Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 09-01 (No.253)

Issued : January 25, 2009

[ Japanese Version ]

Cybele Arena and Chihitsudo Library Open in Yamagata City

by Satoru Ikeda

Cybele Co. Ltd. makes delicious French bread biscuits and other confections sold throughout Japan at the company's own cafes and shops and at dedicated counters in the upscale department stores of major cities. In September, 2008, through the philanthropy of this company and its president, Mr. Shinichi Kumagai, the Cybele Arena and Chihitsudo Library opened in the Zao area of Yamagata Prefecture.

Mt. Zao may be most famous as a volcano with great alpine ski resorts. It is also home to Cybele's "Factory Maison," where the company has its factory, flagship retail shop, an Italian-style caf? and corporate offices. Visitors can tour a special observation bakery to see how Cybele makes its popular "French Rusk" biscuits. Now, on adjacent land owned by the company, the unique new arena and library offer a range of cultural activities to residents and visitors alike.

<< Background of the Library and the Theater >>


A new building with one main entrance and two separate wings houses both the Cybele Arena and the Chihitsudo Library. The library contains some 30,000 books collected by Japan's multiple-award-winning author and playwright Hisashi Inoue and donated by him. Mr. Inoue was born Yamagata Prefecture.

The main purpose of the arena is to serve as an athletic facility for table tennis practice and competitions. However, it also easily converts to an authentic theater space. The idea of adding theater functionality to the arena was the brainchild of Cybele President Kumagai. On a visit to Tokyo, Mr. Kumagai attended a performance of one of Hisashi Inoue's plays performed by Komatsu-za (the theater company he established specifically to perform his works), and staged at Sazan Theater, a venue built on the top floor of Kinokuniya, a major Japanese bookstore chain. Mr. Kumagai was incredibly moved by this performance of Inoue's Taiko Tataite, Fue Fuite ("Drumming the Drum, Blowing the Flute") and he became determined to build a theater back home in Zao.

The Yamagata architectural firm of Toshio Homma & Associates designed the new building and provided construction management services during the project. The architectural firm has also designed other buildings for Cybele. The new structure was the fifth construction project to be built on this Cybele Co. site.

<< The Theater in the Arena >>

Theater Style
Theater Style

Gymnasium Style
Gymnasium Style

The new building is located on a site adjacent to the Cybele Factory Maison on one side and the French Rusk observation bakery on another side. All three structures face the large Cybele visitor parking lot, providing convenient access from vehicles to the entrances of the facilities.

The facade of the new building features a wide outdoor stairway. When ascending this entryway, the larger arena wing is to the left of the stairway and the library wing is on the right.

Cybele Arena's versatility as a venue far exceeds its primary purpose of being a gymnasium-style athletic facility for sports practice and competitions. Generally the flat-floored arena is also used as a lecture hall and auditorium. Moreover, this arena is equipped with a large stage and theater apparatus that, when set in place, turn the arena into a genuine theater for the performance of plays.

<< Cybele Arena's Theater Ambience and Theater Functionality >>

The arena's seating configuration for use as a theater plays a key role in the temporary transformations of the arena interior into an authentic theater environment. When the stage is set in place it has a stage pit in front of the stage apron. Portable, stepped seating can be rolled onto the arena floor for the main audience seating, and additional theater seating can be set up in the galleries along the rear and side walls so that the audience surrounds the stage on three sides. The seating arrangement enhances the sense of being in a theater and, together with the interior design elements selected by the architect, creates the ambience of a contemporary theater designed specifically for plays.

Supporting the theater ambience is a well-appointed set of theater apparatus and lighting equipment that include a gridiron above the stage as well as ceiling, side and pin spotlights, and a control room for operating the lights and other stage set needs. The theater configuration layout also provides for a well-designed back of house, with a loading dock entrance that can handle large backdrop and scenery deliveries, well-planned access and egress between the dressing room area and the stage, and other support facilities such as a laundry room.

