[Author’s Note: This and ensuing sequels are excerpts of a new development from the original essay sequels on Korean Temple Bells and Magoism that first published January 11, 2013 in this current magazine. See (Bell Essay 1) Ancient Korean Bells and Magoism by Helen Hye-Sook Hwang.]
Acoustics of Korean Temple Bells
The Korean temple bell is by no means a simple or monotonic sounding apparatus. Sillan temple bells are comparable with whales as music makers. Like a whale, the bell engenders complex notes. For example, the Divine Bell of King Seongdeok the Great (the Divine Bell hereafter), according to a study, emits more than 50 single sound waves under 1000 Hz (1000 vibrations per second).[1] Put differently, more than 50 kinds of tremors are taking place in the body of the bell upon the strike. It is also known that the Divine Bell travels as far as 40 km.
Music of the Bell
When the bell is struck, the kinetic energy created by striking the bell is transferred to the body of the bell, which causes vibration. The vibration of the bell is transmitted to the air and reaches our ear drums. As our auditory cells are stimulated, we recognize the sound. A specific vibration of the bell is determined by the combination of multiple variable factors including its size and shape as well as material and the striker. Its amplitude varies according to the location of the strike made on the body of the bell. In general, the sound increases in volume, when the bell is struck on the lower part of the body close to the opening. The sound decreases, the higher the body is struck.[2]
According to the Encyclopedia of Korean Culture, “the good sound of the bell” is defined as (1) the clear sound, that is, one must hear a beautiful sound by one’s ear without noise, (2) the reverberation should last long, and (3) there should be a distinctive maengnori (맥놀이), a phenomenon of beat produced when the two different sound waves interfere. These three factors are closely related with the kind of metal alloy, the cooling speed of the iron liquid, the shape, the distribution of thickness, and the arrangement of designs.[3]
Based on various sources on the sounding of the bell, we can summarize it as the sound of a bell as three sectional notes:
The first sectional note is the roaring sound that diminishes within one second after the bell is struck. It includes a number of partial notes.
The second sectional note is a far-reaching sound, also known as the normalized sound, that lasts 5 to 10 seconds after the bell is struck. It refers to the bell sound that travels far.
And the third sectional note is called reverberation, which lasts 30 seconds to one minute after the bell is struck until it gradually diminishes. Reverberation refers to the basic original vibration that hears as sound. The good bell has a gentle and distinctive echo interplay (beat), that is, a prolonged maengnori. Because of the asymmetrical structure of the bell in the arrangement of the designs on the surface and the thickness and the shape determined in casting, the bell sound may comprise two different but similar frequencies, the high frequency and the low frequency. The frequency of reverberation is the difference between the high frequency and the low frequency. Maengnori is generated when the high frequency and the low frequency interact.[4]
To be noted is the phenomenon of beat. It refers to the fact that, when the original sound wave meets the returning sound wave, the sound either becomes stronger (reinforcing interference) or weaker (cancelling interference). The reinforcing interference makes the sound bigger, whereas the cancelling interference makes the sound diminish.[5]
In a comparative light, it is inferred that the Sillan temple bells were cast to mimic the “singing” of the whales by the irregular thickness and the distinctive shape of the body to cause two similar frequencies. It is the echo movement that characterizes them as the music of the bell. The Encyclopedia of Korean Culture continues to characterize Korean temple bells as follows:
Korean temple bells are characterized by a clear and pure timbre (tonal sprectrum), a prolonged reverberation, and a distinctive echo interplay (maengnori). The bell of Sangwonsa, the extant oldest of Sillan temple bells, has 102 Hz for the original frequency, which is known as the best sound. At the 4-0 vibration mode, the high frequency 103.02 Hz and the low frequency 101 Hz are conjoined to make the echo movment of 2.02 Hz frequency… The divne bell of the Great Seongdeok King has 65 Hz for the original frequency and its echo movement frequency is 0.35 Hz.[6]
The frequencies of both the bells of Sangwonsa and the Great Seongdeok King, 65 Hz and 103.02 Hz, are within those of cetacean songs.
