Understanding how underwater sound systems function and the technology that makes them possible.

Harry Houdini's legendary Chinese Water Torture Cell was hardly a comfortable work environment. Not only did it suspend the person upside down in cold water, but listening to music inside was out of the question.

At least that was the case during the 1910s and 1920s.

If the famed escape artist were alive today, he could take advantage of specialized underwater earbuds. Even better, he could equip the entire torture chamber with an impressive underwater sound system. With some AC/DC blasting, it’s likely he could shave off a minute from his escape time.

But let’s face it, you’re no Harry Houdini, and you're not earning a living inside a theatrical drowning chamber. However, underwater sound systems still play a significant role outside the realm of professional illusions.

Consider the world of water dancing. Synchronized swimmers need to hear their music while practicing their craft. In fact, Lubell Labs, one of the oldest makers of underwater speakers, began after a successful product demo at the 1970 National Senior Synchronized Swimming Championships in the U.S. [source: Lubell].

Lap swimmers, scuba divers, marine biologists, cave divers, and underwater film crews all benefit from underwater sound systems. It’s the ideal solution for 18 divers to communicate on an underwater movie set. The technology is also used for communicating with whales and keeping fish away from polluted waters.

So slip into your favorite high-cut swimsuit, secure your ankles, and get ready to submerge yourself into some hi-fi sounds.

Funky Tunes for Your Pool

Is it really possible to hear music underwater in a lake or pool? Absolutely.

Sound moves through both air and water. In fact, sound waves travel 4.3 times faster underwater than in the air [source: NOAA]. Whales and dolphins use sound to navigate and communicate in the ocean, while humans rely on sonar (sound navigation and ranging) technology to map the ocean floor and track animals and ships.

Despite all our submarines and diving gear, humans are creatures of the land. We’ve evolved to interpret sound data on dry ground, which is why we don’t hear as well at the bottom of a river—though some divers have developed the ability to perceive ultrasonic sounds underwater.

Take Parliament's classic 1976 hit "P. Funk" for instance. As frontman George Clinton emphasizes in the lyrics, the song is "doin' it to ya in the earhole." The sound waves vibrate the audio bones in our inner ear, which we refer to as air conductivity hearing. However, when you're underwater, the outer ear fills with water, preventing those vibrations and essentially blocking your air conductivity hearing ability.

Luckily, George Clinton and his band don't just target our ear bones; they also send it through our skull bones. This is known as bone conductivity, where sound is transmitted to the inner ear via the bones of the skull. Although this method is about 40 percent less effective than air conductivity, it remains the main way we hear underwater [source: NOAA].

What does it sound like? Due to the limitations of bone conductivity, stereophonic sound becomes impossible underwater. The skull acts as a single point of sound transmission, unlike air conductivity hearing, which provides two channels—one in each ear. That doesn’t mean the sound is monophonic; rather, it's what Stanford University music researcher John A. Maurer IV referred to as omniphonic sound [source: Maurer].

In a swimming pool, rapid sound waves travel from the underwater speaker, bouncing off the pool's bottom, water surface, and sides. The sound reaches the listener from multiple directions, and the brain can no longer pinpoint the original sound source.

The typical range of human hearing spans from 20 hertz to 20,000 hertz. Some underwater speakers, especially older versions, can't produce sounds below around 1,000 hertz. To put that in perspective, the lowest and highest notes on a standard 88-key piano are 27.5 hertz and 4,186 hertz. However, underwater speakers like the Clark Synthesis Diluvio use voice coil technology—a coil of wire acting as an electromagnet—to reach wavelengths as low as 20 hertz.

Speakers From the Depths

Standard speakers don't perform well underwater, so underwater speakers are specifically engineered not just for quality sound in submerged conditions, but also to avoid issues like short-circuiting, electrocuting swimmers, or disintegrating.

This is a specialized segment of the audio market, with prices ranging from $300 to $2,000 for a quality underwater speaker. These usually feature a waterproof plastic speaker, connected to an above-water sound system through insulated wires. You can opt to install it inside the pool alcove, where an acoustic sound lens directs the sound into the pool, or simply suspend it by a rope into the water.

An underwater speaker doesn't deliver optimal sound above the waterline. It might sound quite poor. Clark Synthesis President Bill Phillips compares a quality underwater speaker to a fine wooden instrument like a cello or violin. The sound emanates across the entire surface of the speaker, rather than focusing on one specific point.

The coverage area of water a speaker can handle depends on the model. For example, Clark Synthesis suggests one Diluvio pool speaker per 20-foot-by-20-foot (6-meter-by-6-meter) section of the pool. The Lubell System 3300 Diver Recall System, designed for use on dive boats, can emit a siren that is audible across a 1-mile (1.6-kilometer) underwater radius, provided the conditions are ideal. These dive speakers allow instructors to communicate with divers, but they can also deliver funky music for both humans and marine life.

The Sound of Underwater Music

Jacques Cousteau may have named it "the silent world," but clearly he never considered playing "Yellow Submarine" from the depths of the Calypso.

Every year, divers gather at Florida’s Looe Key Reef for the Underwater Music Festival, with boat-mounted Lubell speakers blasting tunes to over 300 divers and snorkelers [source: Lower Keys Chamber of Commerce].

But it's not all about classic rock and adventurous scuba divers. French composer Michel Redolfi has carved out a niche in underwater music. His albums blend natural ocean sounds with electronic atmospheres to craft soundscapes purpose-built for underwater listening.

Redolfi's performances, as you might expect, usually take place underwater — often in pools, but sometimes even in the ocean. His 1984 album "Sonic Waters" features hydrophone recordings of an original electronic piece transmitted through the waters off the coast of La Jolla, California. Teaming up with music engineer Daniel Harris, Redolfi unveiled several musical instruments made solely for underwater use, such as the SOSNO underwater percussion instrument (named after its creator) and the electronic DUCS (Digital Underwater Controller System). In 1992, his opera "Chrysalis" even involved a soprano submerged within a 2-ton plastic bubble.

But Redolfi isn't the only one experimenting with underwater opera. In 2009, Juliana Snapper premiered in an opera titled "You Who Will Emerge from the Flood." The performance occurred in a swimming pool in Manchester, England, where Snapper employed a unique "mouth-to-water" singing technique that demanded rigorous research and "hours submerged in my bathtub and borrowed pools" [source: Helmreich].

Not to be outdone, German swimmer-turned-opera singer Claudia Herr made her debut with the underwater opera "AquAria Palaoa" in Berlin on May 1, 2011. The completed work merges opera, underwater music, and synchronized swimming.

Yet all Harry Houdini would have experienced inside his Chinese Water Torture Cell would have been the muffled sounds of the outside crowd and the clink of his chains.