Resources

Nagata Acoustics

Dr. Minoru Nagata is known for having a hand in the acoustical composition of the world's foremost performance spaces. Some of these projects include the Disney Concert hall, Suntory hall, and Sapporo concert hall. The website has a great deal of detailed case studies for many projects of all configurations. Some case studies include detailed technical analysis which is a good reference. Almost every architectural acoustics search I have done has take me back here.

http://www.nagata.co.jp/e_index.html

Shoebox

"Shoebox" is the term given to venues that are long and rectangular (like shoeboxes). For a long time shoebox was the favored configuration because of its simplicity (little was known at the time of acoustical properties). After the advent of the fan shape people once again responded to the shoebox form for its unique and intense echoes and reverberation qualities. Studies have shown that something about the shoebox forms appeal to people. It is my own belief that increased reverberation and echo allow the sound to more strongly "detail" the character of the space, making it more robust and intricate.

Ecotect's animations were very helpful in analyzing the properties of the shoebox form. The above images are stills from animations in which yellow rays represent useful sound and the red rays represent echo. It also helped me understand that the sound being reflected from the back of the stage was masked by the sound being projected from the nearby source. The graph from Ecotect's analysis indicates the ridiculous echo time in a shoebox venue. Appropriate first response (when the sound first returns to the source) in the best concert halls in the world is between 2 and 2.5 seconds. The graph indicates that the response time is more like 12 seconds, and that it can reverberate for up to 50.

This was my first experience modeling completely in Ecotect. It was easy to make a rectangle with a slightly angled floor but in general, I would recommend importing 3-d models from other programs

"Fan" shape acoustics

The fan shape for performance venues is an adaptation of the shoebox. The form mimics the diffusion path of sound waves and reduces the echo effects that occur in more rectangular arrangements. Despite backing of acoustic theory, many people favor the characteristic reverb of a shoebox over the sometimes stale sounding fan configurations.
To better understand how sound travels through a space it is useful to try Ecotect's acoustic ray animations. The animations show how the sound moves with color-coded rays that indicate direct reflecting surfaces, useful sound, masked sound, echoes, border, and reverberation. Unfortunately, I cannot capture these rays in a screen shot. The animation is very useful for analyzing the material and forms of direct reflecting surfaces (particularly at the back of the stage) for their acoustical properties.

Convex Curves

Ecotect's acoustical analysis tools demonstrate here how circles diffuse sound. Because sound waves travel in a spherical pattern, the circular shape allows it to project and spread evenly from the source. Ecotect allows you to view the acoustical analysis in different ways. Above is one in circular waves and another with evenly spaced waves coming out spherically.

DOES ANY CONVEX CURVE DIFFUSE SOUND EVENLY?

NO. I tested this by making a plane and an ellipse in Revit and importing it into Ecotect. The above picture (with the yellow rays) demonstrates that ellipses send a strong focus of sound forward and more off to the side than circles, but not much diagonally. An ellipse would make a poor reflection surface for a stage backdrop, yet its acoustical properties may appeal to unusually shaped venues that want to reflect more sound to the sides while neglecting the corners.

Acoustics of a traditional half-circle ampitheatre

I made the form in revit and uploaded it into Ecotect. Although Ecotect recommends making the forms without importing, it worked fairly well (largely because of the simplicity of the shape). Here you can see rays spreading out spherically and randomly from the source. The Ecotect model demonstrates that the concave curves of the ampitheatre are focusing the sound inwards back to the source, creating an unsavory acoustical environment. As mentioned before the theatre also would generate a picket-fence echo, which cannot be calculated by Ecotect. To avoid picket fence echo one must not make evenly spaced reflective surfaces. Next I will show how the opposite of this shape, a convex curve,distributes sound. I will also look into the acoustical properties of an ellipse to see if it upholds the even sound diffusion qualities of a circular curve.

OBJECTIVES

Goal: To maximize building performance by utilizing Ecotect's environmental simulations to help design a passive cooling system and evaluate acoustical properties. The performance analysis offered by Ecotect is important to the future of architecture because it allows for architects to make more simple and effective design solutions, thus creating less new problems with every new solution.

METHOD

-3-D models will be made in Autodesk Revit and then loaded into Ecotect. These design models will be of a cultural center for Abuja, Nigeria which I am currently designing (for a student competition).

-A very basic 3-D model of the outdoor performance space, along with a study of the acoustic properties of a variety of popular concert hall forms (shoebox, fan, vineyard, half- circle amphitheatre {convex vs. concave curves}).

EXPECTED OUTCOME

-Because I am more or less familiar with the acoustical properties of shoebox, half-circle, and fan shaped venues I will be using Ecotect to provide demonstrations of their properties.

-Shoebox=Alot of reverberation. As we were beginning to understand acoustics the shoebox form was denounced. It eventually made a return to popularity because people simply liked how it sounded.
-Fan=Less reverberation than shoebox but still not perfect. Preferred over shoebox but lacking the ambiguous qualities (in reverb and echo properties) that have drawn people to shoebox venues.
-Half-circle ampitheatre= Terrible acoustical quality. Convex curves focus the sound and even steps cause a "picket fence echo". Successive, evenly spaced reflectors (steps) can produce a strong pinging sound whenever there is a loud sound. Ecotect cannot calculate a picket fence echo through geometric analysis.