In designing the theater, the architect gave full consideration to the "house's" lighting needs both on-stage and in the audience areas. While the flat-floored arena is designed to have natural daylight flow into the interior space, the same space has very different lighting needs when used as a theater. In particular, when used as a theater, the lighting equipment can illuminate just the stage area while keeping the audience area at a lower level of illumination and can darken the stage and the audience areas independently.

<< Acoustical Design for Cybele Arena's Theater Configuration >>

For the theater's room acoustical design, we prioritized clarity of dialogue and other live human speech. In tandem with this goal, we aimed to maximize the level of quiet in the room through sound-isolating measures that keep external noise from leaking into the space and by minimizing noise from the arena's HVAC system.

We distributed the use of ribbed materials with glass wool and glass wool board along the sidewall surfaces and installed perforated panels backed with glass wool (for sound absorption) on the ceiling to control the room's reverberation level. In particular, we targeted preventing an overabundance of low frequency reverberations and echoes. This strategy resulted in our achieving acoustics appropriate for the theater.

<< Cybele Arena's and Chihitsudo Library's Busy Calendar >>

In the short period since the opening of Cybele Arena and Chihitsudo Library, Cybele Co. has hosted a variety of events, from a tryout competition for the Yamagata Hopes table tennis team to a series of lectures by award-winning novelists and other authors, as well as exhibitions at the library. Cybele President Kumagai has even realized his dream of bringing the Komatsu-za Theater Company to perform at the Cybele Arena's theater.

I have been told that performances and other events at the arena and library will be limited to productions sponsored by Cybele Co. Nevertheless, Komatsu-za will perform there once or twice yearly and numerous other events and local artists, such as the Yamagata Symphony Orchestra, are also scheduled, promising a frequent and varied menu of entertainment and cultural offerings.

In the building's entrance hall, a hand-written message from author Hisashi Inoue has been enlarged and permanently installed on one of the walls. It reads, "I've carried my library and my scripts [here]; for many years may they shine, and let us strive to make it so." As a participant in bringing this project to realization, I add my wish that Mr. Inoue's inscription may long be embodied in brilliant performances whenever the Cybele Arena is transformed into a theater.

Cybele Arena and Chihitsudo Library is http://www.cybele.co.jp/chihitsudo/

Progress on the Taichung Metropolitan Opera House Project

by Chiaki Ishiwata

You may already have read about the Taichung Metropolitan Opera House being built in Taiwan's third largest city, Taichung. When Toyo Ito & Associates, Architects won the design competition for this project in 2005, publications and online media spread the visual image of the innovative winning design worldwide, and 3D models appeared at many exhibitions. Currently, with the project's design phase complete, earthwork construction is in progress. Nagata Acoustics' participation in this project began during the design competition, collaborating with Toyo Ito & Associates, Architects on the winning design. We are responsible for the project's acoustical design.

<< Project Overview >>

Exterior View (competition model)j
Exterior View (competition model)
(Photo courtesy of Toyo Ito & Associates, Architects)

The performance halls planned for the Taichung Metropolitan Opera House include a 2,000-seat Grand Theater for opera, an 800-seat Playhouse for drama and a 200-seat space named Black Box for experimental theater. In addition, the complex will have a full range of support rooms for the halls, plus rehearsal rooms and a retail zone that will make this cultural destination worthy of being called a multipurpose complex.

The most unique aspect of the project's architectural design is the use of catenoid surfaces for the rooms' walls, resulting in a structure in which the walls are curved surfaces seamlessly connected to one another. The effect of the catenoids may be compared to spaces carved into a series of connected coves or grottos.

<< The Room Acoustical Designs and the Halls' Catenoids >>

In our room acoustical design work for this project we devoted special attention to the catenoid surfaces of the Grand Theater and the Playhouse. While not every plane in the room is part of a catenoid, significant portions of both these halls are unadulterated catenoid shapes, requiring a complex and unprecedented relationship among the design, structural elements of the building and the building equipment (such as the HVAC system and stage machinery).

