Immense coils of hot, electrified gas in the Sun’s atmosphere behave like a musical instrument, scientists say.These “coronal loops” carry acoustic waves in much the same way that sound is carried through a pipe organ.
Solar explosions called micro-flares generate sound booms which are then propagated along the coronal loops.
“The effect is much like plucking a guitar string,” Professor Robert von Fay-Siebenbuergen told BBC News at the National Astronomy Meeting in Preston.
As the ancient Greeks were placing the last few stones on the magnificent theater at Epidaurus in the fourth century B.C., they couldn’t have known that they had unwittingly created a sophisticated acoustic filter. But when audiences in the back row were able to hear music and voices with amazing clarity (well before any theater had the luxury of a sound system), the Greeks must have known that they had done something very right because they made many attempts to duplicate Epidaurus’ design, but never with the same success.Researchers at the Georgia Institute of Technology have pinpointed the elusive factor that makes the ancient amphitheater an acoustic marvel. It’s not the slope, or the wind — it’s the seats. The rows of limestone seats at Epidaurus form an efficient acoustics filter that hushes low-frequency background noises like the murmur of a crowd and reflects the high-frequency noises of the performers on stage off the seats and back toward the seated audience member, carrying an actor’s voice all the way to the back rows of the theater.
[Snip]
But as Declercq’s team experimented with ultrasonic waves and numerical simulations of the theater’s acoustics, they discovered that frequencies up to 500 Hz were held back while frequencies above 500 Hz were allowed to ring out. The corrugated surface of the seats was creating an effect similar to the ridged acoustics padding on walls or insulation in a parking garage.
So, how did the audience hear the lower frequencies of an actor’s voice if they were being suppressed with other background low frequencies? There’s a simple answer, said Declercq. The human brain is capable of reconstructing the missing frequencies through a phenomenon called virtual pitch. Virtual pitch helps us appreciate the incomplete sound coming from small loudspeakers (in a laptop or a telephone), even though the low (bass) frequencies aren’t generated by a small speaker.
The Greeks’ misunderstanding about the role the limestone seats played in Epidaurus’ acoustics likely kept them from being able to duplicate the effect. Later theaters included different bench and seat materials, including wood, which may have played a large role in the gradual abandonment of Epidaurus’ design over the years by the Greeks and Romans, Declercq said.
