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Getting the feel of the Exploratorium

San Francisco’s Exploratorium is an immense (and immensely popular) hands-on science museum. Exhibits cover the usual range of subjects—electricity, physics, optics, biology, and so on—but with a degree of interactive friendliness that’s rare even in the best science museums (and I’ve seen quite a few). Almost everything is designed to be touched, played with, and experimented on—even by young children, whose destructive impulses know no bounds.

Although I visited the Exploratorium a number of times during the years I lived in San Francisco, there was one exhibit I’d never experienced but always been curious about: something called the Tactile Dome. This is an exhibit for which you must make an advance reservation (and pay extra), and I had never had the foresight to call ahead before visiting the museum to see if there was an open slot. But on one visit when a same-day opening came up, I immediately signed up—after listening to a short speech on all the medical and psychological conditions that would preclude a safe visit and consenting to the non-refundability of the ticket.

A Touching Experience

The Tactile Dome is a smallish geodesic dome within the museum whose stated purpose is to explore the sense of touch—taking the “hands-on” principle to its logical extreme. Inside the dome is a series of oddly shaped chambers lined with a variety of materials. The chambers are completely dark, so visitors must navigate through them—climbing, crawling, sliding, and squeezing—using only the sense of touch for guidance. In an anteroom the eight or so people who have reservations at a given time remove their shoes and any objects that might fall out of pockets and get lost. (They are quite strict about their “no-extraneous-stuff” policy; I wasn’t even allowed to take a ballpoint pen in with me, even though it was capped and sealed in a zippered pocket behind a Velcro flap. I thought that prohibition was a bit silly, but don’t say I didn’t warn you.) Then, in smaller groups (in my case, a group of one), you proceed into the dark chambers.

A complete trip through the dome takes anywhere from five to ten minutes, and guests are spaced far enough apart that they won’t run into each other. The inside of the dome is not a maze; every chamber has just one entrance and one exit. An attendant in the anteroom monitors your progress by listening to the sounds picked up by microphones positioned throughout the dome. If a visitor gets stuck or panicked, a verbal request for help is all that’s needed; every spot in the dome is immediately reachable by hidden access doors. The intercom (which the other visitors waiting in the anteroom can also hear) serves another purpose, too: to discourage, shall we say, extracurricular activities that the dark and solitary environment might suggest. Each group gets to go through the dome several times during their visit.

As I made my way through the dome, I found that even though sight was not available, it was not a purely tactile experience. Each time I entered a new chamber, I could tell something about its size and shape from the sounds I heard, along with the combination of temperature and airflow I could feel. Even smell played a part—the characteristic scents of carpet, wood, plastics, and the smelly socks of the person who crawled through the dome before me all contributed to a mental image. And that effect was a bit eerie—even though I couldn’t see anything, I had the distinct sensation of visual images of the rooms constructed from the other sensory data I was gathering. That impression alone made the experience worthwhile for me.

Copp-ing a Feel

The Tactile Dome was designed by Dr. August F. Coppola (brother of director Francis Ford Coppola) in 1971 and has been in use ever since. Not only in the choices of materials in the dome, but in its overall design and marketing, it’s definitely showing its age—or perhaps I should say, “revealing” its age. (Note that the photo above is from the early 2000s; the dome is now a more stylish black and has better signs, though the basic design is still the same.) By an interesting coincidence, the Tactile Dome is not the only dome-shaped, building-within-a-building attraction in San Francisco that was constructed in the 1970s and designed to be experienced in total darkness. Audium, located across town, shares all these attributes but was designed to explore the sense of hearing rather than touch. If there’s also a Smell-O-Dome lurking somewhere in the city, I’d just as soon not know.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on June 1, 2003, and again in a slightly revised form on July 5, 2004.

Benjamin Franklin was born on this day in 1706. He was, among many other things, a scientist, an inventor, an author, and a diplomat. He led a fascinating life, full of discovery and profound thought, and is certainly among my heroes. (Like all heroes, he was also flawed, but by today’s standards he was practically a saint.) Today, as I take my child to Benjamin Franklin Elementary School (no kidding), I’ll be thinking about the accomplishments and insights of this beloved figure from American history.

Image credit: After Joseph Duplessis [Public domain]

3D audio with just two speakers

I’m old enough to remember when the term high fidelity still meant something—it set apart audio equipment that had been deliberately engineered for faithful sound reproduction and a high signal-to-noise ratio from cheaper, cruder devices. At a certain point, though, pretty much everything was considered “Hi-Fi”; the new buzzword was stereo. Having equipment and recordings with two discrete channels of audio—conveniently matching the average number of human ears—was seen as the new sign of audio competence. Then there was the shift from the analog world of tubes, tapes, and vinyl to digital—a new standard of audio quality. A few years later, yet another phase: an increasing number of carefully positioned speakers and subwoofers to simulate the 360° audio field of the cinema. And now we’re using sophisticated digital signal processing to get better results with fewer speakers, but most people still seem to think two is too few.

