Room-to-Room Privacy and Acoustical Design Criteria

Sound and Vibration, Feb 2004 by Weissenburger, J T

The author would appreciate receiving comments and criticisms on this matter. Perhaps, if there is enough interest, consensus guidelines can be developed where none now exist.

Footnotes

1. As a side issue, the issuing of ANSI S12.60, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools, a year ago has made privacy between classrooms an issue of concern.

2. STC is a laboratory test that tests the transmission of sound through a sample of a basic wall construction with no electrical boxes or other 'violations' of the structure. FSTC is an in situ test identical in most respects to STC except that it is testing a wall in the real world. Both STC and FSTC are reduced to per square foot and corrected for acoustical absorption in the receiving (listener's) room. NIC is similar to FSTC except that no correction is made for wall area or absorption in the receiving room. NIC is a "what you hears is what you gets," to paraphrase a famous comedian. all of these tests are detailed in the American Society of Testing Materials (ASTM) procedures.

3. It is worth noting that theoretically, if FSTC is more than 3 dB loss than STC, more acoustical power is leaking around the wall (flanking) than is transmitted through the hasic wall itself.

4. The entire procedure as set forth in the American Society of Testing Materials (ASTM) E90, Standard Method for Laboratory measurement of Airborne Sound Transmission Loss of Building Partitions, neglects sound below 125 Hz that is often of primary concern in preventing the transmission of low frequency sounds such as Hi Fi with heavy bass and like sounds.

5. ASTM E90, Standard Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions.

6. See American National Standards Institute (ANSI) S3.5, Methods for the Calculation of the Articulation Index.

7. NIC is a single number rating computed in accordance with ASTM 413, Standard Classification for Determination of Sound Transmission Class, based on individual NR measurements.

8. This is not strictly a correct use of AI, but there had to bo a starting place and it agrees reasonably with field experience.

J. T. Weissenburger, Engineering Dynamics International, St. Louis, Missouri

The author can be contacted at: jtw@edi-stl.com.