ACOUSTIC DESIGN

THEATRE

Reverberation time around 1’1-1’4s.

It looks for the proximity between the spectator and the actor.

There is a complete stage house in order to contain high-rise sets.

It materialises a clear frame between spectators and the stage.

The volume per spectator is approximately between 6-7m3/seat.

MUSIC HALL

Reverberation time higher than 1’6s (even up to 2’0s).

It looks for intimacy values and immersion of the spectator into the performance. Spectators can surround theirselves with musicians completely.

It doesn´t have equipment for theatre scenery.

Volume per spectator between 8-10m3/seat.

MULTIPURPOSE

Reverberation time around 1’0-1’2s.

It looks for the adaptability to any usage.

There is not a stage house itself, but the support structure of the equipment´s elements extends over the audience. There is not a limit between the audience and the stage.

Volume per spectator between 5-7m3/seat.

Any room, regardless other acoustic parametres, must have a reverberation time adapted to the use of the room and depending on its volume.

The following graph shows optimum reverberation times according to the use.

CONCERTGEBOUW

Amsterdam

RT empty = 2’00s
RT full = 1’58s
Volume = 18.780m3
Seats = 2.037

SYMPHONY HALL

Boston

RT = 2’00s
Volume = 18.750m3
Seats = 2.625

MUSIKVEREINSSAAL

Vienna

RT empty = 2’00s
RT full = 1’77s
Volume = 15.000m3
Seats = 1.680

Considerations to take into account in order to design the sightlines are:

-The eyes are on average 100mm below the highest point of the head.
-The average height of a person sitting up considered is 1200mm.
-The visual should go over the spectator's head located in the immediately previous row.
-The objective ​​of high quality will happen if you can visualise a point located at 500mm high and 1000mm to the edge´s apron of the stage.

This involves to value the geometry of the laterals and the ceiling in order to achieve a better acoustic quality.

The spatial impression is given by the energy provided by side reflections within the first 80ms.

Laterals, parapet of the terraces included, are the main actors in the stereo effect of the room.

The design goals of the ceiling of the room are:

Define the volume of the room.
Allow the musicians to hear each other.
Distribute sound energy on the plane of hearing.
Reduce the difference in level between the first and the last row.

VOLUME PER SPECTATOR

While absorption of the audience is a fixed datum in a room, the following volumes per spectator are recommended in order not to have problems with the relation between volume, based on the absorption of the audience, and reverberation.

4-6 m3/Seat...........RT < 1,3s

6-7 m3/Seat...........RT < 1,5s

7-9 m3/Seat...........1,5s < RT < 2,0s

9-11 m3/Seat..........RT > 2,0s

REVERBERATION TIME

BASS RATIO (BR)

It represents the wealth of low frequency, the softness and the sickly-sweetness of the music in the room.

It is said that a room has acoustic warmth if it presents a good answer to the bass frequencies. This one is taken as the relation between the average value of the RT in 125 and 500Hz and the RTmid.

BRILLIANCE (Br)

The brilliant adjective is indicative that the sound in the room is clear and rich in harmonics.

Similarly, it is said that the sound of a room is brilliant if it presents a Good answer in high frequencies. The brilliance will be the relation between the average value of the RT in 2.000 and 4.000Hz and the RTmid.

DEFINITION INDEX (D50)

A room with a low definition index is perceived as slightly intimate.

If the definition index increases, it means that the room is better prepared to the speech.

CLARITY (C80)

This parameter values the distinction that you can appreciate between different sounds in a musical composition.

The Clarity index C80 represents the balance between early (inside the first 80ms) and late energy.

LATERAL EFFICIENCY (LF80)

It gives the impression of being surrounded by music, immersed in it, is enhanced with side reflections.

SPEECH TRANSMISSION INDEX (STI)

It measures the degree of clarity in the spoken messages basis of the percentage of understood sounds compared to the total of the produced ones in an oral communication.

In a room for speech, it has to be required, in any case, that any seat must have a STI higher than 0'55, which represents at least an understanding of 70% of words and 98% of sentences.

HOMOGENEITY OF LEVELS (SPL(A))

In this parameter, it is important to establish that the limit between the sound pressure level received by a spectator seated in the first rows in relation with other one located at the bottom of the room is 6dBA maximum.

Acording to the theories of Sabine and Eyring, and the covering materials mentioned before, an estimation of the tonal curve is calculated.

In this section, the acoustic parameters of the acoustic design proposed will be checked by 3D acoustic modelling with Odeon software, in each spectator/musician position.

For each configuration, a summary graph will be presented for each one of the merit values obtained in the acoustic modelling.

Merit value = 1