Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 08-07 (No.247)

Issued : July 25, 2008

[ Japanese Version ]

J.F. Oberlin University's New Chapel and Pipe Organ

by Masaya Uchida

<< The Large Hall's Sound System >>

In March, 2008, J.F. Oberlin University held the dedication ceremony for its new Keikando ("Crown of Thorns") Chapel at the school's campus in Machida City. Machida City is a Tokyo suburb located southwest of Metropolitan Tokyo inside the border of Kanagawa Prefecture. The new building replaces the campus' original Keikando (designed by architect William Merrell Vories and completed in 1959) and includes the chapel sanctuary, a multipurpose social hall and office space. The university commissioned the project to commemorate the 60th anniversary of the university's founding. The chapel sanctuary will be used for worship services, lectures, and pipe organ and other concerts. The new Keikando was designed by Furuhashi Architect and Associates and built by Suruga Corporation.

<< The Chapel's Room Acoustics >>

Keikando Chapel's exterior
Keikando Chapel's exterior

Keikando Chapel's sanctuary
Keikando Chapel's sanctuary

Floor plan view of the sanctuary and chapel building
Floor plan view of the sanctuary and chapel building

Seen from a plan view, the new chapel's curved, continuous interior wall resembles a whirlpool or the pattern of a snail shell. From the left side of the altar dais, the wall wraps around the back of the audience, continuing back to a place above the altar dais's right side. As the wall wraps around the chapel's space and extends upward, its radius diminishes gradually. The single, continuous wall spirals gracefully upward to the chapel's maximum height where it meets a ceiling with a circular perimeter and a round skylight at its center. The space both creates a sense of embracing the people within the chapel and of leading them upward toward the heavens. The chapel's exterior shape follows the general lines of the interior, providing strong visual cues that make for a gentle transition from the out-of-doors into the unique interior of the chapel sanctuary.

In planning the room acoustics for this project, we faced the double challenge of concave interior surfaces and limited air volume per occupant seat. Concave surfaces make a room prone to the undesirable phenomena of sound focusing and echoes. The sparse per person air volume of about 7 cu. m. (247 cu ft) meant that, to obtain robust reverberations, we would want to avoid the use of sound absorbing materials. We therefore needed to rely entirely on physical design elements within the chapel to eliminate the possibility of sound focusing and echoes.

We used an iterative process and our 3D computer simulation application as the primary tool to develop the chapel's room acoustical design. Our solution put acoustically transparent ribbing along the wall, fully implementing the concave wall surface design, and, hidden out-of-sight behind the ribbing, we installed non-concave wall framing and surfaces to acoustically break up the concave wall surface. To make the hidden walls sufficiently heavy and stiff to provide reverberations for the lower octaves of the chapel's pipe organ, we specified four layers of 10 mm. (0.4 in.) fiber-reinforced gypsum board.

Our room design also included the development of detailed specifications for the concave wall's surface ribbing so as to avoid the unintended creation of partial concave surfaces across the ribs and to prevent sound waves of specific frequencies from generating "rib hum" noise off the ribs. We tapered the front surfaces of the ribs and we developed several combinations of various rib widths and depths, spacing and placement angles. We arranged the assortments of ribbing in a random pattern along the entire spiraling wall of the chapel. The chapel's reverberation time measures 1.5 seconds (at 500 Hz, with the chapel unoccupied) and the acoustical characteristics include longer reverberation times for low frequency sounds compared with the reverberation times of mid-frequency sounds.

<< The Sound System with Line Array Loudspeakers >>

In selecting the chapel's loudspeakers, we prioritized the ability to direct the amplified sound to the audience seating areas and limit sound dispersion to other parts of the room. To prevent echoes, we especially aimed to choose a speaker model that would minimize the amount of amplified sound that could reach the concave wall surfaces. We installed Toa Corporation's model SR-S4L compact line array speakers because of the sharpness of their directionality in the vertical dimension. These speakers have an elongated tower shape, which added to their appeal because these proportions would blend well with the room's vertical wall ribbing.

We installed one set of loudspeakers on the right and left sides of the altar dais at the first floor level and another set above the first set at the second floor level to make sure that the audience can hear the amplified sound coming from the altar area.

