Study on the effects of the harmonic choir stalls in the Church of the Certosa di San Martino in Naples

Abstract

The Church of the Certosa of San Martino was built in the 14th century and is characterized by the presence of an elliptical harmonic box built under the floor of the choir stalls, with which it communicates through openings in the floor. The harmonic box was made to remedy sound defects that appeared in the Church after the opening of several windows in the upper part of choir stalls and nave. The opinion of the monks was that these acoustic flaws caused their chants vibrations to be weakened and even lost. This work verifies whether the elliptical volume constructed below the choir stalls has any acoustic purposes. Acoustic measurements were carried out in its current state and then closing the connecting openings between the choir stalls and the cavity below, so as to assess any changes in the acoustic characteristics. The acoustic measurements were carried out by placing a sound source both in the choir stalls and on the altar, along with microphones in the choir stalls and the nave. At the end of taking the measurements, a change was observed in the acoustic parameters EDT, C₈₀, and D₅₀ only when the sound source is in the choir stalls.

Keywords

Church choir stalls nave acoustics harmonic box

Introduction

Several authors have presented the acoustic memories of Churches and the effects of resonant pots included within the walls. The treatise “De Architectura”¹ describes some of the fundamental principles for improving the acoustics of theaters, such as placing resonant pots under the bleachers of the auditorium so as to improve speech understanding. Other authors have reported studies on resonant pots in Orthodox Churches for the effect of resonators on the acoustical performance of a Church is very weak being discussed.^2,3 Weak variations could be observed on the measured acoustic parameters of these Churches by insertion of pots. While the measurements taken inside two Churches in Switzerland have shown that the effect of pots is almost unobservable, the authors concluded that the results do not allow to either affirm or discard the use of pots. This article shows the evaluation of the acoustic characteristics of the Church of the Certosa of San Martino (Naples), characterized by the presence of a harmonic box with a square plan and elliptical section located below the choir stalls, communicating with it by means of openings in the floor. This harmonic box was realized to remedy insurgent acoustic defects following the opening of several windows in the upper part of nave.^4–6 The monks complained about acoustic defects which included the weakening and loss of their chants. The Carthusians realized a cavity so as to make their serious and melancholy chants stronger and more vibrant. The Carthusian monks spent a lot of time singing in the choir stalls since this was their way of praying. It therefore represented an essential spiritual instrument. To test this hypothesis, acoustic measurements were taken in its current state and then by closing the connecting openings between the choir stalls and the underlying cavities, so as to evaluate possible changes and differences of the acoustic characteristics. The acoustic measurements were taken by placing an omnidirectional spherical sound source, initially in the choir and then near the altar, with different microphone points in the Church following the proceeding adopted in other similar experiences.⁷

The Certosa of San Martino

The Certosa of San Martino, placed in a dominant position on the city of Naples, on Vomero hill, next to S. Elmo Castle, was built in obedience to Charles I wishes, eldest son of King Robert of Angiò, in 1325. The Certosa of San Martino is one of the most important witnesses in southern Italian of the Carthusian order culture, whose rule favors choice of life as a hermit, partially mitigated by cenobitism, in light of Benedictine motto ora et labora, and for history of Neapolitan art one of the most important and richest monuments. The Carthusians express the essence of Benedictine creed beyond the concept of a monastery only as a place of prayer, aiming to realize small monastic worlds conceived as model cities; monastic building is considered as a set of parts, each one indispensable to the other and helps to form a complete body. Therefore, an architectural feature is a mediation between two opposite trends: hermit’s life and that of community, which requires differentiated spaces but at the same time united in a simple architectural system. The Certosa of San Martino is divided into three basic architectural nuclei: a Church, a small cloister with chapter house and refectory, and a large cloister with cells. From the square in front of Belvedere di San Martino, to the right of “Dame” Church, is opening up the access to the Certosa that directly leads into cloister of Guest House. The Carthusian monks lived as hermits and penned, characterized by silence and solitude, but also by moments of community prayer and liturgy, the latter always sung and mostly in Latin. Carthusian chant is not fundamentally different from Gregorian chant, but it differs from the latter mainly for sobriety and austere simplicity harmonizing melodies and words and it is strictly performed without accompaniment of musical instruments. The chant is characterized by power, calm, slowness, and communion. The chant seems not immediately melodious, but it is marked by a certain roughness, underlined by noise of stalls and creaking timbers. Over the centuries, many people remained enraptured by the harmonious melody of Carthusian monks chant.

