Building Technology and Architectural Design. Program 4th lecture Case studies Room Acoustics Case studies Room Acoustics

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1 Building Technology and Architectural Design Program 4th lecture Case studies Room Acoustics Break Case studies Room Acoustics Lecturer Poul Henning Kirkegaard :32 P.H. Kirkegaard - Department of Civil Engineering Slide 1/56 Troldtekt acoustics woodcrete panels :32 P.H. Kirkegaard - Department of Civil Engineering Slide 2/56

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6 Prints on acoustics panels :32 P.H. Kirkegaard - Department of Civil Engineering Slide 11/56 Rockfon acoustics panels :32 P.H. Kirkegaard - Department of Civil Engineering Slide 12/56

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10 Concert Hall Acoustics - an Overview Therearethreebasictypes ofconcerthall architectures: theshoebox, thevineyardand thefan form. The classical halls of the nineteenth century were narrow, high, rectangular shoeboxes. These are halls like the Amsterdam Concertgebouw (1888), the Vienna Musikvereinssaal (1870) and the Boston Symphony Hall (1900). The second form, the vineyard, is often made of layered terraces or arenas with prominent diffusing upperreflector surfaces. The audience is devided into smaller sub-seating-areas. These are often asymmetrical and create useful early reflections into all sections of the audience. A typical vineyard hall is the Berlin Philharmonie (1963). The third form, the fan type, proved unsuccessful nearly everywhere. This form was somehow common in the mid-20th century :32 P.H. Kirkegaard - Department of Civil Engineering Slide 19/56 The shoe box - Royal Festival Hall :32 P.H. Kirkegaard - Department of Civil Engineering Slide 20/56

11 The vineyard - Berlin Philharmonie :32 P.H. Kirkegaard - Department of Civil Engineering Slide 21/56 The fan-shaped - Barbican Hall, London :32 P.H. Kirkegaard - Department of Civil Engineering Slide 22/56

12 Clarity C80, C50 (db) The measurement of Clarity is the ratio of the energy in the early sound compared to that in the reverberant sound, expressed in db. Early sound is what is heard in the first 80 msec (C50-50 msec) after the arrival of the direct sound. It is a measure of the degree to which the individual sounds stand apart from one another. If the clarity is too low, the fast parts of the music are not "readable" anymore. C80 is a function of both the architectural and the stage set design. If there is no reverberation in a dead room, the music will be very clear and C80 will have a large positive value. If the reverberation is large, the music will be unclear and C80 will have a relatively high negative value. C80 becomes 0 db, if the early and the reverberant sound is equal. Often the values for 500Hz, 1000Hz and 2000Hz are averaged. This will be expressed by the symbol C80(3). For orchestral music a C80 of 0dB to -4dB is often preferred, but for rehearsals often conductors express satisfaction about a C80 of 1dB to 5dB, because every detail can be heard. For singers, all values of clarity between +1 and +5 seem acceptable. C80 should be generally in the range of -4dB and +4dB. For speech, in comparison to music, the Clarity will be measured as the ratio of the first 50 msec (C50) instead of 80 msec (C80) for music :32 P.H. Kirkegaard - Department of Civil Engineering Slide 23/56 'Deutlichkeit' (Clarity) D-50 Deutlichkeit is the ratio of early sound energy to the total sound energy. In concert hall acoustics it refers to the degree to which individual strands in a musical presentation can be differentiated from each other :32 P.H. Kirkegaard - Department of Civil Engineering Slide 24/56

13 Initial Time Delay Gap ITDG (msec) The time difference between the arrival of the direct sound and the first significant reflection (at a listener's seat in the hall). It corresponds to the subjective impression of 'intimacy'. Preferred values don t exceed 20 msec :32 P.H. Kirkegaard - Department of Civil Engineering Slide 25/56 Intimacy LTDG msec The initial time delay gap measured near the center of the main floor. It is generally determined by the first sound reflection of a side wall or a balcony front after arrival of the direct sound. The music should sound as if heard in a small hall - the listeners should feel an intimate contact with the performers. Texture Texture is the subjective impression the listeners derive from the patterns in which the sequence of early sound reflections arrive at their ears. Good texture requires a large number of early reflections, uniformly but not precisely spaced apart, and with no single reflection dominating the others. Spaciousness Is supported by early reflections that arrive from near lateral directions :32 P.H. Kirkegaard - Department of Civil Engineering Slide 26/56