When it comes to the music of the bell, Korean temple bells are distinguishably characterized by the sound tube (eumtong or yongtong) and the resonance cavity (myeongdong) from her Chinese and Japanese counterparts, to be discussed in detail below. Ancient Korean bell-makers were not only concerned about casting the good bell with the good sound but also enhancing its acoustic quality by engineering these two devices. The sound tube refers to the tube standing upright atop the bell, enveloped by the dragon, Poroe (Pulao). It has an open ended little pipe, with a few adorned bamboo-like nodules engraved on it. The resonance cavity is the recessed half-spherical area below the bell cacity, made on the ground or the floor.
Acoustics of the Divine Bell of King Seongdeok the Great
Also known as the Bell of Bongdeoksa (奉德寺 Virtue Venerating Temple), the Divine Bell is the most favored bell of Korea by Koreans. Even today, its sound is noted for “playing the zither of one’s heart/mind (心琴).” The Korean expression, “sounding the musical instrument of one’s heart/mind,” is not indifferent to the Magoist Cosmogony, which ascribes the sound/vibration/frequency to the power of self-creation innate in all beings. The bell sound is metamorphic in the sense that it prompts resonance in the musical vessel of human heart/mind. In what follows, we will examine how the Divine Bell makes the music of its kind whose sound waves are aligned with those of whales.
According to Jihyeon Yi, the normalized sound of the Divine Bell comprises high and middle ranged frequencies (from 64 Hz to 354 Hz).[7] As aforementioned, the Divine Bell has as many as 50 single sound waves counted under 1000 Hz. Those single frequencies do not absorve or conjoin each other right after the moment of the strike. Each tremor lasts, insofar as it transforms its own kinetic energy into friction energy. The higher the frequency, the more friction enegery required and therefore the faster it diminishes. Within a few seconds, almost all single sound waves vanish in such a way.
The reverberated sound of the Divine Bell lasts more than 1 minute and up to 3 minutes, the longest. Within the range of the normalized sound, the majority of intense sounds diminishes in about 9 seconds. Thereafter, only two frequencies continue: the 64 Hz, which is similar to the sound of our breath and the 168 Hz, which resembles the sound of child’s roar.
In the Divine Bell’s reverberated sound, the most intriguing is its maengnori, according to Seokhyeon Kim and his research team whose research includes the chart of maengnori. The following is a summary of their report:
The
phenomenon maengnori takes place in both frequencies of 168Hz and 64 Hz. The
168Hz emits a sound resembling child’s cry at 9 seconds after the strike. It is
detected to have diminished. However, it has reemitted the same but weak sound
in another 9 seconds. The 168Hz represents the interplay of two sound waves,
168.52Hz and 168.63Hz. The difference (0.11Hz, tremoring 0.11 per second) makes
the cycle of 9 second maengnori.
Meanwhile, the 64Hz lasts till the end. It represents the interplay of two similar
frequencies, 64.07Hz and 64.42Hz. The difference (0.37Hz, tremoring 0.37 per
second) makes the cycle of 3 second maengnori.
Such maengnori phenomena are caused by the asymmetrical feature of the Divine Bell of King Seongdeok the Great. Precisely it is the reason why more than 50 single sound waves are generated. Although the Divine Bell of King Seongdeok the Great appears symmetrical in appearance, its symmetry is cancelled out in designs and engravings made on the body surface. Also, the density of materials and the thickness of the body areas, albeit minutely, vary. Even the amount of air that was arbitrarily trapped in the liquid iron at the time of casting would be different. The bell is intentionally made asymmetrical. Its asymmetry owes not to the lack of technology. Contrarily, the asymmetrical feature engenders a variety of tremors on its whole body, making such beautiful and gentle bell sound caused by the numerous sound waves with varying frequencies.[8]
That said, we are led to recognize that the Divine Bell resembles the biology of a human body. Both are organically symmetrical, so to speak. Unlike man-made machinery or plastic, the Divine Bell is structurally symmetrical but balanced with asymmetrical parts. Symmetry is an overall outlook of the equilibrium that shapes life forms. Like a human body that is not exactly symmetrical–one’s right side body parts may be slightly different from those of the left side, for example–, the bell varies in its parts. In that sense, we can say that the Divine Bell is modeled after an organic body. We are given a work of cultural art that reflects the biology of living beings.
