The Three Options of a Sound Wave

Any sound wave, upon striking an object in its path has the option to do one or all of the following three things:  Be reflected, diffused or absorbed by the object.

The type of object in question and the angle that the sound pressure wave strikes the object will determine what the sound wave does.  All of the sound energy will be captured by the sum of these three actions.  For instance, a signal emanating in a particular direction through air will be applying 100% of its pressure energy in that direction.  Once it hits an object, the sound will be reflected, absorbed, and/or diffused.  If you were to measure the amount of sound pressure energy in all three of these directions, it would add up to 100% of the initial sound energy.

Reflection

A sound wave that strikes an object perpendicular to a flat surface and bounces back toward the direction it came from has been reflected.  Glass, walls, water, and other hard objects are generally good at reflecting sound.  If the sound strikes the object at an angle, it will be reflected in the equal and opposite direction as light reflects off a mirror.  This suggests that glass and smooth surfaces can be difficult to see using echolocation unless you are perpendicular to a flat surface (See calibration surfaces).  When you are at an angle to the surface the sound reflects off in another direction and does not return directly to your ears.  This makes it much harder to see.

Diffusion

A sound wave that is reflected in many different directions at once has been diffused.  Sound is being scattered in all directions and therefore there is much less sound energy to any of the resultant sound waves.  This can make an object more difficult to see since the signal returned is not quite as "clear".  It sometimes sounds "muddied".  Tree bark or very rough walls are a good example of diffusive surfaces.

Absorption

A good percentage of sound waves hitting softer objects will be absorbed by it.  This means that the sound goes inside the pores of the object and expend their sound pressure energy before coming back out of the object.  A soft pillow, or clothing absorbs quite a bit of sound.  This, similar to diffusion makes objects more difficult to see and makes them less "present", or less "clear".

Echolocation Pushups?

I was doing pushups recently and noticed an interesting effect that you might want to experience on your own. I was breathing deeply as one tends to do under exertion and listening to the sound of my breath against the hard wood floor. As my body rose and fell and my face became closer and farther away from the floor, the reflection of my breath phased in and out like a musical instrument.

There's nothing unique about this exercise compared to any other beginner echolocation exercise. However, I think it's important to understand and practice using your own breath as a signal as opposed to a click. There are certainly scenarios and circumstances where a loud click is inappropriate, but ambient noise is generally much more challenging to use to see objects at any distance and even more difficult to distinguish detail from.

By learning how your breath sounds reflected off of objects may serve as a good alternative in a quiet environment if need be. The sound of a deep breath, either through the nose or the mouth, is remarkably similar to white noise which I discuss in greater depth in the book Beginner's Guide to Echolocation.

Basically, white noise offers multitudes of different frequencies, high and low which, as we know, all reflect off of objects differently. Some objects reflect higher tones, some lower tones. In some of the very beginning lessons we suggest using a "SSHH" sound to emulate white noise. Breath isn't as loud as making a "SSHH" sound, but in effect it is very similar.

Another interesting note about pushups is simply the fact that your echolocation target is moving in and out, in and out, over and over again. Even if you're not actively learning anything new by experiencing this effect, it's great practice, it's becoming accustomed and, little by little, getting more in tune with the subtleties of echolocation.

Visualizing the Sounds Around Us

When we echolocate, it's not necessarily important to understand the physics and psychology of what is going on, but for me, that level of detail is fascinating, and while I might not be able to readily apply it in daily practice, it's good to know what's going on behind the scenes.  And inevitably, we will find small ways of implementing these little bits of knowledge.  Understanding sound to a greater level will allow us to visualize exactly what is going on and will give us a more intimate picture of reality.

When we talk about the mechanics of echolocation, it's entirely comprised of sound waves.  Sound, fundamentally is fluctuations in air pressure.  These fluctuations happen fast enough for us to refer to them as "vibrations".   When I say a fluctuation in air pressure, that means a region of high pressure, followed by a region of lower pressure.  These pressures are so low, much lower than atmospheric pressure so we generally can't feel the sounds (although there are cases that sounds are felt and that is another interesting topic) but our ears are very sensitive to these very low pressures and can easily detect them.

When you emit a sound visualize waves of energy emanating from the source (your clapping hands, your mouth, etc.).  Depending on the shape of the object emitting the sound, the sound waves will be shaped differently in all directions.  Sounds coming from your mouth will generally be loudest in the direction straight out from your face.  A megaphone, for instance is not very loud if you were standing beside someone using it, unless they were to aim it directly at you.  The sound energy is much greater in that direction.  A clap will be much more uniform in all directions, however when the sound waves strike your body they will be reflected, absorbed or diffused and will change the sound pattern when observed from a wider perspective.

This is the same for any object.  Supposing a sound source emits sound equally in all directions.  The sound will radiate outward at a certain speed and strike the nearest object first.  As soon as it hits that object sound will stop travelling in that direction and the overall "soundscape" will be affected by that object.  The change in this "soundscape" would be another way to consider echolocation.  Once you start to consider all of the objects that the sound waves may contact during their journey and the infinite amount of interactions they can have, it becomes very interesting to try to visualize the shape of the emanating sound wave.

This is really neither here nor there, but an interesting thought experiment and something to ponder.  Let me know if this thought process leads you to any deep revelations.