As part of our acoustical design responsibilities, we needed to determine how to obtain excellent early sound reflections in these unique shapes and prevent the curved surfaces from producing undesirable sound focusing phenomena, among other objectives. Therefore, during the design phase, this project's acoustical design activities included ongoing, iterative and comprehensive teamwork with the architectural design team until we were able to finalize these two halls' specific shapes.

<< Acoustical Testing in the 1/10 Scale Model >>

1/10 Scale Model of the Grand Theater
1/10 Scale Model of the Grand Theater
(Photo courtesy of Toyo Ito & Associates, Architects)

Simultaneous with the completion of the design phase, we began acoustical testing in a 1/10 model of the Grand Theater built in Taipei to our specifications. Building this 1/10 acoustical model initially put us in a quandary because of the complexity involved in producing the model. Regardless of how we segmented the parts of the hall, every fragment that would be needed was its own unique shape. We discussed where and how to build such a model. Eventually, our colleagues at National Taiwan University of Science and Technology (NTUST) who are partnering with us on the project took on the task of building the model and built it on their campus in Taipei.

To build the 1/10 model, the team at NTUST implemented a painstaking production process that began by first building a framework of the hall shape's vertical cross section, and then adding layer upon layer of thin plywood until the model matched each curved surface of the Grand Theater's design. The superbly wrought model they built is still installed on the NTUST campus.

<< Working On Site in Taichung >>

While performing acoustical testing in the 1/10 model at NTUST, I made a trip to the project site in Taichung. Taipei City is Taiwan's largest metropolis, followed by Kaohsiung City. From Taipei, I took the Taiwan High Speed Rail, which runs at speeds similar to Japan's "bullet" trains, and reached Taichung in an hour. Compared with the bustling pace of Taipei, I found the atmosphere in Taichung a bit calmer.

Da-Ju Architects & Associates, the local architectural firm participating on the project, assisted us during meetings with the local firm in Taiwan. Some of their personnel attended schools in Japan and their fluent Japanese made it easy for me to communicate. They also served as my interpreter in discussions with the local equipment design firm. I noticed that when my Japanese comments were interpreted to Chinese, the interpreters used about twice amount of time as I did to convey my meaning. But when I glanced at some of the project reports written in Chinese, I saw that they seemed more concise than those I am used to seeing in Japanese.

I look forward to beginning work with our partners on the construction phase of the project as well as accomplishment of the unusual and wonderful structure of the Taichung Metropolitan Opera House.

A History of Broadcasting Microphone Invention and Development
Part 4: The Design of Sanken's First 2-Way Unidirectional Condenser Microphone

by Dr. Akio Mizoguchi

In this fourth article about the history of broadcast-quality microphones developed in Japan, I will discuss the last microphone I developed during my tenure at NHK Technical Research Laboratories. The device became Sanken's first 2-way unidirectional condenser microphone.

To my knowledge, this was the first 2-way unidirectional condenser microphone brought to market. The reason that the development of a 2-way model posed a conundrum for so long is as follows. With direct current bias voltage condenser microphones, the frequency range has both a low cutoff frequency (fL) and a high cutoff frequency (fH). The sensitivity of the device and each of these two values have a closely linked relationship. Sensitivity is directly proportional to the square root of the low cutoff frequency and inversely proportional to the high cutoff frequency.

<< The Science behind the 2-Way Unidirectional Condenser Microphone >>

Because of the relationship of sensitivity to the cutoff frequencies, when these two cutoff values are expanded, the sensitivity of the device necessarily becomes less. The more these cutoffs are expanded, the more difficult it becomes to achieve a sufficient signal-to-noise ratio because of the increasing internal noise caused by the microphone's acoustic resistance, electrical circuit and any other internal noise-producing parts of the device. From my perspective, the characteristics of all directional condenser microphones designed with a single diaphragm are destined to be constrained by this unavoidable limitation.

