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Sound science

BY NICK STREICHER
For the Daily
Published April 10, 2007

Despite having the largest seating capacity in the country, Michigan Stadium has a reputation as having one of the quietest crowds in the Big Ten.

Jessica Boullion
Graphic: ASHLEY DINGES SOURCE: University architect Doug Hanna

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University architects hope that the proposed renovations to the 80-year-old structure will change that.

The controversial $226-million project includes skyboxes that will increase the stadium's volume by reflecting the crowd's noise back onto the field like a satellite dish.

Crowd noise is a crucial part of a team's home field advantage. A loud crowd can disrupt an opposing team's offense ability to hear their quarterback's instructions on the field.

The University is working with Architecture Prof. Mojtaba Navvab - who was also a consultant on the acoustics of Hill Auditorium - to evaluate the acoustics of the renovation plans.

During one game last fall, Navvab stood just off the 50 yard line and took readings of the noise level.

He found that the volume ranged between 77 and 87 decibels - about the same noise level as a loud office.

Using computer models of the renovation plans, Navvab predicted that the volume in the stadium will increase to a range of 85 to 95 decibels - just under the volume of the inside of a New York City subway.

That means the stadium would sound almost twice as loud as it does now.

Navvab said that even with the increased volume, much of sound perception is psychological, so it is difficult to predict how the fans and players will react.

The computer models are based the geometry of the stadium and assumptions about where different levels of noise will come from within the stadium.

In November, the University Board of Regents approved preliminary schematic designs, including skyboxes that would run the length of =the east and west sides of the field. The skyboxes will be 10 feet higher than the scoreboards at either end of the stadium.

The University Board of Regents must vote once more to approve detailed schematic designs and grant construction approval before the proposed renovations can begin.

Doug Hanna, a University architect working on the renovations, said the skyboxes will make the stadium louder because the angle of the skyboxes will reflect crowd noise back onto to the field.

John Pollack, who founded Save the Big House, a coalition against the proposed renovations, has developed a counter-proposal that would add 10,000 seats to the bowl, something he said would raise the noise level.

"You put 10,000 screaming fans into the stadium that makes them louder - guaranteed," Pollack said.

Hanna, though, said nothing in the current stadium prevents the noise from escaping the bowl, so cheering louder would have little effect.

Hanna said the skyboxes will create two new paths for sound to travel - one from the fans in the bowl to the skyboxes back down to the field and one from the fans in the skyboxes to the skyboxes on the other side and back down to the field.

Hanna said angling the skyboxes is done primarily to reduce the glare from the sun reflected onto the field but could also amplify the crowd noise.

The greater the angle, the more the sound will bounce back, Hanna said.

In the most recent plans, the skyboxes will be tilted 9 degrees inward toward the field. The angle is limited by structural stability of the skybox and the windows, which wouldn't open easily at a larger angle, Hanna said.

When Penn State University and Ohio State University renovated their stadiums earlier in the decade, the schools did not put any special consideration into the acoustics, officials from both schools said.