Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS

News 08-11 (No.251)

Issued : November 25, 2008

[ Japanese Version ]

Hokkoku Shimbun Akabane Hall

by Akira Ono

Akabane Hall's Interior
Akabane Hall's Interior

Hokkoku Shimbun, a regional newspaper in Ishikawa Prefecture's Kanazawa City, celebrated its 115th anniversary in August 2008 with the opening of Hokkoku Shimbun Akabane Hall. The new hall is located adjacent to the newspaper's main office in the Korinbou, Kanazawa City. From 1957 to 1988, Kanazawa City's residents enjoyed lectures, recitals and other events at Hokkoku Auditorium and the new Akabane Hall reestablishes the newspaper's philanthropic contribution of hall sponsorship after a 20-year hiatus. Initial planning for the new hall included giving it the name "New Hokkoku Hall," but during the project the idea arose to name the hall after the newspaper's founder, Mr. Manjiro Akabane. The hall's name commemorates his legacy.

<< Overview of the Akabane Hall Project >>

The physical structure of Akabane Hall is a four-story, reinforced concrete building. In addition to the 504-seat Akabane Hall, the new building houses a flat-floored multipurpose hall designed for lectures, exhibitions, recitals and other events, and a Newspaper Museum. Nihon Sekkei's Masaru Asaishi served as the project architect, Shimizu Corporation was the general contractor and Nagata Acoustics participated as the acoustical consultant.

<< The Architectural Design and Shoebox Configuration Acoustics >>

The foyer of the hall
The foyer of the hall

The curved exterior of the Akabane Hall building has a skin of glass panels. Through the glass, the wall that separates the entrance foyer from the hall can be seen. It also has a curved surface and is painted with a lustrous black finish. Added to these visual design elements is the foyer ceiling, which has a mirror finish. Overall, the building gives the impression of a huge glass case with a shiny black piano inside.

The hall has a neatly rectangular shoebox configuration embellished with artistically customized details throughout the hall. To promote sound diffusion, the walls and ceiling have sharply-pointed ribbing crafted in blond wood and the lighting at the rear wall of the stage filters through a luminescent glass panel that is also designed as a sound diffusing surface. The style of the hall's colors and simple lines decidedly evoke the feeling of minimalist architecture, but the architect made sure to implement sound-diffusing elements that create fine acoustics.

When a hall has a shoebox configuration, people often assume that its shape guarantees good acoustics. In fact, in addition to needing suitable dimensions and proportions, the walls and ceiling must provide surfaces that produce sound diffusion. If a shoebox-shaped hall was truly a plain box with uninterrupted flat and smooth wall and ceiling surfaces, the result would not be a concert hall with good acoustics.

Current architectural trends favor low-cost, simple designs. Often, architects now use glass and aluminum materials in abundance, and new buildings have white walls and simple designs that seem intended primarily to assert their conformity to the principles of architectural minimalism. A concert hall design cannot be constrained by conformity to minimalism, because only by diverging from minimalism can the necessary conditions be created that produce fine acoustics. Otherwise, instead of a useful work of architecture, the result will be a huge piece of minimalist art.

The Akabane Hall design succeeds because, while implementing simplicity of style in form and function, the design elements do more than show conformity to the minimalist aesthetic. Here, the expression of architectural minimalism can clearly be seen to contain the architect's decisive inclusion of elements necessary to fine acoustics.

<< The Hall's Strong Sponsorship and Early Operational Success >>

Akabane Hall will be operated by the Hokkoku Arts Promotion Foundation, which sponsored a full inaugural calendar of some 30 performances, including plays, "Yose" traditional Japanese comic storytellers, kabuki and concerts. In addition, the 2008 Ishikawa Arts and Culture Festival, which is sponsored by Ishikawa Prefecture, the Ishikawa Prefectural Art Culture Association and Ishikawa Prefecture Musical Cultural Promotion Organization, used the new Akabane Hall as one of its two performance venues, along with Ishikawa Ongakudo. The hall also already has programming in place for several ongoing series that include kabuki seminars by popular kabuki actors, and Yose : "Akabane-tei" comic storytellers' series named after the hall.

Kanazawa City has many large and small public performance venues, especially the prefecture-funded Ishikawa Ongakudo. The persons responsible for Akabane Hall's calendar are already forging a cooperative planning approach together with these other venues and the future looks bright for the new hall to take its place in enhancing the cultural life of Kanazawa City.

Hokkoku Shimbun Akabane Hall home page is http://www.akabane-hall.jp/

A History of Broadcasting Microphone Invention and Development Part 3: Reducing the Size of Mid-side Stereo Condenser Microphones

by Dr. Akio Mizoguchi

In this third article about the history of microphones for the broadcast industry, I will discuss a model developed and marketed some 31 years ago, in 1977. The model, named the CMS-1 and manufacture by Sanken Microphone Co., represented a substantial miniaturization of the mid-side (MS) stereo condenser type of microphone. I developed the design for the CMS-1 and will share the details of that design here.