I was determined to find a solution to this constraint, and I came up with the idea that became the first 2-way unidirectional condenser microphone. I conceived the strategy of using two transducers of differing dimensions. My design apportions the low frequency and high frequency bands between the two transducers so that, overall, the transducers' output can maintain the device's high level of sensitivity, wide frequency range and low internal noise, as well as the microphone's range of low-to-high frequencies, without affecting the directionality of the microphone.

<< Overview of the Microphone and its Design >>

Fig.2 Microphone with the exterior casing removed
Fig.2 Microphone with
the exterior casing removed

Fig.1 Microphone exterior
Fig.1 Microphone exterior

Fig. 1 shows the microphone built using the above-described strategy and Fig. 2 shows the microphone with its exterior casing removed so that the transducers are visible. As can be clearly seen in Fig. 2, the two transducers are positioned one above the other. The top transducer (a) outputs the high frequency range and the bottom transducer (b) outputs the low frequency range.

In this microphone design there are two shielded cases below the two transducers. One of the shielded cases contains a DC - DC converter and the other case contains an output transformer. Also, the portion indicated by "c" in Fig. 2 is the electrical circuit.

<< Dimensions and Calculations for the High Frequency Transducer >>

Fig.3 High frequency transducer sensitivity relationship to the low frequency and high frequency limits
Fig.3 High frequency transducer sensitivity relationship
to the low frequency and high frequency limits

Regarding the design of the high frequency transducer, we began by setting the target high cutoff frequency for the unidirectional device at 8 kHz. Based on this decision, the length of the transducer ("d") would be one cm. In a product implementation, the transducer would have an actual measurement of 16 mm diameter x 2.9 mm. (That is, "d" = the radius + the thickness). Based on these values, the transducer's effective area equals about one sq. cm. Given this dimension, we set the possible diaphragm's total weight at one mg. We also set the electrostatic capacitance between the electrodes (Cb) at 21 pF on the condition that the internal noise including the noise of the electric circuit is kept to a minimal amount. (A "farad" is the international unit of measure for capacitors. A picofarad (pF) is a unit of capacitance and represents about the smallest measure of capacitance used in typical product designs.)

Given the conditions of the values just described, we set a parameter for the high cutoff frequency (fH) that would result in desired values for low cutoff frequency (fL) and sensitivity, taking into consideration the relationship between these two values. The result is as shown on the graph of Fig. 3. On this graph, the dotted line is located where fH is 20 kHz and fL is at the high value of 200 Hz. The result is -31 dB (0 dB = 1V/Pa), and this is the high level of open circuit voltage sensitivity that we expected we would be able to obtain.

<< Range and Sensitivity of the High Frequency Transducer >>

Fig.4 Output directionality characteristics of high frequency transducer
Fig.4 Output directionality characteristics
of high frequency transducer

Based on the above concept, design and calculations, the product developed for the marketplace had a high frequency transducer with the output voltage-frequency response shown on the graph of Fig. 4. When the sound source is located in front of the microphone, it has a flat frequency response in the range of 200 Hz to 30 kHz. In addition, because the device is unidirectional, when the sound source is located 90 degrees from the microphone's front, the microphone's sensitivity decreases by 6 dB, and the response is flat between 200 Hz and 19 kHz. For sound sources located 180 degrees from the front of the microphone, there is reduced response above 20 dB between 200 Hz and 8 kHz. Thus, we achieved unidirectional characteristics as cardioid (heart-shaped) directional microphone by our target cutoff frequency of 8 kHz.

Regarding the sensitivity of this microphone, the converted value on the input side of the impedance converter is -32.5 dB (0 dB = 1V/Pa). Also, if one takes into consideration the loss of sensitivity of about -2.2 dB due to the sum of the stray capacity and the electrical circuit's input capacitance, which is about 6 pF, the open circuit voltage sensitivity is -30.3 dB/Pa, which is about equal to the value we aimed to obtain.