The Church of the Certosa

The Church has a regular plan and is composed of a single nave with eight side chapels as well as other rooms. The original Gothic structure of the Church, under pressure of Counter-Reformation, was renovated and expanded by the end of the 16th century in a late Mannerist and Baroque style. In the nave, in a slightly raised position, there is an altar made of golden wood and faux marble. The apse is rectangular in shape and houses a carved wooden choir stalls with 40 places. The Church floor is made of marble, while a harmonic box with an elliptical cross section (with the same plan dimensions) was built in the apse, with it being intended to make the serious and melancholic chanting of the monks stronger and more vibrant. Figure 1 shows the internal part of the Church, while Figure 2 shows the ground plan of the Church. The nave has the following dimensions: a length equal to 22.0 m, width 27.0 m and a medium height equal to 18.4 m, and a volume of 10,930 m³. At the end of the Church, there are choir stalls, along with a high altar. This part is slightly elevated above the nave and has wooden benches along the perimeter walls, where the monks sat down to sing. The dimensions of the choir stalls are as follows: length equal to 15.0 m, width equal to 9.0 m and a medium height of 13.5 m, and a volume of 1823 m³. The total volume of the Church is about 12,753 m³. Below the choir stalls has an elliptical-shaped section and is connected to them through three openings. The cavity has a height equal to 7.5 m, a length of 15.0 m, a width of 7.5 m, and the volume of about 7000 m³. Table 1 shows the main dimensions of the Church.

Table 1.

Dimensions of the Church.

	Length (m)	Width (m)	Height (m)	Volume (m³)
Nave	22.0	27.0	18.4	10,930
Chorus	15.0	9.0	13.5	1823
Cavity	15.0	9.0	7.5	7000

Figure 3 shows the section of the choir stalls, with a section of the harmonic box highlighted, while Figure 4 shows the details of the opening on the floor covering underlying harmonic box.

The harmonic choir box has an oval flat shape and communicates with the choir stalls above through three small windows carved along a central section of the floor: a large round window in the center and two smaller rectangular, equidistant from the central one, one near the altar and the other at the opposite side. It seems clear that the aspects related to the acoustics and resonance of the choir were particularly well finished since these aspects were of great importance to the Order of the Carthusians.

Acoustic measurements

To objectively evaluate the acoustic behavior of the Church, measurements were taken with the appropriate instruments. They were taken with a dodecahedral sound source, placed at a height of 1.5 m from the floor, fed with a signal maximum length sequence (MLS), in accordance with the standard ISO 3382-1,⁸ with the impulse response technique. The sound source used to take the acoustic measurements consisted of a dodecahedron loudspeaker Peeker Sound JA12 (Peeker Sound Corporation, Reggio Emilia, Italy). MLS signals of order 16 with a length of 5 s were generated by a 01 dB Symphonie system.^9,10 The sound pressure was recorded with a ½″ microphone GRAS 40 connected with a preamplifier 01 dB PRE 12 H. The response was detected by an omnidirectional microphone placed at a height of 1.5 m from the floor; the sound pulse was developed with the Dirac software, which provided the monaural acoustic parameters (T₃₀, EDT, C₈₀, and D₅₀).¹¹

The typical suggested values of the different monaural acoustic parameters for both speech comprehension and music listening are as follows:^12,13,14

Reverberation time T30 should assume values below 1.0 s for a clearer perception of speeches, while it may assume greater values, around 2.0 s for music listening preference.

Clarity C80, expressing the balance between the early and late arriving energy, should have an higher value if the goal is to separate the initial sounds from the diffuse ones and making the discrete sounds stand apart from each other. In a sound field which is not completely diffuse, the clarity C80 is uncorrelated to the reverberation time, and for the purposes of good listening conditions of music is generally reported that C80 should be in the range between −2 and 2 dB, while it is expected to be above 2 dB if speech perception is a priority.

Definition D50 may assume values from 0 to 1.0, but for a good speech comprehension, it is often accepted that D50 should have values above 0.5.

Table 2 shows the synthesis of the optimal acoustic parameter values for the different listening conditions.

Table 2.

Optimal acoustic parameter values for the different listening conditions.

Parameters	EDT (s)	T₃₀ (s)	C₈₀ (dB)	D₅₀
Optimal values for musical performances	1.8 < EDT < 2.6	1.6 < T₃₀ < 2.2	−2 < C₈₀ < 2	<0.5
Optimal values for speech performances	1.0	0.8 < T₃₀ < 1.2	>2	>0.5

The sound source was first placed in the choir stalls and then on the altar (Figure 5), while the microphone receivers were placed at various points of both the choir stalls and nave, in the area occupied by the congregation and 18 locations equally distributed with known coordinates. During the acoustic measurements, the nave was completely empty, while in the center of the choir stalls, there was a wooden lectern and 40 carved wooden stalls along the perimeter walls. The acoustic measurements were carried out under two conditions, in absence of the public, in its current state and then closing the perforated communication openings between the choir stalls and sound box, in order to exclude the contribution to the sound field of the latter. This resulted in a total of four series of acoustic measurements being carried out, two source positions (altar and choir) and two receiver positions (choir and nave, in an area where the congregation remained). An acoustic analysis was carried out with the intention of assessing the potential contribution of the sound box to the acoustics of choir stalls. Figure 6 shows the sound source placed near the altar, and Figure 7 shows the sound source placed in the choir stalls.

