Study On The Effect Of The Shapes Of Orchestra Pit On The Acoustics Of An Opera House

When an opera is performed in a theater,the performance is composed of stage actors and the orchestra in the pit.Therefore,the acoustic of a theater depends largely on the coordination and balance of the stage and orchestra sources.In opera houses,the audience hall,stage and orchestra pit are coupled with each other.Therefore,the coupling effect among them makes the factors that affect the acoustic of the opera houses numerous and complex.There have been a lot of studies on the auditorium and stage,but researches on orchestra pit are still less.The influence of the space and boundary treatment of the orchestra pit on the acoustic of opera houses is still in the preliminary stage of exploration.By using the scale model technology,this paper studied treatments of the orchestra pit shape that may have an effect on the acoustic of the opera house.The research is based on the scale model of Zhuhai Opera House,simulating 5 orchestra forms in the scale model.Impulse responses were measured in the scale model and key acoustic parameters were analyzed,in order to verify whether these treatments of orchestra pit shape have specific effects on the sound field of the opera house or not.The study is divided into two parts:the analysis of the sound field in the auditorium and that in the orchestra pit.Important acoustic parameters included EDT,T₂₀,C₈₀,D₅₀,G,B of opera houses were selected for the analysis of sound field in the auditorium,while ST and G were used for the analysis of sound field in orchestra pit.The results show that:When the overhanging apron covers the pit less than 1/3,no significant effect on G,B,C₈₀,D₅₀,EDT and T₂₀of in the auditorium can be found,no matter if the sound source is placed on the stage or in the pit.When the apron overhanging covered the orchestra pit area largely（reach to 2/3 area of the pit）and the sound source is placed in the pit,C₈₀and D₅₀at the balcony were significantly reduced,indicating that the overhanging apron could block direct sound and early reflected sound of the sound source in the pit.Apron coverage had a great influence on the ST and G of the sound source in the orchestra pit.In the covered area,the ST and G increased significantly while had no influence in the uncovered area.In general,the inward and outward inclination of the pit’s side wall has little effect on G,B,C₈₀,D₅₀,EDT and T₂₀in the auditorium,no matter if the sound source is on the stage or in the pit.However,if analyzing the results in the view of each single point,a trend can be observed that when the sound source is in the stage,the inward inclination pit walls can increase C₈₀and D₅₀in the rear part of the main floor and in the balcony,while decrease in the fore part of the main floor.Besides,the inward and outward treatments of the pit’s side walls have little effect on the ST and G in the pit.For the acoustic of the auditorium,the tilting treatment of the pit’s back wall can significantly improve the G when the sound source is in the pit,making the balance parameter B more favorable to the orchestra sound source.For the acoustic of the pit,the tilting of the back wall reduced the ST and G,which indicated that the tilting of pit’s back wall could reflect more early sound energy from orchestra pit to auditorium,thus reducing the loudness in the orchestra pit.