Title means "Quietness", "Comfortable Sound" and "Excellent Acoustics"
Nagata Acoustics News 98-1iNo.121j
Issued : January 25, 1998
On the Tenth Anniversary of Nagata Acoustics' Newsletter:"Quietness, Comfortable Sound, Excellent Acoustics,"
by Dr. Minoru Nagata
Ten years ago, in January 1988, we launched the publication of our first issue of the Nagata Acoustics Newsletter. (Our company name, now Nagata Acoustics, was then Minoru Nagata Acoustic Engineer & Associates.) At the time, Suntory Hall was little more than one year old and Casals Hall had just opened. In the ten years since, the concert hall environment in Japan has changed immensely.
Even before we began issuing "Quiteness, Comfortable Sound, Excellent Acoustics" on a regular basis, I had long felt the need for this newsletter. My aim was to create a vehicle for deepening the understanding of acousticians' work on the part of hall sponsors' and personnel involved with hall construction. I thought of establishing a project team to take on the creation of a newsletter, but the reality was that we were all so pressured with the demands of keeping up with our heavy load of acoustical engineering responsibilities that no-one believed we could find the time to write articles for a company newsletter.
So I decided to take on the project by myself. I remember well my New Year's "holiday" that 1988. I wrote the newsletter copy and also took care of the printing and addressing and stuffing envelopes. My family pitched in and we did everything by hand. I sent the first issue to perhaps 100 recipients at most.
From the start, I told myself that I would not miss a publication deadline. Today, the production process of our newsletter is no longer the homespun one it was when I began it 10 years ago, but I still hold strictly to my publication date rule. People ask me if isn't hard to think up article topics every month. Actually, I found that once I established the mind-set that I would be writing every month, material for articles came to me quite effortlessly as I pursued my daily acoustical engineering work. I also discovered that I can be a bit reckless in expressing myself when I hold an opinion strongly, and there were times when I was taken to task for my words. I learned that however minor a point of contention may be, those who write must wield the power of the pen responsibly.
During the past 10 years, Nagata and Associates has seen some changes take place in our organizational structure. So has the newsletter. As of Issue No. 100, Hideo Nakamura, our company president, and each of our six other project chiefs have taken on the responsibility of planning and producing the newsletter, on a rotation basis. As a result, I believe that each month's articles increasingly reflect the individual personalities and interests of each author and monthly compiler.
One year ago, in January 1997, we added the monthly newsletter to our website. In April 1997, we added a monthly English translation. Back issues are also available here. I hope that you will make use of the 120 newsletters we have written to date, and that future issues will continue to be of value to you. Your comments and feedback are always welcome.
Symposium on Measurement Methodology of Room Acoustical Parameters
by Keiji Oguchi
On December 9 & 10, 1997, the Architectural Institute of Japan and Acoustical Society of Japan held a joint symposium on "ISO3382 -- Measurement of the Reverberation Time of Rooms with Reference to other Acoustical Parameters." The timing of the symposium was set to coincide with the implementation of changes in the measurement standards for auditorium reverberation time. In addition to covering explanations of changes in the standards, a large portion of the two days was devoted to debate and discussion of concerns, issues, and problems arising from the new standards. My report includes both a summary of points made during the symposium and my own commentary.
Four changes/revisions/additions have been made to the standards: (1) Use of the reverberation time measurement standards is no longer limited to auditoriums and concert halls but will now be applied to all kinds of rooms; (2) The integrated impulse response method proposed by Schroeder was added as an approved method of determining decay curves; (3) Use of the envelope of squared impulse response to directly read a reverberation decline is no longer a recommended method; and (4) Evaluation of room acoustical parameters derived from impulse responses was attached to the standards in separate appendices.
Regarding the use of reverberation time measurement standards in all kinds of rooms, this change means that the new standard will be referred for reverberation time measurement ,not only in halls, but also in projects where the primary objective is the reduction of noise in a work environment or acoustical power estimation in actual fields. However, since most part of the standard describe the reverberation time measurement in halls, I think that it will be slightly hard to pick up necessary procedure to measure the reverberation time for the noise control purposes from the standard.
Regarding the addition of the integrated impulse response method, previously the only method allowed was the interrupted noise method. In the interrupted noise method, the reverberation time is read from the decay curve obtained by direct recording of the decay of sound pressure level after exiting a room with band noise. The new standard approves use of the integrated impulse response method. This owes to the recent progress of a digital signal processing technique which has comparatively more accurate measuring capability. In this method, the decay curve is calculated from reverse-time integration of the squared impulse responses (Schroeder integration).
