There are few sound effects as iconic as Godzilla's mighty roar. Sound engineers generally layer and blend sounds from other animals and objects around them to produce an awesome aural effect. There have been several articles, both in academia and various web sites that have focused on what science says about Godzilla's size and even his urine production.
A YouTube video by Vsauce3 looks at the physics of scaling laws and asks the question whether Godzilla could exist. But what does science say about Godzilla's magnificent roar?
The Science of Making Sound
All sound any organism makes-whether they are amphibians, reptiles or mammals-originates from the larynx; the organ in the neck involved in breathing and sound production. The source of all vocalizations result from vibrations of the vocal folds in this organ.
There are two mechanisms for sound production. The first is known as active muscular contraction (AMC) and is produced as the throat muscles actively contract to quickly vibrate the vocal folds. This is how cats purr and, hence, is known as the "purring" mode.
The other mechanism is the the myoelastic-aerodynamic or "flow-driven" mode. Air from the lungs passes over and vibrates the vocal folds. This is the way that humans talk and sing.
Both modes are limited in the range of frequencies it can produce. In the case of the purring mode, the highest possible frequencies are limited by muscle contraction speeds. Even with super-fast muscle contractions, this cannot get higher than 200 Hz. If Godzilla were to purr like a cat, this would bring him somewhere in the mid-bass range of the auditory spectrum.
Things get even more interesting where the flow-driven mode is concerned. The frequencies are limited by the size of the larynx or rather the size of the vibrating tissue. The longer the vocal cords, the lower the frequency range.
The Mighty Godzilla Purrs! Like a Cat.
The latest incarnation of Godzilla stands at a mighty 106 meters (350 feet). Though this is a rough estimate gleaned from images of Godzilla, we can estimate the larynx, and hence the length of the vocal cords, to be somewhere in the range of 15-20 meters (49-67 feet). The sound from the flow-driven mode will lie in the range of 8 to 11 Hz-below the range of human hearing. More accurate measurements may reveal sound in the infrasonic range.
Though there is considerable variation between individuals, the human hearing range is given as 20-20,000 Hz. This doesn't mean we won't be able to hear the bass of Godzilla's mighty roar. People can hear sound as low as 12 Hz under ideal laboratory conditions.
Of course, Godzilla is a huge beast. He is also the King of Monsters for a reason and we expect him to be loud. Very loud as a matter of fact. Though we may not actually hear his roar through the air, the magnitude of his voice will transmit vibrations through the ground to our feet. That we will be able to hear. Elephants use infrasound to communicate in the same way over extremely distances.
But we can still hear [Godzilla](movie:45291) despite his massive size. While the flow-driven mode is completely dependent on the size of the vocal cords, purring mode is not. This sound depends on how quickly a creature can voluntarily contract those muscles and fits well within the range of human hearing. Could it be that what we hear isn't a mighty roar but a very loud purr?
Herbst, Christian T. et al. “How Low Can You Go? Physical Production Mechanism of Elephant Infrasonic Vocalizations.” Science 337.6094 (2012): 595–599. www.sciencemag.org. Web. 25 May 2014.
Tretter, Thomas R. “Godzilla Versus Scaling Laws of Physics.” The Physics Teacher 43.8 (2005): 530–532. scitation.aip.org. Web. 25 May 2014.