.
caption: A small gap in the wall can greatly reduce the STC rating. This wall did not receive a full perimeter seal.
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