Today, we try to hear the music in a large hall.
The University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
Houston's Jones symphony
hall has gradually been altered over the years --
sound-reflecting surfaces added and taken away. In
1980 we had a good orchestra and a dubious hall.
Now we have a fine orchestra in a much better hall,
and the sound is glorious to hear!
Of course, the problem of providing good acoustics
was far more severe before the 19th century -- when
musical instruments had softer voices, and before
we could enhance sound electronically.
Aristotle knew that air carries sound, though that
fact wasn't verified in a way we'd call scientific
until the 17th century. In the first century AD,
the Roman architect Vitruvius showed how to enhance
sound in halls by placing pots along the walls or
in the ceiling. The pots, of various shapes and
sizes, each resonated to different frequencies.
Better to make the pots of brass, but clay worked
too. You could still find acoustical pots as late
as the 17th century. In fact we use variations on
the idea even today.
When Christopher Wren designed churches during the
17th century, he had his own acoustical formula. He
figured a modest voice could be heard only 50 feet
in front and 30 feet on the sides, so he set
pulpits far out toward the nave. A century later,
the architect of Drury Lane Theater used 92 feet in
front and 75 feet on the sides. (But that was for
trained actors, not the average vicar.)
Eighteenth-century architects began using rules of
light reflection to predict how sound would travel
in closed spaces. They began putting parabolic
reflectors behind altars and orchestras.
All the while new knowledge begat new problems. For
if sound waves travel like light waves, they too
move out spherically, reflecting off every object
in their path. As mathematicians took up acoustics,
the vertical horseshoe of boxes surrounding a
concert stage gave way to today's wedge-shaped
halls flanked by acoustical reflectors and
resonators. And we're back to Vitruvius's pots.
In the 1960s, London's Royal Festival Hall turned
the matter of hall acoustics on its ear. After
years of tinkering, engineers hid microphones about
the rear of the hall and softly played the sound
back through speakers in front. The tiny delay gave
an illusion of rich reverberation. That was kept
secret until the new sound got rave reviews. When
people learned what'd been done, they questioned
the moral implications of doing it! Now with
electronic boosting fairly common, we wonder what
can be next.
Well, last week I spoke in a large hall where I was
both miked and projected on a vast screen by the
podium. What the audience heard was not me. What
they looked at was not me. On the one hand, we seem
to be moving toward a kind of virtual live
performance.
And yet, the direct acoustic hall will survive. The
simultaneous presence of corporeal listeners and
performers is an essential rite. It is a ceremony
we will not be content to lay aside.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Elliott, C. D., Technics and
Architecture. Cambridge, MA: MIT Press, 1992,
Chapter 16.
Lewcock, R., Acoustics. The New Grove
Dictionary of Music and Musicians (Stanley
Sadie, ed.). New York: MacMillan Publishers, Ltd.,
1980, Vol 1, pp. 43-67.
Beranek, L., Concert and Opera Halls: How
They Sound. Woodbury, NY: Acoustical Society
of America, 1996.
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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