Engineers tackle audio challenges at GOP convention

By Beth Nissen, senior correspondent
CNN Interactive

PHILADELPHIA (CNN) -- The most stirring speech made from the podium at the Republican National Convention will fall on deaf ears, if it isn't heard clearly.

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CNN Senior Interactive Correspondent Beth Nissen says acoustic engineers are ensuring speeches will be heard at the GOP convention. Play video (QuickTime, Real or Windows Media)

"Sound is important," said Andrew Card, convention co-chair and chief planner of this week's events. "Obviously, we want the delegates, the people in the hall, and the people outside the hall, to hear what's going on here."

The problem is that a sports arena like the First Union Center was designed so the audience could see the play-by-play, not hear word-for-word.

"We've all seen games when they make play-by-play calls and you can actually hear the call two or three times, due to echoes in the space," said Jack Randorff, an acoustical engineer who is the chief sound consultant at the convention site. "That's the sort of thing you don't want here, because that interferes with what we want in terms of good, clean speech intelligibility."

Those most likely to be able to hear every word from the podium are those outside the arena: the television, radio and online audiences. They'll hear sound broadcast directly from the podium microphone to a pool audio feed, shared by all broadcasters and webcasters. "It usually comes through very, very well," said Steve Stahl, who is supervising convention audio for CNN.

Acoustical engineer Jack Randorff is the chief sound consultant at the convention site.

Those inside the arena will face more of an audio challenge, especially those sitting on the convention floor directly in front of the central podium: the delegates and special guests. "And they're the people most likely to want to hear every word," said Randorff.

Randorff has helped facilitate Republican-to-Republican communication in the past: He was the acoustics consultant for the GOP convention held in the Astrodome in Houston in 1992 and the one held in the convention hall in San Diego in 1996.

Each venue, he said, has its own peculiarities and problems that his acoustical team has to overcome. In Philadelphia at the First Union Center, the problem is an unhappy mix of sound waves and heavy concrete walls. The invisibility of sound doesn't keep acoustic engineers such as Jack Randorff from visualizing sound as a physical object. "And you have to visualize it in three dimensions," said Randorff. "Because that's the way sound behaves."

So imagine a phrase such as "my fellow Republicans" or "no new taxes" as an invisible but three-dimensional object -- a boomerang, for example. As soon as a speaker at the podium says those words, they travel from the microphone through cables to amplifiers, through a console board and mixing panels, and then out through five curved arrays of speakers suspended from the arena ceiling.

Acoustical engineers have lined the ground-level walls with Fiberglas insulation under blue fabric.

The sound travels from the speaker array to the audience's ears. The problem is, sound doesn't stop at the audience: Sound keeps going until it dies out over distance, or hits something hard such as the arena's concrete walls.

"Concrete is a very hard, dense surface that sound bounces off, almost like a billiard ball would bounce off a hard edge," said Randorff, selecting from his broad range of sound metaphors. "Or if you think of a sound wave as a wave of water, it hits a wall and splashes back as an echo. Or if you think of a flashlight pointed at a mirror, that light would bounce right off and create a glare -- an echo is like an acoustical glare."

A bounceback echo acts as a kind of audio mugger, hitting those on the convention floor from behind, and robbing them of comprehension.

"If we have echoes, those echoes step on top of the spoken word, and then you can't understand it," said Randorff. "And if you can't understand the words here, there's no reason for a convention."

To avoid baffling the arena audience, acoustical engineers are baffling the sound: They've lined the ground-level walls of the arena with three-and-one-half inches thick Fiberglas insulation -- "the same type of material that you put in your attic for insulation," said Randorff.

The red carpet on the convention floor helps to absorb some of the sound.

Atop the insulation, they've stapled, glued and draped a large volume of soft blue fabric. The combined padding absorbs 90 percent of the sound; most of the rest is absorbed by a few miles of red carpet laid over the arena's cement floors.

Acoustics experts were unable to put any sound baffles on a long wall of green slate that serves as a backdrop for the podium, and that worries them somewhat.

"Slate's very, very hard," said Randorff. "If too much sound from the crowd hits that stage wall, it will bounce back and hit the speaker at the podium from behind as a giant echo, and that could really disturb them as they're delivering a speech."

Audio engineers are pinning their hopes on a final piece of padding that will be installed in the arena's seats as soon as the convention opens. "You throw in 20,000 or 30,000 people in there, and it absorbs a lot of the sound," said Steve Stahl, audio supervisor for CNN.

That leaves the audience inside and outside the hall to try to absorb the convention's message.