Revealing The Acoustic Mysteries Of Byzantine Churches

Volume 49, Issue 3 :: By Sharon E. J. Gerstel and Chris Kyriakakis

View into dome of the Church of the Savior (Soteraki), Thessaloniki, with images of angels surrounding Christ.

Those who attend musical performances at the world’s greatest concert halls are quick to laud the otherworldly sound of orchestras and virtuoso artists. Assisted by the acoustic properties of the concert hall, a performer can transport the listener from the mundane to the sublime. Like modern-day architects involved in sound design, the builders of medieval churches also created spaces in which chanted and spoken words lifted supplicants into the realm of the sacred. They created spaces in which sound was both intelligible and immersive.

In the context of modern performance spaces, sound is almost always coupled with visual spectacle, one sense informing and heightening another. In Byzantium—the millennium-long empire centered in Constantinople—the walls of Orthodox churches were covered with full-length images of holy men and women, as well as by angelic beings, the Virgin Mary, and Jesus Christ. These figures frequently hold text scrolls, which empower the literate viewer to hear the spoken word through vocalization of the written text. Beyond these figures, however, the physical body of the church—its shape and its fabric—also empowered the word, both communicated and received. Within the sacred space of the Byzantine church, the dome assumes a critical role, both metaphorically and acoustically. It was likened to the firmament, the heavens above, and was frequently decorated with angels whose wings appear to flutter in movement. Captured in this space, celestial beings manifest for the faithful the joining of heaven and earth through liturgical celebration. The perception that the heavenly and human co-mingled within the confines of the church is not a modern construct. As early as the fourth century, the patriarch of Constantinople, John Chrysostom (the “Golden Mouth”), commented on the place of man encircled by angels in sacred space: “Think beside whom you stand, with whom you are about to call on God—with the Cherubim.”

Even when the doors of churches were closed, the Byzantines believed that the saints—captured in their painted icons—continued to interact with one another on behalf of the faithful in a powerful and perpetual process of intercession. Were these interactions imagined, or can we perceive the echoes of sacred words exchanged within the walls of the church? Scientists have theorized that the reverberations of sound are omnipresent and eternal. The faint traces of sound thus may be present in churches, even when buildings stand empty. When sound is coupled with icons, the perceived marriage of sound and image evokes emotional and spiritual reactions in the faithful. Can these traces of sound be documented scientifically, or are they the product of our own expectations of sacred space? Can the transformative effects of sound in Orthodox churches be compared to those in modern concert halls? How do the sound effects of medieval churches differ from those of modern Orthodox churches, which frequently make use of microphones and even organs? Two years ago, as part of an international group of scholars, we began to map sounds in the Orthodox churches of medieval Thessaloniki, the second most important city of the Byzantine empire, a city with a rich tradition of ecclesiastical architecture and hymn composition. The ongoing collaboration of art historians, architects, musicologists, chanters, and acoustical engineers generated innovative questions and continues to yield some surprising answers.¹

Chambers for Sacred Sound

Unlike other forms of worship that include musical instruments, the medieval Orthodox liturgy was spoken and intoned by priests, chanters, and choirs. The need for audibility imposed requirements on speech intelligibility that, in turn, guided the acoustical design of the spaces. Like the most finely tuned concert halls, Byzantine churches were constructed as sound spaces. To identify how these buildings were built for sound, we studied eight Byzantine churches in Thessaloniki, Greece, ranging in shape from longitudinal basilicas to small, domed chapels. Impulse response measurements were taken at various locations within each church and were analyzed to extract the relevant acoustical parameters. We also invited chanters to participate in re-creating the soundscapes of Byzantine churches, from the virtuoso performance of a single chanter, to the resounding voices of a male choir. While the properties of the sounds can be scientifically documented, immersion into the soundscape of a lost empire had an enormous impact on every member of the team; some even claimed to hear the voices of angels.

When a sound stops being emitted, the space around the source takes over. This is most readily observed when we clap our hands and listen, but it can also be observed in the short silences between spoken or chanted words. The sound bounces from surfaces until it eventually decays below our audibility limit. The time it takes for a sound, once stopped, to decay to an inaudible level is an important characteristic of large spaces and is called reverberation time. Measurements taken in eight Byzantine churches in Thessaloniki demonstrate that the reverberation time is generally longer in spaces with larger volumes (see Table 1).

