L'Auditori

Acoustic design by Higini Arau

Sala 1 Pau Casals is characterised by a regular geometry in line with the great classical halls with the best acoustic conditions, with a regular plant of 2x1 proportions and a horizontal ceiling. The continuity in the interior organisation of the hall is intended to guarantee homogeneous conditions for seeing and hearing for all the audience. The only lining material used in the ceiling, floor and walls of the hall was plywood covered with a sheet of cork of variable thickness depending on the required sound diffraction.

The ceiling is defined by a system of structural transversal beams crossed by an added section of longitudinal beams distributed at variable intervals according to the law of progression, which is a multiple of 3 of the Fibonnacci series. The aim of the design is to provide a sound diffraction setup that balances diffuse with specula reflection. As the height of the ceiling with respect to the audience falls progressively to the back of the hall, the progression in the formal complexity of this reticular ceiling as the distance from the stage increases, guarantees that the first plans of the ceiling, closer to the front wall, are highly reflective of the medium and high frequency sounds, whereas in the last section of the ceiling, where the acutes lie, have another frequency and are highly directional and will be dispersed by diffuse reflection to guarantee the specula reflection of low frequency sound.

The acoustic calculations for different frequency bands and with the hall full give the following reverberation time values, and also the values of the TMID (mean reverberation time value at 500 and 1000 Hz), the TLOW (mean value at 125 and 250 Hz) and the THIGH (mean value at 2000 and 4000 Hz):

	Frequency						Mean values
	125	250	500	1000	2000	4000	TMID	TLOW	THIGH
Reverberation times	2.46	2.40	2.15	1.98	1.90	1.69	2.07	2.43	1.80

Furthermore, the optimal TMID reverberation time calculation in relation to the air volume of zone V (24298 m3) and the surface area of the Audience SA (1621 m2) obtained from the number of spectators N (2326 spectators), gives us the following results:

• T = 2.29 s
• TMID min = 1.63 s
• TMID design = 0.9 x TMID max = 2.06 s
• TMID sized = 2.04 s

(See H. Arau, "Variation of the Reverberation Time of places of public assembly with audience size", Building Acoustics, Vol.4 Nm.2, 1997).