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Treebeard's Stumper Answer
25 October 2002

The Sound of Sound

We listened to gospel music and a distinguished speaker last Friday at a local college indoor gym. It was a great show, but we all felt that the sound was not right. Dunn Middle School kids described it as: "too loud," "too much echo," "distorted," "could not understand what they were saying," "not clear," "hard," "fuzzy," "boomy," "echoey," "blended," and "annoying." I reckon the real problem was that it sounded like a gym. You know what I mean. Why do gymnasiums all sound that way? The problem isn't volume, but being intelligible. What would make it sound better?

The scene of the crime is the local community college Sports Pavilion in Santa Maria. It's a basketball-sized gym with wood floors and bleachers and mostly bare walls. The gospel choir and band have their own speakers on stands behind them. They also fed the sound through the black P.A. speakers on the ceiling. That's us in the foreground seated opposite a second set of ceiling P.A. speakers not quite visible to the right of the photo. There was great gospel music and good words, but why was it so hard to understand in the gym? What would make it better?


An opera singer can fill an auditorium with just one voice. But gyms are noisy places built for sports. Very little sound energy travels directly from the source to our ears. The rest bounces off the hard wood walls and seats creating echoes and background reverberation that takes seconds to die down. The gospel choir had their speakers at the far end of the gym, but they also used the overhead P.A. speakers that were closer to us, which made the echoes even worse. Acoustic engineers earn their keep by designing sound systems that are clear and intelligible.

Notes:

"If you remember the 60s, you weren't there." WelI, I do (vaguely) remember seeing Jimi Hendrix and the Airplane and the Doors in the UCSB Robertson Gym, and the Yardbirds at the Earl Warren Showgrounds back in the late 60s, all with such terrible sound that I could barely listen. I also (vaguely) remember seeing the Grateful Dead and the New Riders of the Purple Sage together outdoors at UCSB in 1974 when the Dead had their original "Wall of Sound" sound system. The sound was clean at the stage and a half-mile away in Isla Vista. That's good acoustics! I find it amusing that kids learning electric guitar always turn up the distortion control when the real sound problem (and expense) is to eliminate the distortion.

I'm sure the echoes were the problem at the gospel choir concert in the college gym last week. It was like trying to see in a house of mirrors. There were too many confusing reflections.


Jim Anderson photo of the Dead's Wall of Sound
circa 1974. There's a technical description here.

But that's not the whole story. Echoes are also why we sound so good singing in the shower or playing guitar in the college dorm stairwell late at night. With an electric guitar amp, it's irresistible to turn the reverb up a notch to sound "more natural". I remember visiting an anechoic chamber at UCLA many years ago that was carefully designed to have no echoes. It was a very strange experience, like someone was pulling the words from my mouth and tossing them away too soon, definately not natural. The real challenge of acoustics is to get the right amount of echos at the right time to enhance the sound rather than destroying it, no matter where you are seated.

I don't have any easy answer for this stumper. If I did, I'd be consulting as an acoustic engineer myself!

Gyms, churches, and new movie theaters are all built long and high, so it's interesting to compare how they sound. I was at the Santa Barbara Riviera Theater last night, and I noticed that the physical room was very similar to the college gym last week: longer than wide, main attraction and speakers up front, and extra speakers on the side walls. I couldn't hear the side speakers at all from my center seat, though I assume they were adding to the sound. The college gym sounded very different.

I think the biggest problem at the gym was the overhead speakers. We were seated at the far end of the gym, so we heard the ceiling P.A. speaker before the band. We locate a sound by what we hear first. Any echoes that arrive within about 50 milliseconds will reinforce the sound, but any later echoes are perceived as confusing separate sounds. Sound travels about 1130 ft/sec, about 60 feet in 50 ms. A college basketball court is 84 feet long with more at the ends, big enough to be a factor. I got to move around during the gospel concert to take some photos, and I noticed the sound was much clearer up front without the distracting overhead speakers. It would have been a better show without the P.A.

Graybear wasn't there, but he had the same thought:

If the gym is to be used as a concert hall/auditorium, it needs acoustical dampening material on the walls and ceiling... especially the ceiling. It appears to have masonry walls, which don't move much by sound waves, but that metal roof can really distort sound. Also, I believe it would have been better if they had used the stage speakers only, and not tried to pump the sound through the ceiling speakers. I remember pep rallies at my high school... It's a good thing the principal said the same old stuff each time, because no one could understand a word that he said.

Acoustic paneling in the gym would definately help. Any empty room in a new building sounds "echoey", but rugs and sofas and bodies help by absorbing and dispersing extra sound reflections, and acoustic panels and reflectors are even better. Sophisticated (and expensive) electronic delay lines in the P.A. system could delay the overhead speakers a few milliseconds so that the stage sound still arrives first even at the far end where we were seated. But there is no left-side stage at a basketball game, so that's not usually an option in a gym designed for sports.

Audience noise echoes around the auditorium as much as the performance. Audience noise can even be a feature, e.g. the UCSB Thunderdome where the decibels can reach jet plane levels and the local fans are proud of it. Concert halls are different. I know I automatically hold my breath during the quiet moments because those moments really are breathless. The audience noise (and lack of it) makes a big difference in the listening experience.

It's like pulling off the freeway to a stop sign and suddenly realizing that the car radio is blasting. Of course it's been blasting the whole time, but you didn't notice. We need the signal to be louder than the noise, and our ears have a remarkable ability to filter out the background noise. Sound can be painfully loud and we don't even notice. But I think my body feels it even while my ears accommodate it. I get tired and irritable when the sound is too loud, and I get headache and ringing in my ears afterwards. Over time that ringing doesn't go away, and I do have a bit of that permanent ringing that becomes tinnitus. I worry that kids growing up with Walkman-style headphones will have a worse problem when they're my age. Good acoustics means lower volumes. It's a health issue.

I asked the Dunn Middle School kids to describe the gospel concert after the show. Along with "echoey" and "boomy", a few kids pointed out that it was easier to hear the ladies than the men. There's a cluster of interesting questions here about sound pitch:

I'll save these for future stumpers!

Here are some Web links for more research on acoustics:

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Copyright © 2002 by Marc Kummel / mkummel@rain.org