Step 2: Choosing the seats for the audience
Structure, material, dimensions...
We have a seating area of 918 square meters and 160 square meters for the stage area. The stage is designed for 100 piece orchestra. In our design we prefer to use conventional seats that are usually used in concert halls. The dimensions and the shape of such a seat can be seen on the figure below.
We need 0.60 square meter per seat. Therefore we can put 1530 seats in our seating area. The seat comprises a metal structure and springs, a polyurethane foam block, upholstery, shell and hinge pins. The seats have the following characteristics:
Absorption of the seats is very important in this kind of hall. Most part of the incident waves is absorbed by the seats. Also the audience and orchestra affect the absorption coefficients of the hall. So we should take into account both audience and orchestra while calculating the absorption coefficients. These calculations are done in an anechoic chamber. In our design we used the data from Leo Beranek's book. We assumed that the seats we used are covered with light upholstered.
Absorption coefficients for chairs in unoccupied seating areas
Absorption coefficients with 100% occupancy
The absorption coefficient of the human body affects the overall absorption coefficient. The absorption coefficient of the field is less affected by the degree of sound diffusion in the sound field at mid and high frequencies, however at low frequencies the value of the absorption coefficient of the field is highly dependent on the angle of incidence. Because of that the following figure only shows how the incident wave effects the absortion coefficients in 125Hz and 250Hz.