Comparison of Schroeder integration curve and squared envelope of impulse response; F.Satoh & H.Tachibana, "Marked Matters for the Integrated Impulse Response Method ( Comparison Study with Direct Method)", Symposium Proc.
In theory, it has been shown that the decay curve obtained by averaging an unlimited number of measurements using the interrupted noise method equals that of the Schroeder integration. However, actual practice reveals that when the signal-to-noise ratio of the impulse responses are not enough or the data's length of them are not long enough, reverberation time cannot be accurately read. In these circumstances, according to reports given at the symposium (refer to figure), the reverberation time can be read more accurately from the now non-recommended envelope of squared impulse response. Therefore, I think that it will be difficult to give up use of the envelope method, especially in the case of rooms such as concert halls where the sound decays exponentially. The symposium reaffirmed for me that a critical aspect of the measurement process is our ability to check the decay curves with our own eyes in determining our reading of reverberation times. Also, the point was made that the synchronous averaging used to improve the accuracy of impulse response measurement is subject to changed responses if the conditions in which the measuring is done change.
Regarding the addition of appendices on deriving other acoustical parameters from impulse responses, the appendices defines a number of quantifiably measurable physical parameters and measurement methods. These parameters were proposed as the result of research on the relationship between subjective evaluations and quantifiably measurable physical parameters as they relate to the overall acoustics of a hall. They are, the Strength G related to the Loudness, the Early decay time EDT related to reverberance, the Deutlichkeit D, the Clarity C and the Center time Ts related to the Clearness, and the Early lateral energy fractions LF and the inter-aural cross correlation coefficient IACC related to the Apparent source width ASW.
Some of the correspondences or interrelationships detailed in the appendices are still in the research stage, which is why they appear in an appendices rather than as part of the new standards. In particular, it appears that the controversial IACC was included in Appendix 2 because of heavy support from the United States in favor of its inclusion. At the symposium, it was emphasized that there are many points in the appendices whose content is as yet insufficiently researched.
From the perspective of one who engineers acoustical designs in the real world, I would especially like to see ample publication of information on impulse response measurement methods. At present, there is only an enumeration of sound source signals and the problems that are likely to occur, but no commentary on what to do when these problems arise. While it is true that items insufficiently researched were relegated to the "appendix," I still wonder why they were allowed to be published without sufficient review, or why the necessary review was not or could not have been done. It is now clear to me that both I and other Japanese acousticians should have expressed our concerns more strongly at the draft stage of the new standards. The next time revisions or changes are proposed I will know how important it is to speak up.
The recent symposium was attended by virtually everyone in Japan who is involved in the measurement of room acoustics on a day-to-day basis. One of the successes of the symposium was elucidating and strengthening the consensus among all parties in Japan concerning the requirements and issues to be addressed with regard to the new standards.
In Japan, where our country is ostensibly pursuing the integration of our domestic standards (known as JIS standards) with those used worldwide, I found it deplorable to learn at the symposium that there has been no government funding for representatives from Japan to host or attend meetings of the ISO commission. The ISO is a most important organization and the government should help us make the voices of Japanese acousticians heard.
Sound System Renovations for Halls
Part III in a Series, with Case Studies
by Nagata Acoustics Sound System Design Group
In Part III of this series, we turn our discussion to the importance of the control booth in overseeing and serving as "Control Central" for the acoustical equipment in a hall.
First, let us summarize the optimal conditions of an acoustics control booth. Most important, of course, is ensuring that the equipment in the booth (or "room") is laid out so that every piece can be easily accessed and used. Additionally, it is essential that the control booth be located and designed so that the people inside it can see and hear the entire hall well, and that they are able to communicate by voice with people inside the hall and on stage. It is also beneficial if the control booth is located so that there is easy physical access to both the seating area and the stage as this will improve the efficiency of pre-performance preparations and activities.
In designing the placement of equipment in the control booth, we begin with a flat, two-dimensional layout. It is important to keep in mind not only the equipment that has been officially ordered as part of the construction of the hall, but also all of the equipment and accessories that will be required in the control booth when the hall is actually functioning. For example, it is easy to overlook the need for shelves or cabinets to house cables, cords, and other seemingly insignificant yet essential necessities that will invariably take up space in the control booth. Two-dimensional layouts often give the illusion of greater space than is actually available, and it is a recipe for disappointment if everything that will need space in the control booth is not accounted for while working with the two-dimensional layout.
