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Fig. 3. Rock mufflers in El Salvador (Courtesy LaGeo).
one had determined the depth of rock required to slow the flow down and keep the rocks in the box. The first trial turned out to be more of a rock launcher than a rock muffler since quite a few rocks were blown out of the top of the box. Later, addi- tional depth was added until the weight of the rocks counterbalanced the pressure of the flow.
Eventually rock mufflers were installed at each plant so the entire stream could be vented during shut down. I measured 72 dBA while standing next to one during a full plant vent test, almost a 60 dB reduction from raw well venting. This has become the industry standard methodology for controlling geothermal power plant noise throughout the world (Fig. 3). Later, Dick Stern and I worked under a Department of Energy program to quantify geothermal noise during
1 drilling and production. AT
the back of a flat bed truck. In the first prototype, the well References
pipe was introduced horizontally into the base of a large steel box. The truck was backed up to a well and the steam pipe was welded to the entrance pipe of the box. The pipe at that point had a diameter of about 30 inches. Unfortunately no
1 M. Long and R. Stern, “Evaluation of Noise Associated with Geothermal Development Activities,” Department of Energy, Department of Environment, under Contract DEAC-01 79- EV06200 (1982).
Marshall Long received a BSE degree from Princeton University in 1965, attended the University of Grenoble in France and the University of Madrid in Spain in 1966. He received M.S. and Ph.D. degrees in engineering from UCLA in 1971. While still a grad- uate student, he founded his own acoustical consulting firm, now in its 38th year. Marshall Long
Acoustics specializes in architectural acoustics, audiovisual design, noise and vibration control, and other technical areas related to acoustics. He enjoys sailing, judo, soccer, reading, and writing, and is living with his family in Sherman Oaks, California. He is a Fellow of the Acoustical Society of America.
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