Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 10-02 (No.266)

Issued : February 25, 2010

[ Japanese Version ]

The New "Artebell" Cultural Center Opens in Sakai City's Mihara Ward

by Chiaki Ishiwata

In November 2009, a new hall opened in Mihara Ward of Sakai City, which is part of the Osaka Metropolitan Area. After Sakai City became a governmentally "designated city" (giving the local government similar authority to that of a prefecture due to the city's population size), the 2006 establishment of Mihara Ward as part of Sakai City became the opportunity for construction of a new ward administrative building, a hall and facilities for lifelong learning and sports. The new cultural center I will discuss in this article was constructed as part of the new ward office building as a mixed-use development project.

The Mihara Cultural Center portion of the building includes music practice studios and arts and crafts workshops, other rooms for lifelong learning activities, the hall and a rehearsal room. AXS Satow Inc. provided the architectural design and a joint venture led by Kurimoto Construction Industry Inc. built the facility. Nagata Acoustics provided acoustical consulting services for the cultural center portion of the building.

<< A Multipurpose Hall with the Priority on Theatre >>

Fig. 1: Plan and section of hall
Fig. 1: Plan and section of hall

Fig. 2: Distribution of initial sound reflections
Fig. 2: Distribution of initial sound reflections

The cultural center's hall seats an audience of up to 541 persons and was designed as a multipurpose hall. Sakai City has another hall of similar scale, so the programming and design of this new hall aimed to provide characteristics distinct from those of the existing hall. As a result, the primary focus of this hall is plays. At its widest point, the hall measures 24 m. in width and in depth from front of the stage to the rear-wall of the audience floor has only 18 m., both excellent dimensions for theatre productions. The audience seating area slopes upward toward the rear of the hall, ensuring good sight lines to the stage from every seat.

Our acoustical design aimed to provide an appropriate sound environment for non-amplified theatre productions. This kind of theatre production requires that when actors speak their lines, the audience can hear them with sufficient sound volume and clarity. To achieve these characteristics, our design aimed to obtain optimal distribution of the sound reflections that are considered to be the very earliest of the early sound reflections.

Because of the large width of the hall, it would be difficult for sound reflections to reach some parts of the audience from the hall's sidewalls. Therefore, in our acoustical room design we gave special attention to ensuring that sound reflections from the ceiling would sufficiently reach the sections of the audience seating that would be beyond the reach of sound reflections from the sidewalls.

While this project included only a modest installation of stage lighting and equipment, the plans for the ceiling did include control rooms for the ceiling lights and pin spot lights, as well as space to embed proscenium loudspeakers and other stage equipment. These chambers unavoidably resulted in a ceiling design having sections of several different heights. In order to achieve effective sound reflections under these ceiling conditions, the Nagata Acoustics room design proposed a curved ceiling shape that at each part of the ceiling has the best curvature for producing the sound reflections.

Fig. 2 shows the paths of initial sound reflections from both the ceiling and the sidewalls to the sloped audience seating area. At its highest point, the height of the ceiling measures 11 m. (from the floor stage) and the reflections shown in Fig. 2 reach the audience seating fast, within a delay of not more than 30 milliseconds (ms) after the generation of the direct sound.

<< A Hall Adapted for Multipurpose Use >>

Stage configured with the stage curtain
Stage configured with the stage curtain

Stage configured with the on-stage sound reflection panels
Stage configured with the on-stage
sound reflection panels

In the hall's room acoustical design, we gave first priority to acoustics for theatre performances. Nevertheless, in order for the hall to be used by as many people as possible and for a wide variety of purposes, we also designed sound reflection panels for the hall's stage. Unlike the primarily black interiors of many halls devoted to theatre performances, this hall's interior features wood-grain finishes and the on-stage reflection panels continue the wood-grain appearance of the audience sidewalls to create a smooth transition between the audience and the stage. In this configuration, the wood-grain finishes give the hall a strong feeling of continuity and an appearance that will serve as excellent surroundings for celebratory events and ceremonies, as well as concerts. The hall does not have the full, rich acoustics of a multipurpose hall designed to prioritize acoustics for concerts, but it delivers plenty of sound volume and clear tones, making its acoustics a strong and dependable environment for music performances.

