Quietness, Comfortable Sound and Excellent Acoustics NAGATA ACOUSTICS


News 08-09 (No.249)

Issued : September 25, 2008

[ Japanese Version ]

Saitama City "Plaza North" Private Finance Initiative (PFI) Development Project

by Akira Ono

<< The "Plaza North" Site and the Project's Organizational Structure >>

Saitama Prefecture's Saitama City has been promoting renewal projects focused on building a mix of commercial, administrative and cultural facilities in each quadrant of the city. Following the completions of "Plaza East" and "Plaza West" projects, the "Plaza North" project in the city's northern Miyahara District became the most recently completed development project in March of this year.

The Plaza North site is located on a very large plot of land adjacent to Stellar Town, a large-scale shopping mall and high-density, high-rise housing complex. >From 1931 to 1939, Japan's then third-largest horseracing track filled the site. In 1939, the race track closed and Nakajima Aircraft (which later became Fuji Heavy Industries Ltd.) acquired the land and used it for its large-scale Omiya airplane engine factory.

For the Plaza North project, Saitama City, Fuji Heavy Industries, municipal urban renewal organizations and other local stakeholders formed an Urban Development Council and have been working together successfully to revitalize the district with the new, high quality Plaza North development project. Unlike Saitama City's earlier two projects in its east and west quadrants, for which funding came from the municipal Saitama City Culture Promotion Organization, the Plaza North project is a Private Finance Initiative (PFI) in which all aspects from design through construction (and the ongoing maintenance service contracts) are entirely entrusted and executed with private capital by the private sector.

<< Plaza North Building and Hall Overview >>

Plaza North's exterior
Plaza North's exterior

Plaza North is a 4-story, reinforced concrete structure, with an architectural design that features a center atrium and intentional, clear delineation of the spaces used for the five functions of the building. These five functions include the city's North District municipal administration offices and the 400-seat hall that is the most prominent feature of the building, plus rooms for activities related to artistic endeavors (especially Japan's traditional comic-story-telling performance art), as well as conference rooms and a flat-floored multipurpose room. All of the buildings five functions benefit the citizens of Saitama City and promote community interaction.

Nihon Sekkei Inc. served as the architect for the Plaza North PFI. Kajima Corporation was the project's general contractor and construction manager, and Nagata Acoustics participated as the acoustical consultant, with a primary focus on the hall's acoustical design. We also provided overall acoustical consulting expertise for all aspects of the project.

The 400-seat hall
The 400-seat hall

A key design aim of the 400-seat hall was to place the audience seats as close to the stage as possible to create a feeling of intimate connection between stage and audience. To achieve this aim the seating area stretches across a wide distance compared with the overall size of the room. In our room acoustical design, we use balcony sections along the sides and rear of the auditorium in a squared-off horseshoe shape, so that the vertical, varied-height walls of the balcony sections send sound reflections that reach to the center area of the main floor's seating. Because of our creative design approach, at every seat in the hall we achieved the feeling of both visual and acoustical intimacy between the performance on stage and the audience.

<< PFI Participant Selection and Financial Impact >>

Plaza North is Saitama City's first project financed using a PFI structure. The companies engaged in the project were selected after submitting bids to the city. Kajima Corporation, together with 11 other selected companies won contracts that last 15 years and that include maintenance service and operational responsibilities for Plaza North. The 12 companies established Plaza North Management Company to coordinate and administer the contracts.

Proponents of PFI-structured projects often point out that this financing method benefits local municipal organizations by bringing the cost-saving expertise of the private sector to the design and construction of infrastructure projects. In the case of the Plaza North project, the PFI method is expected to save the city 2.2 billion yen (roughly equivalent to US$20.4 million or EURO 14.4 million) over the life of the contract, compared to traditional financing methods.

Among the bids that the city received for this PFI, the Kajima Group submitted the bid with the highest total price. However, the group's proposal contained details about how the Kajima Group will maintain the facility and also how it will plan and run the facility's operations. The competition's decision-makers saw high quality and value in the detailed content of the Kajima Group proposal, which led to the group being awarded the PFI.

