巨石阵:回音壁?

I’ve heard speculation that when Stonehenge was complete in 2,200 BC, the outer sarsen circle might have behaved like a whispering gallery.Although as Rupert Till points out in a comment below, at best he thought it might be “some sort of partial whispering gallery effect.” Another suggestion is that reflections from the uprights might go beyond just creating reverberation to “perhaps [create] a series of discrete delays or echoes sounding somewhat like a galloping horse.” [1]

从外sarsens从建议的反射路径[1]

Certainly curved surfaces can focus sound and create distinctive flutter echoes, false localisation and whispering gallery effects (see the sphericalMappariumfor example).But Stonehenge stones have uneven shapes and there are gaps between them, both of which will reduce the focussing.In a previous blog I wrote about how our measurements showmanbetx ios 。What happens when the talker (or whisperer!) and listener are at the edge of the circle?

I and colleagues Richard Hughes and Bruno Fazenda have been exploring what really happens when sound circulates just inside the outer sarsen circle.We’ll start by looking at some computer simulations, and then look at what the measurements in the acoustic scale model of Stonehenge show.

What is a whispering gallery?

Let’s start by looking at an authentic whispering gallery, to see what we’d expect if Stonehenge worked in that way.When someone talks along a concave wall, you can get sound that stays close to the edge.Figure 1 shows a classic way of illustrating this, considering sound to be a snooker ball bouncing around a circular table.

在回音壁图1高频声音[2]

But modelling sound as a bouncing ball doesn’t work when you get wave effects like衍射。So Rick simulated sound more accurately using a method called时域有限差分(FDTD)。Look out for the回音壁波in the video below, it’s the one that takes the longest time to get to the bottom of the circle, hugging the wall all the way.(If you’re unclear which part of the wavefront to look at, see Figure 3).

图2波在一个回音壁。该人士是在一个顺时针方向设计对发送的声音越来越强烈。
图3中的回音壁波在绿色椭圆突出。

Figure 4 shows the response you’d pick up on a microphone at the bottom of the circle if the person made a short impulsive sound at the top (e.g.clapped their hands).First sound peak is the direct sound travelling straight across the circle from top to bottom.The very last peak to arrive is the whispering gallery wave, because it follows the longest path around the edge.Notice how much louder it is than the direct sound;this is a key feature of classic耳语画廊像圣保罗大教堂。The sound hugging the walls is surprisingly loud compared to the sound going direct across the circle, making the whispers appear to emerge from the walls.

You can also see a series of peaks arriving a bit earlier created by reflections from the side.These are easier to describe if we revert back to approximating sound as a snooker ball.The peak labelled “(1)” has reflected from the side of the circle once at 3 o’clock.Figure 5 illustrates this reflection path for high frequency sound.

图4模拟为一个圆形回音壁脉冲响应,分别与源和接收器的顶部和底部。
从圆在高频率图5一阶反射。

Whispering gallery with gaps?

There are gaps between the sarsen uprights in Stonehenge, what does that do to whispering gallery waves?Let’s start by looking at a simplified case of broken circle.I thought it was best shown side-by-side with the complete circle.

图6。回音壁和虚线圆并排侧

With the broken circle, as the sound skims past the gaps, diffraction creates little circular wavefronts going in all directions.This means the whispering gallery wave hugging the wall gradually diminishes.Figure 7 shows the impulse response.By the time the sound reaches the bottom, the whispering gallery wave is no longer visible.

图7在模拟打破圆脉冲响应

What about Stonehenge?

With Stonehenge we don’t just have gaps, we also have the irregular shapes of the stones.Also, there are other stones that get in the way, like the the bluestone circles and the inner trilithon.As the video in Figure 8 and the impulse response in Figure 9 show, there is no whispering gallery effect in Stonehenge.

We’ve also lost the focussed reflections that happened with circles – there is no stand-out reflection around the label (1).These are lost due to diffraction and scattering from the obstructing inner stones.

图8。搜索在耳语巨石阵画廊效果。
图9。在巨石阵模拟脉冲响应

Measurements

仿真有很多限制,并非最不重要的是,他们使用2D到巨石阵模型的平面切割约胸部高度。真正的巨石阵是3D!所以,我们用我们的巨石阵的声1:12比例模型看看我们是否可以测量任何回音壁波。图10示出的设立为最短源到接收器的距离。我们测量6个话筒位置在圆弧上大致均匀地间隔开,最接近的是所述一个可以在图10中看到的,并具有在圆的相对侧上的麦克风最远。

图10。设立回音壁测量的最短距离进行测试。扬声器是向左,和麦克风的权利。

图11示出了6点麦克风的位置的脉冲响应。任何回音壁波应显示大致围绕在红色标记一条线在地块中间的时间。回音壁波的证据被认为是因为没有突出的反射。

图11测量巨石阵的声1:12比例模型。位置1是最接近源,和位置6最远。

摘要

在巨石阵回音壁波的证据是看到了FDTD计算机仿真和测量,同时在声学1:12比例模型。这是因为外sarsen立柱之间的间隙衰减回音壁波,象石头的有些不规则的形状。

此外,从外sarsen圈反射不会创建“一系列离散延迟或回声听起来有点像奔马”。这主要是由于散落的声音和衰减任何聚焦反射许多其他石头的存在。

积分

耳图标:通过ScotXW,基于工作由Tatmouss - 文件:00 - 主 - hand.jpg,CC BY-SA 3.0

[1]https://soundsofstonehenge.wordpress.com/theoretical-analysis/访问的27/4/20

[2]考克斯,T.,2014。索尼克仙境:声音的科学奥德赛。兰登书屋。