Sound quality in Finnish Lutheran churches Frida Vikström School of Electrical Engineering Thesis submitted for examination for the degree of Master of Science in Technology. Espoo 10.10.2016 Thesis supervisors: Prof. Ville Pulkki Thesis advisor: M.Sc. Henrik Möller aalto university abstract of the school of electrical engineering master’s thesis Author: Frida Vikström Title: Sound quality in Finnish Lutheran churches Date: 10.10.2016 Language: English Number of pages: 8+94 Department of Signal Processing and Acoustics Professorship: Acoustics and Audio Sound Processing Supervisor: Prof. Ville Pulkki Advisor: M.Sc. Henrik Möller Acoustical measurements were made in twenty churches in the Helsinki area, and their acoustical properties were compared to each other. The churches varied in size from small village churches to large cathedrals, were built between the 1470’s and 2005, and were built of stone, tile or wood. The churches were measured following the ISO 3382 standard. The results showed no clear distinctions between churches of different ages. The average reverberation time was longer than what is recommended for concert halls, with a small correlation to the volume of the church. The results of the modern churches were varying for all measured parameters, with no apparent correlation to the materials, sizes or ages of the churches. The average STI of 0.5 for all measured churches indicates that sound systems are needed in churches for the speech intelligibility to improve in the otherwise reverberant space. Keywords: acoustics, churches, acoustic measurements, church acoustics aalto-universitetet sammandrag av högskolan för elektroteknik diplomarbetet Författare: Frida Vikström Titel: Ljudkvalitet i Finlands lutherska kyrkor Datum: 10.10.2016 Språk: Engelska Sidantal: 8+94 Avdelningen för Signalbehandling och akustik Professur: Akustik och ljudbehandling Övervakare: Prof. Ville Pulkki Handledare: DI Henrik Möller Akustiska mätningar genomfördes i tjugo kyrkor i Helsingforsregionen och deras akustiska egenskaper jämfördes sinsemellan. Kyrkorna var av varierande storlek, från bykyrkor till stora katedraler, byggdes mellan 1470-talet och 2005, och var bygg- da av sten, tegel eller trä. Kyrkorna mättes enligt standarden ISO 3382. Resultaten visade inga tydliga skillnader mellan kyrkor av olika ålder. Medelefterklangstiden var längre än vad rekommenderas för konsertsalar och korrelerade lätt med kyrkans volym. De moderna kyrkornas resultat varierade för alla uppmätta parametrar, och ingen korrelation verkade finnas till kyrkans material, storlek eller ålder. Ge- nomsnittsvärdet 0,5 för parametern STI tyder på att ljudsystem är nödvändiga i kyrkor för att förbättra talhörbarheten i de i övrigt ekande rummen. Nyckelord: akustik, kyrkor, akustiska mätningar, kyrkoakustik iv Preface Many thanks to my advisor mr. Henrik Möller for providing me with the idea to research church acoustics, and his help in choosing the churches. His expertise on all things related to room acoustics has been invaluable. Likewise, my supervisor professor Ville Pulkki deserves a big thank you for his input on the contents of this thesis. I am also very grateful to Akukon Oy for lending me the measurement equipment. The congregations I visited while measuring the churches deserve a special thank you. The vergers who allowed me inside the churches at varying times of the day and endured my questions about how the church hall was used, and the secretaries who let me dig through their archives in search of architectural drawings: thank you for your help and patience. An extra thank you to the real estate agency at Helsingin seurakuntayhtymä for providing me with excellent drawings of all the churches in Helsinki. I am also indebted to the vicars, cantors and architects who took time out of their schedules to answer my questions. My deepest gratitude goes to my father for the unwavering support through all the phases of this work. His comments on the text and inquiring phone calls in the evenings played a big role in this thesis getting finished. Finally, to the wonderful people at Teknologföreningen and especially its subgroup at Nyagamla. Without you, my years of studying would have been fewer, more difficult, and infinitely more boring. Thank you for the inspiration, fascinating discussions, and much needed laughs at any and all time of the day. Otaniemi, 10.10.2016 Frida Vikström v Contents Abstract ii Abstract (in Swedish) iii Preface iv Contentsv Symbols and abbreviations vii 1 Introduction1 1.1 Thesis formulation............................1 2 Behaviour of sound and hearing3 2.1 Basic measures..............................3 2.2 Sound waves................................4 2.3 Sound field in a room...........................5 2.4 Hearing..................................6 3 Room acoustics8 3.1 Impulse response.............................8 3.2 Reverberation time............................ 10 3.3 Clarity................................... 