In addition, because the full performance of a sound system can only be realized when there is access to the controls that adjust its settings, we installed the equipment with the sound system's controls near the altar dais at an unobtrusive location next to the sanctuary entrance. We also made sure that it is easy to adjust the microphone volume while listening to the speakers' output. When the university president spoke at the chapel's dedication ceremony, his amplified voice sounded clear and natural, and it carried through the full audience with plenty of sound volume.

<< The Orgelbau Felsberg Pipe Organ >>

The pipe organ is installed at the height of the chapel's balcony (second floor) level. The organ was commissioned to the Swiss organ builder Orgelbau Felsberg and has 33 stops, three manuals and foot pedals. The organ makes extensive use of blond maple and has a simple design that complements the modern style and colors of the podium and altar dais chairs.

The chapel's dedication ceremony was followed by a pipe organ dedication concert featuring organist Naoko Imai. Her performance filled the hall with the pipe organ music and, in its new home, the instrument's sound had both bright fullness and sweet delicateness.

The new chapel will serve both the university and general community as did its predecessor structure. I hope that the new Keikando Chapel will earn a strong affection in the hearts of those who use it.

J.F. Oberlin University's website address is http://www.obirin.ac.jp/en/

Introducing the NHK Laboratories' Achievements to Our Readers

by Dr. Minoru Nagata, Founder of Nagata Acoustics

I started my employment at NHK Technical Research Laboratories in 1949, and the Acoustical Department of the laboratories was founded in 1951. In that year, six groups were created within the department, each devoted to one of the following areas of research: acoustical devices; architectural acoustics; low-frequency circuits; sound effects; and, acoustical materials.

At the time, radio was still in its heyday, and radio still meant AM band broadcasting. In Japan, the prevalent receiver was known as the "normal four" because of its four vacuum tubes. We used magnetic loudspeakers and carbon microphones, and we played "SP" 78-rpm records on phonographs (also called gramophones). This was a time before the magnetic recording of programs, so all shows were broadcast live. Looking back at those days now, the technology in Japan at the time seems as if it had barely progressed since Japan opened itself to the West in the mid-1800s.

The Acoustical Department of the NHK Technical Research Laboratories came into being in this nebulous environment and became one of the significant and driving forces that propelled the nascent Japanese acoustical field forward. Employees in the department's six groups made technological breakthroughs, established design methodologies and standards, and shared their discoveries and knowledge at academic gatherings. They contributed prominently to advances in both Japan's audio and sound industry and scientific academic community. The profound influence of the laboratory's employees owes much to the leadership of its longtime director, the late Prof. Yasuo Makita. He provided the philosophical compass that guided us in our research and work in the broader community.

In August, 1970, NHK disbanded the Acoustical Department. In response to this turn of events, a number of employees decided to leave NHK. I was one of the people who left.

In the decades since the department's disbanding, many of the employees, interns and even part-time workers have stayed in touch with each other. We gather once a year, in September, typically at NHK's clubhouse, to strengthen our professional and personal connections. More recently, since January, 2004, the employees from the department's six groups have been meeting once every two months. At these meetings, we share information about the successes of our professional work and talk with longing about research topics we have not yet had the time or opportunity to pursue. Sometimes we talk about what our careers might have been had we continued to work at NHK. From these gatherings I learned one thing for certain. While each of the six groups had some inkling of the work being done by the other five groups, we had no idea of the huge amount of effort and tribulations each group endured while pursuing their research objectives. I think it is important that future generations understand the hard work and sacrifices behind the department's many notable advances and I am now contemplating how best to preserve a record of these stories.

This newsletter offers an appropriate media to introduce our readers to some of the accomplishments of my NHK colleagues. Our first contributor is Dr. Akio Mizoguchi, who worked in the group focused on acoustical devices and who has been an expert on microphone technology throughout his career. I hope you will find his article in this issue, and his future contributions, informative and enlightening.

<< A Short Biography of Dr. Mizoguchi >>

  • 1929 born in Nagano Prefecture
  • 1951 graduates Yamanashi Technical School (now the University of Yamanashi Engineering Department)
  • 1952 joins NHK and is assigned to the Fukui Broadcasting Station
  • 1959 transfers to NHK Science & Technical Research Laboratories
  • 1977 receives his Ph.D. from Nagoya University
  • 1983 retires from NHK and joins Aiwa Corporation
  • 2005 retires from Aiwa Corporation
  • 2006 joins Sanken Microphone Co., Ltd.
  • 2007 retires from Sanken Microphone Co., Ltd.