The Divine Bell, and other Sillan temple bells for that matter, is characterized by two other built-in devices, which refine and reinforce her music: the sound tube and the resonance cavity (see image xxx). Some experts see them as a duo mutually supporting to enhance the sound quality. According to Seokhyeon Kim, both the sound tube and the resonace cavity work like a wind instrument. The bell, the percussion instrument, becomes the player of these two wind instruments, so to speak. In the case of the sound tube, built on the top of the Heavenly Plate (Cheonpan), the ceiling part of the bell, it connects the inside and the outside of the bell through its little tube. Kim describes that the sound tube, measured 770mm long in length, is made in the shape of a trumpet rather than a pipe, having the top end (148mm) larger than the bottom end (82mm). The size of its air hole, as is for a wind instrument, controls the sound details. The sound tube involves two effects, first it transmits resonance and secondly it filters the acoustic. Kim explicates about the sound tube and the resonance cavity, as follows:
The sound tube generates specific notes according to the size of the air hole. That is, as the influx sound and the reflected sound get interfered inside the tube, the sound with specific frequencies becomes resonated and reinforced… Also as an acoustic filer, the sound tube either transmits the sound outward or reserves it inside according to the magnitude of frequencies. The sound tube of the Divine Bell is proven to aptly transmit the high frequencies more than 300Hz…
Scientific research has proven that a resonance cavity influences the bell sound greatly. The resonance cavity creates an enclosed space as an extension of the interior cavity of the bell. The enclosed space generates resonance, according to its size and shape… If the frequency of the sound caused by the vibration of the bell is the same as that of the resonance, the bell sound amplifies due to the increase in resonance. It is of utmost importance to create an enclosed space in which the frequencies of the bell sound and its resonances become assimilated. For most bells, the main cavity of the bell alone is hardly big enough to satisfy the optiomal condition for the increased sound. Thus, a resonance cavity functions to broaden the bell’s cavity.[9]
The resonance cavity, much larger than the sound tube, is there to optimize the resonance of the bell sound.
(To be continued)
(Meet Mago Contributor) Helen Hye-Sook Hwang, Ph.D.
[1] Jihyeon Yi, “The Secret of the Divine Bell of King Seongdeok the Great: The Scientific Sound and its Vibrational Principle” in The Science Times (February 11, 2007). https://bit.ly/2IoRom6 (February 19, 2019).
[2] “Beomjong” in Encyclopedia of Korean Culture http://encykorea.aks.ac.kr/Contents/Item/E0022598 (April 28, 2019).
[3] Ibid.
[4] Ibid.
[5] Jihyeong Yi, “The Secret of the Divine Bell of King Seongdeok the Great: The Scientific Sound and its Vibrational Principle” in The Science Times (February 11, 2007).
[6] “Beomjong” in Encyclopedia of Korean Culture.
[7] Jihyeon Yi, “The Secret of the Divine Bell of King Seongdeok the Great: The Scientific Sound and its Vibrational Principle” in The Science Times (February 11, 2007). https://bit.ly/2IoRom6 (February 19, 2019).
[8] Jihyeon Yi, “The Secret of the Divine Bell.”
[9] Seokhyeon Kim, “Two Holes of the Divine Bell of King Seongdeok the Great: The Value that Transcends 1,200 years” in Cultural Heritage Administration (January 30, 2018). https://bit.ly/2DRjAZi (February 4, 2019)