Scuba diving is about minimizing distraction, but you wouldn't know it from looking at a scuba diver. Ignore the standard equipment, the buoyancy compensator, the regulator that seems at first a limitation but soon a comfort, the huge tanks of compressed air. Divers are rarely content with just the essentials. Soon every spare D-ring holds a new contrivance. Lights to counteract the red-sapping murk. Spare air in cans of dubious capacity. Swinging knives that swell from utility to shark-dueling length.

So why would you want to add an iPod? Because, like all those seemingly superfluous bits of tinsel, sometimes music is exactly the tool a diver needs to make a mundane dive as otherworldly as the very first splash in the water.

H2O Audio makes iPod cases, more or less. And unless you spent first-grade science period inattentively carving carnivorous plants into your notebook, you can probably guess the mythical element in which those cases are designed to operate. (Hint: It's fire.)

Most of their product line is really more splashproof than waterproof. That's not an indictment—I strapped one of H2O Audio's Amphibx iPhone armbands around the tan biceps of a Bulgarian kiteboarding instructor in Hattaras just a week ago; a 15-foot depth rating was plenty to make him smile.

But 15 feet underwater for a scuba diver barely registers. (At 15 feet, I'm hardly done panicking about the fact that I'm breathing out of a rubber trachea.) Most recreational, consumer underwater gear will get you to around 30 feet, just under one atmosphere of hydrostatic pressure, twice the pressure one feels at sea level. If you're lucky you'll see a rating for something around 130 feet—four atmospheres, and beyond the limits of recreational diving.

That's why it's all the more impressive that H2O Audio's iDive300 works all the way down to 300 feet—over twice as deep as I've ever been, or ever will be.

That makes the iDive 300, which would just fit into an empty carton of cigarettes, useful to even those deep divers who have to take long nitrogen decompression stops, giving them something to do while resting on ascent lines, sometimes for hours, as the nitrogen leeches from their blood and is exhaled. Listening to music or watching movies is more feasible than smoking that carton, though Lord knows I've tried.

For the recreational diver, though, the iDive 300 adds more complexity. The positively buoyant case strains against its lanyard, popping into your face at inopportune times, or, as I discovered after strapping it to a D-ring low on my vest, bobbing up between your crotch, making a simple volume adjustment maneuver into an especially awkward moment for your dive buddy as he watches you probe between your legs, searching for something you can't quite grasp.

You could mitigate this by strapping weights on the iDive 300, slipping it into the pockets of a BC with weight, or lashing it onto an arm. It's a big hunk of extra equipment—large enough that every diver will want to find their own method to stash or secure it.

The iDive 300 is large because of the extra electronics onboard. This isn't just a simple Lexan case. A circuit board runs the entire length of the bottom half, wedding the standard Apple iPod connector to a set of spring-loaded controls that run along the spine like trumpet valves, as well as a chamber for the three AAA batteries necessary to power the underwater speakers—an iPod's headphone jack won't make nearly enough juice to power the integrated clip-on headphones, especially deep underwater where the pressure makes the speakers work all that much harder to vibrate.

And they're definitely speakers—silver-dollar-sized with no padding, large holes to let out the sound, connected to the case by integrated rubber cords about four feet long that can't be detached. A plastic clip is screwed on to the side of each, designed to allow the speakers to be threaded through the straps of your mask; I chose to slip them inside my hood—clips and all—once I was underwater.

I didn't have to just jump in with the cords and speakers flying, thanks to the considerate dive operator running the liveaboard dive boat off Catalina in California's Channel Islands. Instead of making us jump off the boat with all our attendant gear, one of the deck hands would lower our cameras and other delicate gear down to us on a line after we were in the water. Like all sensitive dive gear that must maintain a seal, you'd want to be very careful about catapulting in with the iDive 300 simply clipped onto your body.

If you can stomach the rollicking seas, a liveaboard is a wonderful way to dive: Full red moons oozing into a starless night; divers in dry suit underwear on the deck enjoying an adult slumber party; beautiful galley girls with long legs and marble-mouthed accents; tan, lean crew in folded down wetsuits and broad grass coolie hats; rocks jutting up along the coast painted white with gull shit; shivering divers crawling onto deck to gulp steaming coffee in full sun; tales of a boat named "Fujimo" (as in "Fuck You, Jane, I'm Moving Out"); long flies with wings like post hole diggers; a 10th-grade English teacher wearing sweatpants with "Soul Mate" stenciled on the ass.

