Why Orcas Are Terrified of a Sound

August 11, 2026
The head of an adult male sperm whale accounts for about one-third of the total body. For an animal averaging 16 meters (52 feet) in length, that means a head around five to six meters long — a block so disproportionate that the scientific name reflects it directly: Physeter macrocephalus, from the Greek makrokephalos, meaning big-headed. Inside that block sits an acoustic system with no equivalent in any other animal on Earth.

Three major structures. Start at the top.

The spermaceti organ — the case, as whalers named it — runs almost the full length of the head, from the blunt front of the snout back to the bony amphitheatre of the skull. In the foundational 1972 paper favoring its acoustic function, Kenneth Norris of UCLA and George Harvey of the Oceanic Institute wrote that it occupies "as much as 40 percent of the entire length of the whale." The organ is filled with a waxy, semi-liquid oil called spermaceti. Its outer wall — a matrix of interlocking ligamentous cables, some as thick as a man's thumb by Norris and Harvey's own description — is dense enough that, in their words, it's "difficult to pierce even with a sharp knife." In fresh specimens, penetrating that wall causes liquid spermaceti to exude, they noted, "as if under considerable pressure."

Below the spermaceti organ, sitting directly on the bony rostrum of the skull, is the junk. The whalers' term for a secondary fat structure they value less than the oil above it. The junk consists of fatty compartments shaped like lenses, arranged in a series and separated by dense connective tissue, running front-to-back along the lower forehead. Huggenberger, André, and Oelschläger's 2014 morphological study in the Journal of the Marine Biological Association identified a structure at the rostroventral edge of the junk they called the "terminal acoustic window" — the exit point of the forward-directed signal — and a "connecting acoustic window" at the interface between the spermaceti organ and the junk, where acoustic energy transfers between the two structures. The junk's function is acoustic focusing: it takes incoming sound energy and collimates it into a directional beam.

Between those two fat bodies, running as a flattened sub-horizontal tube along the right side of the head, is the right nasal passage. At the very front of that passage — just beneath the blowhole — is the click generator.
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