<< Concerns about the Use of PFI Financing to Fund Halls >>

For the Plaza North project, the city prioritized proposal content over price. However, PFI competitions allot 40 points out of a total of 100 points to price, making it a very significant factor. The result is that the participating companies in competitions for PFI projects often tend to put all their effort into submitting a proposal that makes them the lowest bidder. In my opinion, the PFI method of simultaneously evaluating both the design proposals and their bid prices leaves something to be desired. In addition, because PFI competitions require bidders to develop and submit designs completed to a level of detail that closely approximates actual construction documents, and all of the non-selected design work goes entirely unused and unremunerated, firms smaller than Japan's major general contractors cannot afford to devote their employees' time to preparing these proposals. The PFI method can lead to proposals being constrained to designs with no particular appeal and just a few decor embellishments, while single-mindedly pursuing the lowest price that can still deliver the required functionality.

In the current economic environment and for the foreseeable future, with Japan's national, regional and local governments strapped for infrastructure funds, Japan's construction industry eagerly encourages expanded use of the PFI method of project financing. But if hall projects provide insight into the nature of PFI projects in general, there is much cause for concern. The local and regional government organizations that rely on PFIs to finance hall projects lack knowledge about hall operations, so much so that the requirements and standards they document in their requests for proposals (RFPs) clearly have entire sections lifted from other projects' RFPs. This situation will eventually backfire on the governmental administrations and communities that fund their halls using PFIs.

When governmental bodies build and operate multipurpose halls and concert halls as part of society's public cultural infrastructure, they do so to bring as much high quality performance programming as possible to the community at prices that the general public can afford. Expecting to generate a profit from this kind of endeavor is unrealistic. On the other hand, if the hall's operations are entrusted to a for-profit company, it is only natural that the company will do what it can to reduce operating costs and try to keep from operating in the red. Unfortunately, the simplest way to do this is to use the hall as infrequently as possible.

In raising these concerns, I do not wish to imply that they pertain to Plaza North. Nevertheless, the hall's home page does not feature a listing of the hall's performance schedule. I am told that the listing is only available at the hall. Is the lack of a calendar on the website evidence of an operational bias that wishes to limit interest on the part of the community? This facility will be filled daily with residents who have business with the city's administrative offices and who gather here for classes, meetings and performances. I hope that the companies in charge of maintaining and promoting Plaza North will take a proactive approach that attracts the city's residents to enjoy all aspects of the new facility, including its hall.

Plaza North's English-language home page is http://www.plazanorth.jp/english/index.html



A History of Broadcasting Microphone Invention and Development Part 2: The Compact Unidirectional Condenser Desktop Microphone

by Dr. Akio Mizoguchi

<< Introduction >>

In this second installment on the history of broadcast microphones, I will discuss a product that we developed and brought to market some 36 years ago, in 1972. This product, the compact unidirectional condenser desktop microphone continues to be manufactured and widely used today.

In 1972, most TV broadcast studios recorded speech using the U.S. manufacturer RCA's Type BK-5B microphone. This unidirectional microphone (called a "uniaxial microphone" by RCA) used a metallic ribbon as its vibrating element.

While the Type BK-5B provided excellent functionality, its large size made it bothersome to TV studios, directors and others who were trying to achieve a certain look and visual imagery on the TV screen. The TV industry clamored for a smaller recording microphone.

In response to this need, I took up the challenge of designing a more compact condenser microphone. I set as my first objective the goal of reducing the size of the microphone's vibrating diaphragm, because this part of the microphone determined its overall size. In pursuing this goal, I developed the design method for a tiny vibrating diaphragm, so that all of the specifications for a more compact unidirectional condenser desktop microphone could be satisfactorily achieved.

<< The 1972 Unidirectional Condenser Desktop Microphone Design >>

Fig. 1 The 1972 compact unidirectional condenser desktop microphone I developed for NHK TV.
Fig. 1 The 1972 compact unidirectional condenser
desktop microphone I developed for NHK TV.

In the accompanying Fig. 1, the reader can see an illustration of the first desktop microphone produced according to the design method I developed. This microphone has a 90 mm (3.5 in.) diameter base and the microphone head is connected to the base by a supporting arm made of both rigid and flexible gooseneck tubing. The base sits on four anti-vibration mounts that have concealed springs, as illustrated in Fig. 2.

