Acoustic Design in Architecture
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The purpose of this report is to produce a design scheme for the conversion of a large room to a multi use theatre. The report will present the necessary things that need to be considered to ensure a satisfactory acoustic environment by measuring the problems encountered with acoustic design and how to tackle them. The report will look at the problems related to this space and present possible solutions and recommendations based on the information available.
As in every case, this room presents it's own unique set of problems, which involve very common factors such as the shape and size of the room, the intended use of the space, the budget and the basic laws of acoustics.
The stage will be best positioned at the centre of the east wall, as shown in Fig.1 The audience depth will be shallow and wide so that the best can be appreciated from a presentation or performance both visually and acoustically. More importantly, the sound reaching the audience will be evenly distributed.
With the stage positioned on the east wall, the obvious step is to place the mixing desks and equipment storage in the boxed area opposite the stage. The walls are made of plasterboard. The room measures 15.176m wide and 12.176 long with an extra 'pocket' on the side measuring 5m by 3.396m. The seating capacity will be approximately 80-100.
Although this is the logical way to position the stage and seating, there is a big problem with the design that needs to be ironed out; the roof is high and airy on one side of the room yet low and dense on the other. As symmetry is critical in acoustic design, this is a big problem. However, difficulties would also arise if the stage were positioned at one of the narrower sides of the room because the audience would still not get even sound distribution.
The windows pose another big problem for the proposal of the design. If they were a desired feature a sound-reducing window could be fitted, but these are expensive and usually favoured in recording studios or places where visual presentation is not involved. For the purposes of this project, which must accommodate controlled lighting and projectors, daylight and the changes in daylight would be unacceptable. The need for windows in this case is redundant.
The project funding cannot warrant electrical devices to control reverberation but sufficient commitment needs to be made towards sound reinforcement. For the purpose of renting the space to organisations outside of the university, it needs to be classed as a music venue, which brings with it it's own set of requirements in terms of equipment and maintenance as well as in the acoustic design.
Tests with sound inside the space need to be conducted before the speaker arrangement can be determined.
Solutions and recommendations
The wall opposite the stage will need diffusers to distribute or absorb the sound and regulate reverberation time. Curtains along the back of the stage area will give more options once the venue is up and running and could also be extended to the north and south walls, in addition to the absorbers and diffusers. Rigid Rocksil walling is excellent, but expensive. There are many fiberboard solutions on the market, which would be a cheaper alternative. These can be screwed to the existing wall.
A cheap and effective option for the floor is heavy felt carpet underlay with a compressed carpet on the top. An attractive, but more expensive alternative would be to lay wooden flooring over the top of the thick underlay; the hard surface of the wood could enhance the sound quality; too much soft furnishing may 'deaden' the sound.
The best solution to the problem with the ceiling is to find a balance between the sound generated under the high ceiling, with that being generated under the low side. As the area on one side of the room will have a different sound quality to the other side, absorbers need to be fitted to the high ceiling to counteract echo and a set of diffusers to the low ceiling to maximise the quality of the sound, (see figure 2). An aesthetic feature can be made of the high section of the ceiling using the reflectors and absorbers.
Windows & doors
The solid fire doors will not leak much sound. Vibration leaked through the doorframe can be greatly decreased using doorframe sound gaskets. The windows would be best removed or blocked with absorbers. An air conditioning system will need to be installed, even if the windows remain, air conditioning is still absolutely necessary with so much insulation.
Free standing absorbers
Another ideal way to add flexibility to the working design of the studio is to include freestanding sound absorbers, deflectors and diffusers. These can be moved around to fit with the nature of performance or presentation and the size of the audience. They can also be custom made without too much expense.
The initial problem facing this project faces is the multi purpose use for which it has been designated and the flexibility that is required from the finished design. Live music and speech require different methods of application in acoustic design.
Speech and drama performances depend largely on design made with good intelligibility in mind, where as acoustic design for music venues needs to take other factors into consideration that may not work out best for speech and vice versa. In addition to this, The University has limited funds for the project. The important factor here is that the design must be finished to a competitive standard and the venue must be able to operate smoothly if The University is to make the theatre a commercial success.
More research needs to be carried out inside the room to determine how, exactly, the issue with the ceiling can be properly resolved. The acoustics of the space will need to be tested before work is carried out, using a small sound system that can establish the extent of change in sound from one side of the room to the other.
Makrinenko, L., Ed, Bradley, J.S.,1986. Acoustics of Auditoriums in Public Buildings, New York: Acoustical Society of America.
Elsea P, 1996. ACOUSTIC TREATMENT FOR HOME STUDIOS, California: University of California Santa Cruz.
Ed. Wallace Clement Sabine, 1921. Collected Papers on Acoustics, New York:v Acoustical Society of America
Acoustic Absorbers and Diffusers: Theory, Design, and Application
by Trevor J. Cox, Peter D’Antonio, Spon Press (April 1, 2004)