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Mythbusters Challenges Rifle Gunshot Legend with Meyer Sound Subwoofers
"Mythbusters" Build Team—Kari Byron, Tory Belleci, and Grant Imahara—visited Meyer Sound's Berkeley headquarters as part of their quest to verify the claim that a Russian-made SKS rifle could be set off by the vibration of a high-powered subwoofer.
Mythbusters" often calls on Meyer Sound when it comes to investigating audio-related myths. The show, which features a team of five special effects and science experts who put some of the most outrageous urban legends to the test, has turned to Meyer Sound to prove or debunk such popular claims as a duck's quack not echoing, the human voice breaking glass, or the existence of the dreaded "Brown Note."
While the "Brown Note" episode called for modifying electronics to accept frequencies well below the normal operating range, this time the test involved four of Meyer Sound's 600-HP compact high-power subwoofers. Two subwoofers per side were stacked in Meyer Sound's six-inch thick concrete isolation chamber, and driven far beyond their typical usage patterns, well beyond pain threshold.
"This was an interesting episode because we were tasked with moving a physical object with a substantial amount of force, using vibrating air (sound) to move a piece of metal (the firing pin)," explains Dr. Roger Schwenke, Meyer Sound's staff scientist. "We used a lot of different signals in a wide range of peak-to-average ratios, from sine tones and sweeps to pink noise. I worried about somebody opening the chamber door at the wrong time and hurting our ears, but at no time was I worried about hurting the speakers."
In the end, yet another urban legend fell by the wayside as the attempts to move the firing pins with sound waves were unsuccessful. "The only way air was going to move something with that much mass is if we could build up energy over several cycles," Schwenke concludes. "That's fundamentally what a resonance is, when energy from one cycle adds coherently with the energy stored from previous cycles. What's great about this episode is that we got to demonstrate this simple principle: In order to have a resonance you need a mass (the firing pin) and a restoring force (like a spring). No spring, no resonance, no displacement from equilibrium. Myth Busted."