The microphone portion of this model has a cylindrical shape with a diameter of 11.5 mm (0.5 in.) and a length of 56 mm (2.2 in.). It is a unidirectional microphone with a tiny vibrating diaphragm of 8 mm (0.3 in.) diameter.


Fig. 3 The microphone's wind screen
Fig. 3 The microphone's wind screen

Fig. 2 Anti-vibration spring in the microphone base
Fig. 2 Anti-vibration spring
in the microphone base

When the microphone is placed in close proximity to a speaker's mouth and the speaker's breath creates wind noise, the wind noise can be effectively eliminated by adding the wind screen shown in Fig. 3.

The wind screen measures 24.4 mm (1 in.) diameter at its widest circumference and is 41.1 mm (1.6 in.) long. The wind screen is usually attached to this microphone when it is used for TV broadcasting and recording.

Fig. 4 The microphone's output voltage and unidirectional frequency characteristics
Fig. 4 The microphone's output voltage
and unidirectional frequency characteristicsy

Next, let me provide some information about this microphone's performance characteristics. Fig. 4 shows the output voltage and directional frequency characteristics of this microphone. When we brought this microphone to market, it included a phantom power supply designed specifically for this model. Phantom power is a method that evenly weights the DC voltage so that the voltage can be supplied through the two signal wires of a balanced-type microphone cable. The voltage supplied by the phantom power supply is the internationally recognized standard voltage of 48 V.



<< Condenser Microphone Diaphragms and Low Frequencies >>

The microphone that I have been discussing uses typical condenser microphone technology. In a condenser microphone, when bias (also known as bias voltage) is supplied to the microphone's diaphragm and the back plate, an electrical charge is maintained. This circuit produces the signal voltage of a typical condenser microphone. Depending on the specifications of this kind of condenser microphone, the diaphragm may collapse towards the back plate when low frequency sound passes into the microphone.

If the diaphragm tension of a condenser microphone is set loosely and the microphone is unidirectional, then the lower end of the microphone's frequency range will be expanded. However, in setting the diaphragm's tension, this benefit must be weighed against the possibility of setting the tension so loosely that the diaphragm touches the back plate.

To mitigate the possibility of this kind of problem (sometimes called a "suction problem"), the product design that uses the tiny microphone diaphragm I developed is set to a slightly high diaphragm tension that allows a minimum frequency (at - 3 dB) of 200 Hz in the body of the microphone. The product's electric circuitry contains a low frequency boost to compensate for frequencies as low as 60 Hz.

<< Two Features Address Low Frequency Phenomena >>

When a person places his or her mouth very close to a unidirectional microphone and speaks into it, the voice's low frequency sounds become emphasized. This phenomenon is called the "proximity effect." To address this phenomenon, on the 1972 model of our desktop microphone we added a switch on the phantom power supply that enables the speaker to adjust the microphone's low frequency characteristic to eliminate excess low frequency sound. On the graph of Fig. 4, the dot-and-dash line shows the frequency characteristic of the microphone when the proximity effect switch is set to eliminate the excess low frequency sound.

Another undesirable low frequency phenomenon is the noise generated by vibrations from wind or nearby machinery and other devices. To eliminate this kind of low frequency noise, the microphone has a low frequency filter that reduces the output voltage of frequencies that are below 40 Hz.

<< The 1972 Desktop Microphone's Other Specifications >>

The small desktop microphone I designed in 1972 has sensitivity at 1 kHz of -51 dB/Pa (decibel/Pascal unit). The microphone's internal noise is equal to the sound pressure "A" plus the coefficient value of 22 dB.

The output impedance is 560 Ohms. In addition, this model's 48V of phantom power includes 13V for FET (Field Effect Transistor) circuit impedance conversion and the remaining 35V for powering the electrical charge maintained in the microphone.

<< The 1972 Desktop Microphone Then and Now >>

In this article about the 1972 Desktop Microphone, I provided technical details about the device. From a historical perspective, of equal interest is the longevity of this microphone's use in the broadcast industry. This microphone continues to be manufactured and used more than 35 years after it was developed. In particular, in Japan, the TV broadcast network Asahi TV (Channel 10 in Tokyo) uses this microphone for its talk shows, a staple of Japanese TV.


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 ]