[MUSIC] Okay, so let's talk about the external ear. The external ear stretches from what we call the ear which is actually called in medical language, we call this the pinna and then the auditory canal, the ear canal. And it ends, the, the boundary between the external ear and the middle ear is called the eardrum and in the vernacular, and also called the tympanic membrane, the tympanic membrane. So, this is all the external ear, and it all air. So, what is the, what's the whole point of the external ear? Well, the ear, the pinna is to gather sound. So you can, just, just as though, if you were trying to hear somebody and you can't quite hear them, you do this. You're trying to get the sound to bounce off of the back of your hand, and make it more likely that you're going to gather sound that is coming in from all directions. And you could put a tube here, as Beethoven did he, when he, as he was losing his hearing he used to use these large ear drums that would collect more sound. No, they're not called eardrums, sorry. The point of the earhorns, Beethoven would use a ear, an ear horn, is to gather sound. It's the same thing with this ear canal, you're gathering sound, but you're doing one more thing you're, you're using something called, instructive interference. So, all these bouncing around sounds are going to up, and they're going to grow in magnitude. So that this, the amount of the intensity of the sound, if we, if we look at the intensity of the sound from the outside to the inside, to the point of the tympanic membrane, it's actually going to increase. This external ear, and and as well as an ear horn. Will serve to increase the magnitude of the sound. Now, it, there are two additional points that I want to make about this. First is that it doesn't increase sound at all frequentsly, frequencies equally. The ear canal for humans is built to increase sound in the frequencies of speech. And it's actually built so that the, the frequencies that are not involved in speech are reduced in magnitude, so already in the ear canal we have a modification of what's present on the outside. It's not a modification is not present in a simple tape recorder. So we're already modifying the stimulus. We're increasing frequencies related to speech, we're decreasing the intensity of frequencies that are not related to speech. So the second, the second point that I want to make about the external ear is. You know, why do we increase in magnitude? This is a teleological argument, but, the question is, why is it advantageous to increase the amount of sound present at the tympanic membrane, versus present at the outside of the external ear? And the answer is because we know we are going to lose a lot of intensity as we go through the rest of the ear. It's inevitable, we're going to lose energy, we're going to lose sound energy. And so this is a big boost as much as possible to increase the, intensity of a sound prior to, to going on to the next step where we're going to lose intensity, where it's inevitable that we're going to lose intensity. What I've shown here is that we've, we're just considering this part, airborne sounds are, are, lower in magnitude at the edge of the pinna, compared to the boundary between the external and middle ear, which is the tympanic membrane. They grow in magnitude. The, the bottom line is that the external ear, is going to take you from a sound of one intensity and in, and increase the intensity of that sound, particularly if that sound has frequencies in the speech range. All right, in the next segment we're going to look at the middle ear. [MUSIC]
