Acoustics from A to Z
Editors Note: We are republishing Eric Ungar’s Acoustics from A to Z and Stig Ingemansson’s Noise Control: Principles and Practice from previous NNI issues as part of our initiative to include more educational articles. Their lessons are just as valid today. Look for more in future issues and on noisenewsinternational.net.
By Eric E. Ungar
During the March 1999 joint meeting of the Acoustical Society of America with the European Acoustics Association, held at the Technical University of Berlin, I had the opportunity to visit the Institute of Technical Acoustics of that university. Prominently posted on a bulletin board in a corridor, I found an eleven page 1958 article which was coauthored by Lothar Cremer, the late former director of the institute.
This unusual publication, whose title may be translated as “The ABC of the Acoustics of Buildings,” consists of brief verses. There is one verse for each letter of the alphabet; each deals lightheartedly with some aspect of acoustics, each is illustrated by a cartoon structured around the letter, and each is followed by a brief summary of related facts. I was so intrigued with this article’s approach that I resolved to translate it and asked the director of the Institute, Professor Michael Möser, to send me a copy. Soon, after he kindly complied with my request, it became clear that translating the article without losing its basic spirit was beyond me. So, I decided to give up and start from scratch, developing my own verses and discussions, but maintaining the spirit. Here’s the result.
ACOUSTICS deals with sound and noise; One may be pleasant, one annoys.
How sound’s produced and propagated,
And put to use, attenuated,
And how perception plays its part – It is part science and part art.

The story is told about George Washington Carver, the famous African American scientist who studied peanuts and developed many uses for them, that as a young man he prayed that God reveal to him the secrets of the universe. Because God replied that “the peanut is more your size,” Dr. Carver focused on a more limited field.
Many of us who work in acoustics also had ambitions to know all about acoustics, but we soon learned that the field is much too diverse. Acoustics, as Ira Dyer of MIT has said, deals with “anything that moves and many things that don’t.” That statement may be a little far-fetched, but it does convey the breadth of this art and science. To get an idea of this breadth one merely needs to look at the Journal of the Acoustical Society of America, for example. The topics covered there range from physics and engineering – aeroacoustics, underwater sound, ultrasonics, transduction, vibration, signal processing – through physiological and psychological acoustics – including speech production and perception, as well as human and animal bioacoustics – to noise effects and noise control, architectural acoustics, music and musical instruments. Many other fields are closely tied to acoustics – sound systems, audiology, acoustic oceanography and ultrasonic instrumentation to name a few. You can undoubtedly think of many others.
Clearly, the science of acoustics is well developed, and research is progressing on many fronts. The news lately has been rife with talk about such things as acoustic microscopy, acoustical refrigerators with no moving mechanical parts, and cochlear implants that enable people that have severely damaged hearing to hear again. Often, however, more than science is needed. In cases involving the noise exposure of communities or work areas, human relations and politics also play major roles. And, the artful application of judgment is usually needed to solve practical problems. Typically, they involve tradeoffs between conflicting requirements.
In BUILDINGS where we have employment,
Or want to sleep or have enjoyment,
We need to stop intruding noise
From streets, TVs, and neighbors’ toys, From footfall impacts, other shocks,
Most anything that squeaks or knocks.

One person’s music is another person’s noise. It all depends on what we want to hear. Achievement of the desired acoustical environment in a room involves providing envelope structures that block noise intrusion from adjacent areas and adding acoustical absorption to avoid the build-up of noise that gets through the envelope.
In addition to dealing with audible “air-borne” noise in adjacent areas, one also needs to address “structure-borne noise” – that is, noise that results from mechanical vibrations of the envelope structures. The walls, floor and ceiling of a room tend to act somewhat like loudspeaker membranes whose vibrations in the audio frequency range radiate sound. Structurally radiated noise in rooms may result from people walking or chairs scraping upstairs and from vibrating equipment (refrigerator compressors, unisolated plumbing or the legs of pianos, for example) in contact with walls or floors.
What can you do to deal with noise from the neighbors? Ask them to avoid annoying activities at times when you don’t want to hear them. Get them to install thick rugs or, better yet, a floating floor. Get vibrating equipment isolated. Build an isolated ceiling and secondary walls, so that you in effect have an isolated room within a room. Start living with permanent earplugs. Or, move elsewhere.