14 Diffusion Every successful hall for music has irregularities, both large and small, on walls, balcony faces and ceilings which create a rich and dense sound structure. Such irregular surfaces diffuse the high frequency portions of the early reflected sound waves, adding patina to the overall sound. Stage Support is a measureofstrengthoforchestralsound returned by nearby reflecting surfaces to the ears of each player in the orchestra, the acoustical support, that a hall gives a player on stage. Measured as the ratio of the arriving sound energy at the first 10 msec and the arriving sound energy between 20 and 100 msec. Measurement source is an omnidirectional sound source in a distance of 1 meter. The sound arriving in the later interval has been reflected in the hall and the stage environment already. The measurements are made at several positions and the data are averaged. Strength G (db) The strength G is defined as the difference between the sound level in db at listeners position in the hall and the level of the same source in free field in the reference distance 10 m from the centre of the source. The strength of the sound, which is related to loudness, is a quantity that must be as uniform as possible throughout the hall. Interaural Cross Correlation Coefficient IACC The measure of the difference in the sounds arriving at two ears of listener facing the performing entity in a hall. IACC is usually measured with a dummy head. IACC3 is the average of IACC's for the three octave frequency bands with center frequencies of 500, 1000 and 2000 Hz :32 P.H. Kirkegaard - Department of Civil Engineering Slide 27/56 Bass Ratio, Bass Strength BR BR is a measure of the support which the reverberation in the hall gives to the low notes of the music. The Bass Ratio is objective counterpart of the subjective criterion "Warmth". It is the ratio of RT between low frequencies (octaves 125 and 250 Hz) and medium frequencies (octaves 500 and 1000 Hz). The preferred values of the BR are between 1.1 to 1.25 for halls with high RT's, and 1.1 to 1.45 for halls with RT's of 1.8 sec or less. Envelopment Envelopment is quantified by the amount of sound that comes not directly from the source. But the total amount of sound that comes on the horizontal plane on a listener's position. Can be displayed in a soundrose, a circular representation of the directions from which a listener receives sound impulses. A hall with good lateral (side wall) reflections usually has a better feeling of intimacy. Halls are designed with the goal to let the hall sounding as small as possible. That way the audience feels up close and personal with the orchestra. %ALCONS (%) The measured percentage of Articulation Loss of Consonants by a listener. %ALCONS is derived from the direct to total arriving sound energy ratio. %ALCONS of 0% to 3% indicates perfect clarity and intelligibility with no loss of sentence understanding, while 10% and beyond is growing toward poor intelligibility, and 15% typically representing the maximum loss acceptable. Echoes The room and stage must be free from audible echoes :32 P.H. Kirkegaard - Department of Civil Engineering Slide 28/56

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17 Strategies to Mitigate Sound Focusing 1) Stepped gradations for the auditorium ceiling; (2) Suspended convex reflection panel at center of ceiling; (3) Retractable soundabsorbing curtains and curtains for the front portions of the glass sections of the auditorium walls :32 P.H. Kirkegaard - Department of Civil Engineering Slide 33/56 Challenges in Modeling this Auditorium Large number of faces Curved surfaces approximated with planar surfaces Sensitive to absorption & scattering coefficients Large surfaces If in doubt, try with both high and low values [for scattering coefficients] and see if the results are sensitive or not (it depends on the hall shape and the absorption distribution and is very difficult to know in advance). - Bengt-Inge Dalenbäck (CATT user s web page) Coupled room Transmission coefficients for some surfaces :32 P.H. Kirkegaard - Department of Civil Engineering Slide 34/56

18 Music Center at Strathmore The Music Center at Strathmore in Montgomery County Maryland has a particularly complex and grand array of variable acoustic devices that required a control system that could organize, display, and execute the movement and position status of 110 electro mechanical elements :32 P.H. Kirkegaard - Department of Civil Engineering Slide 35/56 Acoustic adjustment of rooms The system modifies the hall s acoustic in a natural way by filling in the missing reflections from each surface and can even, electronically, move those surfaces to acoustically more desirable positions. Microphones to capture the sound on stage and in the auditorium Loudspeakers discretely positioned around the auditorium to reproduce the missing reflections and reverberation Central equipment comprising an advanced digital processor, amplifiers, and a control panel for selection of the acoustic settings and other functions such as line input and line output :32 P.H. Kirkegaard - Department of Civil Engineering Slide 36/56

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