I have not yet had the pleasure of attending a performance in the newly opened hall and the community center's home page does not yet show scheduled theatre events. I do see dates on the hall's schedule for a series of jazz concerts. I think these will be appropriate performances for this hall. I hope that the community will quickly develop a sense of ease about attending and using the hall, and that the hall will serve as a performance venue for the people of Mihara Ward for many years to come.

Listening to Acoustic Control Systems B.V.'s Multi-channel "ACS" System

by Dr Keiji Oguchi

Electrical enhancement systems alter the acoustics of a room using electronic and electrical programming methods and related hardware. Specifically, these sound reproduction systems use microphones placed near the musicians as pick-ups for the direct sound, then use DSPs to add time delays and sound reflection sequencing to the sound, and, finally, they output the results from loudspeakers placed on the sidewalls and ceiling of the room.

Royal Festival Hall in London (2,500 seat capacity) was the first major hall to implement this kind of system. The vendor, AIRO, installed its AR (Assisted Resonance) system, a multiple unit, multi-channel system consisting of microphones (equipped with resonators), amplifiers and loudspeakers installed in the hall ceiling. The system lengthened the reverberation time of low frequency sounds.

In Japan, too, theatres and conference centers have implemented these kinds of systems to adjust room acoustics that have short reverberation times to acoustics suitable for concerts, or to lengthen the already long reverberation time of a concert hall to make the acoustics more suitable to pipe organ music. The systems these venues have installed include the AIRO AR system and Yamaha's AFC (Active Field Control) system, among others.

Auditorium, Delft University of Technology (Photo by ACS)
Auditorium, Delft University of Technology
(Photo by ACS)

In autumn, 2009, I had the opportunity to experience one of these kinds of systems that I had not before encountered, the ACS (Acoustic Control System) developed and manufactured by the company of the same name (Acoustic Control Systems B.V.). Acoustic Control Systems is headquartered in the Netherlands and has already installed its ACS in about 50 halls in the Europe and the United States. The ACS installation is similar to other electrical enhancement systems in its use of large numbers of microphones and loudspeakers, but it is unique in the complex way in which it ties microphone inputs through its DSPs to the loudspeakers.

In addition to lengthening a hall's reverberation time, the ACS can add early sound reflections and through this application can add sound clarity. An add-on module also enables the acoustics of a "virtual" orchestra shell to be added to support the sound heard by performers on stage.

For this listening demonstration, I was invited to Zoetermeer City, located not far from Amsterdam. The demonstrations were held in the Stadstheater Zoetermeer (the city's municipal theatre, with 800 seat capacity) and in the auditorium of nearby Delft University of Technology. Trumpet player Malcolm Morton of the Residentie Orkest, Hague performed. Together with other invitees, I listened as the ACS system was adjusted to a number of different patterns of room acoustics, most of which were variations in the reverberation times.

The Stadstheater Zoetermeer has a proscenium stage. The ACS microphones are installed toward the upper part of the proscenium arch and the loudspeakers are installed in the proscenium arch, the audience area walls and the ceiling. In the Delft University of Technology auditorium, the stage for music performances is configured at front central area of the room's audience area as a arena stage. The ACS microphones and loudspeakers were suspended in a mixed configuration from a truss system above the arena stage. Both of these venues have a reverberation time of one second when the ACS is off, and, depending on the mode selected, can have reverberation times as long as three seconds when the ACS is on.

I listened to the demonstration performances and my first impression was of rather natural sounding acoustics. In the Delft University of Technology auditorium, the microphones and the loudspeakers were located almost adjacent to one another, yet I did not hear any howling phenomena ("feedback"). Also, it strongly caught my interest that when the system was set to "speech" mode, enabling the functionality that adds early reflections, and the system was on, the clarity of speaking voices improved even if the person speaking was not holding a microphone or wearing it attached to a piece of clothing.

