People who know me from my posts on the ManWithoutFear.com message board are probably well aware of my interest in superhero science (now why does that sound like an oxymoron?). As are, I suspect, most people who follow this blog regularly. At the very least you would get that idea from reading my posts on “wacky powers.” So, from reading the title of this post, one or two of you might even wonder why I’m not slapping the wacky label on this one too. Well, the truth is that this might be one of Daredevil’s least wacky powers. And if you’ll indulge me for a few minutes, I’ll tell you why…
In general, humans hear quite well. We have this idea that other animals, such as cats and dogs, hear much better than we do, and that’s essentially true, but that also depends on what we mean by “hearing well.” The sounds we hear have two basic properties, amplitude and pitch (i.e. frequency). The amplitude of a sound tells us how loud it is, and is commonly measured in decibels (dB). The pitch tells us wether the sound is the high shrill of a prepubescent boys’ choir or the low rumble of an old refrigerator, and is measured in hertz (Hz).
When we say that dogs and cats hear better than we do, we mean that they can pick up on a larger range of sounds than we can. They can hear high-pitched sounds that we can’t perceive. When it comes to amplitude, however, humans hear about as well as most other animals in the frequency range that we are the most sensitive to. Very few animals can hear below the human hearing threshold of 0 dB at any frequency.
Of course, neither humans nor animals hear equally well over all frequencies. The 0 dB hearing threshold is only valid for humans in a very narrow frequency range. That means that our sense of hearing doesn’t necessarily reflect physical reality. Sounds of very low or high frequencies must be very loud – in the pure physical sense – for us to hear them. If you imagine that superhearing means being equally sensitive to a very large range of frequencies, without this human limitation, hearing heartbeats would actually be plausible. What makes it implausible is the scale of the human inner ear (and head). Because, heartbeats – and most other body sounds – are are at their loudest at low frequencies. Heart sounds are the “loudest” (i.e. has the highest amplitude) around 50 Hz, a frequency the human ear can hear but is not very sensitive to.
So, to make a long story short: In order to hear heartbeats, you need is a flat hearing curve. There are, of course, many reasons why you wouldn’t want to hear as well at 50 Hz as you do at around 2,000 Hz. Because you wouldn’t only hear heartbeats. You’d also hear people’s bowels moving constantly, not to mention that most of the rumble of big cities would appear to be many times louder than what you’re used to. Low frequency sounds also easily pass through walls which would make the noise very hard to block out. For me personally, super-hearing is not something that sounds all that appealing. Even if it would make you kick ass at hide and seek, and makes Daredevil nearly impossible to hide from.
The only thing I consider to be wacky about Daredevil’s ability to hear heartbeats is perhaps the heavy reliance on this as a means of identifying people. I don’t doubt that this is possible, but it makes about ten times more sense to use a heightened sense of smell for that.