A History of Broadcasting Microphone Invention and Development Part 1: Close-talking Microphones

by Dr. Akio Mizoguchi

<< Introduction >>

For close to a quarter century (1961 ? 1985), I worked at NHK's Science & Technical Research Laboratories, where I was engaged in the research and development of broadcast microphones. During a portion of these years, I also had the pleasure of being a colleague of Dr. Minoru Nagata, founder of Nagata Acoustics. In this and a number of future articles, I gladly plan to share some historical highlights and useful information about microphones and to "rub shoulders" with the other contributors to the monthly Nagata Acoustics newsletter.

<< The Now Ubiquitous Close-talking Microphone >>

The topic I chose for my first appearance in this newsletter is the close-talking microphone. Starting about 10 years ago, TV sportscasters began wearing headphones that had small, arm-like attachments. The attachment extended alongside the face of a sportscaster and connected to a special microphone that, thanks to the little arm, stayed in front of the sportscasters' mouth, suspended in mid-air. For this kind of microphone to work as intended, it needs to be placed close to the mouth of the person using it, which is why its technical name is "close-talking microphone." Close-talking microphones have the special characteristic of being able to clearly capture only the voice of the speaker, even in places where there is a large amount of ambient noise.

Whether attached to a set of headphones or supported by an apparatus around the neck or by other means, close-talking microphones have become a ubiquitous AV peripheral. The reader may be surprised to learn that the product development of the close-talking microphone dates back more than 44 years to the time of the Tokyo Olympics, the first Olympics held in an Asian country.

<< Close-talking Microphone Technology Prior to the Tokyo Olympics >>

At the Olympic games, TV announcers from around the world sit side-by-side in press booths and report on the events in live broadcasts transmitted to their home countries. The announcers talk simultaneously in "real time" to their audiences back home. If the announcers were to use standard broadcast microphones, the microphones would pick up not only each announcer's voice, but also the voices of the announcers sitting to the left and right. The audio transmission would contain the sound of the mingled voices and the broadcasts would be unintelligible.

Prior to the Tokyo Olympics, two types of close-talking microphones already existed: RCA's ribbon microphone and the BBC's moving-coil microphone. However, both of these microphones have the disadvantages that they need to be held by the user's hand and are large and heavy pieces of equipment. It is a challenge to try and keep either of these microphones at a consistently close distance from one's mouth. This difficulty results in the speaker's sound varying in quality and loudness as the microphone sways closer and farther from the speaker's mouth while being used. At the 1960 Rome Olympics, announcers covering the games used moving-coil microphones and they adopted the practice of holding the microphone so that the top of the microphones always touched the undersides of the tips of their noses. This technique enabled the announcers to keep the microphones consistently close to their mouths but also resulted in the announcers voicing considerable complaints and disgruntlements.

<< A Hands-free Innovation for the 1964 Tokyo Olympics >>

For the announcers at the 1964 Tokyo Olympics, we developed the novel design of attaching the main body of a moving-coil microphone to a cap worn on the head (Fig. 1) and with two acoustic tubes added to the ends of the microphone's diaphragm (Fig. 2). The acoustic tubes extend close to the user's mouth and accomplish bidirectional capture of close sound. We covered the end of the acoustic tubes with felt and added a close-fitting cover (Fig. 3) that enables the acoustic resistance of the felt to be adjusted, minimizing the occurrence of noise in the form of sound reflections within the tubes. We also added an on-off switchbox to our design.

Fig. 1 Close-talking microphone cap developed in the early 1960s
Fig. 1 Close-talking microphone cap
developed in the early 1960s
Fig. 2 Mouthpiece design for close-talking microphone used at the Tokyo Olympics
Fig. 2 Mouthpiece design for close-talking microphone
used at the Tokyo Olympics

Fig. 3 Encased end of microphone mouthpiece (early 1960s)
Fig. 3 Encased end of microphone
mouthpiece (early 1960s)

This bidirectional close-talking microphone's sensitivity to different sound frequencies is shown in Figure 4. As we can see in the graph, when the microphone is 2 cm. (0.8 in.) from the user's mouth, we obtain a flat characteristic, but when the distance between the mouth and microphone is 50 cm. (19.7 in.), frequencies under 2,000 Hz exhibit an inversely weak characteristic. In addition, regardless of the distance of the microphone from the mouth of the user, this microphone remains bidirectional, and at 90° the directionality is zero ("0"). That is, the microphone has a figure-eight-shaped polar pattern.