Discussion

For each measurement point, values of the following acoustic parameters were obtained: T₃₀, EDT, C₈₀, and D₅₀. Figures 8 and 9 show the average values and relative standard deviations of the measured parameters with the sound source in the choir stalls and with the sound source near the altar. The acoustic parameters are reported in octave bands from 125 Hz to 4.0 kHz.^15,16,17 The effects of the sound box on the sound field in the Church are analyzed. This analysis is carried out closing the communication openings between the choir stalls and the sound box.

The average values of the acoustic parameters with the sound source placed in the choir stalls are more scattered than when the sound source is placed near the altar. This shows how when the source is in the choir stalls, the acoustics vary from point to point. The graphical representation of the measured average values do not allow for any assessment of the effects of the presence of the sound box under the choir stalls. The average values of C₈₀ are below the optimal range for musical performance. Furthermore, the average values of the reverberation time are about 2.5 s. The average values of D₅₀ correspond to the condition of low speech understanding. Furthermore, Figures 10 –12 show the spatial distribution of measured acoustic parameters T₃₀, C₈₀, and D₅₀ (in octave band at the frequency of 1.0 kHz) with the sound source near the altar in its current state.

Evaluation of the harmonic box effects

In order to better understand the effects of the harmonic box, measurements in the current state were carried out with the source in the choir stalls and on the altar and 6 microphone points in the choir stalls and 12 equally spaced points in the nave. The values of the individual measured acoustic parameters were analyzed by relating all the measured points to each other (both with open cavity and when the closed cavity between the choir stalls and the box were closed) as well as to the frequencies (in octave bands from 125 Hz to 4 kHz). The measured values in the two measurement configurations are represented on a graph which reports the values of the acoustic characteristics with open cavity, along with the values of the acoustic characteristics without any contribution of the cavity below the choir stalls (closed cavity), with the sound source both in the choir stalls and the nave. Figure 13 shows the acoustic parameters when the sound source is near the altar and the receivers are in the choir stalls. Figure 14 shows the acoustic parameters when the sound source is near the altar and the receivers are in the nave. Figure 15 shows the acoustic parameters when the sound source is in the choir stalls and the receivers are in the choir stalls. Figure 16 shows the acoustic parameters when the sound source is in the choir stalls and the receivers are in the nave.

It is possible to assume that the acoustic characteristics change depending on whether the sound source is placed in the choir stalls or near the altar.

The graphs in Figures 13 –16 show how, in both cases, the values for the acoustic characteristics are located in the segment that divides the quadrant. Figure 13 shows, when the sound source is near the altar and the receivers are in the choir, the T₃₀ values do not vary; EDT values decrease with closed cavity; C₈₀ and D₅₀ increase with closed cavity. Furthermore, when the cavity is opened (current state), the values of C₈₀ come close to values required by Barron for good music listening. When the sound source is placed near the altar (Figure 14), in the nave, the acoustic characteristics do not vary if cavity is opened or cavity is closed.

When the sound source is placed in the choir stalls, the acoustic characteristics trend changes both for the values measured in the choir stalls and those measured in the nave (Figures 15 and 16).

With the sound source and receivers located in the choir stalls (Figure 15), the T₃₀ values do not change, while the EDT values increase when cavity is closed. The presence of the cavity reduces the value of the EDT in this area. With open cavity the values of D₅₀ increase; therefore, the presence of the cavity improves speech understanding in the choir stalls, furthermore in this configuration the values of C₈₀ increase.

While when the sound source is positioned in the choir stalls and the receivers in the nave (Figure 16), there was a trend reversal. Although in the choir stalls, the T₃₀ values do not change, those of the EDT are reduced when cavity is closed.

With open cavity the values of D₅₀ decrease; therefore, the presence of the cavity reduces speech understanding in the nave, and in this configuration the values of C₈₀ decrease. In the nave, when cavity is opened, the values of C₈₀ come close to values required by Barron for good music listening.

Paradoxically, the presence of the cavity in the choir stalls generates an acoustically optimal environment for music listening in the nave area, while in the choir stalls, the C₈₀ values move away from the optimum.

Conclusion

The analysis of the results show how when the sound source is near the altar, the acoustic characteristics in the nave remain largely unchanged. It is not possible to detect any significant differences in this condition. However, when the sound source is in the choir stalls, despite the values of T₃₀ not changing, there is a clear change in the EDT, C₈₀, and D₅₀ values; in particular in the nave, when cavity is opened, the values of C₈₀ come close to values required by Barron for good music listening.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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