It is very important that the entire stage be visible through the window of the control booth because decisions on sound volume, sound quality, and even when to begin sound broadcasting or enhancements are all dependent on observation of the action on stage. In order to see to the very front of the stage apron, as well as to the edges of stage right and stage left, due consideration must be given to the shape and height of the control booth's window, as well as to the height of sound consoles and the depth of the control booth. When the control booth is located on the second or third floor of a hall, the height of the window must be determined with particular care to ensure that the entire stage is visible.
For theater and operatic performances, it is also essential that the proscenium speakers be visible from the control booth, and the control booth window must be able to be fully opened so that amplification of the spoken voice and sound reproduction can be clearly and directly monitored. If the hall is not dedicated to theatrical performances, it is typical for a portion of the control booth window to be immobile.
When even a portion of the control booth's window can be opened, it immensely improves the efficiency of communications between the control booth and other hall personnel during the set-up and other preparations before a performance. Older halls sometimes have a studio-like window that is entirely blackened and closed shut. This just becomes an impediment to communications between the personnel in the control booth and the crew or performers on stage and in the hall's seating area during set-up preparations and rehearsals.
In some halls, the control booth is located at the very top and back of the hall. This may be okay in a small hall, but in a large hall with several tiers of balconies, it becomes a real chore to go back and forth between the control booth and the stage right wing where personnel in charge of the performance usually locate themselves. In addition, if the only way to reach the stage from the control booth is via the audience seating area, then it becomes impossible for personnel in the control booth to get to the backstage area during a performance. We cannot emphasize enough how important it is to have easy access from the control booth to the stage and backstage areas. There are still too many halls that have not prioritized this sufficiently.
Another area of concern is the ventilation system for the control booth. In too many hall, the control booth ventilation is exactly the same as the ventilation for the audience seating area. This problem is often overlooked. The heat generated in the control booth and the hours of usage often differ considerably from that of the audience seating area, and ventilation should be planned accordingly.
The control booth may be used for long hours during set-up preparations, rehearsals, and maintenance activities while there is no audience. Also, the proper way to set the environment for acoustical equipment is to raise the temperature to the required level as quickly as possible, and then to control the ambient temperature so that it stays constant.
Heating and cooling requirements for lighting control booths and sound control booths are usually different, with the lighting control booth needing a warmer ambient temperature and the sound control booth needing air conditioning. Therefore, each of these facilities should be able to be heated and cooled independent of each other. For concert halls requiring high standards of quietness and in situations where the control booth is in close proximity to audience seating, special attention should be given to soundproofing the control booth window. When the control booth is located at the side of the stage, it is absolutely necessary to use double-paned windows and airtight frames around the control booth window.
Below are examples of actual control booth situations and issues we have encountered and the solutions we recommended.
(1) In the mid-size theater of the multi-theater structure "T Art Space Theater," the control booth was located in the rear of the second balcony at stage left. When the theater was completed, it was realized that the window was set too high. Control booth personnel had to stand in order to see the stage. We removed all of the equipment from the control booth, raised the control booth floor 30 cm, then replaced all of the equipment.
(2) In sports arena "W," the window of the control booth was also set too high. We raised the control booth floor so that the control booth personnel could see the arena from a seated position.
(3) In "K" public auditorium, the control booth was located in the center of the side wall at stage right (with a flat window). As a result, the stage right wing was not visible from the control booth. We extended the entire control booth (including the floor) out into the audience area so that at least a small portion of the stage right wing became visible from the booth.
(4) In one hall we changed the window so that it opened completely.
(5) For the International Culture Center in Sumibe City, and Furusato Auditorium in another city, we designed manually accessible storage space under the control booth's window.
(6) In a hall in Toyama City, we designed storage space under the window, operated by electrical controls.
We would also like to make note of the most significant basic improvements and problems that require attention:
(1) Improving the location, doors, or access routes from the control booth to the audience seating area to facilitate pre-performance preparations;
(2) Designing a special corridor along the most direct route between the control booth and the stage for control booth, hall, and performance personnel to use during performances;
(3) Soundproofing control booths so that the audience cannot hear telephone calls and intercom communications from the control booth;
(4) Painting the inside of the control booth matte black;
(5) Providing sufficient space in the control booth. Do not locate the control booth where there will be a column, beam, or other obstacle in the center of the room. Also, be careful that there is enough depth across the control booth and do not make the ceiling too low;
(6) Avoiding placing the window of the control booth directly under a beam as this makes it difficult to install fire shutters and monitors;
(7) Providing independently adjustable heating and cooling systems for both the sound control booth and the lighting control booth; and,
(8) Adapting the lighting in the control booth to the needs of personnel in the booth both during pre-performance preparations and actual performances.
Nagata Acoustics News 98-1iNo.121j
Issued : January 25, 1998
Nagata Acoustics Inc.