Thursday, April 26, 2012

The Whisper Dish Gets a Pilot Seat

Our visitors were having problems with the Whisper Dishes. I'm talking about two huge, aluminum satellite dishes in our East exhibit gallery.

If you stand with your ear at the focal point of the paraboloid formed by the dish, you can hear a whisper from across the museum. It's really fantastic. The dishes even have a stainless steel attachment that helps our visitors know where the focal point is.

If you speak into this ring, the sound bounces off the dish and collects at the focal point of the other dish. This happens because a sound that originates at the focal point will bounce off the dish and travel perpendicular to the direction the dish is pointing, every time. This is why your paraboloid-shaped headlight reflectors cast a forward beam, and its this effect that allows a satellite dish to gather information beamed from space.

Ok, back to the problem with the Whisper Dishes. For a 12-foot dish like ours, the focal point is about 5 and a half feet off the ground. It's the perfect height if you happen to be a person around 6 feet tall, like me. Everybody else needs to get their mouth and ears a little higher or a little lower. Generally, children will grab a stool from nearby and stand on the stool to access the focal point. This is fine; we even have stools specifically designed for standing upon.

Now, it's much easier to climb atop a stool if you have something to hold on to. So, our visitors would grab on to the focal point ring to steady themselves. That's the problem.

With each chin-up, the apparatus becomes more and more bent. Eventually, one of them broke. I welded it back together, but it broke elsewhere. So, my goal was to develop an alternative method for visitors to access the focal point.

At first, the exhibit team thought about building a standing platform with a hand rail. I studied our visitors habits and found some interesting design roadblocks to the platform theory:
  1. The focal point needed to be accessed by people of all heights; toddlers, children, and adults. A standing platform for children would be as tall as a stool, but adults using a platform that tall would be required to lower themselves to the focal point by stooping or kneeling.
  2. The focal point was frequently shared by more than one visitor. We witnessed school children in groups of two and three standing on stools and competing for the focal point. A standing platform would need to accommodate several people, otherwise it would be used unsafely. This meant the platform would need to be, well, pretty wide and deep.
  3. A handrail around the platform would need to surround all sides of it, otherwise it is a fall hazard.
  4. Pre-school children on platforms are usually accompanied by an adult at arms' length away, because the potential for falling off the platform makes parents anxious. A platform of sufficient size to accommodate several children, and deep enough to not be a fall hazard, will be too deep for a parent to stand at arms' length, unless they, too, stand on the platform. 
  5. A platform will require stairs, which can be climbed by crawling infants. And crawling infants can fall down stairs. So, I will need to invent some clever anti-baby stairs.
My study revealed another visitor phenomenon: many people faced the wrong direction when using the dishes! Without any kind of cue to face toward the dish (and away from your partner across the room), many people turned inward and found that the dishes did not work. So, I began to think about ways to get people to understand how to face the right way, without explicitly saying so with a graphic element of some sort.

This thought experiment prompted me to begin a series of drawings for investigation. Working out some design elements with drawing would ultimately determined the overall form of the prototype.

I began thinking about using bicycle handlebars as an attractive and recognizable place for hands to rest, therefore showing the visitor which way to face.

Next, I realized it could be possible to move the visitor's mouth or ear away from the focal point with some sort of sound tube. Physical prototyping began, and the result was a PVC device and the coining of a new word: the "audio-periscope."

Ultimately, I decided the PVC pipe had good sound quality and made it possible for a standing child to use the whisper dish without climbing anything. Now there is no risk of falling! I also discovered this allowed the user to change the direction of their voice, enabling the user to face the other dish and see their partner(s) across the room.

After that, it was simply a matter of choosing prototype materials that were visitor-friendly and putting it all together. Here's the working prototype, and it has survived a lot of abuse in the last two months!

And here's a video! Enjoy!


  1. Excellent! I'm proposing a whisper dish project for outdoors in a park. Do you know what range it will have for a 2 meter dia. dish?

  2. Hi,

    Great project. I'm looking to install some whisper dishes in an arts festival. Could you tell me who made these for you?