Both demonstration venues are not very large halls. I experienced the sensation of them seeming to become larger when the ACS was set to long reverberation time mode. While this kind of "artificial" system produces a knee-jerk, adverse reaction from many musicians, if this kind of system is introduced and implemented judiciously, it may be an effective technology in smaller venues.

Listen to the Loudspeakers! - Discerning Choices from a Thicket of Possibilities

by Makoto Ino

Of all the components that comprise any sound systems, the most important ones have always been thought to be the microphones and the loudspeakers, and for good reason. Microphones take sound that has been emitted into the air and convert it to electrical signals, and speakers convert the electrical signals back to sound. Thus, these two components form the entry and exit gates of the entire sound system. Especially with regard to the speakers, in spacious indoor locations such as halls, large numbers of people listen to the amplified sound, form impressions and judge what they hear based on how it is supplied to them from the sound system's exit points-that is, the speakers. Therefore, the loudspeakers are the pivotal key of a sound system.

<< The Integration of Amplified Sound from Direct and Reflected Surfaces >>

The sound generated from loudspeakers directly reaches listeners' ears. The sound also reflects off the room's architectural and interior elements, including the seating, as well as off people and other surfaces, and continues to repeatedly reflect off surfaces so that the sound reaching the listeners' ears becomes an indistinguishable mixture of direct and reflected sounds. The nature of the reflected sound depends on the geometrical shapes of the architectural aspects of a room interior, other surfaces and the properties of the materials used.

The nature of the direct sound, however, depends on the characteristics of the loudspeakers, and the choices made about where and how to place them and combine them with other units. Moreover, the sound technician's operation of the sound system, as well as the way actors and other people use the microphone(s) also greatly influence the nature of the direct sound. Furthermore, the listening and viewing audience-albeit unconsciously-also influences how the amplified sound is heard. To summarize, during the process of interaction among the listening human beings and many physical things (equipments, objects and waves), these elements all become integrated, influence each other and come to function in an integrated way.

<< Adopting a Positive Attitude toward Loudspeaker Selection and Use >>

Among sound system designers and installers, it is not unusual to hear the comment that "loudspeakers are hard to understand, they're just difficult." Architects often comment about speakers that "From the perspective of the interior design, I don't like having to include that kind of shape." When halls gather audiences of listeners for listening demonstrations as part of the process of selecting new speakers, the halls' sound technicians may be heard making comments such as "These speakers are impossible to use," and, even when the sound techs make more positive comments, they usually contain a measure of doubt, such as "Hmm, I wonder if I can make these work."

When I hear these kinds of grumblings and concerns, I mediate the situation with a mix of apology and positive thinking. I explain that while sound systems have experienced steady progress from the first electrical circuits and vacuum tubes to the era of transistors, to digital integrated circuits (IC) and large-scale integrations (LSI), loudspeakers have barely changed since their beginnings in the early 20th century. In order to cause large air vibrations, speakers need certain appropriate dimensions. As long as air and the human ear remain as they are, some aspects of speakers cannot be expected to change. "The key to speakers is how we use them," I conclude, moving the conversation from concern to practicality and enthusiasm.

<< Navigating the Loudspeaker Selection Process with Listening Events >>

Loudspeaker selection event
Loudspeaker selection event

Everyone involved in loudspeaker selection wants the same objective of "fine sound", but the path forward often seems like trying to navigate a dense thicket using trial and error. To find an "open clearing" where opinions can be exchanged, and a direction and path forward decided, hall owners organize listening demonstrations to compare various speaker options.

For example, as part of Suntory Hall's 20th anniversary renovation project, which included the selection and installation of new loudspeakers, we held several listening demonstrations. We placed the speakers to be evaluated on stage and used CDs as the sound source, and we also had people give speeches using the hall's microphones. The attendees included the hall's programming staff and operations management, on-site technical staff and independent acoustical professionals.

