David W. Kahn

Why do traditional opera houses work so well for opera

Most computer models of room acoustics assume geometric acoustics (as if sound behaves like light). This has assisted our understanding of how room shape (fan shape versus rectangular, for example) can affect the acoustics of concert halls. When one applies geometric acoustics modeling to the traditional opera house, typically all one finds is a single ceiling reflection. The geometric approach holds little promise for understanding the magic of opera house acoustics. One of the acoustical attributes ignored by the geometric model is edge diffraction of sound. Our research has shown edge diffraction to be essential in predicting the superior acoustics of the traditional opera house. We have developed an alternative to the geometric acoustics model based on edge diffraction. In a two‐dimensional representation, the locus of points with equal delay time is an ellipse; in three dimensions, the locus is the volume of revolution of an ellipse. By studying where this ellipsoidal volume intersects with the balco...

Balancing uniform visual appearance with the need for adjustable acoustics in a concert venue: A case study

An acoustician’s recommendations for adjustable acoustics curtains in a concert venue sometimes comes into conflict with the architect’s aesthetic vision for the space. The architectural intent is usually for patrons to have a uniform visual experience of the room, regardless of the setting of the adjustable acoustics elements. This leads to the need for architecturally interesting, acoustically transparent elements, such as perforated metal or wooden grills, that can fully or partially hide the adjustable curtains from the eyes of the audience. This paper presents a summary of the collaboration between Acoustic Distinctions and the architectural firm HGA in designing sound-transparent, patterned wood grills that enable a visually attractive and consistent architectural aesthetic, regardless of the settings of the adjustable acoustics curtains behind, in the Kracum Performance Hall at Carleton College. The wood grills—designed collaboratively by the acoustician and architect—were mocked-up and acoustical ...

An integrated passive and active room acoustics + sound reinforcement system design solution for a large worship space

The United Methodist Church of the Resurrection, with more than 16,000 adult members and an average weekly worship attendance of more than 8,600, recently completed a new 3,500-seat worship space. The new sanctuary building has an ellipsoidal plan shape and a very tall ceiling to address an important programmatic goal to achieve “A Sense of Majesty”. Acoustical goals included warm speech throughout all seating areas with acoustics inspiring to create a high level of energy therefore encourage high level of participation. Furthermore, the church wants to support both traditional (orchestra and choir) and contemporary (Praise band with vocalists) styles of music in this new worship space. These programming goals, to some extent, are in conflict with one another. Particularly the architectural goal of having a soaring space is in conflict with the goals for a space that provides acoustical support of corporate worship. Since the walls and ceiling are too far away from most of the seating area to provide bene...

Working with student musicians on developing standard settings for concert stages with adjustable acoustics

The acousticians work on concert stages with adjustable acoustics usually includes a so called “tuning” process. This tuning process is unique and different for students attending music school as compared with, for example, a professional orchestra. We describe a tuning process, working with student musicians, at a new concert hall in Texas. Adjustable elements include movable ceiling elements, movable doors on the upper wall surfaces surrounding the concert platform, and retractable curtains that cover both the upper and lower wall surfaces surrounding the platform.

Recent drama theater design experience.

The four projects Acoustic Dimensions submitted for inclusion to the “Drama Theatres” book represent a range of design approaches to the challenges inherent in the design of these spaces. This presentation will focus on the approach to finding acoustic design solutions in a collaborative process with the architect, theater consultant, and other design team members as illustrated by our work on the Royal Shakespeare Theatre, RSC Roundhouse, Williams College ‘62 Center for Theatre and Dance, and Woolly Mammoth Theatre.

Key acoustical issues associated with the renovation and restoration of the Southern Theatre, Columbus, Ohio

For an acoustics designer of performing arts facilities, the renovation and restoration of a landmarked facility can be frustrating, as there are rarely opportunities to alter the original architecture, and therefore alter the original acoustics. The Southern Theatre renovation and restoration was somewhat unique with respect to the extent to which the theater interior was altered to address code issues, and to incorporate HVAC systems. The Southern Theatre originally opened in 1896. The stagehouse, main floor, and second balcony were rebuilt as part of the renovation. The second balcony, which originally had a separate entrance from the street, was redeveloped to incorporate contemporary theater seating, as well as some additional technical support spaces including control rooms and new lighting positions. With the wide scope of the renovation came the opportunity to introduce some important acoustic improvements. Among the key issues discussed are the acoustical design of a unique silent air supply syst...

Flexible acoustics for two purpose‐built organ recital halls

It is rare today for any purpose‐built music performance spaces to be commissioned, be they opera houses, concert halls, organ recital halls, etc. In order for any performance venue to be truly successful today, it must have flexibility included in its design, allowing the space to function well for the wide range of performance types that will inevitably be scheduled. The same can be said for purpose‐built pipe‐organ recital halls. While the highest design priority might be organ music, all but the most esoteric of these rooms will also be required to support far more than pipe‐organ music. This paper will discuss two ‘‘purpose‐built’’ pipe‐organ recital halls with flexible acoustics devices which allow these spaces to function well for uses other than pipe‐organ recitals. North Hall at the Peabody Conservatory at Johns Hopkins University in Baltimore, MD, is now used primarily as a pipe‐organ recital hall for a new Holtkamp tracker organ. This hall also continues to function as a rehearsal room for larg...

Low‐noise terminal design for HVAC systems

In the design of noise‐critical spaces such as music and theatre performance and rehearsal spaces, low background noise levels are essential. Therefore, noise emanating from the supply and return air terminals of the HVAC system must be kept to a minimum. This requirement often dictates the need for many large terminals. This approach can be a very expensive alternative. In addition to the expense, the large area of duct terminals can have a negative impact on the room acoustics, particularly in a concert hall where sound absorptive materials/openings must be kept to a minimum. A number of different supply and return air terminals that create a minimum amount of noise at relatively high outlet velocities (up to 600 fpm) have been designed and tested. The results of these tests and guidelines for the design of low noise terminals will be discussed.

An investigation of the sound field above the audience in large lecture halls with a scale model

Measurements of steady-state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was measured on a 1:10 scale model and was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats in the model was calculated by subtracting the direct field from the measured total field and was found to be dependent on the magnitude and particularly on the placement of absorption. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate depends strongly on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. These consequences are discussed with respect to prediction of speech intelligibility.

Scale modeling in architectural acoustics

Several types of models are available to the acoustician for the study of room acoustics. Although mathematical modeling has now become popular, due to recent advances in computer technology, the author chose to use scale modeling techniques. A 1:10 scale model was constructed to study the sound field above the audience in a large lecture hall. A steady‐state jet sound source was developed to model the standard ILG reference sound source. A model of unoccupied audience seating was designed and constructed and a new approach to air absorption compensation was used. A data acquisition procedure was developed for easy and accurate comparison of data taken in both the model and the full‐scale lecture hall. Verification of the model was carried out with measurements of both reverberation time and steady‐state sound levels. This scale model continues to provide a useful tool for the study of sound propagation over audience seating. It also enables simple modifications to determine the dependence of the reverber...