posted 19.06.2014

TESTTESTStem to Stern

Over the last ten years an increasing number of purpose designed theatres have been installed on superyachts around the world. Although in many ways technically more demanding than residential installations, the very real developments in acoustical and modelling tools are providing us with prediction and design capabilities of great sophistication – and new generations of extraordinary onboard facilities.

It is perhaps unfair to say that detailing of the more specialised theatre facilities has been regarded as a design playground for architects and interior designers, but there are few rooms that live up technically and functionally to the impact of their aesthetics. The success of these installations is not just reliant on the quality of the equipment installation; what you experience when you listen to a playback is a convolution of the speaker system, the installation, and the success of the room acoustics – much of which may well have defined the look and feel of the room itself. If the room interior and acoustics have been considered in the design process, it has been traditional to define the required performance with the simplest of statistical parameters; the room decay time. Theatres on yachts, and indeed in most private installations, are never large enough to satisfy the Cremer- Muller requirement for statistical space. The role of room decays in design are often misunderstood, poorly predicted, and largely irrelevant in a sophisticated facility.

The requirements for vibration and low frequency isolation, the invisible integration of loudspeakers, control, and projection equipment continues as it always has, but the acoustical design of a modern multiple format playback system is now complex, as is the system integration with the room interior. If it is the designer’s role to provide a satisfying aesthetic, it is the Theatre Designer’s to provide the tools that enable the optimisation of room surfaces and treatments whose effects would traditionally have been extremely hard to predict. However, as the processing power of desktop computers continues to increase, complex modeling tasks are becoming possible. In the architectural industry, renderings and computer walkthroughs are becoming commonplace. The concept of surface attributes is now being extended to acoustical modeling. In addition to room surfaces having a texture, finish, colour, and other conventional properties, they can now also have lighting, thermal, sound absorption and diffusion attributes. What this means is that we are now able to predict the acoustical performance of various room designs and surface treatments, optimise the playback performance, and actually listen to the room before it is built!

While optical architectural rendering is a relatively mature field, acoustical rendering, or “auralization” as it is referred to, is in its fledgling years. This is due to the fact that visible light wavelengths are very small compared to the surfaces they illuminate, satisfying the geometrical specular assumption. On the other hand, acoustical wavelengths are comparable, and often larger, than the surfaces that scatter or absorb sound, thus increasing the importance of diffusion and diffraction. While boundary element methods offer the greatest accuracy in predicting scattering, geometrical acoustics is the preferred approach due to its speed and increasing accuracy. This increasing accuracy is in part due to improved scattering coefficients and diffraction modeling. While the first 100 years of architectural acoustics has addressed standardised measurement and evaluation of absorbing materials, the characterisation of scattering surfaces is only now in its infancy. The use of geometric computer room modeling has becoming a useful predictive tool in large performance spaces, and comparisons between prediction and experimental measurements have shown good agreement when diffusion was included in the model. Acousticians are now beginning to apply computer modeling to smaller critical listening rooms, such as recording studios and home theatres.

The design process starts with a 3D wire frame drawing of the room – each of the room surfaces being described by a plane. Each plane is assigned frequency dependant absorption and diffusion coefficients to characterize how sound is scattered from the surface of that plane. The model includes loudspeaker sources – each with a directivity pattern and frequency response, and an audience plane. Using geometrical acoustics, octave band echograms are predicted for each receiver location in the room. From this data it is possible to post process conventional numerical measures of performance such as clarity, intelligibility and reverberation times, as well as plot and identify the history of strong competing lateral and contra-lateral specular reflections that might damage imaging and location. More intriguingly, it is possible to calculate the full binaural impulse responses at any one position, from which we can determine the objective parameters that we equate with perception. Through a process known as auralization, the binaural impulse responses can be convolved with anechoically recorded music or speech giving an impression of how music or speech would sound if replayed in the modeled theatre. The process involves digital signal processing and Head-Related Transfer Functions (HRTFs). In addition to binaural responses, directive microphone, stereo, and B-format responses are possible. Convolution with anechoic material is made either directly in software or via special hardware. Having modeled the theatre, and predicted the room performance, it is then possible to modify base dimensions, planes, and materials to suit changing architectural requirements. This process of optimisation is extremely powerful, and allows us to work with complex shapes, curves and materials that have conventionally been difficult to deal with in acoustically critical theatres, lounges, studies, and listening rooms. Optimisation increases the palette of materials available to the designers and provides a more sophisticated path of integration between the room’s aesthetic and technical requirements. This allows designers to provide ever more sophisticated design solutions for the most demanding of installations. Now, how does this relate to the practical process of designing a facility within the constraints of a live project? There are two likely scenarios; either you will be presented with an already defined space, quite possibly remaindered from the rest of the interior design process, or you will be asked to define the boundaries that would be optimally required for the facility specified by the client. Both approaches can work, and have had their successes; the first purpose built theatre on board a De Vries-built Feadship was designed into a left over space on the Méduse, whereas a few years later a purpose designed theatre was integrated as a centre piece on the Andrew Winch designed Lady Aviva.

