Daredevil Message Board

[jumonji]

Not that anyone asked for it, but I'm having fun digging this stuff up so I figured I might as well share what I've found. As it turns out, my little "mini lecture" on the sense of touch (thread over HERE) was a breeze to put together compared to figuring out just how well you need to hear in order to hear heartbeats. But, here's what I've got so far, and if there are any physicians out there (hello? anyone?), please weigh in.

First of all, I should say that the MUH description of DD's sense of hearing is complete bogus. I mentioned this somewhere in the radar thread, but to state that the human hearing threshold is 20 dB is simply an inaccuracy that I'm surprised they've left in place through at least a couple of editions. The hearing threshold in the most sensitive frequency range is 0 dB. I even suspect that at least half of the people who post on this board would know that from high school biology, but I digress.

So, looking in the MUH doesn't help much, except that it states that DD can hear heartbeats from a distance of over twenty feet. Obviously writers often have him hearing heartbeats from much greater distances than that (such as when Foggy was "murdered"), but if my little theory of how he does this is valid, this idea isn't as far-fetched as one might think.

Here's the thing, most of the sound that the heart makes isn't audible to normal humans no matter how much you amplify the sound (using a stethoscope or something similar) since it falls outside the frequency range of normal hearing of 20 to 20,000 Hz. Rather, most of the "sound" output of the heart is somewhere between 4 and 7 Hz. This is a frequency normal humans would register as vibration (if "loud" enough). Some animals are very sensitive to infrasound (frequencies below 20 Hz), and there is some speculation that this is how animals can pick up on the early signs of seismic activity. If DD was still living in San Francisco that might have been an interesting storyline with him and all animals in ear shot heading for the hills when there's an earthquake... Okay, back on topic. Most mammals register infrasound as vibrations, but many species of fish, for instance, use their organs of hearing to pick up infrasound so it's not beyond Marvel Universe reason to assume that DD would hear infrasound, just like he can hear all that ultrasonic stuff that only dogs pick up on.

Now, the beauty of infrasound is that it can travel quite far, and is conducted fairly easily through most mediums without a big loss in intensity. This would make it possible for someone whose hearing is amped up enough to hear heartbeats to be able to hear them from quite far away or through walls. Cool, huh?

I have yet to figure out how loud the beat of the human heart is (in decibels), but I'll get back to you in that one...
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The Other Murdock Papers