12 3.4 Bass ratio................................. 13 3.5 Speech transmission index........................ 13 4 Earlier studies 16 4.1 Acoustics of concert halls in Finland.................. 16 4.2 Acoustics of churches........................... 17 5 Perceived acoustics of churches 19 5.1 Architecture and function........................ 19 5.2 Music and speech............................. 21 5.3 Sound systems............................... 21 6 Measurement and methods 23 6.1 Devices and program........................... 23 6.2 Setup.................................... 25 6.3 Measured churches............................ 25 7 Results 37 7.1 Reverberation time............................ 37 7.2 Clarity C80 ................................. 39 7.3 Bass ratio................................. 41 7.4 Speech transmission index........................ 42 vi 7.5 Summary................................. 44 8 Conclusions 48 References 50 A Measurement report: Pohja church 54 B Measurement report: Tuusula church 56 C Measurement report: Lapinjärvi church 58 D Measurement report: Karjalohja church 60 E Measurement report: St. John’s church 62 F Measurement report: Kallio church 64 G Measurement report: St.Paul’s church 66 H Measurement report: Kulosaari church 68 I Measurement report: Munkkiniemi church 70 J Measurement report: Kannelmäki church 72 K Measurement report: Temppeliaukio church 74 L Measurement report: Roihuvuori church 76 M Measurement report: Oulunkylä church 78 N Measurement report: Myyrmäki church 80 O Measurement report: St. Matthew’s church 82 P Measurement report: Myllypuro church 84 Q Measurement report: Masala church 86 R Measurement report: Church of the Good Shepherd 88 S Measurement report: Laajasalo church 90 T Measurement report: Viikki church 92 vii Symbols and abbreviations Symbols αi Absorption ratio of a material A Absorption area cair Sound velocity in air C50 Clarity C80 Clarity C80,mid Clarity, mid-frequencies (500 Hz, 1000 Hz) δ(t) Dirac delta function dB Decibel f Frequency h(t) Impulse response I Sound intensity I0 Reference intensity LI Sound intensity level Lp Sound pressure level LSN Signal-to-noise ratio level LW Sound power level p Sound pressure p(t) Sound pressure p0 Reference sound pressure P Sound power P0 Reference sound power P a Pascal Q Directivity of a sound source SNapp Apparent signal-to-noise ratio T Temperature T20 Reverberation time [(-5 dB – -25 dB) × 3] T30 Reverberation time [(-5 dB – -35 dB) × 2] T30,mid Reverberation time, mid-frequencies (500 Hz, 1000 Hz) T60 Reverberation time Ts Centre time V Volume wj Weight factor for octave bands used in weighted averaging W Watt viii Abbreviations A/D Analog-to-digital BR Bass ratio EDT Early decay time IACC Inter-aural cross-coefficient ISO International Organization for Standardization LF Lateral energy fraction MAF Minimum audible field MLS Maximum length sequence MTF Modulation transfer function RASTI Rapid speech transmission index RH Relative humidity RT Reverberation time SFS Finnish Standards Association SNR Signal to noise ratio STI Speech transmission index 1 Introduction When asked to imagine a typical church, most people seem to form a picture of a large, reverberant room with a high ceiling, the very atmosphere of which prompts you to still and quiet down. In a historical context this makes sense: for hundreds of years the Christian church was the largest institution in Europe, and the congregations needed to be able to host all their members for the weekly services. The priest needed to make himself heard to everyone in the room, and without modern sound systems the room itself had to provide the means. While modern sound systems nowadays can be found in most Finnish churches, the church halls tend to be unfit for many of the events the Lutheran church now offers. While every congregation still celebrates service of worship every Sunday, the number of attendants is dwindling, and the services are perceived as outdated and boring by much of the younger generation. Other types of activities, such as youth nights, discussion groups, and choir practises, tend to be much more popular, but usually the church halls are deemed unfit for such activities. The acoustics of the church halls play a big role in this: if the room echoes too much, trying to keep a discussion going is not going to work. Participants in more modern forms of worship, where electrically amplified instruments and microphones are used, also find church halls hard to work in, since they are not built with amplified music in mind. Although churches have been a