<< Design of the Low Frequency Transducer >>

Fig.5 Low frequency transducer design cross-section showing back plate and baffle
Fig.5 Low frequency transducer design
cross-section showing back plate and baffle

For the low frequency transducer, my strongest priority was maximizing the low frequency performance characteristic. To this end, I gave this transducer exterior a slightly larger size than the high frequency transducer. The low frequency transducer has a diameter of 24 mm x 12.5 mm. I attached a baffle panel and the special design shown in Fig. 5, which shows the transducer and baffle panel from the back side.

In the design shown in Fig. 5, a portion of the sound waves that flow from the back of the transducer through the opening indicated by "r1", come through the opening indicated by "r2" and flow into a separate air chamber. As a result, the sound pressure on the rear of the diaphragm is divided into the partial pressure of "r1" and "r2", reducing it slightly compared to the sound pressure on the front of the diaphragm.

Because the differences in the sound pressure on the front and back of the diaphragm are not based on differences in the direction of the emitted sound waves, the result is an omnidirectional sound component. This omnidirectional sound component is added to the low frequency output and compensates for the unidirectional characteristic's reduction of low frequency sound.

<< Range and Sensitivity of the Low Frequency Transducer >>

Fig.6 Output directionality characteristics of low frequency transducer
Fig.6 Output directionality characteristics
of low frequency transducer

The graph of Fig. 6 shows the output voltage-frequency response of the low frequency transducer. At angles between 0 degrees and 90 degrees, the response becomes flat by 20 Hz and the effectiveness of the compensating for low frequency sound becomes evident.

In addition, at an angle of 180 degrees, the increase in the low frequency by the proximity effect that occurs when there is no compensating effect is negated, so that the response is decreased more than 20 dB up to 20 Hz. Regarding the high frequency characteristic, the frontal high cutoff frequency is 10 kHz. Because of the large size of the transducer ("d" is about 2.5 cm), the high frequency limit to have good unidirectional characteristic is about 3.5 kHz; that is, it becomes considerably degraded. However, by passing through a low-pass filter, we prevent the high frequency transducer from impacting the low frequency transducer, producing the results shown by the dotted line on the graph of Fig. 6. This is one of the advantages of the 2-way design. By the way, a large polarizing bias voltage of 100 V is used for both the low frequency and high frequency transducers.

<< Combined Characteristics of the Low and High Frequency Transducers >>

Fig.7 Output directionality characteristics of combined transducer
Fig.7 Output directionality characteristics
of combined transducer

The graph of Fig. 7 shows the combined output characteristics of a low frequency transducer and high frequency transducer such as the ones described above, when passed through low-pass and high-pass filters that reduce by 6 dB per octave and set the crossover frequency at 1 kHz. As can be seen in the graph of Fig. 7, the output results for an angle between 0 degrees and 180 degrees are extremely good. The frontal characteristic has a very flat frequency response between 20 Hz and 20 kHz (plus or minus 0.5 dB). Because the output transformer reduces the sensitivity by 10 dB, the sensitivity for 1 kHz is -42.5 dB/Pa.

On the graph of Fig. 7, if we next look at the characteristics at a 90 degree angle, we see that a flat frequency response is obtained from 20 Hz to 19 kHz. Also, at 135 degrees, there is a deviation of plus or minus 2 dB between 20 Hz and 8 kHz. In summary, the unidirectional pattern is extremely good through the broad frequency range of 50 Hz to 8 kHz. In addition, the internal noise of the microphone has a comparatively low equivalent sound pressure level of 15 dB (A) and the output impedance is 150 ohms.

The microphone of the above-described design was brought to market by Sanken Microphone Company. It was very well received both in Japan and internationally, and continues in use today. The same design has also been used with a transistor output circuit instead of a transformer, and this has also been a popular model for many years.

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 ]