Is the sound heard in the conch the sound of the ocean?

Take a walk along the beach, pick up a conch carried by the waves to the beach, and put it next to your ear to hear the sound of the sea. If someone gives you a horn-like conch, it is like giving you a piece of blue sea. You can listen to the sea breeze and the surging sea tide anytime and anywhere, and hum "You like the salty breath of the sea breeze, stepping on the wet gravel" anytime and anywhere, and go to "face the sea, spring flowers bloom". Just thinking about it is a super romantic thing!

So, is the conch the phonograph of the sea? Is the sound we hear through the conch really the sound of the sea?

(Image source: Institute of Acoustics, Chinese Academy of Sciences)

Practice is the only criterion for testing truth. If we put our fingers together and bend them into a semi-closed concave shape, or put a cup, a small bowl or other container close to our ears and listen carefully, we can also hear the sound of the "sea". These containers are not from the sea, so could the sound coming out of them be the sound of the sea? Of course not. Then, the sound heard in the conch is naturally not the sound of the sea.

Is the sound you hear from the conch the sound of blood flowing?

(Photo source: veer photo gallery)

Some people say that the sound heard in the conch is the sound of blood flowing, because when the conch is placed against the ear, it amplifies the sound of blood flowing.

Let's do another small experiment. In the same sound field environment, let the same person listen to the conch in a normal state and after strenuous exercise. There is no obvious difference between the two sounds. The sound does not become sharper or louder due to strenuous exercise. This shows that the sound in the conch is not the sound of blood flowing in the human body.

Where does the sound in the conch come from?

So where do the sounds heard in conches and similar small containers come from?

We can also do a small experiment to verify this. Find several cups of different sizes and slowly bring them close to your ears. When the mouth of the cup is just about to touch a certain position of your ear, you can hear a sound similar to "the sea". The sounds you hear are slightly different when using cups of different sizes. The larger the cup, the deeper the sound; the smaller the cup, the clearer the sound. The sound we hear is the cup filtering the ambient noise. At this time, the cup can be regarded as a sound filter, which is professionally called a filter.

(Photo source: Qianku.com)

In summary, the sound in the conch is not the sound of the sea, but the noise of the sound field environment filtered by the conch . If you listen to the sound in the conch at the seaside, what you hear is mainly the sound of the sea after filtering. If you are in a sound field environment other than the sea, what you hear in the conch is not the sound of the sea.

(Photo source: veer photo gallery)

Conch is a live streaming expert

The sound of the sea in the conch does not come from its original ecological memory, but a live broadcast of the current sound environment. The live broadcast of the conch relies on a common phenomenon in physics - resonance . Resonance refers to two objects with the same vibration frequency. When one object vibrates, it causes the other object to vibrate. In the field of acoustics, resonance is called "resonance", which refers to the phenomenon that an object makes a sound due to resonance. Conch, small bowls, cups, etc. are physical systems that are prone to resonance. When the sound frequency is consistent with the cavity's intrinsic frequency, resonance will occur, amplifying the sound. At this time, you can hear the sound of the "sea" by putting it next to your ear.

GIF source: "Come on, to the future"

Tuning fork used to demonstrate resonance

(Image source: Institute of Acoustics, Chinese Academy of Sciences)

The Helmholtz resonator, designed and named by German physicist and biologist Hermann von Helmholtz in 1850, is similar to the principle of listening to the sound of the "sea" through a conch. The design concept of the Helmholtz resonator is to distinguish sounds of different frequencies or tones in noise or music through the principle of resonance. The original shape of the Helmholtz resonator is a container with a thin neck or a small mouth. The sound in the environment causes air disturbance, and the pressure changes due to the elastic deformation of the air, which pushes the air column at the thin neck or small mouth of the container to reciprocate. This continuous oscillation process will produce sound. Both conchs and Helmholtz resonators have a small mouth and a large cavity structure, and their sound-generating principles are also the same. In a sense, the conch can be regarded as a live broadcast "expert" in nature. It not only filters environmental noise, but also has the effect of amplifying sound.

Schematic diagram of Helmholtz resonator

(Image source: Institute of Acoustics, Chinese Academy of Sciences)

From listening to the "sea" from conch shells to ancient acoustic applications

The principle of sound resonance has been applied in ancient China. As early as the early Warring States Period, "Mozi·Bei Xue" recorded the resonator used for military defense: dig a deep well at a certain distance under the base of the city wall, bury a jar with a large belly and a small mouth, cover the mouth of the jar with thin leather, and then put it into the well. Send people with sensitive hearing to lie on the mouth of the jar to listen to the sound, so as to judge the direction of the enemy's tunnel and then fight back. This device suitable for defending the city is called "urn listening", also called "ground listening". Regarding "setting up urns to help sound", the ancient stage of Longtian Temple in Shita Village, Fenyang City, Shanxi Province is a good example. The gables on both sides are symmetrically embedded with three types of large, medium and small pottery urns, a total of 14, and the mouths of the pottery urns are facing each other to achieve the effect of amplification.

14 pottery urns embedded on the gable of the ancient Longtian Temple stage in Shita Village, Fenyang, Shanxi

(Image source: Document 3)

In ancient times, in order to facilitate carrying during marches and battles, the design of "ground listening" tended to be light and practical. Li Quan of the Tang Dynasty recorded a hollow pillow called "empty Hu簏" in "Taibai Yinjing·Youyi Di Ting Pian". He wrote: "Choose those who sleep less and let them sleep with an empty Hu簏. When people and horses are marching thirty miles away, there will be sounds in the Hu簏 from all directions, which is called 'ground listening'." Shen Kuo of the Northern Song Dynasty described the production materials and general shape of this warning pillow in "Mengxi Bi Tan·Qiyong": "In ancient times, cowhide was used as an arrow cover, and it was used as a pillow when lying down. Take the hollow part in it and put it on the ground as a pillow. If there is a sound of people and horses within a few miles, you can hear it. It is because the hollow part can absorb the sound." This kind of "ground listening" is a quiver made of cowhide. When resting during marching, it is placed on the ground as a pillow. Because it is hollow, it can "absorb the sound". Just imagine, when the ancient soldiers were camping and resting, they could use these magical gadgets to hear the enemy’s marching movements from dozens of miles away, and make corresponding countermeasures. The ancients were really smart!

The ingenuity of the application of ancient acoustic knowledge is admirable. The seeds of science were sown in people's hearts as early as in ancient times, and the flowers of science bloomed in ancient history books. In modern times, the resonance phenomenon is widely used in all aspects of social life, such as medical stethoscopes, resonance boxes of pianos, violins, guitars and other musical instruments, microwave ovens, oscillators for construction, etc.

When we put a conch next to our ear, we hear the noise in the environment, and the conch acts as a filter and amplifier of the environmental noise.

So, what we hear from the conch is not just the sound of the sea, but the sound of nature!

References:

[1] Ma Dayou. The development of Helmholtz resonator[J]. Physics, 1993(08):452-456.

[2] Yang Yang, Gao Ce. The dispute over “setting up a jar to help with sound”: a case in the history of science [N]. Guangming Daily, 2016-04-06(T14)

[3] Yang Yang, Gao Ce, Ding Hong. Acoustic technology of pottery urns installed on the ancient stage of Longtian Temple in Shita Village, Shanxi Province[J]. Journal of History of Natural Sciences, 2014, 33(01): 70-82.

Produced by: Science Popularization China

Author: Wang Lina and Yang Fujin (Underwater Environment Information Perception Laboratory, Institute of Acoustics, Chinese Academy of Sciences)

Producer: China Science Expo