Fig.1 Combined directionality of the mid-side method
Fig.1 Combined directionality of the mid-side method

The MS type of stereo microphone combines a unidirectional "mid" microphone and a bidirectional "side" microphone in one unit. By using the MS microphone's summed output and the difference between the mid and side microphones' outputs, MS microphones can reproduce left and right stereo signals as shown in Fig. 1.

Around the time when I began work on the CMS-1, two German companies led the MS stereo microphone market: Georg Neumann GmbH, maker of the model SM-69 condenser microphone; and Schoeps GmbH, maker of the CMTS-50IU. In particular, Japanese broadcasters used the SM-69 exclusively. But these two microphone models shared the disadvantage of being large and bulky.

<< My Design for a Small SM Condenser Microphone >>

Fig.2 Size comparison of microphone models (at left is the SM-69 and at right is the CMS-1)
Fig.2 Size comparison of microphone models
(at left is the SM-69 and at right is the CMS-1)

Fig.3 CMS-1 microphone design and dimensions
Fig.3 CMS-1 microphone design and dimensions

Fig.4 Transformer box
Fig.4 Transformer box

To design a smaller model, I decided to try changing the microphone transducer's long-established configuration of pairing one diaphragm to one back pole plate. (The standard configuration was to have a back pole plate only on one side of the diaphragm.) In my new design, instead of one back pole plate, I used two, one on each side of the diaphragm. By adding a push-pull circuit, this design gave twice the output of the single back pole plate design. In addition, the design reduced the microphone's internal noise while improving the unit's sensitivity and also significantly reduced the size of the microphone.

The photograph of Fig. 2 shows the microphone I designed placed next to a SM-69 microphone. Fig. 3 illustrates the dimensions and internal mechanism of my microphone design. As shown in the illustration on the right, the entire microphone has a diameter of just 19 mm. (0.7 in.) and is only 59 mm. (2 in.) long. The left illustration of Fig. 3 shows that, starting at the top of the microphone, it contains a unidirectional transducer (the mid microphone), under which is a bidirectional transducer (the side microphone). Below the bidirectional transducer, my design placed FET (field effect transistor) source follower circuits that act as impedance converters and, at the very bottom of the microphone, a 7-pin cannon connector. Of the connector's 7 pins, 2 pins supply bias voltage to the unidirectional and bidirectional transducers and 1 pin is a ground. The remaining 4 pins are the unbalanced terminal outputs for the FET source follower circuits. The FET circuits require 4 pins because they need 2 for the 2 back pole plates of the unidirectional transducer and 2 for the 2 back pole plates of the bidirectional transducer.

The 4 outputs are converted by the 2 transformers of a transformer box (shown in Fig. 4) to one unidirectional (mid) and one bidirectional (side) balanced output (using 3-pin connectors). That is, when the power from the 2 unbalanced outputs of each of the microphones (mid and side) passes through the primary side of the transformer, each has a push-pull circuit that doubles its power, and balanced power is pulled from the transformer's secondary side. The power supply uses a 48V phantom power method.

<< Specifications of the Mid and Side Microphone Parts >>

Fig. 5 and Fig. 6 illustrate the unidirectional and bidirectional transducers in my SM condenser microphone design. For both of these transducers, I specified a design around the diaphragms that ensures they have the required tension and on both sides of the diaphragms I specified the placement of amply perforated back pole plates.

Fig.5 Unidirectional transducer design and dimensions
Fig.5 Unidirectional transducer design and dimensions
Fig.6 Bidirectional transducer design and dimensions
Fig.6 Bidirectional transducer design and dimensions

In the mid (unidirectional) transducer of Fig. 5, the diaphragm made of plastic is attached in the right side of the back pole plate. This diaphragm has the effect of expanding the low frequency range of the microphone's sensitivity to sound sources positioned directly in front of the microphone head.

Fig. 6 illustrates that the side (bidirectional) transducer has 2 air chambers of equal spatial volume on its left and right sides. On the exterior of this portion of the device I added sound-resistant material. This symmetrical design on the two sides of the diaphragm results in symmetrical directionality across the spectrum of sound frequencies, including high frequencies.

<< Frequency Characteristics of the Mid and Side Microphones >>

Fig. 7 and Fig. 8 chart the frequency characteristics of the mid (unidirectional) and side (bidirectional) microphones that together comprise the MS condenser microphone. In particular, the mid microphone's diaphragm exhibits a compensating effect for low frequency sound, providing a 3 dB attenuation at around 25 Hz. Compared with the front of this microphone, the rear of the microphone's sensitivity has more than a 15 dB attenuation up to about 5 kHz, achieving the desired directional characteristic. By comparison, at 90 degrees from the sound source, the side microphone's sensitivity provides greater than a 20 dB attenuation for frequencies below 20 kHz, providing excellent bidirectional sensitivity.