Yet thirty divers plus crew on an 85-foot boat can make a man antsy: the pervasive overtone of urine like a seaborne nursing home; charmless, cantankerous Jimmy Buffet fans who use bravado and volume in lieu of wit, inexplicably crowning "Margaritaville" as "real music" but honking beardful laments about the corniness of Captain & Tennille; every spare inch filled with piles of gear, cameras and knives and lights and spare cans of air and extra sets of wet suits in case dry suits flood; shamefully little alcohol.

By the time I tested the iDive 300 on my second full day of diving, I was ready for a transcendent experience. The giant kelp forests were fascinating on the first day—as a tropical diver I'd never experienced anything like them—but the dives were quickly becoming unremarkable, and a cold lassitude had already begun to infect my dives. Splash in, drop to forty, watch the legally unmolestable garibaldi wave their sexy orange caudal peduncles in my face, bop around the rocks and through the kelp, rinse, repeat.

I affected an air of what I hoped would be perceived the other divers as seasoning before I jumped in with the iDive 300.

"Seems like a pain in the ass to me," I groused. "Just one more thing to break." The other divers on deck responded in kind, mostly preoccupied with their own pre-flight checklists. "Don't know why you'd want to even listen to music, really," I said to their backs.

And I was right—it was a huge pain in the ass. At least at first, with the headphone cords whipping around my head very much like kelp; the case itself trying to spring to the surface, twisting the screen of my iPhone upside down; the music at once blaring and then fading to muddled distortion as my middle ear pressure equalized. (Truth be told, I could never quite figure out why the volume would vary so much, as it would often fluctuate even while I remained at a consistent depth. There's something about the way the speakers make pressure and sound that I don't quite understand.)

Worse, the music I had chosen, a sort of dancey indie rock thing, was driving me crazy, not unlike the way favorite songs can raise hackles when you're on a road trip or slightly high.

My brief review of the controls on the surface was enough to make it possible for me to scan through my iPhone's music selection and find something else while my dive buddy patiently waited. Pressing the "Mode" button at the top flips between, well, modes. When there's an iPhone inside the iDive 300, modes are basically just different sections on the iPod and—for some reason, because you can't actually view any—Photos.

There was a weird guilt in changing my music selection at first: partially because I did not yet trust the integrity of the iDive 300, so every button press felt like an opportunity to send water flooding around my overpriced iPhone that I couldn't really afford to replace; it also felt bad to be wasting air sitting at the bottom just trying to find something to play.

But then I found the right album.

Silent Shout, by weirdo-fashion-electro brother-and-sister producers The Knife—metallic panoramic sweeps and spare dewdrop synths meted out with haunted Swedish meticulousness. In an instant my miserable one-man undersea dance party metamorphosed into an investigation of an orange, impish forest. No longer feeling as if a band were chiding me for not dancing while I was trying to keep my attention focused on not breathing water, my awareness spread wide into the water like dye, the music slipped into soundtrack, and I was parting kelp curtains to enter backlit algae cathedrals and bending my androgyne form into gloomed dells like a Miyazaki spirit.

So it works, if you get all the kinks worked out.

The iDive 300 won't be added to my standard diving rig. The less gear the better—and simply by dint of what it is, the iDive 300 adds a lot of complexity that I can't imagine will be welcome on every dive. (My second dive with the iDive 300, listening to an episode of The Bugle, was a bit of a drag. No fault of Zaltzman and Oliver, of course—they're simply an above-sea-level indulgence.)

Still, for generous divers, passing the $350 iDive 300 around for specialty dives would be a noble act. Every diver should try listening to music underwater at least once.

Sturdy, simple design

Only iPod case rated for such extreme depths

Offers an experience beyond that of most dive gear

Expensive (costs more than an iPhone)

So large that it can get in your way

Headphone cables add two more wavy bits around your mask and regulator

[H20 Audio]