Steve Rittmueller (left) and Kerry J Haps (right, section vice chair), Chicago AES Section, January 31, 2018.
Steve is an acoustical engineer for Masonite, which is a supplier of acoustically-rated doors. He works to optimize the Sound Transmission Class (STC) of doors in addition to the Outdoor/Indoor Transmission Class (OITC) through careful design. Transmission loss is the attenuation of sound as it moves through a partition (such as a door). It is measured by creating a loud, acoustically diffuse noise on one side of the partition, and then measuring the sound level on the other side of the partition. Doors almost never perform up to their rated specification when installed in a building. This is due to flanking effects of sound being transmitted around the door, through floor, walls, or ceiling.
The mathematical definition of the problem is a partition (that has certain mechanical properties) that is loaded by a fluid (air) on both sides. The full equations for this are quite complicated, however they can be simplified by eliminating and approximating terms.
Some things we learned from Steve's presentation are that having a vacuum in between layers of a partition is actually problematic. Stiffness is also a problem. To understand the problem of stiffness, think about throwing a baseball at a trampoline vs. throwing a baseball at a sheet hanging from a clothes line. The sheet absorbs and dissipates the energy of the ball. Another interesting point was that the acoustic properties of a partition can actually change quite a bit depending on the incidence angle at which the sound is hitting it.
The talk concluded with a Q&A session with the audience.
Much more information can be obtained through Steve's PowerPoint deck here:
https://www.slideshare.net/AES_ChicagoSection/structural-acoustics-lecture-97529400
Steve also pointed us to an excellent set of animations demonstrating acoustical phenomena by Dan Russell, professor of acoustics at Penn State University:
http://www.acs.psu.edu/drussell/demos.html
