Mysterious: Magic Circle

I've been to DC a number of times and haven't seen this, but here is my idea.

A corner reflector reflects light, or radio waves, back to its source.

This looks like the same idea only with a different geometry. Sound bounces off the "corner" made up of the horizontal and vertical surfaces of the steps, and because the steps are circular with the center of curvature where the person is standing, back to the source, the person at the center of the circle.

Since there are multiple steps, the person gets multiple echoes so the sound will have frequencies that reinforce and frequencies that cancel.

Next time I'm in DC, I'll have to see if I can find it.

There's a similar effect in the whispering gallery of St. Paul's cathedral in London. Someone whispering at one end can be heard at the other end.

Locally, we have the surviving WW1 sound mirrors which were intended to be an early warning system for the approach of enemy aircraft.

At the Parkes telescope in Australia they have a couple of parabolic sound reflectors aimed at each other with the focal point marked for visitors to whisper messages to each other while standing with their backs to each other. Maybe 40m apart.

Maybe the steps being displayed are like a slices of a Fresnel lens for sound reflection.

There is an area in the Capitol Rotunda where everything can be heard. A 18th century Congressman discovered this and placed his office there.

In NYC Grand Central Station there are several alcoves where this occurs.

Small hand held parabolic discs are used by sports announcers to pick up sounds from a particular location by simply moving the disk's focal point from the primary focus to the side to pick up sounds.

Imagine a concentric array of these, each with a slightly different focal point. A slight movement of the listener would result in a different sound. If you turned your head toward the direction of a sound, you would be hearing a slightly different sound.

At one time I was installing the old large satellite dishes. When installing a solid dish, you could hear amplified audio from miles away if you were in the focal point.

A slight movement of your head would change the sound source.

Draw a curved line from left to right and a line following the depth of the steps, and you will probably find a set of focal points corresponding to parabola with each step having a different focal point.

As I mentioned previously the Maya had this figured out long ago using only empirical evidence from observation.

To calculate the focal point of a parabolic dish:

F=(D)iameter squared divided by 16X depth(H)

A slight difference in depth(the steps) will result in a slightly different focal point.

A precise measurement of the shape and depth of the steps would allow a calculation of the focal point of each step.

As I mentioned previously the Maya had this figured out long ago using only empirical evidence from observation.

"Everything old is new again."( credit to unknown source).

A parabolic shape would focus sound from a distant source to the person at the focus, or vice versa. A circular arc would focus sound from the center back to the person at the center. It's obvious the picture is distorted, but the steps (to me) appear to be circular arcs.

Since the step surfaces are horizontal and vertical, the sound would be reflected back to the central axis at the same height that it originated after a double bounce, as shown in the figure below of light reflected from perpendicular mirrors.

“The Maya pyramids had arranged their steps and shape to provide sound to all of the audience regardless of how far away from the speaker they were located.”

I don’t recall this. There is, however, the odd chirping echo from the steps at the base of the Mayan El Castillo pyramid (Chichen Itza).

IIRC, it remains unresolved if this unique chirp echo is a feature, or a bug. I believe that the majority of opinions lean pretty far to the ‘bug’.

I can't locate those steps in this aerial view of the embassy:-

Just my opinion, but I don't think the stairs are a large enough feature to cause such a large effect, so, I was looking for some larger features nearby.

Another possibility is that the steps function as a Fresnel lens, except for sound instead of light; Concentric circles focused to a single point.

Here is a very good link explaining how a Fresnel lens works. I think same principle applies to sound.

https://www.youtube.com/watch?v=_nBNnlu6Rqo