A few years ago a friend of mine had finally had it with the wide, flat habitat filled with critters that was his living room. Specifically the carpet. In Hawaii there’s just no way to keep a carpet clean…and completely unoccupied. He threw his hands in the air, slapped his wallet three times (there’s no place like home, there’s no place like home with no carpet) and had the whole thing tiled. There were two immediate and long-lasting effects that I noticed the first time I spent a Sunday morning at his place watching football. First, every time someone opened the fridge, the dog (certain that there was something edible coming his way) would come rampaging through the room and do a full-on NASCAR 4-wheel skid into the wall trying to make the corner. It was just a tornado of flailing paws, spinning tail and wagging tongue (that never gets old; it’s funny every time). The second thing was that it got LOUD IN THAT ROOM. The flap of rubber slippers sounded like somebody dribbling a basketball in a gym. Hard. He ended up getting some area rugs to dampen it down and make it livable.
It got me to thinking about the different venues that the Windward Choral Society has visited as well as the science behind where the sound all goes. It turns out that there is a Sound Absorption Coefficient (SAC) associated with pretty much any material. It varies with frequency* on a scale of zero (doesn’t absorb squat) to one (where sounds go to die) and explains a lot. For example, the only thing with a coefficient of 1.0 is nothing. As in open space. As in the mauka side of the sanctuary at Kailua United Methodist Church. So THAT’S why nobody in the back can hear.
Another great slurper of sound? Humans. Especially in herds. Our audience has a SAC somewhere around 0.6, meaning that 60% of the sounds ends up inside them. Somewhere in the middle are things like soft wood at 0.28 (which is why St. Ann’s is so nice), window glass at 0.35 (which is why the Rose Auditorium up at Chaminade sounds like it does) and plain ol’ sheet rock walls at 0.29. These surfaces take the edge off a little and reflect back enough to make a joyful noise just the one time instead of bouncing around for a while so we here it over and over (echo…echo…echo…). I could get into the whole overtone and tone depth thing but that’s got too much math. Trust me, a SAC between 0.25 and 0.4 is perfect.
What about the other end of the scale? What is it that absorbs nothing and throws it back like a tennis ball with some Serena steam behind it? There’s a clear winner, the lowest SAC on the planet at a miniscule 0.008 but I want you to guess at that one. Concrete blocks are great sound suckers at 0.36 but put a coat of paint on them and they become a booming 0.1, which is also the SAC of a smooth concrete floor. My buddy’s glazed tile floor? A bouncy 0.01. No wonder it sounded like we were AT the football game. The linoleum kitchen floor that we all remember if we’re of a certain age is a nice and noisy 0.02, which is the same SAC as brick.
So why do we care? Because we’re doing our December 13 concert in a parking garage. Let’s see:
– Concrete overhead is 0.1. Boing.
– Painted concrete wall on one side is also 0.1. Boing, boing.
– Open air on the other side at 1.0. See ya, bye-bye, thanks for coming.
I suspect that the boings are going to win as the sound begins and it’s gonna be LOUD. I also suspect that the echo factor will be reduced by the open side. The wild card is the buildings that surround the open spaces…THEY might bounce the sound back in (speed of sound divided by the distance there and back, carry they one, scratch my head, crumple up the paper) less than a second but still out of synch with what we’re doing. The lesson here is that we’ll really need to be on our game. If the sound is goofy our best (only) weapon is concentration on Susie and not losing track of Joanne on the piano. The good news is that, if we can do that, I believe that the acoustics in that place are going to be seriously awesome. I hope I’m right because it’s really the only venue where we can’t ever run out of room for an audience and places for them to park. Wouldn’t be great to finally have our own “home field”?
And have you guessed what the lowest SAC number belongs to?
A nice smooth pile of water. No wonder you can hear fog horns for a zillion miles. And yes, there’s a whole different dynamic UNDER the water but I don’t care. I’ll be singing there the day after I grow gills and I don’t see that happening any time soon!
* I’m using a comparative scale because just LOOKING at the whole frequency/SAC table made my head hurt. The numbers change but not much.