J & A Enterprises, Inc.
Noise and Vibration Control Engineers

16 Broadway
Salem, MA 01970
01 + 978-741-1551
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The underwater acoustic environment is quite different from the one most people experience as part of their daily lives. J&A Enterprises is happy to bring a sampling of various sounds that fill the ocean ... natural .... and man made.

The physics of underwater sound creates effects that the uninitiated might find unusual. For example, sound speed varies with depth creating a "SOFAR" channel that traps sound allowing it to travel thousands of miles. Whales use the sound channel to communicate over vast distances. Among man's first uses of this phenomenom was the location of downed aircrew. By detonating a small charge in the SOFAR channel, downed aviators could send a signal thousands of miles to underwater listening ranges. Operators at these ranges could use the differing time of arrival of these sounds to calculate an approximate position of the aircrew. Click on the link below to hear an example of this sound.

Underwater charge from thousands of miles. (59 kB)

Note how the sound of the explosion is "smeared" out over a long period of time. This is due to dispersion.
Basically, different parts of the sound travel at different speeds ... some take entirely different paths. For the more mathematically inclined, one could say that this sound travelled as a set of coupled normal modes in a range dependent channel ... but we won't pursue that feature any longer.

Among the more vocal residents of the deep are the whales. Their calls can be detected thousands of miles from the source as they navigate the world's oceans. Below are a few examples of whale vocalization.

Beluga Whale (71 kB)     Gray Whale (52 kB)

Humpback Whale (137 kB)      Sperm Whale (109 kB)

Whales are by no means alone in their symphonic calls. Dolphins, fish, and even shrimp fill the sea with sounds not often heard ashore. Natural sources of sound also include non-living earth processes. The sound of seismic events fill the ocean, as does the sound of rain, lightning and the crackling of ice.

Dolphins (96 kB)     Croaker (57 kB)

Seismic Disturbance (85 kB)

Snapping Shrimp (85 kB)

Cracking Ice as heard beneath an ice sheet (71 kB)

Since the day man first ventured onto the sea, he has added the sound of his own activity to the ocean basins. As we built larger, and more powerful ships the seas became filled with the sound of cavitating propellers. The "background noise" in most areas today is dominated by the sound of the world's shipping.

Propeller cavitation from a large tanker (63 kB)

Propeller cavitation from a tug boat (115 kB)

With the arrival of men on the seas came military activity. Sonar systems, first developed in the early part of this century, have become more sophisticated and deadly. Beginning as a lowly hydrophone used to detect the sound of a vessel's machinery, sonar has evolved into complex sensor systems using hundreds or thousands of individual hydrophones. These systems not only listen for the sounds of human activity, but actively fill the ocean with bursts of energy designed to probe the deep or to take one last "look" before firing a weapon.

A snorkling submarine (65 kB)

An active sonar tracking a target as it moves away (65 kB)

An active sonar tracking a target as it moves closer (71 kB)

An active sonar tracking a close target (49 kB)