While the loudspeakers emitted sound, I moved them to different on-stage locations. Depending on the location, the quality of sound heard by the listeners ranged from muffled to clear. Keeping in mind the goal of comparing and selecting new speakers for the hall, when I determined that the best sound could be obtained by putting the speakers toward the front of the stage at stage right or left, this is where I located each speaker while it was being evaluated. When the evaluations resulted in a choice between two speaker models, I changed the setup to better mimic the planned permanent installation, which would be located at the border between the edge of the stage and the start of the audience seating, and at a height midway from the stage floor to the ceiling 12.5 m. overhead. I used a temporary aluminum truss to suspend each of the two speaker models and repeated the listening tests. Thereafter, the listening demonstration participants discussed the two options and arrived at a decision on the speaker selection.

<< Comparing Loudspeakers by Listening and by Their Physical Properties >>

In general, loudspeaker comparative listening events are held for one of two reasons, either in order to select models to use in a particular space or as part of the marketing efforts of a manufacturer. The planners of a listening demonstration should be very clear about the event's objective. Their decisions about where to hold the event, how to set up the equipment and what sound source(s) to use should all be based on the event's objective.

When selecting loudspeakers for a theatre or hall, listeners' impressions and evaluations of the speakers are not the only consideration. Other factors include quantifiable physical properties such as sensitivity, frequency response, and maximum SPL (loudest output level without exceeding a particular distortion level), as well as physical dimensions, shape, installation requirements, appropriateness in combination with other speaker units and cost.

For some listening demonstrations, it may be fine to use live music, such as a band or ensemble. But if the objective of listening to the loudspeakers is to choose the best speakers for a theatre or hall, the listeners' attention may be distracted by the live performance, and this will interfere with concentrating on evaluating the speakers' performance and contaminate the evaluation results.

When manufacturers hold product demonstrations, some manufacturers emphasize solely the quantifiable physical properties of their products. Based on my experience with fine tuning sound systems on location, when the loudspeakers sound good to the human ear, most of the time the speakers also perform well in terms of their physical properties. However, when we focus solely on analyzing how a product performs in relation to a list of physical properties, then, even if the product earns high evaluations based on the quantifiable properties, there is the counterintuitive result that such speakers rarely seem to produce amplified sound that satisfies listeners. This inverse relationship may be due to the difficulty of simultaneously observing the multiple physical properties in a focused way, or it may be that something about the essence of the sound becomes lost. It seems to me that this topic merits further study and investigation.

Surely, in the context of preparing a theatre or hall's loudspeakers for ongoing use, the acoustical consultant must adjust the sound system until he or she achieves accurate observation of the maximal physical properties. In addition, the acoustical consultant must repeatedly test the speakers using consistent CD software and microphones. When the optimal settings are achieved, the acoustical consultant shares the information about these settings and adjustments with the project owner and the on-site sound system technical staff. Unfortunately, this aspect of the acoustical consultant's role in the process of speaker selection and installation often remains unrecognized or undervalued. Nevertheless, I consider it part of the acoustical consultant's mission to support our hall and theatre clients in achieving balance and cohesion in their use of the speakers and entire sound systems of their venues.

Nagata Acoustics Inc.

(Tokyo Office)
Hongo Segawa Bldg. 3F, 2-35-10 Hongo
Bunkyo-ku, Tokyo 113-0033, Japan
Tel: +81-3-5800-2671, Fax: +81-3-5800-2672

(LA Office)
2130 Sawtelle Blvd., Suite 307A
Los Angeles, CA 90025, U.S.A.
Tel: +1-310-231-7818, Fax: +1-310-231-7816

(Paris Office)
75, avenue Parmentier
75011 Paris, France
Tel: +33 (0)1 40 21 44 25, Fax: +33 (0)1 40 21 24 00

E-mail: info@nagata.co.jp

[ Japanese Version ]