The greatly decreased sensitivity of this microphone to far field distant sound as compared to its sensitivity to sound from a near field results in effective noise suppression. In addition, the microphone's bidirectional sensitivity significantly enhances the noise canceling effect and the lower sound volume of recorded far field sound also contributes to the robust noise canceling capability of this microphone. When this close-talking microphone is used, the speech of people to the immediate right and left of the user is only picked up at very low levels. For practical purposes, ambient noise cannot be heard in the microphone's transmitted output.

Fig. 4 Sensitivity characteristics of the close-talking microphone used at the Tokyo Olympics
Fig. 4 Sensitivity characteristics of
the close-talking microphone
used at the Tokyo Olympics

Sanken Microphone Co., Ltd. manufactured the newly designed microphone. At the Tokyo Olympics, we supplied 300 units to Japanese announcers and all of the announcers visiting from overseas. The microphones were well received and even earned the appellation "magic mike."

Our development of this close-talking microphone began three years before the Tokyo Olympic games. Announcers used prototypes and early versions of the microphone at national sporting events in Japan, for marathon race broadcasting, rugby games and other sports broadcasting. We proactively obtained feedback from the broadcast announcers who used the early versions in the field and made a number of improvements that led to us being able to supply a better device at the Tokyo Olympics.

<< Developing a Microphone for Cold Temperatures >>

In preparation for the 1972 Winter Olympics in Sapporo, Japan, I again worked on ways to improve the close-talking microphone. To make this new design small and lightweight, we used a condenser microphone. We attached an acoustic tube to a headphone set and attached the small condenser microphone at the end of the acoustic tube (Fig. 5). Figure 6 shows a model wearing the close-talking microphone used during the Sapporo Olympics and Figure 7 shows the microphone's sensitivity at 4 cm. (1.6 in.) and 100 cm. (39 in.).

Fig. 5 Close-talking microphone used at Sapporo Winter Olympics
Fig. 5 Close-talking microphone
used at Sapporo Winter Olympics
Fig. 6 A model wearing the close-talking microphone
Fig. 6 A model wearing
the close-talking microphone
Fig. 7 Sensitivity characteristics of the close-talking microphone used at the Sapporo Winter Olympics
Fig. 7 Sensitivity characteristics of the close-talking microphone
used at the Sapporo Winter Olympics

This microphone was also bidirectional. As shown in Figure 7, when compared with the sensitivity of the microphone at a distance of 4 cm. (1.6 in) from the user's mouth, the sensitivity to far field distant sound of 100 cm. (39 in.) exhibits an inversely weakening sensitivity below 1,500 Hz.

In taking our new microphone design from concept to product launch for the Sapporo Olympics, a key criterion of success was the microphone's ability to perform in cold temperature conditions. We took an early prototype to Hokkaido for testing and when we moved it into a warm indoor environment after use in the cold outdoors, moisture condensation created annoyingly large amounts of noise.

To address the problem of moisture condensation, we filled the area around the vibrating membrane's back plate and the area around the insulation material with silicon rubber, thereby creating complete and durable insulation. We achieved a sensitivity variance of no more than 2 dB for temperatures of -20 to 40 degrees Celsius (-4 to 104 degrees Fahrenheit) and the same variance for humidity levels of 45 to 90%.

As with the close-talking microphone developed for the Tokyo Olympics, we began work on the microphone for the Sapporo Olympics three years before the games began. In 1971, we supplied a "beta" version of the microphone to announcers covering that year's winter international competitions in Sapporo and it received rave reviews. The next year, Sanken again manufactured the microphones and provided 300 sets to the announcers at the Sapporo Olympics. The announcers expressed their appreciation of the new microphones and the listening public around the world benefited from an improved listening experience.

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

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2130 Sawtelle Blvd., Suite 307A,
Los Angeles, CA 90025, U.S.A.
Telephone: (310) 231-7818
Fax: (310) 231-7816

E-mail: info@nagata.co.jp

[ Japanese Version ]