Fig.7 Mid (unidirectional) microphone output directionality characteristics (at 3 m. [10 ft] from the sound source)
Fig.7 Mid (unidirectional) microphone output directionality characteristics (at 3 m. [10 ft] from the sound source)
Fig.8 Side (bidirectional) microphone output directionality characteristics (at 3 m. [10 ft] from the sound source)
Fig.8 Side (bidirectional) microphone output directionality characteristics (at 3 m. [10 ft] from the sound source)

In addition, both microphones have direct sensitivity of -41 dB/Pa. Using the frequency response curve that most closely resembles human hearing, the mid microphone's noise measures 15.2 db(A) and the side microphone's noise measures 17.0 db(A).

The tiny MS condenser microphone I designed in the late 1970s gave the broadcast industry great freedom of movement while clearly capturing sound. For this reason, it influenced the evolving styles of artistic direction and production of broadcast content in more ways than may be generally realized.

Nagata Acoustics' Intern from Brazil - Luis Enrique Tachibana

by Fumiaki Sakamaki

I have the pleasure of using this space to introduce our readers to Nagata Acoustics' intern from abroad. His name is Luis Enrique Tachibana and, as his surname hints, he is a third generation ("sansei") Japanese-Brazilian. Luis is also one of a number of young people chosen to participate in a Japan internship program sponsored by the Japan International Cooperation Agency (JICA) and the Association of Nikkei and Japanese Abroad (ANJA). His internship at Nagata Acoustics began in April 2008 and will continue through January 2009.

In order to apply to the JICA internship program, candidates must be of Japanese descent (within three generations) and residents of a Central or South American nation. The goal of the internship program is to provide technical training that will contribute to the development of the participants' home countries. Each year, more than 50 interns come to Japan to participate in the program, including both a cohort of Japanese language teachers who train in a group setting and selected individual participants who join research organizations or companies that match their areas of research or technical competency. The internships last from one month to as long as a whole year, and the content of the training spans a broad range of endeavors, from Japanese language teaching skills to agriculture, manufacturing, engineering, medicine and information technology.

Currently, at Nagata Acoustics, Luis observes, learns and experiences the content, processes and important role of acoustical design (sound isolation, noise control and room acoustical design) and acoustical measurement work in the context of architectural acoustics projects. In particular, we emphasize on-the-job training and include Luis in all facets of our work, from interacting with architects and construction contractors on specific issues to developing acoustics designs, because we consider this the best approach to help him achieve his two internship goals of improving his acoustics technical engineering skills and his Japanese language proficiency.

On a more personal note, Luis was born in Japan and lived in Japan until the age of three. He even has a vivid early childhood memory of watching the snow fall on a winter day, a common site in the land of his birth, but not in Brazil. When his parents moved back to Brazil, he accompanied them and completed his education in his home country, including studying and earning a degree in architecture at a Brazilian university. He enjoys playing several instruments and his strong attraction to music led him to become interested in room acoustical design. During his third year at university, he completed an internship at a local acoustical consulting company.

In Brazil, people in industries related to acoustical consulting are aware of this engineering specialty field, but clients and architects generally do not yet recognize that room acoustic designs can be essential to the success of many projects. As a consequence of this situation, acoustical consultants are rarely hired during the initial planning phase of projects and it is not unusual for clients to submit post-construction claims because of problems with the acoustical performance of completed buildings. At the Brazilian acoustical consulting company where Luis did his first internship, much of the firm's work consists of remedial projects to improve the room acoustics of already completed buildings.

After completing his internship at Nagata Acoustics, Luis hopes to attend a graduate program in acoustics at a Japanese university. Thereafter, he plans to return to Brazil where he eagerly wants to contribute to improving the acoustical environment. By working and interacting with our professional staff, by experiencing and learning from their diverse expertise and by hands-on participation in project tasks and assignments, we are confident that his internship at Nagata Acoustics will be meaningful and useful as he pursues his acoustical consulting career.

Nagata Acoustics Paris Office Opens

Nagata Acoustics announces the opening of our Paris Office. The new office will serve our growing clientele and project operations throughout Europe. The Paris Office is our second office outside of Japan.

Yasuhisa Toyota has been appointed Director of the Paris Office, while also retaining his position as Director of the Los Angeles Office. Marc Quiquerez, who currently works in our Los Angeles Office, will return to his home country to staff the new office on a daily basis.

The Nagata Acoustics Paris Office is conveniently located just steps from the Paris Metro's Line 3 Parmentier Station. The address and contact information is:

<< Nagata Acoustics Paris Office >>

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

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

(US Office)
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 ]