Room dimensions are critical to the low frequency performance of any theatre. The ratio of length to breadth to height of the room influences the distribution of the low frequency modes of resonance, and this in turn defines the bandwidth and extension of the room’s support for low frequencies. Non ideal room ratios are not in themselves disastrous, assuming skill on the part of the designer, but it is much more satisfactory to have the full co-operation of the design team at the layout stage of the deck general arrangements. Symmetry is also desirable. The success of the surround sound field relies in part in the bi-lateral acoustic symmetry of the room, and again the co-operation of the design team helps ensure correct locations for the room access, projection and booth, along with ideal room ratios and symmetries.

Having defined the available space, this must then be isolated from vibration and external noise sources. It should also be considered that a modern theatre can generate substantial low frequency sound pressure levels, and it is desirable to isolate these in turn from adjacent guest, or public quarters. Although traditional isolation systems rely on the substantial mass of an isolation shell, it has been possible to design remarkably effective isolated rooms by using stiff lightweight structures de-coupled from the ship with resilient bearings. It is then necessary to ensure that all duct-work and cable ways are routed past and around the theatre in order to avoid flanking paths that would otherwise couple the room back into the main frame surrounding it. Services to the theatre are themselves de-coupled and isolated.

Our theatre is now defined as a floating, isolated, symmetrical shell, with optimal internal ratios. Often the internal floor is raked – headroom allowing. This provides optimal sight-lines to the screen, creates technical space within which ducts, cabling and mechanical system extracts can be located, and provides low frequency absorption and control as an added extra. Within this space another shell, the acoustic shell, is defined. This construction carries all of the treatment that controls the acoustic performance of the theatre, the finishes, lighting, mechanical and electrical fixtures and fittings, and any technical furniture that has been designed for the theatre. Here again, the co-operation of the other consultants as a design team is essential, co-ordinating not just all of the interior finishes that may have carefully been designed around the Owner’s specifications, but also the mechanical and electrical requirements for a technical space. For example, in the case of M&E, in order to maintain desirable low background noise levels, larger volumes of air must be moved more slowly than normal, in and out of the room, substantial electrical supplies must be routed to machine and projection areas, often transformer de-coupled and electrically filtered. Computer optimisation now plays a key role in this final process. Historically, room design would be based around the use of a series of acoustic panels whose performance under free field conditions were know, and whose collective performance in situ was predicted using statistical techniques. As discussed earlier, the rooms that are being installed on yachts are non-statistical, and great success has been achieved with the optimisation of the performance of the materials and architecture developed with the whole design team. It is now possible for the interior designer to develop a much larger palette of styles which can be optimised with great success to work ideally, yet retain the architectural feel developed for the rest of the project. Within the acoustic shell, the technology behind the sound and picture are integrated – ideally invisibly since the function of the room is illusion and hardware is intrusive. There are a series of surround sound formats available to our clients, the most common commercial format being labelled 5.1. This is based on the forward front of house speakers – left, centre, and right, being located behind a micro-perforated screen, or immediately surrounding a large format plasma display. Low frequency effects speakers are installed either behind the screen or integrally with the raised floor and seating, with rear left and rear right surround speakers integrated with the side and rear walls. Some formats require the rear centre section to be routed independently, (6.1) or the forward left and right surround section to be routed independently (7.1). All of the signal processing and routing in a contemporary installation takes places in software under the system control.

It is expected that the techniques now available to us will allow the development of an ever wider range of architectural styles that will also support first class picture and audio; and the resulting theatre installation will be ever better, especially in the demanding yacht market.