For Those Who Have Ears to Hear…

While the number of speakers in the typical living room has increased since the days of my youth, the number of ears on the typical head has not. Humans somehow have the ability to locate the source of a sound spatially with only two inputs; even with a single ear, most people can pinpoint the direction a sound is coming from. Crucially, this sound-locating ability is not restricted to a single plane; we can also determine if a sound is coming from above, below, or anywhere in between (not to mention in front and behind). No home audio system I’ve ever seen (or heard) addresses the Z axis (up and down)—and neither, for the most part, do cinemas; for the most part, the only way to experience truly 3D sound artificially is to go into a special environment such as San Francisco’s Audium where speakers are physically placed above, below, and all around you.

If humans can determine the location of a sound anywhere around them with just two ears, it’s reasonable to imagine there must be some way of reproducing spatially accurate sound with just two speakers. But what’s the trick? What can ears and brains do that microphones and speakers can’t?

The Ears Have It

A large part of what enables people to identify the position of a sound is attributable to the hardware—the unique shape of the ear folds and ear canal. Because sounds coming from one direction will be reflected and channeled into the ear canal with slightly different characteristics than sounds coming from another direction, the brain is able to use these subtle clues to unconsciously create a mental picture of where the sound must have originated. While digital signal processing equipment can add depth and spatial separation to a stereo signal, there’s a much different and older approach to solving the problem: a method of recording known as binaural audio. A binaural recording is made with two microphones and a two-track recorder, just as a stereo recording would be. The difference is that the microphones are placed inside a dummy head—shaped just like a human head, complete with rubbery ears, sinus cavities, and so on. The microphones are right where the eardrums would be, so the signal they pick up is much closer to what ears would hear. The resulting recording—always most effective when heard through headphones—produces a vastly more accurate spatial rendition than would be achieved by using a pair of conventional microphones.

A well-executed binaural recording can sound shockingly realistic, even if the sound quality itself is not pristine. But binaural recording is appropriate only for live recordings; it’s also inconvenient, expensive (some pro-quality dummy heads retail for over US$8,000), and, frankly, just plain weird—all of which, along with the fact that you need to listen through headphones for maximum impact, helps to explain why you don’t encounter such recordings very often.

Hooked on Holophonics

But there’s a clever, patented variation on binaural recording that claims to go far beyond the simple microphones-in-the-dummy-head approach. It’s called holophonic recording, and the realism it produces, especially in the up/down dimension, is uncanny, eerie…even—as a friend of mine likes to say—freakadelic.

Ordinary holograms are produced by mixing reflected laser light with a second beam hitting an object from another angle; the resulting interference pattern of the two waves is what’s actually recorded on film. Expose the film to the same wavelength of light again, and a 3D image emerges from the interference pattern. Italian inventor Hugo Zuccarelli wondered whether a similar process could be used to record sounds, since after all, sound waves can form interference patterns with each other just as light waves can. His holophonic process starts with a type of binaural dummy head, but it reportedly records the interference pattern formed by mixing the sound with an inaudible, digitally superimposed reference signal. Zuccarelli believes that the human auditory apparatus, when listening to sounds, adds the same signal to the input, effectively decoding the interference patterns previously recorded. All that may sound like a bunch of mumbo-jumbo—and Zuccarelli certainly has detractors who claim “holophonic” sound is nothing more than binaural with maybe a few bells and whistles. All I can say is: hearing is believing. The holophonic recordings I’ve heard are simply remarkable—much more impressive than conventional binaural recordings—but I encourage you to listen for yourself (remember, use headphones!) and form your own opinion.

There is, of course, a little snag. As with all binaural recordings, holophonic sounds lose most of their spatial characteristics when played through ordinary speakers (though Zuccarelli has designed a special speaker system that enables holophonic sounds to be appreciated even outdoors by a large audience). As things stand now, you won’t be able to enjoy a holophonic soundtrack on your home theater system—no matter how many speakers it has—unless you and everyone else watching the film wear headphones. Nevertheless, a number of recording artists, including Michael Jackson, Stevie Wonder, and Pink Floyd, have employed holophonic technology in recordings or concerts, and it has also been featured in both films and commercials. Holophonic sound may be slow to catch on as a mainstream technology, but it’ll make your Surround Sound system sit up and go “Wow.”

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on July 17, 2003, and again in a slightly revised form on October 12, 2004.

Image credit: U.S. Patent and Trademark Office

If you’re sick and tired of all these daily observations of anything and anyone (whether serious or silly), today, January 16, is just for you. It’s National Nothing Day, a non-holiday to not celebrate a non-event—and has been since columnist Harold Pullman Coffin declared it so in 1973. So you don’t have to do anything, or celebrate anything, or protest anything today. If you have to watch TV, maybe you should watch the show about nothing, or just go around quoting your favorite line from Game of Thrones.

Image credit: darwin Bell from San Francisco, USA [CC BY 2.0], via Wikimedia Commons