Table 1. Reverberation time (RT60) and its relation to volume

Beyond just the acoustical definition of reverberation time, however, there is also psychoacoustic perception. The sensation of spaciousness and envelopment by reverberant sound is very powerful because it arrives at our ears from many different directions. In fact, the more complex the reflection pattern, the more dissimilar is the sound arriving at each of our ears. The increased feeling of spaciousness and envelopment combined with the reverberant sounds that appear in the silences between the words could have been responsible for the perception of the co-mingling with the heavenly described by John Chrysostom and other Byzantine theologians. These elements are completely lost when listening to a

View of central nave of Acheiropoietos Basilica, Thessaloniki.

modern-day recording of sacred music produced by two loudspeakers that are unable to reproduce properly the spatial reverberation cues required for envelopment. A recreation of the experience requires a playback system with multiple loudspeakers surrounding the listeners, replicating the arrival of sounds as dictated by the shape of the medieval building with its domes, vaults, and other acoustic devices. The sensation of envelopment in the church is also completely distorted when the liturgy is performed using microphones and poorly placed loudspeakers. Spaciousness is frequently sacrificed to achieve higher intelligibility. Sound—even the sound of angels—yields to visual spectacle.

The perception of reverberation is also influenced by the sound energy density in the lower and higher frequency ranges. Acousticians refer to the perceived fullness of low frequency sounds as “warmth,” and this is characterized by the Bass Ratio (ratio of reverberation times at mid frequencies to reverberation times at low frequencies). Similarly, the subjective perception of sound rich in high frequency harmonics is called “brilliance” and is characterized by the Timbre Ratio (ratio of reverberation times at higher frequencies to lower frequencies). Warmth is often described by listeners as “smooth sound,” but too much warmth makes the space sound “dark.” Brilliance is described as “bright” or “clear” sound, but too much brilliance makes the sound “harsh” or “shrill.”

Acoustic Quality Over Centuries

How do Byzantine churches compare to modern-day concert halls in terms of sound? Leo Beranek studied the acoustical characteristics of concert halls around the world and correlated them to subjective preferences.² In Beranek’s study, the halls that were subjectively rated at the top exhibited a Bass Ratio in the range of 0.93 – 1.18 and a Timbre Ratio range of 0.77 – 1.04. In our measurements we found the Bass Ratio and Timbre Ratio values of the eight churches as shown in Table 2.

Table 2. Warmth (Bass Ratio) and Brilliance (Timbre Ratio) in the eight churches

Beranek further recommended that a Bass Ratio between 0.9 – 1.0 is the ideal range for speech. It is astounding that the churches of Thessaloniki, built from the 5th through the 14th century, exhibit such a close match to the optimal acoustical parameter ranges that were not formalized in the acoustics literature until the 20th century.

Byzantine churches were not only spaces for chant; they were also sites of homilies —many preserved for us until this day. Preaching to a full church in highly rhetorical language earned certain churchmen fame and followers. Certainly many of Byzantium’s great church orators must have preferred to deliver homilies in spaces that facilitated the spoken word, which had to be both audible and intelligible. Speech intelligibility is described by the Definition Measure C50, which corresponds to the ratio of sound energy arriving in the first 50 milliseconds (ms) after the direct sound to the remaining sound energy arriving after 50 ms. C50 is calculated in the range of 500 to 4000 Hertz (Hz) and it is considered to be “good” when it is above 0 decibels (dB). Concert halls typically have C50 values in the -1 dB to -4 dB range because they are designed for music and not speech. The eight churches that we measured showed very high values for C50. Table 3 summarizes the results and also reveals some unexpected findings. In general, shorter reverberation times are associated with an increase in intelligibility. This is supported by the measurements in St. Nicholas Orphanos, a 14th-century church that had the lowest reverberation time and the highest speech intelligibility. Surprisingly, however, the Acheiropoietos, a late-5th-century basilica with a long nave and side aisles, exhibited very high intelligibility despite having the second highest reverberation time. These findings, which were verified by chant recordings and several hours of listening, supports the historical record that the church was used for homilies. Certainly these powerful speeches were enhanced by the orators’ use of a high ambo located at the east end of the nave. Like many church furnishings that augment sound effects within the building, the Acheiropoietos ambo was long ago removed from the building, along with marble slabs that blocked the lower openings of the colonnades, rendering the nave a sound corridor.

Table 3. Definition (intelligibility) remains high despite long reverberation times

Speakers and recording equipment in St. Nikolaos Orphanos, Thessaloniki, during testing.

Reverence for Aural Sacredness

What is astonishing is the critical role that sound played in the construction of Byzantine churches. Sound—human, angelic, primordial, heavenly—is fundamental to the formation and perception of the sacred. Nearly every religion acknowledges the importance of sound, which is manifested in the voice of God, the call to prayer, collective chant, and in other profound ways. Sound unifies communities in sacred worship. It affirms sacred hierarchies. It is captured in images and contained in built environments. What is becoming increasingly clear to scholars is that medieval builders were as aware of the importance of sound environments as we are today. Even without the benefit of scientific testing and modern instrumentation, these innovators were able to create spaces that were transformative.

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